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Response of Bovine Serum Prolactin and Growth Hormone to Duodenal, Abomasal, and Oral Administration of Thyrotropin-Releasing Hormone1
Response o f B o v i n e S e r u m Prolactin and G r o w t h H o r m o n e t o D u o d e n a l , A b o m a s a l , and Oral A d m i n i s t r a t i o n of T h y r o t r o p i n - R e l e a s i n g H o r m o n e I V. G. SMITH, R. R. HACKER, J. H. BURTON, and D. M. VEIRA Department of Animal and Poultry Science University of Guelph Guelph, Ontario, Canada N1G 2W1
(8). In addition, administration of TRH to lactating women caused breast engorgement, milk let down, and increased content of fat and protein in milk (11). These effects may be due to increased availability of hormones acting independently or in concert since the administration of TRH will increase serum concentrations of thyroid stimulating hormone (TSH), prolactin, growth hormone (GH), thyroxine, and insulin (2, 3, 4, 5, 6, 11). The experiments reported herein were designed to study prolactin and GH concentrations in blood serum of cattle following the administration of TRH into the gastrointestinal tract. To guard against possible degradation of TRH by rumen microflora, TRH was administered into the duodenum and abomasum of cattle with developed rumens and was fed to calves on milk diets. Concentrations of TRH were 100 to 4000 times greater than the intravenous dose which caused a plateau of prolactin and GH in blood serum of heifers (12). An oral dose of TRH has to be at least 40 times greater than an intravenous dose to obtain a comparable increase in concentrations of TSH in blood serum of mice (1).
ABSTRACT
Thyrotropin-releasing hormone was injected into the duodenum of two 500-kg steers, placed into the abomasum of two prepubertal bulls, and fed to four bull calves (1 to 3 wk of age) to test the effect on concentrations of prolactin and growth hormone in blood serum. Before 20 and 200 mg of thyrotropin-releasing hormone were injected into the duodenum, prolactin in serum averaged 7.5 and 9.4 ng/ml and increased to 52.5 and 129.6 ng/ml at 45 and 35 min after treatment. Average growth hormone concentration of serum was increased also, b u t the response was more variable than prolactin. Peak concentrations of prolactin and growth hormone in blood serum were 5 to 10 times greater after treatment with thyrotropin-releasing hormone (40 mg/100 kg b o d y weight into abomasum) than before treatment. Within 30 min after oral administration of thyrotropin-releasing hormone (0, .5, 1, and 2 mg/kg body weight) growth hormone concentration of serum was 30, 306, 356, and 317% greater than pretreatment. Prolactin concentration of serum, however, was increased in only one calf.
MATERIALS AND METHODS Experiment 1
INTRODUCTION
Parenteral administration of thyrotropin-releasing hormone (TRH) has increased gain in body weight and feed efficiency of dairy calves (6), caused wether lambs to reach slaughter weight at an earlier age than untreated iambs (3), and stimulated lactogenesis in dairy cattle
Received February 14, 1977.
IT his work was supported in part by Ontario Ministry of Agriculture and Food, B. H. Bull Fund and N.R.C. Grant A-6247. 2Supplied by Dr. R. H. Ripple, Abbott Laboratories. 1977 J Dairy Sci 60:1624-1628
Saline or TRH 2 was administered in seriinto the duodenum of two 500-kg steers (1 Hereford, 1 Holstein x Angus)via re-entrant duodenal cannulae on each of 2 consecutive days. Twenty and two hundred milligrams of TRH were administered on days 1 and 2, respectively. Each day one steer received TRH in 10 ml of .85% NaCI and the other steer received 10 ml of .85% NaC1. After treatment blood was collected via a jugular vein cannula at intervals indicated on Fig. 1 and 2. At 120 rain after injection, the TRH-saline treatment sequence was reversed; i.e. the steer injected with saline received TRH, and the steer injected with TRH received saline. Thereafter, blood was
alum
1624
RESPONSE OF PROLACT1N AND GH TO TRH
1625 35
A
50 45
/ /
C- as
--
20 0 18 tY"
PRL 20rag TRH
GH
'I 30 o 2s
z_
"
20 10
_.. ~
:::, "~''-'-" . . . . . . . 03
' .........
