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Ovarian hormones and meal patterns in rats: Effects of progesterone and role of gastrointestinal transit
Physiology & Behawor, Vol. 19, pp. 2 3 - 2 7 . Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.
Ovarian Hormones and Meal Patterns in Rats: Effects of Progesterone and Role of Gastrointestinal Transif JEFFREY
D. B L A U S T E I N 2 A N D G E O R G E N. W A D E 3
Department o f Psychology, University o f Massachusetts, Amherst, MA 01003 ( R e c e i v e d 12 A u g u s t 1 9 7 6 ) BLAUSTEIN, J. D. AND G. N. WADE. Ovarian hormones and meal patterns in rats: effects of progesterone and role of gastromtestinal transit. PHYSIOL. BEHAV. 19(1) 2 3 - 2 7 , 1977. - - T h r e e experiments determined: (1) whether progesterone treatment would reverse the effects of estradiol benzoate (EB) on meal patterns of ovanectomlzed (OVX) rats, and (2) whether changes m gastrointestinal transit were responsible for the EB-induced changes m meal patterns. Progesterone (5 mg/day) reversed the effects of EB by increasing meal size and decreasing meal frequency m OVX, EB-treated rats. Progesterone had no effect on these measures in OVX rats that were not given EB. In a comparison of the rate of gastrointestinal transit, the rate of gastrointestinal transit was found to be faster in OVX rats injected with EB daily for two weeks than m OVX, oil-treated controls as measured under anesthesia with infusmn of ten ml of liqmd diet. However, this alteration in gastrointestinal transit does not appear to be responsible for the decreased meal size of EB-treated, OVX-rats, because the gastrointestinal changes are not observed 3 4 - 3 8 hr after an EB injectmn, a time at which meal size is already affected.
Meal patterns Food intake
Ovarian hormones Estradiol
Progesterone
Gastrointestinal transit
f o o d r e t a k e is a c c o m p h s h e d b y a f u r t h e r increase in meal f r e q u e n c y ; meal size r e m a i n s p e r m a n e n t l y s u p p r e s s e d as l o n g as i n j e c t i o n s are m a i n t a i n e d . T h e results o f t h e s e h o r m o n a l m a n i p u l a t i o n s o n meal p a t t e r n s h a v e led t o t h e c o n c l u s i o n t h a t e s t r a d i o l affects t h e m e c h a m s m ( s ) t h a t t e r m i n a t e i n d i v i d u a l meals [ 3,13 ]. P r o g e s t e r o n e a n t a g o m z e s virtually all of e s t r a d i o l ' s beh a v i o r a l effects t h a t h a v e b e e n s t u d i e d , i n c l u d i n g e s t r a d i o l ' s suppressive effects o n e a t i n g as m e a s u r e d b y t o t a l daffy f o o d r e t a k e [ 2 3 ] . H o w e v e r , p r o g e s t e r o n e b y itself h a s n o effect in o v a r l e c t o m i z e d ( O V X ) rats t h a t h a v e n o t b e e n t r e a t e d w i t h e s t r a d m l . If p r o g e s t e r o n e , in fact, acts o n l y t o a n t a g o n i z e t h e effects o f e s t r o g e n o n eating, as h a s b e e n suggested [ 2 3 , 2 4 ] t h e n p r o g e s t e r o n e s h o u l d reverse estradlol's effects o n m e a l p a t t e r n s , ~t s h o u l d n o t have a n y e f f e c t in O V X rats t h a t have n o t received estradiol. E x p e r i m e n t s 1 and 2 e x a m i n e d t h e effects o f p r o g e s t e r o n e o n t h e meal p a t t e r n s o f O V X a n d E B - t r e a t e d , O V X rats. T h e r e is a great deal o f e v i d e n c e t h a t suggests an i n t e s t i n a l c o n t r i b u t i o n to t h e t e r m l n a t m n o f s h o r t - t e r m
L A T E P R O E S T R U S , t h e stage of t h e e s t r o u s cycle d u r i n g w h i c h sexual r e c e p t i v i t y occurs, a n d w h i c h follows p e a k levels of b l o o d p l a s m a estradiol-I 7t3 [ 5 ], is a c c o m p a n i e d b y a s u p p r e s s i o n m dally f o o d xntake [ 4 , 2 0 ] This d e c r e a s e d f o o d i n t a k e is a c c o m p h s h e d b y a decrease in the size of m d w x d u a l meals a n d a less t h a n c o m p e n s a t o r y increase m the f r e q u e n c y o f meals [ 3 , 9 ] . These c o r r e l a h o n s a p p e a r t o be a result o f c h a n g i n g levels of e s t r a d m l [24] for t h e f o l l o w i n g reasons. O v a r l e c t o m y results in a t r a n s i e n t increase in f o o d i n t a k e [12,21 ] w h i c h is r e f l e c t e d in an increase m m e a l size a n d a less t h a n c o m p e n s a t o r y decrease in meal f r e q u e n c y [ 3,13 ]. T h e m e a l size increase is p e r m a n e n t . W h e n t o t a l daffy f o o d i n t a k e r e t u r n s t o c o n t r o l levels, m e a l size r e m a i n s elevated, b u t meal f r e q u e n c y decreases [ 3 ] . R e p l a c e m e n t o f e s t r a d m l b y daily r e j e c t i o n s o f e s t r a d i o l b e n z o a t e (EB) reverses t h e effects of o v a n e c t o m y . T h e r e is a t r a n s i e n t decrease in t o t a l daily f o o d r e t a k e w h i c h is a c c o m p l i s h e d b y a decrease m meal size a n d a less t h a n fully c o m p e n s a t o r y increase m meal f r e q u e n c y [ 3 ] . T h e r e t u r n t o c o n t r o l levels o f daffy
1This research was supported by Research Grant NS-10873 and Research Career Development Award N S - 0 0 0 9 0 from the National Institute of Neurological and Communicahve Disorders and Stroke, and by Training Grant MH 11823 from the National Institute of Mental Health. We are grateful to John Ieni and Dorrine Conrad for techmcal assistance, to Edward Roy for his probing question, and to Mark Friedman and Paul Sawchenko for helpful discussions 2Present address: InsUtute of Ammal Behavior, Rutgers Umverslty, 101 Warren Street, Newark, NJ 07102. 3 To whom reprint requests should be sent. 23
24
B L A U S T f I N ,\NI) V~,\IH ~
f o o d intake ([10, 18, 251, but cf. 181~ As already discussed, E B - t r e a t m e n t results in a decrease m meal size Two surgical m a m p u l a t i o n s that result in decreased meal size are v a g o t o m y in rats on a liquid diet [6,1c/] and lateral h y p o t h a l a m i c lesions [7,14]. Both of these m a m p u l a t i o n s also result in an increase in the rate of gastrointestinal transit [15,17] Conversely, v e n t r o m e d m l h y p o t h a l a m l c lesions result in increased meal size [1, 2, 22] and a decrease in the rate of gastrointestinal transit 115] In E x p e r i m e n t s 3 and 4, we examine this aspect ol ovarian influences on meal patterns We test the hypothesis that ovarian h o r m o n e s cause changes in the rate of gastric e m p t y i n g and intestinal transit, variables which often correlate with alterations in meal patterns, using the OVX, EB-treated rat as a model.
