Abdominal vagatomy does not modify endotoxic shock in rats

Life Sciences, Vol. 33, pp. Printed in the U.S.A.

1033-1037

Pergamon Pres

ABDOMINAL VAGOTOMYDOES NOT MODIFY ENDOTOXIC SHOCK IN RATS A r t h u r B. Pitterman, Gary F r i e d l a n d e r , Gerald K e l l y , Thomas G. Ropchak Daniel J. Goldstein and Harry R. Keiser National Heart, Lung, and Blood I n s t i t u t e , National I n s t i t u t e s B u i l d i n g lO, Room 8C-I03, Bethesda, Maryland 20205 (Received in final form June 24,

of Health,

1983)

Summary B i l a t e r a l subdiaphragmatic vagotomy does not improve the c l i n i c a l course nor the s u r v i v a l of Sprague-Dawley rats i n j e c t e d i n t r a v e n o u s l y with E. c o l i l i p o p o l y s a c c h a r i d e . These r e s u l t s show that whatever p e r i p h e r a l signals are e l i c i t e d by endotoxin to generate the c e n t r a l l y mediated hypotensive response, they are not conveyed to the central nervous system by abdominal vagal a f f e r e n t f i b e r s . The mechanisms by which the central e f f e c t s of the b r a i n / g u t peptides are exerted a f t e r systemic i n j e c t i o n remain to be understood ( ] ) . At least in two instances - a n g i o t e n s i n I I induced d r i n k i n g (2) and c h o l e c y s t o k i n i n induced s a t i e t y (3) - a f f e r e n t abdominal vagal f i b e r s seem to be involved in the transmission of p e r i p h e r a l l y o r i g i a n t e d s i g n a l s to the central nervous syste,7. A common central e f f e c t , however, does not imply a s i m i l a r route: the s a t i e t y induced by bombesin a f t e r systemic i n j e c t i o n is not affected by vagotomy (4). I t is known that enkephalins and g-endorphin exert well defined c e n t r a l e f f e c t s a f t e r systemic a d m i n i s t r a t i o n , which l a s t long a f t e r the peptides have disappeared from the blood stream (1). Morphine (5) and many of the endogenous o p i o i d s , as well as some of t h e i r anlogues (6), induce hypotension in the anesthesized r a t , and t h i s e f f e c t is blocked by c e r v i c a l vagotomy. The dramatic reversal by naloxone of the c a r d i o v a s c u l a r consequences of hypovolemic (7), endotoxic (8), spinal (9) and a n a p h y l a c t i c (lO) shocks have awakened considerable i n t e r e s t in the role of endogenous opioids in the r e g u l a t i o n s of blood pressure and cardiac f u n c t i o n . The e f f e c t s of naloxone seem to be central (9), even though B-endorphin l e v e l s have been found to be elevated f o l l o w i n g spinal i n j u r y ( l l ) . We studied the e f f e c t s of b i l a t e r a l subdiaphragmatic vagotomy (Vgx) on the hypotensive e f f e c t of endotoxin in the r a t , as well as the consequences of the i n t e r r u p t i o n of the abdominal vagal pathways on the s u r v i v a l a f t e r endotoxic shock. Methods Endotoxic BP Response in Vagotonized Rats. Male Sprague-Dawley rats 275-350 g were anesthetized with p e n t o b a r b i t a l 50 mg/kg i n t r a p e r i t o n e a l l y (IP) (Carter-Glogan L a b o r a t o r i e s , I n c . ) w h i l e the abdominal vagi were severed b i l a t e r a l l y f o l l o w i n g the technique developed by G.P. Smith (3). The v e r i f i c a t i o n of vagotomy was made f o l l o w i n g the procedure described in ( 3 ) .

0024-3205/83 $3.00 + .00 Copyright (c) 1983 Pergamon Press Ltd.