0 TIME
'''
--""~ '
.........
'
3°00 z
90
t_, 'I,
80
0
60
4
; .... ~ '
~120 ~ 110
2 '
20 40 '6'0 75 90 105 120 (MIN) AFTER INJECTION
/
~
/
I \ t
• PRL 30 - - 200rag TRH:L25 0
..... .8s
.aC,
20
03
FIG. 1. Mean prolactin (PRL) and growth hormone (GH) concentrations in serum of steers given duodenal injection of saline or 20 mg of thyrotropin-releasing hormone (TRH) on day 1.
0
16 "T ~"
,o
O~
40 ~UJ
=
"-'-"
[::C 30 i,i 20
"~'A'x'~/'° .... "'"-.
03
".-.,.,*'-.,...,
.........
8
~
6
:D
4
2:::::::::::1::2 2
I,~
O3
10 o . . . . .20 ....
TIME
(MIN)
, 6 . . 60 . . 75 . . 90. .105 120
AFTER
INJECTION
FIG. 2. Mean prolactin (PRL) and growth hormone
(GH) concentrations in serum of steers given duodenal injection of saline or 200 mg of thyrotropin-releasing hormone (TRH) on day 2.
collected for an additional 120 min at intervals as per the period of first injection. In addition, blood was collected each day at 30, 20, 10, 5 min, and immediately before (t=0) the first injection.
design with four Holstein male calves (1 to 3 wk of age) and four concentrations of TRH (0, .5, 1, and 2 mg/kg body wt). Thyrotropin releasing hormone was incorporated in milk replacer and fed at 0700 h on each of 4 Experiment 2 consecutive days. Blood was collected via a Thyrotropin releasing hormone or casein was jugular vein cannula prior to feeding (two encased in gelatin capsules (Park Davis & Comp. samples) and at 15 rain intervals for 60 min Ont. Canada) and placed via abomasal fistulae after feeding and 30 min intervals thereafter, into the abomasum of four prepubertal Holthrough 360 min. stein bulls (age 4 to 6 mo; 140 to 160 kg). Two All blood samples were allowed to clot at bulls received casein, and two bulls received room temperature for 2 to 4 h, held at 5 C for TRH (40 mg/100 kg body wt). Casein also was 18 h, and centrifuged at 2,300 × g for 30 min. placed in the gelatin capsules containing TRH Serum was stored at - 2 0 C until assayed for such that the weight of each capsule and prolactin and GH by double antibody radioimmaterial was 400 rag. Water and alfalfa hay munoassay procedures. Serum prolactin was were supplied ad libitum, and 30 min before determined according to (9). Bovine prolactin treatment each animal received 2.5 kg of (NIH-B1) 3 was the reference standard. cracked corn. Blood was collected pretreatment Radioiodination of bovine GH, radioimas in experiment 1 and at 15 min intervals for munoassay procedures, and specificity of bo240 rain after treatment. vine GH antiserum a were the same as (7). A 1:4000 dilution of antibovine GH serum was Experiment 3 used in all assays. At this dilution 30 to 45% of This experiment was a 4 x 4 latin square [125 I] bovine GH was bound in tubes containing no unlabeled GH. Antiguinea pig gamma globulin prepared in our laboratory was used to precipitate the original antisera. Dose response curves for serum from cattle were parallel to 3Supplied by Endocrinology Study Section, Nathe GH reference standard (NIH-B12) 4. When tional Institute of Health. 4 Supplied by E. M. Convey, Michigan State Univer- known amounts of N1H-B12-GH were added to sity. 150 #1 of bovine serum, 76 to 108% of the Journal of Dairy Science Vol. 60, No. 10
1626
SMITH ET AL.