EXPERIMENT
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Twelve Sprague-Dawley rats purchased from a c o m m e r cial suppher (Charles River Breedmg Laboratories, Wilmington, MA) were O V X at least three m o n t h s prior to use The rats weighed 3 0 0 - 4 5 0 g at the start of t r e a t m e n t and were rejected daffy with 2 ug EB m 0 1 ml sesame oil B e g m m n g on the second week of injections rats were maintained on a h q m d diet described previously [3]. During Week 5, meal patterns were r e c o r d e d for a four-day baseline period. At the end of this permd, one group received 5 mg progesterone (n = 6; EB + progesterone) and one group (n = 6, EB) received 0.1 ml sesame off daffy in addition to the daffy EB injections. Injections were c o n t i n u e d for 24 days and meal patterns were m o n i t o r e d c o n t i n u o u s l y Environmental fflummatlon was provided from 0 7 0 0 - 1 9 0 0 hr daffy and r o o m t e m p e r a t u r e was maintained at 2 1 - 2 3 ° C . All injections were administered b e t w e e n 0 8 0 0 - 1 0 0 0 hr, and at this h m e , rats were weighed, bottles cleaned and fresh l l q m d diet given. F o r detaffs of the diet, apparatus and procedure for analysis of meal patterns (see [ 3 ] ) Since it was n o t possible to m a t c h groups on all variables of the meal patterns and f o o d mtake, data were converted to percentage of the four-day baseline
Results and Dzscusszon F o r analysis, the results were divided into Days 1 - 1 2 and Days 1 3 - 2 4 after the start of progesterone t r e a t m e n t During Days 1 - 1 2 the EB + progesterone group gamed weight at the rate of 0.47% (-+0.07)/day c o m p a r e d with 0 15% (-+0.08/day for the EB group, t(10) = 2.800, p < 0 02 (Fag, 1). By the second half of t r e a t m e n t , b o t h groups were gaming at a p p r o x i m a t e l y the same rate. There was a transient increase in the daily f o o d intake of the EB + progesterone group when c o m p a r e d with the EB group During the first half of t r e a t m e n t the EB + progesterone group ate 114% (-+4 0) of basehne levels and the EB group ate 103% (-+4.4) of basehne, t(10) = 1.833, p < 0 0 5 , one-taff This difference was absent during the second half o f t r e a t m e n t (114% -+ 7.3 vs. 111% -~ 6 4). Mean dady meal size was 119% (-+3.3) of baseline levels
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Progesterone inhibits estradlol's suppressive effects on total daffy f o o d intake and b o d y weight m a i n t e n a n c e In the first e x p e r i m e n t we evaluate the effects of progesterone on meal patterns in EB-treated, O V X rats
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FIG 1 Body weight and food retake of ovariectomlzed rats rejected with 2~g/day of estradlol benzoate for four weeks prior to momtoring of meal patterns After a 4-day baseline, rats were also rejected with 5 rag/day of progesterone (EB + P group) or od (kB group), indicated by arrow for the EB + progesterone group during Days l 12 c o m p a r e d with 98% (+ 8 7) for EB controls, t(10) = 2 282. p < 0 05, Fig 2) This difference persisted during the second half of t r e a t m e n t ( 1 4 6 ~ + 8 8 vs 110~; + 13 1, t ( 1 0 ) 2.269, p < 0 05. Meal frequency was 98% (~ 3 2) of basehne for the EB + progesterone group during the first 12 days c o m p a r e d with 109% (, l0 1) of basehne for controls By the second half of treatment, the EB + progesterone group had decreased to 80% (± 5 4) as many ineals as during basehne and EB controls were taking 107~'¢ (~ 8 4) ot baseline, t(10) = 2 744, p < 0 05 E x p e r i m e n t 1 demonstrates that progesterone can reverse estradlol's effects on meal patterns The transient increase in f o o d intake and rate of body wexght gain when c o m p a r e d with controls confirms previous flndmgs [16] The increase in meal size by progesterone along with a decrease in meal frequency was predicted from progesterone's antlestrogenlc influences on total daffy food intake It has previously been suggested that ovarian h o r m o n e s influence meal patterns prlmarll3, by affecting factor(s) that determine short-term food intake (meal size) and not on the m t e r m e a l interval (meal frequency) The results of this e x p e r i m e n t are consistent with this interpretatlon. During Days 1- 12, all of the EB + progesteronetreated rats increased their meal size but only one rat decreased its meal frequency by more than 3% of baseline
EXPERIMENT
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In measures of total dally food intake and body weight maintenance, progesterone has no effect in the absence of estrogens [24] E x p e n m e n t 2 demonstrates that proges-
OVARIAN HORMONES AND MEAL PATTERNS
25 weight, f o o d intake, meal size or meal f r e q u e n c y during Days 1 - 1 2 or Days 1 3 - 2 4 approached stahstical significance. E x p e r i m e n t 2 once again confirms that progesterone is w i t h o u t effect on total dally food intake or b o d y weight maxntenance in the absence of estradlol [ 2 4 ] . Experiments 1 and 2 e x t e n d the situations in which progesterone reverses estradlol's effects to include meal patterns.
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FIG. 2. Meal size and meal frequency of ovariectomlzed rats rejected with 2 #g/day of estradlol benzoate for four weeks prior to monitoring of meal patterns. After a 4-day baseline rats were also injected with 5 mg/day of progesterone (EB + P group) or oil (EB group), indicated by arrow. terone does n o t affect meal patterns in O V X rats that have not been pretreated with EB. Procedure
Eight Sprague-Dawley rats purchased from a c o m m e r c i a l suppher (Charles River Breeding Laboratories) were OVX at least three m o n t h s prior to use. The p r o c e d u r e was the same as m E x p e r i m e n t 1 e x c e p t that no EB t r e a t m e n t was gwen. Groups recewed either 5 mg progesterone in 0.1 ml sesame oil/day ( n = 4 ; progesterone) or 0.1 ml sesame o d / d a y (n = 4, od) beginning after the four days of basehne recording of meal patterns. Results and Dtscusszon
As p r e d i c t e d progesterone had no effect on the meal patterns of OVX rats that were not treated w~th estradiol None of the progesterone vs. oll comparisons for b o d y
Estradlol benzoate t r e a t m e n t results in a decrease in meal size, as do v a g o t o m y in rats on a liquid diet [6,19] and lateral h y p o t h a l a m i c lesions [7,14]. Both of these surgical m a n l p u l a t o n s also result in an increase in the rate of gastrointestinal transit [ 1 5 , 1 7 ] . In the case of v a g o t o m y , gastric e m p t y i n g speeds up as measured m awake rats [ 1 7 ] , with lateral h y p o t h a l a m l c lestons, the rate has been measured m response to a forced stomach-load of milk in anesthetized rats [ 1 5 ] . Since there is evidence for an intestinal c o n t r i b u t i o n to the t e r m i n a t i o n of short-term f o o d retake, as already discussed, we lnvestxgated the poss~bllity that E B - t r e a t m e n t m OVX rats w o u l d result m more rapid gastric e m p t y i n g a n d / o r intestinal transit. The procedure that was used involved stomach-loading into a food-deprived a n e s t h e h z e d rat. This technique was chosen because of its effectiveness m dissociating V M H - and L H - l e s l o n e d rats from controls [15] Procedure