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Vol. 33, No. ii, 1983

At the conclusion of vagotomy the experiments the completeness of vagal d i s c o n n e c t i o n was checked by D.J.G. w i t h o u t previous knowledge of the p h y s i o l o g i c a l r e s u l t s and the previous s u r g i c a l procedures. The vagotomies were judged complete i f no nerve f i b e r s connected the cut ends. A shamoperated group received the same procedure except the vagi were manipulated but l e f t i n t a c t . A f t e r 3 to 5 weeks, the rats received p e n t o b a r b i t a l , 50 mg/kg ( I P ) , w h i l e the t a i l a r t e r y and j u g u l a r vein were cannulated w i t h PE-50 t u b i n g as described by Chiueh and Kopin (12). The catheters were brought through the skin at the back of the neck and threaded through a small diameter f l e x i b l e spring f o r p r o t e c t i o n . The catheters were heparinized (250 u n i t s / c a t h e t e r ) and each rat was placed in a separate cage 11.5 x 7 x 5 inches. Twenty four hours l a t e r , the a r t e r i a l c a t h e t e r was connected to a micropressure transducer (P2306 Strathom-Gould) and recorder (2400 Brush Gould). A f t e r the BP recording was s t a b l e , the awake and f u l l y mobile animal received endotoxin l i p o p o l y s a c c h a r i d e from E. c o l i sertoype No. 055:B5, (Sigma Co.) followed by a s a l i n e f l u s h , 0.4 ml, via the venous c a t h e t e r . Endotoxin M o r t a l i t y in Unrestrained Rats. Three to s i x weeks a f t e r the vagotomy and sham o p e r a t i o n , a j u g u l a r c a t h e t e r was i n s e r t e d as p r e v i o u s l y described. Each animal was placed in a cage and 24 hours l a t e r the rat received e n d o t o x i n , I00 mg/kg via the c a t h e t e r , followed by a 0.4 ml s a l i n e f l u s h . The number a l i v e at 24 hours was determined. Endotoxin M o r t a l i t y in Atropine M e t h y l n i t r a t e - T r e a t e d Rats. SpragueDawley male rats 300-500 g were anesthetized (Ether USP JT Baker Chemical Co.) p r i o r to i n s e r t i o n of a PE-50 c a t h e t e r in the j u g u l a r v e i n . The animals were place in i n d i v i d u a l cages. Twenty four hours l a t e r the rats received e i t h e r a t r o p i n e m e t h y l n i t r a t e (Sigma Co.), l mg/kg IV, or s a l i n e followed by e n d o t o x i n , 70 mg/kg IV. The cannula was then connected to an i n f u s i o n (Harvard I n f u s i o n Pump, Harvard Co.) of a t r o p i n e m e t h y l n i t r a t e , l mg/kg/hr, or s a l i n e , 0.0035 ml/min, to the c o n t r o l animals. The i n f u s i o n was continued f o r 24 hours and then the number a l i v e was counted. Analysis of the data. The d i f f e r e n c e in BP response of the vagotomy and sham-operated groups was analyzed using the rank sum t e s t of two independent samples (13) and the m o r t a l i t y rate of the treatment group was compared w i t h t h a t of the control group by F i s h e r ' s exact p r o b a b i l i t y t e s t (14). Results The i . v . a d m i n i s t r a t i o n of endotoxin in u n r e s t r a i n e d , awake animals, induces a biphasic decrease in blood pressure. The f i r s t hypotensive episode (Bl) occurs immediately a f t e r the i n j e c t i o n of the l i p o p o l y s a c c h a r i d e and l a s t s approximately lO minutes. The secod hypotensive episode (B2) s t a r t s approximately 45 minutes a f t e r the a d m i n i s t r a t i o n of e n d o t o x i n . There was no s i g n i f i c a n t d i f f e r e n c e between Vgx and sham-opperated rats in s y s t o l i c , d i a s t o l i c and mean a r t e r i a l blood pressures in e i t h e r the Bl or the B2 hypotensive phases (Table I ) . The time of onset of hypotension was not s i g n i f i c a n t l y d i f f e r e n t in the two groups. The endotoxin-induced m o r t a l i t y was not s i g n i f i c a n t l y Vgx and sham-operated animals (Table I I ) .

different

between

The a d m i n i s t r a t i o n of atropine m e t h y l n i t r a t e , an a n t i c h o l i n e r g i c drug t h a t does not cross the b l o o d / b r a i n b a r r i e r (15), did not protect i n t a c t rats from death induced by endotoxin (Table I l l ) .