TABLE 1. Recovery of exogenous NIH-B12-GHadded to bovine serum a. Amount added (ng)
Amount recovered (ng) "X
.25
.19
•5
.42
1 1.5 2 2.5 3 4
.92 1.56 2.06 2.56 3.24 4.26
SE .01 .02 .02 .05 .06 .06 .11 .05
aAmounts recovered represent the means and SE of four determinations.
exogenous GH was recovered (Table 1). Aliquots from a pool of bovine serum were analyzed in duplicate four times at two dilutions in each assay to serve as an internal control. The intra- and inter-assay coefficients of variation for this pooled serum sample were 4.2 and 8.5%, n = 6. All serum samples were assayed in duplicate at appropriate dilutions (range 1:4 to 1:40) to fall within the workable range (80 to 20% binding) of the GH standard curve.
when the TRH-saline treatment sequence was reversed at t=120 rain, serum prolactin was elevated in the steer that received TRH at the first injection period, and this accounted for high prolactin concentration at t=0 just prior to saline injection. Although average serum GH appeared to increase after TRH injection, the variation between steers was large. In response to 20 and 200 mg of TRH, serum GH in the Holstein x Angus steer increased 20 and 75% as compared with 700 and 1200% in the Hereford steer.
Experiment 2
Both prolactin and GH concentrations of serum were increased (P<.01) after TRH was placed into the abomasum (Fig. 3). At t=O, prolactin and GH concentrations averaged 11.5 and 4.4 ng/ml then increased to 120 and 21.6 ng/ml at 30 min after TRH administration. Serum GH was elevated 135 min after TRH treatment and then decreased linearly (P<.05) to 3.2 ng/ml at 210 min after TRH administration. Neither prolactin nor GH concentration was affected by casein administration.
Experiment 3 RESULTS Experiment 1
Prolactin and GH concentrations of serum were increased after TRH was injected into the duodenum (Fig. 1 and 2). Prolactin averaged 7.5 ng/ml of serum before 20 mg of TRH were injected (Fig. 1) and increased to 52.5 ng/ml at 45 min after TRH injection. Serum GH averaged 2.2 ng/ml before TRH injection and increased to 11.4 ng/ml at 20 rain after TRH injection. Relative to pretreatment concentrations, serum prolactin but not GH was elevated at 120 min after TRH injection. Before 200 mg of TRH were injected, serum prolactin averaged 9.4 ng/ml and increased to 129.6 ng/ml at 35 min after TRH injection (Fig. 2). Serum GH averaged 2.6 ng/ml at t=O and was 32.2 ng/ml 20 min later. Both prolactin and GH concentrations of serum were greater at 120 min after TRH injection than at t=0. Concentrations of prolactin and GH were unchanged by injections of saline. Each day Journal of Dairy Science Vol. 60, No. 10
Serum GH response to oral administration of TRH is in Fig. 4. Analysis of variance on the logarithmic transformed data (10) revealed that serum GH was increased (P<.05) after TRH administration. Growth hormone averaged 14.2, 9.6, 7.4, and 11.5 ng/ml of serum prior to the feeding of 0, .5, 1, and 2 mg of TRH/kg body weight and increased 30, 306, 356, and 317%, during the first 30 min after TRH administration. The increase in serum GH was not related to the dose (.5, 1, and 2 mg/kg body wt) of TRH (P>.05). In contrast to GH, average serum prolactin concentration (Fig. 5B) was not affected (P>.05) by oral administration of TRH, and there was no significant difference among days. In one calf, however, prolactin concentration appeared to increase after TRH administration (Fig. 5A), and this accounted for the apparent increase in average prolactin concentration in Fig. 5B. The concentration of prolactin at t=O was highest in the calf showing increased prolactin after feeding TRH.