Sixteen Sprague-Dawley rats O V X for two or three m o n t h s and weighing 3 3 0 - 4 4 0 g were mjected with 2 tzg EB/0.1 ml sesame oll (n = 8) or 0.1 ml sesame oll (n = 8) daily for t w o weeks prior to the test. One week prior to the test, all rats were maintained on a liqmd diet described previously [3]. T w e n t y - f o u r to 28 hr prior to the test t h e y were f o o d deprived. Tap water was freely available at all times. Rats were anesthetized with s o d m m p e n t o b a r b i t a l (40 m g / k g b o d y weight, N e m b u t a l ) and then laparotomlzed. With the rat in a supine positron 10 ml of hquid diet were refused into the stomach through the gastroesophageal j u n c t i o n . A 10 ml syringe c o n n e c t e d to the needle with p o l y e t h y l e n e tubing was used to manually refuse the diet into the stomach at a constant rate over one m m (I ml/6 sec). At the c o m p l e t i o n of the infusion, the gastroesophageal j u n c t i o n was lzgated with sdk suture that had previously been loosely wrapped around the esophagus, and the pylorus was clamped i m m e d i a t e l y , seahng the c o n t e n t s
TABLE I MEAN BODY WEIGHT, FOOD INTAKE, MEAL SIZE AND MEAL FREQUENCY DURING DAYS 1-12 AND 13-24 OF OVARIECTOMIZED RATS TREATED DAILY WITH OIL OR PROGESTERONE (5 rag)* Body Weight
Food Intake
Meal Size
Meal Frequency
Days 1-12 Oil Progesterone
102 0 (_+0.3) 102.8 (_+0 6)
108.3 (+5.6) 113.3 (_+13.1)
103 1 (+3.6) 101.0 (_+9.8)
107.0 (_+7.0) 110.5 (_+6.1)
Days 13-24 Oil Progesterone
106.4 (_+1.1) 105.6 ( + 1 4)
106 5 (_+7.0) 99.4 ( _+13.4)
107.1 (_+1.4) 93.2 ( _+12.1)
101.7 (_+6.8) 105.4 ( _+3 5)
*Data are expressed as percentage of basehne (_+ standard errors)
26
BLAUSIFI\ FABLE
TABLE 2 MEAN (± SEMI INTESTINAL TRANSIT AND GASTRIC RETENTION OF LIQUID DIET IN OVARIECTOMIZED RATS TREATED WITH 2 /xg E S T R A D I O L BENZOATE~DAY OR S E S A M E OIL FOR TWO WEEKS PRIOR TO TESTING
MEAN (± SEMI INTESTINAL TRANSIT AND GASIRIC R E I E N I I ( I N OF LIQUID DIET IN OVARIECTOMIZED RATS TREATED WI'FIt /zg ESTRADIOL BENZOATE OR SESAME OIL I~: DAYS PRIOR "1¢) TEqT1NG
Intestinal Transit (cm) Gastrmc Retentmn (roll
Intestinal Transit (cm) Gastric Retentmn (ml) Estradml Benzoate Oil
71 9 (_+6 1) 454(_+40)
,\'~l) W\11t
4 0 {_+0 5) 59(_+04)
of the s t o m a c h . F i f t e e n s e c o n d s later, t h e distal p o i n t t h a t the milk h a d travelled t h r o u g h the i n t e s t i n e was c l a m p e d , the s t o m a c h was r e m o v e d , and t h e v o l u m e o f the s t o m a c h c o n t e n t s was m e a s u r e d T h e antestine was t h e n g e n t l y dissected away f r o m the o m e n t a , a n d t h e d i s t a n c e b e t w e e n the p y l o n c a n d i n t e s t i n a l c l a m p s was m e a s u r e d The e x p e r i m e n t was c o n d u c t e d w i t h the e x p e r i m e n t e r b h n d to treatment Results EB t r e a t m e n t r e s u l t e d in a 58% increase in d i s t a n c e travelled b y t h e milk, t ( 1 4 ) = 3 632, p < 0 . 0 1 , a n d 32% decrease in gastric r e t e n t i o n w h e n c o m p a r e d w i t h oil-treated c o n t r o l s , t ( 1 4 ) = 2 873, p < 0 02 (Table 2) EXPERIMENT 4
A l t h o u g h t h e results o f E x p e r i m e n t 3 s u p p o r t the n o t m n t h a t EB t r e a t m e n t affects g a s t r o i n t e s t i n a l t r a n s i t , the test was p e r f o r m e d a f t e r t w o weeks o f h o r m o n e t r e a t m e n t Perhaps, r a t h e r t h a n EB causing g a s t r o i n t e s t i n a l changes w h i c h t h e n a l t e r m e a l p a t t e r n s , EB m i g h t first a l t e r meal size m s o m e o t h e r way, a n d this results m the gastroint e s t i n a l change. It is necessary to d e t e r m i n e w h e t h e r t h e g a s t r o i n t e s t i n a l c h a n g e o c c u r s wath a s u f f i c i e n t l y s h o r t lat e n c y to a c c o u n t f o r t h e a l t e r a t i o n in meal size In the n e x t e x p e r i m e n t , we test for darect e f f e c t s of estradiol on g a s t r o i n t e s t i n a l t r a n s i t b y testing 3 4 - 3 8 h r a f t e r a single EB r e j e c t i o n , we have f o u n d previously t h a t meal size as s l g m f i c a n t l y r e d u c e d 2 2 - 3 4 h r a f t e r EB i n j e c t i o n ( 2 ug) m O V X rats. In o r d e r to d e t e r m i n e w h e t h e r or n o t the g a s t r o i n t e s t i n a l c h a n g e s are i n d e p e n d e n t o f a l e r a t i o n s in f o o d r e t a k e , rats were f o o d d e p r i v e d f r o m the tame of the EB l n j e c t m n t o t h e test. In an a t t e m p t to optamlze the l i k e l i h o o d o f d e t e c t i n g a c h a n g e w i t h EB t r e a t m e n t , the EB dose was increased to 5 tzg Procedure E i g h t e e n S p r a g u e - D a w l e y rats O V X for t w o to t h r e e m o n t h s a n d weighing 3 5 0 - 4 5 0 g were m j e c t e d w i t h e i t h e r 5 tag EB (n = 11) or 0.1 ml o f the sesame oil vehicle (n = 7) s u b c u t a n e o u s l y and were s i m u l t a n e o u s l y f o o d d e p r i v e d 3 4 - 3 8 h r b e f o r e testing. T h e t e s t i n g p r o c e d u r e for gastric r e t e n t i o n a n d i n t e s t i n a l t r a n s i t was i d e n t i c a l to t h a t of Experiment 3 R e s u l t s a n d Discussion N e i t h e r gastric r e t e n t i o n n o r i n t e s t i n a l t r a n s i t was significantly a f f e c t e d b y EB t r e a t m e n t (Table 3) In fact the E B - t r e a t e d a n d oil-treated g r o u p s are q m t e similar to e a c h o t h e r a n d to t h e off-control g r o u p f r o m E x p e r i m e n t 3
Estradml Benzoate Od
41.9 ~±2 5) 44 5 (_+4 3j
s 9 (+0 3) s 5 (±0 5)
despite the d i f t e r e n c e s m time o f d e p r i v a t i o n These results l n d m a t e t h a t the meal size changes precede the changes m g a s t r o i n t e s t i n a l t r a n s i t in EB-treated O V X rats and suggest t h a t g a s t r o i n t e s t i n a l changes are n o t the cause c,1 the decrease in meal size DISCUSSION
The results ol E x p e r i m e n t 1 e x t e n d the a n t l e s t r o g e m c Influences o f p r o g e s t e r o n e to include meat p a t t e r n s As w i t h m e a s u r e s o f t o t a l dally food i n t a k e and b o d y weight, p r o g e s t e r o n e had n o effect b y itself, it increased meal size and decreased m e a l f r e q u e n c y only m O V X rats t h a t had also b e e n reJected w i t h EB dally. The effects of progeat e r o n e o n meal p a t t e r n s of OVX, E B - t r e a t e d rats were q u a h t a t l v e l y similar to t h o s e seen w h e n estrogens are withdrawn by ovarlectomy [ 3 ] We have previously s h o w n t h a t the effects ol ovarle c t o m y a n d estradlol r e p l a c e m e n t on meal s~ze are perm a n e n t . In b o t h cases, meal size r e m a i n s altered even w h e n t o t a l dally food i n t a k e r e t u r n s to n o r m a l . This has suggested to us t h a t the e l f e c t s of ovarian h o r m o n e s are primarily on the mechanism(s) that terminate short-term f o o d retake. The changes are n o t s e c o n d a r y to changes m t o t a l dady f o o d i n t a k e n o r do they seem to be s e c o n d a r y to changes in meal f r e q u e n c y The findings of E x p e r i m e n t 1 are c o n s i s t e n t w i t h the suggestion t h a t the p r i m a r y e f t e c t ol ovarian h o r m o n e s is to m o d i f y the meal saze r a t h e r t h a n the m t e r m e a l i