Vol. 33, No. ii, 1983

Endotoxic Shock and Vagotomy

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TABLE I Blood Pressure Before and A f t e r Endotoxin in U n r e s t r a i n e d Rats* Blood Pressure ( t o r r s ) Before Endotoxin

A f t e r Endotoxin Decrease d u r i n g Decrease d u r i n g initial h y p o t e n s i o n delayed h y p o t e n s i o n

Vagotomized (n = I 0 ) Systolic

137 + 9

Diastolic

94+4

37 + 7 18+6

6+

4

25 + 6

17 +

6

142 + 6

32 + 5

43 +

4

93 + 4

9 + 5

7 +

3

109 + 4

18 + 5

19 +

3

108 + 5

Mean

33 + I0

Sham-Operated (n = I 0 ) Systolic Diastolic Mean P g r e a t e r than

0.05

0.05

0.05

* 70 mg/kg i . v . P= Comparing vagotomized and sham-operated groups:

Results are mean + S,E,M,

TABLE I I Mortality

of Vagotomized or Sham-Operated Rats A f t e r E n d o t o x i n * V.agotomi.zed

Sham

Alive

5

9

Dead

15

17

Percent Dead

75

89

* 70 mg/kg i . v ,

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Vol. 33, No. ii, 1983

TABLE I I I Mortality

of A t r o p i n e M e t h y l i n i t r a t e or Saline Treated Unrestrained Rats After Endotoxin*

Atropine** Methylnitrate

Saline

Alive

7

9

Dead

6

4

46

31

Percent Dead

* 70 mg/kg i . v . ** 1 mg/kg i . v .

followed by an i n f u s i o n l mg/kg/hr Discussion

B i l a t e r a l subdiaphragmatic vagotomy did not modify e i t h e r the hypotensive e f f e c t s of endotoxin or the s u r v i v a l rate of Sprague-Dawley rats a f t e r endotoxic shock. Peripheral c h o l i n e r g i c blockade by a t r o p i n e m e t h y l n i t r a t e , an a n t i c h o l i n e r g i c drug t h a t does not cross the b l o o d / b r a i n b a r r i e r , did not p r o t e c t the rat from the d e l e t e r i o u s consequences of ioV. administered e n d o t o x i n . We have not examined the e f f e c t of b i l a t e r a l subdiaphragmatic vagotomy on the naloxone reversal of c a r d i o v a s c u l a r parameters in endotoxic shock. I t is known t h a t naloxone's e f f e c t s are blocked by b i l a t e r a l c e r v i c a l vagotomy or m e t h y l a t r o p i n e a d m i n i s t r a t i o n in the spinal shock model (16), suggesting t h a t the e f f e c t of endogenous opiates might be mediated by parasymathetic e f f e r e n t nerves o r i g i n a t i n g in brain stem. Our r e s u l t s show t h a t n e i t h e r c h o l i n e r g i c ( e f f e r e n t ) nor a f f e r e n t abdominal vagal nerves are d i r e c t l y i n v o l v e d in the hypotension of the endotoxic shock in the r a t . Given the number of peptides known so f a r to be present in the vagal trunks ( V . I . P . , c h l o e c y s t o k i n i n , substance P, g a s t r i n ) (17), we can not rule out the p a r t i c i p i a t i o n of other n e u r o t r a n s m i t t e r s or neuromodulators derived from vagal e f f e r e n t s in the genesis or the modulation of the p h y s i o l o g i c a l derangements induced by i . v . e n d o t o x i n . The clarification of t h i s p o i n t w i l l be made possible only a f t e r the developement of r e l i a b l e and s p e c i f i c antagonists of these peptides. On the other hand, our data allow us to exclude a vagal a f f e r e n t pathway as the route by which the c e n t r a l , n a l o x o n e - s e n s i t i v e receptors, are a c t i v a t e d by the p e r i p h e r a l l y administered l i p o p o l y s a c c h a r i d e . We do not know i f c i r c u l a t i n g opioid peptides are i n v o l v e d in the process, but even i f they were, the abdominal vagi and t h e i r receptors can be ruled out as the conveyors to the c e n t r a l nervous system of s i g n a l s e l i c i t e d by them. References l °

2. 3.

A.J. KASTIN, R.I). OLSON, A.V. SCHALLY and D.H. COY, L i f e Sci. 25 401414 (1979). D.J. GOLDSTEIN and J.A. HALPERIN, Proceedings of the VII I n t e r n a t i o n a l Congress of Pharmacology, Pergamon Press, London (1978). G.P. SMITH, C. JEROME, B.J. CUSHIN, R. ETERNO and K.J. SIMANSKY, Science 213 1036-1037 (1981)

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