RESPONSE OF PROLACTIN AND GH TO TRH
120
E
;
z 80 ~ 70
PRL GH __ TRH ___CASEIN
~
/ ~
~
//
,
118 ~
'\
z
\
/I
40
~
\
\\
"
Jlo
~-
ta
"~
,
/
2o
, o
ZERO .5
.
2
"L
I
20 10
~
60
20 ¢e
( r a g / k g body wt.)
TRH
8O
22
,
~0 so •
t
•
110 _~I00
1627
20 J
(n -10 O
30
60
90 120 150 TIME IN MINUTES
180
210
240
FIG. 3. Mean prolactin (PRL) and growth hormone (GH) concentrations in serum of prepubertal bulls a f t e r placement of casein or thyrotropin-releasing hormone (TRH) into the abomasum.
DISCUSSION
10
t
~ ~
~ ~,
S --o
-15 O 30 60 90 120
180
240
300
360
TIME IN MINUTES
FIG. 5. Effect of oral administration of thyrotropin-releasing hormone (TRH) on prolactin concentration (A) in serum of one bull calf and on mean prolactin concentration (B) in serum of four bull calves.
This is the first report to demonstrate increased concentrations of prolactin and GH in serum of cattle after administration of large concentrations of TR H into the gastrointestinal tract. The action of T R H at these high concentrations appears to be prolonged in view of sustained elevation (for at least 2 h) in serum concentrations of prolactin and GH after duodenal and abomasal administration of TRH. Serum GH concentration was elevated for at least 3 h after oral administration of TRH. Oral administration of T R H did not increase serum prolactin concentration in three calves.
700 O
:E
TRH
600
(m9 1 kg body wt. )
X
•
ZERO
•
2
1 1
:E
4OO
~
300
~ <
200
~
t00
z_
g
o
0
30
60 90 120
180
240
300
as0
TIME IN MINUTES
FIG. 4. Mean change in growth hormone concentration in serum expressed as a percent of pretreatment concentration (a) following oral administration o f thyrotropin-releasing hormone (TRH) to hull calves.
This apparent lack of effect of TRH could not be due to total degradation of TRH since GH concentration was increased in all calves. Furrhermore, we have observed recently (unpublished) increased concentrations of prolactin and GH in serum of calves (3 to 5 wk of age) after oral administration of TRH (.25 mg/kg body wt). Whether the gastrointestinal tracts of calves (1 to 3 wk of age) elicit changes in the reactive group of TRH that stimulates prolactin release awaits further experiments. Elevation in GH concentration of serum was not related to the oral dose of TRH. This may indicate that the lowest concentration of TRH (.5 mg/kg body wt) was adequate to achieve maximum release of GH. Concentrations of prolactin and GH in serum of heifers also appear to reach a plateau after intravenous administration of TRH (12). Despite the limited number of animals we conclude that large concentrations of TRH have biological activity after absorption from the gastrointestinal tract of cattle. In view of earlier reports that parenteral administration of TRH increased GH concentration of serum and potentiated growth of dairy calves (6) and lambs (3) we suggest that oral administration of TRH to young calves may stimulate growth. The proteolytic activity of the rumen microflora, however, may necessitate administration of T RH before a rumen is developed or protection of TRH from rumen microbial degradation. Journal of Dairy Science Vol. 60, No. 10
SMITH ET AL.