n t e r v a l (meal t r e q u e n c y ) . All of the EB p r o g e s t e r o n e t r e a t e d rats increased t h e i r meal s~ze m the first 12 days o f t r e a t m e n t Only one o f six decreased her meal f r e q u e n c y by m o r e t h a n 3 ~ d u r i n g this tame The changes m meal f r e q u e n c y , t h e r e f o r e , a p p e a r to follow the changes in meal size. L~ke the a b b r e v m t m n of meal size caused by estradlol, this a u g m e n t a t m n by p r o g e s t e r o n e ~s p e r m a n e n t as long as daily h o r m o n a l t r e a t m e n t ~s continued In o u r c o m p a r i s o n of olt- and E B - t r e a t e d O V X rats, we o b s e r v e d large d i f f e r e n c e s m gastrac r e t e n t m n and rate of i n t e s t i n a l transat of liquid diet w h e n tested a f t e r t w o weeks of daily i n j e c t i o n s However, the results o f E x p e r i m e n t 4 suggest t h a t this g a s t r o i n t e s t i n a l c h a n g e is n o t the cause of the d i m i n i s h e d meal size u n d e r the i n f l u e n c e o f EB t h a t we have previously r e p o r t e d [3] I n j e e t m n ol 2 u g of EB significantly altered meal size m O V X rats w i t h i n 22 34 hr (Blaustean a n d Wade, u n p u b h s h e d o b s e r v a t i o n s ) , but m E x p e r i m e n t 4 t h e r e was n o i n d i c a t i o n o f a change m the g a s t r o i n t e s t i n a l t r a n s i t of h q u l d dmt 3 4 - 3 8 hr a f t e r 5 ,tg EB. P e r h a p s the slight m e t h o d o l o g i c a l d i f f e r e n c e s b e t w e e n E x p e r i m e n t s 3 a n d 4 are responsible for the absence of effect an E x p e r i m e n t 4. The d e p r i v a t i o n p e r i o d o f E x p e r > m e n t 4 was slightly longer ( 3 4 - - 3 8 h r ) t h a n the d e p r i v a t i o n
OVARIAN HORMONES AND MEAL PATTERNS
27
p e r i o d in E x p e r i m e n t 3 ( 2 4 - 2 8 hr). Nevertheless, the resuits o f t h e oil-treated c o n t r o l g r o u p s f r o m t h e t w o e x p e r i m e n t s were r e m a r k a b l y c o n s i s t e n t , suggesting t h a t t h e increased d e p r i v a t i o n was w i t h o u t effect. Since t h e s e are negative results, t h e possibility c a n n o t be e x c l u d e d t h a t t h e r e a c t u a l l y is a rapid c h a n g e in g a s t r o i n t e s t i n a l t r a n s i t t h a t is caused d i r e c t l y b y e s t r a d l o l b u t t h a t o u r t e c h n i q u e s are n o t s u f f i c i e n t l y sensitwe t o resolve ~t. T h e results o f E x p e r i m e n t 3 in w h i c h a l t e r a t i o n s were o b t a i n e d w i t h l o n g - t e r m EB t r e a t m e n t argue against this possibility. In s u m m a r y , t h e g o n a d a l h o r m o n e s t h a t are k n o w n t o
affect m e a l p a t t e r n s n o w i n c l u d e p r o g e s t e r o n e . We have also o b s e r v e d a c h a n g e in t h e rate o f g a s t r o i n t e s t i n a l t r a n s i t m l o n g - t e r m E B - t r e a t e d , O V X rats t h a t was suggestive of a p o t e n t i a l m e c h a m s m for the ovarian i n f l u e n c e o n meal size. T h e final e x p e r i m e n t suggests, h o w e v e r , t h a t this gastroint e s t i n a l c h a n g e is n o t h k e l y to be the cause o f the m e a l size a l t e r a t i o n s i n d u c e d b y ovarian h o r m o n e s . A m o n g t h e possibilities b y w h i c h the meal size changes m i g h t be m e d i a t e d are c h a n g e s in n e u r a l criteria for m e a l t e r m m a h o n or a l t e r a t i o n s m the p o s t a b s o r p t w e m e t a b o l i c p a t t e r n s [111
REFERENCES 1 2. 3. 4
5.
6 7.
8 9 10. 11. 12
Balagura, S. and L. D Devenport. Feeding patterns of normal and ventromedlal hypothalamic lesioned male and female rats. J comp. physiol Psychol. 71: 357-364, 1970. Becker, E. and H. R. Kisslleff. Inhibitory controls of feeding by the ventromedial hypothalamus. Am. J Phystol. 226: 3 8 3 - 3 9 6 , 1974. Blaustem, J. D. and G. N Wade Ovarian influences on the meal patterns of female rats. PhystoL Behav. 17: 201-208, 1976. Brobeck, J. R., M. Wheatland and J. L. Strominger. Variations m regulation of energy exchange assocmted with estrus, diestrus and pseudopregnancy in rats Endocrmology 40: 6 5 - 7 2 , 1947 Butcher, R. L., W. E. Colhns and N. W. Fugo. Plasma concentrations of LH, FSH, prolactm, progesterone and estradlol-17/3 throughout the 4-day estrous cycle of the rat Endocrmology 9 4 : 1 7 0 4 - 1 7 0 8 , 1974. Davis, J D. and D. A. Booth. Vagotomy in the rat reduces meal size of diets containing fat. Phystol. Behav. 12: 6 8 5 - 6 8 8 , 1974. De Castro, J. M and S Balagura. The ontogeny of meal patterning in rats and ~ts recapitulation during recovery from lateral hypothalamlc lesions J comp physioL Psychol 89: 7 9 1 - 8 0 2 , 1975. Deutsch, J. A , F. Mohna and A. Puerto. Conditioned taste aversion caused by palatable nontoxic nutrients. Behav. Btol 16: 161-174, 1976. Drewett, R. F. The meal patterns of the oestrous cycle and their motlvatxonal significance. Quart Jl exp Psychol 26: 4 8 9 - 4 9 4 , 1974. Ehman, G. K., D J Albert and J L. Jamleson. Injections into the duodenum and the induchon of satiety in the rat. Can J Psychol. 25: 147-166, 1971. Friedman, M I. and E M Stricker. The physiological psychology of hunger A physiological perspectwe. Psychol Rev. 83: 4 0 9 - 4 3 1 , 1976. Gentry, R T and G N Wade Androgenic control of food retake and body weight m male rats. J. comp. phystol Psychol 97: 18-25, 1976
13 14. 15. 16. 17 18. 19. 20. 21 22. 23. 24.
25
Kenney, N. J. and D. G Mook. Effects of ovariectomy on meal pattern m the albino rat. J. comp. physiol. Psychol 87: 3 0 2 - 3 0 9 , 1974 Kissileff, H. R. Free-feeding m normal and "recovered lateral" rats monitored by a pellet-detecting eatometer. Physiol. Behav 5: 163-173, 1970. Ralph, T. L and P E. Sawchenko. Differential effects of lateral and ventromedial hypothalamlc lesions on gastrointestinal transit in the rat. Phystol. Behav, in press. Roberts, S., N. J. Kenney and D. G. Mook. Overeating reduced by progesterone m the ovarlectom~zed, adrenalectom~zed rat. Hormones Behav. 3: 267-276, 1972. Snowdon, C. T. Gastrointestinal sensory and motor control of food intake. J. comp. physiol. Psychol 71: 6 8 - 7 5 , 1970. Snowdon, C T Produchon of satiety with small mtraduodenal infusions m the rat J comp physiol. Psychol 88: 231-238, 1975 Snowdon, C. T. and A. N. Epstein Oral and mtragastric feeding m vagotomized rats. J comp. phystol. Psychol. 71: 5 9 - 6 7 , 1970. Tarttelin, M. F. and R. A GorskL Varmtlons m food and water intake m the normal and acylic female rat Phystol Behav 7: 8 4 7 - 8 5 2 , 1971. Tarttelln, M. F. and R A. GorskL The effects of ovarian steroids on food and water intake and body weight in the female rat. Acta endocr 72: 5 5 1 - 5 6 8 , 1973. Teitelbaum, P. and B A Campbell. Ingestion patterns in normal and hyperphaglc rats. J comp phystol Psychol 51: 135-141, 1958. Wade, G N. Some effects of ovarian hormones on food intake and body weight in female rats. J comp phystol Psychol. 88: 183-193, 1975. Wade, G N. Sex hormones, regulatory behaviors and body weight. In" Advances tn the Study of Behavtor, Vol. 6, edited by J. S. Rosenblatt, R. A. Hmde, E. Shaw and C. C Beer New York: Academic Press, 1976 Young, R. C., J Gibbs, J. Antra, J. Holt and G. P Smith. Absence of satiety during sham feeding m the rat J comp phystol Psychol. 87: 7 9 5 - 8 0 0 , 1974.
Ovarian Hormones and Meal Patterns in Rats: Effects of Progesterone and Role of Gastrointestinal Transif JEFFREY
D. B L A U S T E I N 2 A N D G E O R G E N. W A D E 3
Department o f Psychology, University o f Massachusetts, Amherst, MA 01003 ( R e c e i v e d 12 A u g u s t 1 9 7 6 ) BLAUSTEIN, J. D. AND G. N. WADE. Ovarian hormones and meal patterns in rats: effects of progesterone and role of gastromtestinal transit. PHYSIOL. BEHAV. 19(1) 2 3 - 2 7 , 1977. - - T h r e e experiments determined: (1) whether progesterone treatment would reverse the effects of estradiol benzoate (EB) on meal patterns of ovanectomlzed (OVX) rats, and (2) whether changes m gastrointestinal transit were responsible for the EB-induced changes m meal patterns. Progesterone (5 mg/day) reversed the effects of EB by increasing meal size and decreasing meal frequency m OVX, EB-treated rats. Progesterone had no effect on these measures in OVX rats that were not given EB. In a comparison of the rate of gastrointestinal transit, the rate of gastrointestinal transit was found to be faster in OVX rats injected with EB daily for two weeks than m OVX, oil-treated controls as measured under anesthesia with infusmn of ten ml of liqmd diet. However, this alteration in gastrointestinal transit does not appear to be responsible for the decreased meal size of EB-treated, OVX-rats, because the gastrointestinal changes are not observed 3 4 - 3 8 hr after an EB injectmn, a time at which meal size is already affected.
Meal patterns Food intake
Ovarian hormones Estradiol
Progesterone
Gastrointestinal transit
f o o d r e t a k e is a c c o m p h s h e d b y a f u r t h e r increase in meal f r e q u e n c y ; meal size r e m a i n s p e r m a n e n t l y s u p p r e s s e d as l o n g as i n j e c t i o n s are m a i n t a i n e d . T h e results o f t h e s e h o r m o n a l m a n i p u l a t i o n s o n meal p a t t e r n s h a v e led t o t h e c o n c l u s i o n t h a t e s t r a d i o l affects t h e m e c h a m s m ( s ) t h a t t e r m i n a t e i n d i v i d u a l meals [ 3,13 ]. P r o g e s t e r o n e a n t a g o m z e s virtually all of e s t r a d i o l ' s beh a v i o r a l effects t h a t h a v e b e e n s t u d i e d , i n c l u d i n g e s t r a d i o l ' s suppressive effects o n e a t i n g as m e a s u r e d b y t o t a l daffy f o o d r e t a k e [ 2 3 ] . H o w e v e r , p r o g e s t e r o n e b y itself h a s n o effect in o v a r l e c t o m i z e d ( O V X ) rats t h a t h a v e n o t b e e n t r e a t e d w i t h e s t r a d m l . If p r o g e s t e r o n e , in fact, acts o n l y t o a n t a g o n i z e t h e effects o f e s t r o g e n o n eating, as h a s b e e n suggested [ 2 3 , 2 4 ] t h e n p r o g e s t e r o n e s h o u l d reverse estradlol's effects o n m e a l p a t t e r n s , ~t s h o u l d n o t have a n y e f f e c t in O V X rats t h a t have n o t received estradiol. E x p e r i m e n t s 1 and 2 e x a m i n e d t h e effects o f p r o g e s t e r o n e o n t h e meal p a t t e r n s o f O V X a n d E B - t r e a t e d , O V X rats. T h e r e is a great deal o f e v i d e n c e t h a t suggests an i n t e s t i n a l c o n t r i b u t i o n to t h e t e r m l n a t m n o f s h o r t - t e r m
L A T E P R O E S T R U S , t h e stage of t h e e s t r o u s cycle d u r i n g w h i c h sexual r e c e p t i v i t y occurs, a n d w h i c h follows p e a k levels of b l o o d p l a s m a estradiol-I 7t3 [ 5 ], is a c c o m p a n i e d b y a s u p p r e s s i o n m dally f o o d xntake [ 4 , 2 0 ] This d e c r e a s e d f o o d i n t a k e is a c c o m p h s h e d b y a decrease in the size of m d w x d u a l meals a n d a less t h a n c o m p e n s a t o r y increase m the f r e q u e n c y o f meals [ 3 , 9 ] . These c o r r e l a h o n s a p p e a r t o be a result o f c h a n g i n g levels of e s t r a d m l [24] for t h e f o l l o w i n g reasons. O v a r l e c t o m y results in a t r a n s i e n t increase in f o o d i n t a k e [12,21 ] w h i c h is r e f l e c t e d in an increase m m e a l size a n d a less t h a n c o m p e n s a t o r y decrease in meal f r e q u e n c y [ 3,13 ]. T h e m e a l size increase is p e r m a n e n t . W h e n t o t a l daffy f o o d i n t a k e r e t u r n s t o c o n t r o l levels, m e a l size r e m a i n s elevated, b u t meal f r e q u e n c y decreases [ 3 ] . R e p l a c e m e n t o f e s t r a d m l b y daily r e j e c t i o n s o f e s t r a d i o l b e n z o a t e (EB) reverses t h e effects of o v a n e c t o m y . T h e r e is a t r a n s i e n t decrease in t o t a l daily f o o d r e t a k e w h i c h is a c c o m p l i s h e d b y a decrease m meal size a n d a less t h a n fully c o m p e n s a t o r y increase m meal f r e q u e n c y [ 3 ] . T h e r e t u r n t o c o n t r o l levels o f daffy
1This research was supported by Research Grant NS-10873 and Research Career Development Award N S - 0 0 0 9 0 from the National Institute of Neurological and Communicahve Disorders and Stroke, and by Training Grant MH 11823 from the National Institute of Mental Health. We are grateful to John Ieni and Dorrine Conrad for techmcal assistance, to Edward Roy for his probing question, and to Mark Friedman and Paul Sawchenko for helpful discussions 2Present address: InsUtute of Ammal Behavior, Rutgers Umverslty, 101 Warren Street, Newark, NJ 07102. 3 To whom reprint requests should be sent. 23
24
B L A U S T f I N ,\NI) V~,\IH ~
f o o d intake ([10, 18, 251, but cf. 181~ As already discussed, E B - t r e a t m e n t results in a decrease m meal size Two surgical m a m p u l a t i o n s that result in decreased meal size are v a g o t o m y in rats on a liquid diet [6,1c/] and lateral h y p o t h a l a m i c lesions [7,14]. Both of these m a m p u l a t i o n s also result in an increase in the rate of gastrointestinal transit [15,17] Conversely, v e n t r o m e d m l h y p o t h a l a m l c lesions result in increased meal size [1, 2, 22] and a decrease in the rate of gastrointestinal transit 115] In E x p e r i m e n t s 3 and 4, we examine this aspect ol ovarian influences on meal patterns We test the hypothesis that ovarian h o r m o n e s cause changes in the rate of gastric e m p t y i n g and intestinal transit, variables which often correlate with alterations in meal patterns, using the OVX, EB-treated rat as a model.