1628 REFERENCES
1 Bowers, C. Y., A. V. Schally, F. Enzmann, J. Boler, and K. Folkers. 1970. Porcine thyrotropin releasing hormone is (pyro) glu-his-pro (NNH 2 ). Endocrinology 86:1143. 2 Convey, E. M., H. A. Tucker, V. G. Smith, and J. Zolman. 1973. Bovine prolactin, growth hormone, thyroxine and corticoid response to thyrotropin-releasing hormone. Endocrinology 92:471. 3 Davis, S. L., K. M. Hill, D. L. Ohlson, and J. A. Jacobs. 1976. Influence of chronic thyrotropin-releasing hormone injections on secretion of prolactin, thyrotropin, and growth hormone, and on growth rate in wether lambs. J. Anim. Sci. 42:1244. 4 Fell, L. R., J. K. Findlay, I. A. Cumming, and J. E. Goding. 1973. Effect of synthetic TRH on prolactin release in the sheep. Endocrinology 93:487. 5 Kelly, P. A., K. N. Bedirian, R. D. Baker, and H. G. Friesen. 1973. Effect of synthetic TRH on serum prolactin, TSH and milk production in the cow. Endocrinology 92:1289. 6 McGuffey, R. K., J. W. Thomas, and E. M. Convey. 1977. Growth, serum growth hormone, thyroxine,
Journal of Dairy Science Vol. 60, No. 10
prolactin and insulin in calves after thyrotropinreleasing hormone or 3-methyl-thyrotropin releasing hormone. J. Anita. Sci. 44:422. 7 Purchas, K., R. Macmillan, and H. Hafs. 1970. Pituitary and plasma growth hormone levels in bulls from birth to one year of age. J. Anita. Sci. 31:358. 8 Schams, D., U. Andreae, V. Reinhardt, and H. Karg. 1974. The influence of TRH on release of prolactin and lactation in the bovine. Acta Endocrinol. (Kbb) Suppl. 184:111. (Abstr.) 9 Smith, V. G., R. R. Hacker, and R. G. Brown. 1977. Effect of alterations in ambient temperatures on serum prolactin concentration in steers. J. Anim. Sci. 44:645. 10 Sokal, R. R., and F. J. Rohlf. 1969. Biometry. The principles and practice of statistics in biological research. W. H. Freeman and Co., San Francisco. 11 Tyson, J. E., H. G. Friesen, and M. S. Anderson. 1972. Human lactational and ovarian response to endogenous prolactin release. Science 177: 897. 12 Vines, D. T., H. A. Tucker, and E. M. Convey. 1976. Serum prolactin and growth hormone response to thyrotropin-releasing hormone in prepubertal heifers. J. Anim. Sci. 42:681.
(8). In addition, administration of TRH to lactating women caused breast engorgement, milk let down, and increased content of fat and protein in milk (11). These effects may be due to increased availability of hormones acting independently or in concert since the administration of TRH will increase serum concentrations of thyroid stimulating hormone (TSH), prolactin, growth hormone (GH), thyroxine, and insulin (2, 3, 4, 5, 6, 11). The experiments reported herein were designed to study prolactin and GH concentrations in blood serum of cattle following the administration of TRH into the gastrointestinal tract. To guard against possible degradation of TRH by rumen microflora, TRH was administered into the duodenum and abomasum of cattle with developed rumens and was fed to calves on milk diets. Concentrations of TRH were 100 to 4000 times greater than the intravenous dose which caused a plateau of prolactin and GH in blood serum of heifers (12). An oral dose of TRH has to be at least 40 times greater than an intravenous dose to obtain a comparable increase in concentrations of TSH in blood serum of mice (1).
ABSTRACT
Thyrotropin-releasing hormone was injected into the duodenum of two 500-kg steers, placed into the abomasum of two prepubertal bulls, and fed to four bull calves (1 to 3 wk of age) to test the effect on concentrations of prolactin and growth hormone in blood serum. Before 20 and 200 mg of thyrotropin-releasing hormone were injected into the duodenum, prolactin in serum averaged 7.5 and 9.4 ng/ml and increased to 52.5 and 129.6 ng/ml at 45 and 35 min after treatment. Average growth hormone concentration of serum was increased also, b u t the response was more variable than prolactin. Peak concentrations of prolactin and growth hormone in blood serum were 5 to 10 times greater after treatment with thyrotropin-releasing hormone (40 mg/100 kg b o d y weight into abomasum) than before treatment. Within 30 min after oral administration of thyrotropin-releasing hormone (0, .5, 1, and 2 mg/kg body weight) growth hormone concentration of serum was 30, 306, 356, and 317% greater than pretreatment. Prolactin concentration of serum, however, was increased in only one calf.