EXPERIMENT
~" 120~c ~--~ :
Twelve Sprague-Dawley rats purchased from a c o m m e r cial suppher (Charles River Breedmg Laboratories, Wilmington, MA) were O V X at least three m o n t h s prior to use The rats weighed 3 0 0 - 4 5 0 g at the start of t r e a t m e n t and were rejected daffy with 2 ug EB m 0 1 ml sesame oil B e g m m n g on the second week of injections rats were maintained on a h q m d diet described previously [3]. During Week 5, meal patterns were r e c o r d e d for a four-day baseline period. At the end of this permd, one group received 5 mg progesterone (n = 6; EB + progesterone) and one group (n = 6, EB) received 0.1 ml sesame off daffy in addition to the daffy EB injections. Injections were c o n t i n u e d for 24 days and meal patterns were m o n i t o r e d c o n t i n u o u s l y Environmental fflummatlon was provided from 0 7 0 0 - 1 9 0 0 hr daffy and r o o m t e m p e r a t u r e was maintained at 2 1 - 2 3 ° C . All injections were administered b e t w e e n 0 8 0 0 - 1 0 0 0 hr, and at this h m e , rats were weighed, bottles cleaned and fresh l l q m d diet given. F o r detaffs of the diet, apparatus and procedure for analysis of meal patterns (see [ 3 ] ) Since it was n o t possible to m a t c h groups on all variables of the meal patterns and f o o d mtake, data were converted to percentage of the four-day baseline
Results and Dzscusszon F o r analysis, the results were divided into Days 1 - 1 2 and Days 1 3 - 2 4 after the start of progesterone t r e a t m e n t During Days 1 - 1 2 the EB + progesterone group gamed weight at the rate of 0.47% (-+0.07)/day c o m p a r e d with 0 15% (-+0.08/day for the EB group, t(10) = 2.800, p < 0 02 (Fag, 1). By the second half of t r e a t m e n t , b o t h groups were gaming at a p p r o x i m a t e l y the same rate. There was a transient increase in the daily f o o d intake of the EB + progesterone group when c o m p a r e d with the EB group During the first half of t r e a t m e n t the EB + progesterone group ate 114% (-+4 0) of basehne levels and the EB group ate 103% (-+4.4) of basehne, t(10) = 1.833, p < 0 0 5 , one-taff This difference was absent during the second half o f t r e a t m e n t (114% -+ 7.3 vs. 111% -~ 6 4). Mean dady meal size was 119% (-+3.3) of baseline levels
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Progesterone inhibits estradlol's suppressive effects on total daffy f o o d intake and b o d y weight m a i n t e n a n c e In the first e x p e r i m e n t we evaluate the effects of progesterone on meal patterns in EB-treated, O V X rats
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FIG 1 Body weight and food retake of ovariectomlzed rats rejected with 2~g/day of estradlol benzoate for four weeks prior to momtoring of meal patterns After a 4-day baseline, rats were also rejected with 5 rag/day of progesterone (EB + P group) or od (kB group), indicated by arrow for the EB + progesterone group during Days l 12 c o m p a r e d with 98% (+ 8 7) for EB controls, t(10) = 2 282. p < 0 05, Fig 2) This difference persisted during the second half of t r e a t m e n t ( 1 4 6 ~ + 8 8 vs 110~; + 13 1, t ( 1 0 ) 2.269, p < 0 05. Meal frequency was 98% (~ 3 2) of basehne for the EB + progesterone group during the first 12 days c o m p a r e d with 109% (, l0 1) of basehne for controls By the second half of treatment, the EB + progesterone group had decreased to 80% (± 5 4) as many ineals as during basehne and EB controls were taking 107~'¢ (~ 8 4) ot baseline, t(10) = 2 744, p < 0 05 E x p e r i m e n t 1 demonstrates that progesterone can reverse estradlol's effects on meal patterns The transient increase in f o o d intake and rate of body wexght gain when c o m p a r e d with controls confirms previous flndmgs [16] The increase in meal size by progesterone along with a decrease in meal frequency was predicted from progesterone's antlestrogenlc influences on total daffy food intake It has previously been suggested that ovarian h o r m o n e s influence meal patterns prlmarll3, by affecting factor(s) that determine short-term food intake (meal size) and not on the m t e r m e a l interval (meal frequency) The results of this e x p e r i m e n t are consistent with this interpretatlon. During Days 1- 12, all of the EB + progesteronetreated rats increased their meal size but only one rat decreased its meal frequency by more than 3% of baseline
EXPERIMENT
2
In measures of total dally food intake and body weight maintenance, progesterone has no effect in the absence of estrogens [24] E x p e n m e n t 2 demonstrates that proges-
OVARIAN HORMONES AND MEAL PATTERNS
25 weight, f o o d intake, meal size or meal f r e q u e n c y during Days 1 - 1 2 or Days 1 3 - 2 4 approached stahstical significance. E x p e r i m e n t 2 once again confirms that progesterone is w i t h o u t effect on total dally food intake or b o d y weight maxntenance in the absence of estradlol [ 2 4 ] . Experiments 1 and 2 e x t e n d the situations in which progesterone reverses estradlol's effects to include meal patterns.
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FIG. 2. Meal size and meal frequency of ovariectomlzed rats rejected with 2 #g/day of estradlol benzoate for four weeks prior to monitoring of meal patterns. After a 4-day baseline rats were also injected with 5 mg/day of progesterone (EB + P group) or oil (EB group), indicated by arrow. terone does n o t affect meal patterns in O V X rats that have not been pretreated with EB. Procedure
Eight Sprague-Dawley rats purchased from a c o m m e r c i a l suppher (Charles River Breeding Laboratories) were OVX at least three m o n t h s prior to use. The p r o c e d u r e was the same as m E x p e r i m e n t 1 e x c e p t that no EB t r e a t m e n t was gwen. Groups recewed either 5 mg progesterone in 0.1 ml sesame oil/day ( n = 4 ; progesterone) or 0.1 ml sesame o d / d a y (n = 4, od) beginning after the four days of basehne recording of meal patterns. Results and Dtscusszon
As p r e d i c t e d progesterone had no effect on the meal patterns of OVX rats that were not treated w~th estradiol None of the progesterone vs. oll comparisons for b o d y
Estradlol benzoate t r e a t m e n t results in a decrease in meal size, as do v a g o t o m y in rats on a liquid diet [6,19] and lateral h y p o t h a l a m i c lesions [7,14]. Both of these surgical m a n l p u l a t o n s also result in an increase in the rate of gastrointestinal transit [ 1 5 , 1 7 ] . In the case of v a g o t o m y , gastric e m p t y i n g speeds up as measured m awake rats [ 1 7 ] , with lateral h y p o t h a l a m l c lestons, the rate has been measured m response to a forced stomach-load of milk in anesthetized rats [ 1 5 ] . Since there is evidence for an intestinal c o n t r i b u t i o n to the t e r m i n a t i o n of short-term f o o d retake, as already discussed, we lnvestxgated the poss~bllity that E B - t r e a t m e n t m OVX rats w o u l d result m more rapid gastric e m p t y i n g a n d / o r intestinal transit. The procedure that was used involved stomach-loading into a food-deprived a n e s t h e h z e d rat. This technique was chosen because of its effectiveness m dissociating V M H - and L H - l e s l o n e d rats from controls [15] Procedure
Sixteen Sprague-Dawley rats O V X for two or three m o n t h s and weighing 3 3 0 - 4 4 0 g were mjected with 2 tzg EB/0.1 ml sesame oll (n = 8) or 0.1 ml sesame oll (n = 8) daily for t w o weeks prior to the test. One week prior to the test, all rats were maintained on a liqmd diet described previously [3]. T w e n t y - f o u r to 28 hr prior to the test t h e y were f o o d deprived. Tap water was freely available at all times. Rats were anesthetized with s o d m m p e n t o b a r b i t a l (40 m g / k g b o d y weight, N e m b u t a l ) and then laparotomlzed. With the rat in a supine positron 10 ml of hquid diet were refused into the stomach through the gastroesophageal j u n c t i o n . A 10 ml syringe c o n n e c t e d to the needle with p o l y e t h y l e n e tubing was used to manually refuse the diet into the stomach at a constant rate over one m m (I ml/6 sec). At the c o m p l e t i o n of the infusion, the gastroesophageal j u n c t i o n was lzgated with sdk suture that had previously been loosely wrapped around the esophagus, and the pylorus was clamped i m m e d i a t e l y , seahng the c o n t e n t s
TABLE I MEAN BODY WEIGHT, FOOD INTAKE, MEAL SIZE AND MEAL FREQUENCY DURING DAYS 1-12 AND 13-24 OF OVARIECTOMIZED RATS TREATED DAILY WITH OIL OR PROGESTERONE (5 rag)* Body Weight
Food Intake
Meal Size
Meal Frequency
Days 1-12 Oil Progesterone
102 0 (_+0.3) 102.8 (_+0 6)
108.3 (+5.6) 113.3 (_+13.1)
103 1 (+3.6) 101.0 (_+9.8)
107.0 (_+7.0) 110.5 (_+6.1)
Days 13-24 Oil Progesterone
106.4 (_+1.1) 105.6 ( + 1 4)
106 5 (_+7.0) 99.4 ( _+13.4)
107.1 (_+1.4) 93.2 ( _+12.1)
101.7 (_+6.8) 105.4 ( _+3 5)
*Data are expressed as percentage of basehne (_+ standard errors)
26
BLAUSIFI\ FABLE
TABLE 2 MEAN (± SEMI INTESTINAL TRANSIT AND GASTRIC RETENTION OF LIQUID DIET IN OVARIECTOMIZED RATS TREATED WITH 2 /xg E S T R A D I O L BENZOATE~DAY OR S E S A M E OIL FOR TWO WEEKS PRIOR TO TESTING
MEAN (± SEMI INTESTINAL TRANSIT AND GASIRIC R E I E N I I ( I N OF LIQUID DIET IN OVARIECTOMIZED RATS TREATED WI'FIt /zg ESTRADIOL BENZOATE OR SESAME OIL I~: DAYS PRIOR "1¢) TEqT1NG
Intestinal Transit (cm) Gastrmc Retentmn (roll
Intestinal Transit (cm) Gastric Retentmn (ml) Estradml Benzoate Oil
71 9 (_+6 1) 454(_+40)
,\'~l) W\11t
4 0 {_+0 5) 59(_+04)
of the s t o m a c h . F i f t e e n s e c o n d s later, t h e distal p o i n t t h a t the milk h a d travelled t h r o u g h the i n t e s t i n e was c l a m p e d , the s t o m a c h was r e m o v e d , and t h e v o l u m e o f the s t o m a c h c o n t e n t s was m e a s u r e d T h e antestine was t h e n g e n t l y dissected away f r o m the o m e n t a , a n d t h e d i s t a n c e b e t w e e n the p y l o n c a n d i n t e s t i n a l c l a m p s was m e a s u r e d The e x p e r i m e n t was c o n d u c t e d w i t h the e x p e r i m e n t e r b h n d to treatment Results EB t r e a t m e n t r e s u l t e d in a 58% increase in d i s t a n c e travelled b y t h e milk, t ( 1 4 ) = 3 632, p < 0 . 0 1 , a n d 32% decrease in gastric r e t e n t i o n w h e n c o m p a r e d w i t h oil-treated c o n t r o l s , t ( 1 4 ) = 2 873, p < 0 02 (Table 2) EXPERIMENT 4
A l t h o u g h t h e results o f E x p e r i m e n t 3 s u p p o r t the n o t m n t h a t EB t r e a t m e n t affects g a s t r o i n t e s t i n a l t r a n s i t , the test was p e r f o r m e d a f t e r t w o weeks o f h o r m o n e t r e a t m e n t Perhaps, r a t h e r t h a n EB causing g a s t r o i n t e s t i n a l changes w h i c h t h e n a l t e r m e a l p a t t e r n s , EB m i g h t first a l t e r meal size m s o m e o t h e r way, a n d this results m the gastroint e s t i n a l change. It is necessary to d e t e r m i n e w h e t h e r t h e g a s t r o i n t e s t i n a l c h a n g e o c c u r s wath a s u f f i c i e n t l y s h o r t lat e n c y to a c c o u n t f o r t h e a l t e r a t i o n in meal size In the n e x t e x p e r i m e n t , we test for darect e f f e c t s of estradiol on g a s t r o i n t e s t i n a l t r a n s i t b y testing 3 4 - 3 8 h r a f t e r a single EB r e j e c t i o n , we have f o u n d previously t h a t meal size as s l g m f i c a n t l y r e d u c e d 2 2 - 3 4 h r a f t e r EB i n j e c t i o n ( 2 ug) m O V X rats. In o r d e r to d e t e r m i n e w h e t h e r or n o t the g a s t r o i n t e s t i n a l c h a n g e s are i n d e p e n d e n t o f a l e r a t i o n s in f o o d r e t a k e , rats were f o o d d e p r i v e d f r o m the tame of the EB l n j e c t m n t o t h e test. In an a t t e m p t to optamlze the l i k e l i h o o d o f d e t e c t i n g a c h a n g e w i t h EB t r e a t m e n t , the EB dose was increased to 5 tzg Procedure E i g h t e e n S p r a g u e - D a w l e y rats O V X for t w o to t h r e e m o n t h s a n d weighing 3 5 0 - 4 5 0 g were m j e c t e d w i t h e i t h e r 5 tag EB (n = 11) or 0.1 ml o f the sesame oil vehicle (n = 7) s u b c u t a n e o u s l y and were s i m u l t a n e o u s l y f o o d d e p r i v e d 3 4 - 3 8 h r b e f o r e testing. T h e t e s t i n g p r o c e d u r e for gastric r e t e n t i o n a n d i n t e s t i n a l t r a n s i t was i d e n t i c a l to t h a t of Experiment 3 R e s u l t s a n d Discussion N e i t h e r gastric r e t e n t i o n n o r i n t e s t i n a l t r a n s i t was significantly a f f e c t e d b y EB t r e a t m e n t (Table 3) In fact the E B - t r e a t e d a n d oil-treated g r o u p s are q m t e similar to e a c h o t h e r a n d to t h e off-control g r o u p f r o m E x p e r i m e n t 3
Estradml Benzoate Od
41.9 ~±2 5) 44 5 (_+4 3j
s 9 (+0 3) s 5 (±0 5)
despite the d i f t e r e n c e s m time o f d e p r i v a t i o n These results l n d m a t e t h a t the meal size changes precede the changes m g a s t r o i n t e s t i n a l t r a n s i t in EB-treated O V X rats and suggest t h a t g a s t r o i n t e s t i n a l changes are n o t the cause c,1 the decrease in meal size DISCUSSION
The results ol E x p e r i m e n t 1 e x t e n d the a n t l e s t r o g e m c Influences o f p r o g e s t e r o n e to include meat p a t t e r n s As w i t h m e a s u r e s o f t o t a l dally food i n t a k e and b o d y weight, p r o g e s t e r o n e had n o effect b y itself, it increased meal size and decreased m e a l f r e q u e n c y only m O V X rats t h a t had also b e e n reJected w i t h EB dally. The effects of progeat e r o n e o n meal p a t t e r n s of OVX, E B - t r e a t e d rats were q u a h t a t l v e l y similar to t h o s e seen w h e n estrogens are withdrawn by ovarlectomy [ 3 ] We have previously s h o w n t h a t the effects ol ovarle c t o m y a n d estradlol r e p l a c e m e n t on meal s~ze are perm a n e n t . In b o t h cases, meal size r e m a i n s altered even w h e n t o t a l dally food i n t a k e r e t u r n s to n o r m a l . This has suggested to us t h a t the e l f e c t s of ovarian h o r m o n e s are primarily on the mechanism(s) that terminate short-term f o o d retake. The changes are n o t s e c o n d a r y to changes m t o t a l dady f o o d i n t a k e n o r do they seem to be s e c o n d a r y to changes in meal f r e q u e n c y The findings of E x p e r i m e n t 1 are c o n s i s t e n t w i t h the suggestion t h a t the p r i m a r y e f t e c t ol ovarian h o r m o n e s is to m o d i f y the meal saze r a t h e r t h a n the m t e r m e a l i n t e r v a l (meal t r e q u