MATERIALS AND METHODS Experiment 1
INTRODUCTION
Parenteral administration of thyrotropin-releasing hormone (TRH) has increased gain in body weight and feed efficiency of dairy calves (6), caused wether lambs to reach slaughter weight at an earlier age than untreated iambs (3), and stimulated lactogenesis in dairy cattle
Received February 14, 1977.
IT his work was supported in part by Ontario Ministry of Agriculture and Food, B. H. Bull Fund and N.R.C. Grant A-6247. 2Supplied by Dr. R. H. Ripple, Abbott Laboratories. 1977 J Dairy Sci 60:1624-1628
Saline or TRH 2 was administered in seriinto the duodenum of two 500-kg steers (1 Hereford, 1 Holstein x Angus)via re-entrant duodenal cannulae on each of 2 consecutive days. Twenty and two hundred milligrams of TRH were administered on days 1 and 2, respectively. Each day one steer received TRH in 10 ml of .85% NaCI and the other steer received 10 ml of .85% NaC1. After treatment blood was collected via a jugular vein cannula at intervals indicated on Fig. 1 and 2. At 120 rain after injection, the TRH-saline treatment sequence was reversed; i.e. the steer injected with saline received TRH, and the steer injected with TRH received saline. Thereafter, blood was
alum
1624
RESPONSE OF PROLACT1N AND GH TO TRH
1625 35
A
50 45
/ /
C- as
--
20 0 18 tY"
PRL 20rag TRH
GH
'I 30 o 2s
z_
"
20 10
_.. ~
:::, "~''-'-" . . . . . . . 03
' .........
0 TIME
'''
--""~ '
.........
'
3°00 z
90
t_, 'I,
80
0
60
4
; .... ~ '
~120 ~ 110
2 '
20 40 '6'0 75 90 105 120 (MIN) AFTER INJECTION
/
~
/
I \ t
• PRL 30 - - 200rag TRH:L25 0
..... .8s
.aC,
20
03
FIG. 1. Mean prolactin (PRL) and growth hormone (GH) concentrations in serum of steers given duodenal injection of saline or 20 mg of thyrotropin-releasing hormone (TRH) on day 1.
0
16 "T ~"
,o
O~
40 ~UJ
=
"-'-"
[::C 30 i,i 20
"~'A'x'~/'° .... "'"-.
03
".-.,.,*'-.,...,
.........
8
~
6
:D
4
2:::::::::::1::2 2
I,~
O3
10 o . . . . .20 ....
TIME
(MIN)
, 6 . . 60 . . 75 . . 90. .105 120
AFTER
INJECTION
FIG. 2. Mean prolactin (PRL) and growth hormone
(GH) concentrations in serum of steers given duodenal injection of saline or 200 mg of thyrotropin-releasing hormone (TRH) on day 2.
collected for an additional 120 min at intervals as per the period of first injection. In addition, blood was collected each day at 30, 20, 10, 5 min, and immediately before (t=0) the first injection.
design with four Holstein male calves (1 to 3 wk of age) and four concentrations of TRH (0, .5, 1, and 2 mg/kg body wt). Thyrotropin releasing hormone was incorporated in milk replacer and fed at 0700 h on each of 4 Experiment 2 consecutive days. Blood was collected via a Thyrotropin releasing hormone or casein was jugular vein cannula prior to feeding (two encased in gelatin capsules (Park Davis & Comp. samples) and at 15 rain intervals for 60 min Ont. Canada) and placed via abomasal fistulae after feeding and 30 min intervals thereafter, into the abomasum of four prepubertal Holthrough 360 min. stein bulls (age 4 to 6 mo; 140 to 160 kg). Two All blood samples were allowed to clot at bulls received casein, and two bulls received room temperature for 2 to 4 h, held at 5 C for TRH (40 mg/100 kg body wt). Casein also was 18 h, and centrifuged at 2,300 × g for 30 min. placed in the gelatin capsules containing TRH Serum was stored at - 2 0 C until assayed for such that the weight of each capsule and prolactin and GH by double antibody radioimmaterial was 400 rag. Water and alfalfa hay munoassay procedures. Serum prolactin was were supplied ad libitum, and 30 min before determined according to (9). Bovine prolactin treatment each animal received 2.5 kg of (NIH-B1) 3 was the reference standard. cracked corn. Blood was collected pretreatment Radioiodination of bovine GH, radioimas in experiment 1 and at 15 min intervals for munoassay procedures, and specificity of bo240 rain after treatment. vine GH antiserum a were the same as (7). A 1:4000 dilution of antibovine GH serum was Experiment 3 used in all assays. At this dilution 30 to 45% of This experiment was a 4 x 4 latin square [125 I] bovine GH was bound in tubes containing no unlabeled GH. Antiguinea pig gamma globulin prepared in our laboratory was used to precipitate the original antisera. Dose response curves for serum from cattle were parallel to 3Supplied by Endocrinology Study Section, Nathe GH reference standard (NIH-B12) 4. When tional Institute of Health. 4 Supplied by E. M. Convey, Michigan State Univer- known amounts of N1H-B12-GH were added to sity. 150 #1 of bovine serum, 76 to 108% of the Journal of Dairy Science Vol. 60, No. 10
1626
SMITH ET AL.
TABLE 1. Recovery of exogenous NIH-B12-GHadded to bovine serum a. Amount added (ng)
Amount recovered (ng) "X
.25
.19
•5
.42
1 1.5 2 2.5 3 4
.92 1.56 2.06 2.56 3.24 4.26
SE .01 .02 .02 .05 .06 .06 .11 .05
aAmounts recovered represent the means and SE of four determinations.
exogenous GH was recovered (Table 1). Aliquots from a pool of bovine serum were analyzed in duplicate four times at two dilutions in each assay to serve as an internal control. The intra- and inter-assay coefficients of variation for this pooled serum sample were 4.2 and 8.5%, n = 6. All serum samples were assayed in duplicate at appropriate dilutions (range 1:4 to 1:40) to fall within the workable range (80 to 20% binding) of the GH standard curve.
when the TRH-saline treatment sequence was reversed at t=120 rain, serum prolactin was elevated in the steer that received TRH at the first injection period, and this accounted for high prolactin concentration at t=0 just prior to saline injection. Although average serum GH appeared to increase after TRH injection, the variation between steers was large. In response to 20 and 200 mg of TRH, serum GH in the Holstein x Angus steer increased 20 and 75% as compared with 700 and 1200% in the Hereford steer.
Experiment 2
Both prolactin and GH concentrations of serum were increased (P<.01) after TRH was placed into the abomasum (Fig. 3). At t=O, prolactin and GH concentrations averaged 11.5 and 4.4 ng/ml then increased to 120 and 21.6 ng/ml at 30 min after TRH administration. Serum GH was elevated 135 min after TRH treatment and then decreased linearly (P<.05) to 3.2 ng/ml at 210 min after TRH administration. Neither prolactin nor GH concentration was affected by casein administration.