e n c y ) . All of the EB p r o g e s t e r o n e t r e a t e d rats increased t h e i r meal s~ze m the first 12 days o f t r e a t m e n t Only one o f six decreased her meal f r e q u e n c y by m o r e t h a n 3 ~ d u r i n g this tame The changes m meal f r e q u e n c y , t h e r e f o r e , a p p e a r to follow the changes in meal size. L~ke the a b b r e v m t m n of meal size caused by estradlol, this a u g m e n t a t m n by p r o g e s t e r o n e ~s p e r m a n e n t as long as daily h o r m o n a l t r e a t m e n t ~s continued In o u r c o m p a r i s o n of olt- and E B - t r e a t e d O V X rats, we o b s e r v e d large d i f f e r e n c e s m gastrac r e t e n t m n and rate of i n t e s t i n a l transat of liquid diet w h e n tested a f t e r t w o weeks of daily i n j e c t i o n s However, the results o f E x p e r i m e n t 4 suggest t h a t this g a s t r o i n t e s t i n a l c h a n g e is n o t the cause of the d i m i n i s h e d meal size u n d e r the i n f l u e n c e o f EB t h a t we have previously r e p o r t e d [3] I n j e e t m n ol 2 u g of EB significantly altered meal size m O V X rats w i t h i n 22 34 hr (Blaustean a n d Wade, u n p u b h s h e d o b s e r v a t i o n s ) , but m E x p e r i m e n t 4 t h e r e was n o i n d i c a t i o n o f a change m the g a s t r o i n t e s t i n a l t r a n s i t of h q u l d dmt 3 4 - 3 8 hr a f t e r 5 ,tg EB. P e r h a p s the slight m e t h o d o l o g i c a l d i f f e r e n c e s b e t w e e n E x p e r i m e n t s 3 a n d 4 are responsible for the absence of effect an E x p e r i m e n t 4. The d e p r i v a t i o n p e r i o d o f E x p e r > m e n t 4 was slightly longer ( 3 4 - - 3 8 h r ) t h a n the d e p r i v a t i o n
OVARIAN HORMONES AND MEAL PATTERNS
27
p e r i o d in E x p e r i m e n t 3 ( 2 4 - 2 8 hr). Nevertheless, the resuits o f t h e oil-treated c o n t r o l g r o u p s f r o m t h e t w o e x p e r i m e n t s were r e m a r k a b l y c o n s i s t e n t , suggesting t h a t t h e increased d e p r i v a t i o n was w i t h o u t effect. Since t h e s e are negative results, t h e possibility c a n n o t be e x c l u d e d t h a t t h e r e a c t u a l l y is a rapid c h a n g e in g a s t r o i n t e s t i n a l t r a n s i t t h a t is caused d i r e c t l y b y e s t r a d l o l b u t t h a t o u r t e c h n i q u e s are n o t s u f f i c i e n t l y sensitwe t o resolve ~t. T h e results o f E x p e r i m e n t 3 in w h i c h a l t e r a t i o n s were o b t a i n e d w i t h l o n g - t e r m EB t r e a t m e n t argue against this possibility. In s u m m a r y , t h e g o n a d a l h o r m o n e s t h a t are k n o w n t o
affect m e a l p a t t e r n s n o w i n c l u d e p r o g e s t e r o n e . We have also o b s e r v e d a c h a n g e in t h e rate o f g a s t r o i n t e s t i n a l t r a n s i t m l o n g - t e r m E B - t r e a t e d , O V X rats t h a t was suggestive of a p o t e n t i a l m e c h a m s m for the ovarian i n f l u e n c e o n meal size. T h e final e x p e r i m e n t suggests, h o w e v e r , t h a t this gastroint e s t i n a l c h a n g e is n o t h k e l y to be the cause o f the m e a l size a l t e r a t i o n s i n d u c e d b y ovarian h o r m o n e s . A m o n g t h e possibilities b y w h i c h the meal size changes m i g h t be m e d i a t e d are c h a n g e s in n e u r a l criteria for m e a l t e r m m a h o n or a l t e r a t i o n s m the p o s t a b s o r p t w e m e t a b o l i c p a t t e r n s [111
REFERENCES 1 2. 3. 4
5.
6 7.
8 9 10. 11. 12
Balagura, S. and L. D Devenport. Feeding patterns of normal and ventromedlal hypothalamic lesioned male and female rats. J comp. physiol Psychol. 71: 357-364, 1970. Becker, E. and H. R. Kisslleff. Inhibitory controls of feeding by the ventromedial hypothalamus. Am. J Phystol. 226: 3 8 3 - 3 9 6 , 1974. Blaustem, J. D. and G. N Wade Ovarian influences on the meal patterns of female rats. PhystoL Behav. 17: 201-208, 1976. Brobeck, J. R., M. Wheatland and J. L. Strominger. Variations m regulation of energy exchange assocmted with estrus, diestrus and pseudopregnancy in rats Endocrmology 40: 6 5 - 7 2 , 1947 Butcher, R. L., W. E. Colhns and N. W. Fugo. Plasma concentrations of LH, FSH, prolactm, progesterone and estradlol-17/3 throughout the 4-day estrous cycle of the rat Endocrmology 9 4 : 1 7 0 4 - 1 7 0 8 , 1974. Davis, J D. and D. A. Booth. Vagotomy in the rat reduces meal size of diets containing fat. Phystol. Behav. 12: 6 8 5 - 6 8 8 , 1974. De Castro, J. M and S Balagura. The ontogeny of meal patterning in rats and ~ts recapitulation during recovery from lateral hypothalamlc lesions J comp physioL Psychol 89: 7 9 1 - 8 0 2 , 1975. Deutsch, J. A , F. Mohna and A. Puerto. Conditioned taste aversion caused by palatable nontoxic nutrients. Behav. Btol 16: 161-174, 1976. Drewett, R. F. The meal patterns of the oestrous cycle and their motlvatxonal significance. Quart Jl exp Psychol 26: 4 8 9 - 4 9 4 , 1974. Ehman, G. K., D J Albert and J L. Jamleson. Injections into the duodenum and the induchon of satiety in the rat. Can J Psychol. 25: 147-166, 1971. Friedman, M I. and E M Stricker. The physiological psychology of hunger A physiological perspectwe. Psychol Rev. 83: 4 0 9 - 4 3 1 , 1976. Gentry, R T and G N Wade Androgenic control of food retake and body weight m male rats. J. comp. phystol Psychol 97: 18-25, 1976
13 14. 15. 16. 17 18. 19. 20. 21 22. 23. 24.
25
Kenney, N. J. and D. G Mook. Effects of ovariectomy on meal pattern m the albino rat. J. comp. physiol. Psychol 87: 3 0 2 - 3 0 9 , 1974 Kissileff, H. R. Free-feeding m normal and "recovered lateral" rats monitored by a pellet-detecting eatometer. Physiol. Behav 5: 163-173, 1970. Ralph, T. L and P E. Sawchenko. Differential effects of lateral and ventromedial hypothalamlc lesions on gastrointestinal transit in the rat. Phystol. Behav, in press. Roberts, S., N. J. Kenney and D. G. Mook. Overeating reduced by progesterone m the ovarlectom~zed, adrenalectom~zed rat. Hormones Behav. 3: 267-276, 1972. Snowdon, C. T. Gastrointestinal sensory and motor control of food intake. J. comp. physiol. Psychol 71: 6 8 - 7 5 , 1970. Snowdon, C T Produchon of satiety with small mtraduodenal infusions m the rat J comp physiol. Psychol 88: 231-238, 1975 Snowdon, C. T. and A. N. Epstein Oral and mtragastric feeding m vagotomized rats. J comp. phystol. Psychol. 71: 5 9 - 6 7 , 1970. Tarttelin, M. F. and R. A GorskL Varmtlons m food and water intake m the normal and acylic female rat Phystol Behav 7: 8 4 7 - 8 5 2 , 1971. Tarttelln, M. F. and R A. GorskL The effects of ovarian steroids on food and water intake and body weight in the female rat. Acta endocr 72: 5 5 1 - 5 6 8 , 1973. Teitelbaum, P. and B A Campbell. Ingestion patterns in normal and hyperphaglc rats. J comp phystol Psychol 51: 135-141, 1958. Wade, G N. Some effects of ovarian hormones on food intake and body weight in female rats. J comp phystol Psychol. 88: 183-193, 1975. Wade, G N. Sex hormones, regulatory behaviors and body weight. In" Advances tn the Study of Behavtor, Vol. 6, edited by J. S. Rosenblatt, R. A. Hmde, E. Shaw and C. C Beer New York: Academic Press, 1976 Young, R. C., J Gibbs, J. Antra, J. Holt and G. P Smith. Absence of satiety during sham feeding m the rat J comp phystol Psychol. 87: 7 9 5 - 8 0 0 , 1974.