Experiment 3 RESULTS Experiment 1
Prolactin and GH concentrations of serum were increased after TRH was injected into the duodenum (Fig. 1 and 2). Prolactin averaged 7.5 ng/ml of serum before 20 mg of TRH were injected (Fig. 1) and increased to 52.5 ng/ml at 45 min after TRH injection. Serum GH averaged 2.2 ng/ml before TRH injection and increased to 11.4 ng/ml at 20 rain after TRH injection. Relative to pretreatment concentrations, serum prolactin but not GH was elevated at 120 min after TRH injection. Before 200 mg of TRH were injected, serum prolactin averaged 9.4 ng/ml and increased to 129.6 ng/ml at 35 min after TRH injection (Fig. 2). Serum GH averaged 2.6 ng/ml at t=O and was 32.2 ng/ml 20 min later. Both prolactin and GH concentrations of serum were greater at 120 min after TRH injection than at t=0. Concentrations of prolactin and GH were unchanged by injections of saline. Each day Journal of Dairy Science Vol. 60, No. 10
Serum GH response to oral administration of TRH is in Fig. 4. Analysis of variance on the logarithmic transformed data (10) revealed that serum GH was increased (P<.05) after TRH administration. Growth hormone averaged 14.2, 9.6, 7.4, and 11.5 ng/ml of serum prior to the feeding of 0, .5, 1, and 2 mg of TRH/kg body weight and increased 30, 306, 356, and 317%, during the first 30 min after TRH administration. The increase in serum GH was not related to the dose (.5, 1, and 2 mg/kg body wt) of TRH (P>.05). In contrast to GH, average serum prolactin concentration (Fig. 5B) was not affected (P>.05) by oral administration of TRH, and there was no significant difference among days. In one calf, however, prolactin concentration appeared to increase after TRH administration (Fig. 5A), and this accounted for the apparent increase in average prolactin concentration in Fig. 5B. The concentration of prolactin at t=O was highest in the calf showing increased prolactin after feeding TRH.
RESPONSE OF PROLACTIN AND GH TO TRH
120
E
;
z 80 ~ 70
PRL GH __ TRH ___CASEIN
~
/ ~
~
//
,
118 ~
'\
z
\
/I
40
~
\
\\
"
Jlo
~-
ta
"~
,
/
2o
, o
ZERO .5
.
2
"L
I
20 10
~
60
20 ¢e
( r a g / k g body wt.)
TRH
8O
22
,
~0 so •
t
•
110 _~I00
1627
20 J
(n -10 O
30
60
90 120 150 TIME IN MINUTES
180
210
240
FIG. 3. Mean prolactin (PRL) and growth hormone (GH) concentrations in serum of prepubertal bulls a f t e r placement of casein or thyrotropin-releasing hormone (TRH) into the abomasum.
DISCUSSION
10
t
~ ~
~ ~,
S --o
-15 O 30 60 90 120
180
240
300
360
TIME IN MINUTES
FIG. 5. Effect of oral administration of thyrotropin-releasing hormone (TRH) on prolactin concentration (A) in serum of one bull calf and on mean prolactin concentration (B) in serum of four bull calves.
This is the first report to demonstrate increased concentrations of prolactin and GH in serum of cattle after administration of large concentrations of TR H into the gastrointestinal tract. The action of T R H at these high concentrations appears to be prolonged in view of sustained elevation (for at least 2 h) in serum concentrations of prolactin and GH after duodenal and abomasal administration of TRH. Serum GH concentration was elevated for at least 3 h after oral administration of TRH. Oral administration of T R H did not increase serum prolactin concentration in three calves.
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~ <
200
~
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o
0
30
60 90 120
180
240
300
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TIME IN MINUTES
FIG. 4. Mean change in growth hormone concentration in serum expressed as a percent of pretreatment concentration (a) following oral administration o f thyrotropin-releasing hormone (TRH) to hull calves.
This apparent lack of effect of TRH could not be due to total degradation of TRH since GH concentration was increased in all calves. Furrhermore, we have observed recently (unpublished) increased concentrations of prolactin and GH in serum of calves (3 to 5 wk of age) after oral administration of TRH (.25 mg/kg body wt). Whether the gastrointestinal tracts of calves (1 to 3 wk of age) elicit changes in the reactive group of TRH that stimulates prolactin release awaits further experiments. Elevation in GH concentration of serum was not related to the oral dose of TRH. This may indicate that the lowest concentration of TRH (.5 mg/kg body wt) was adequate to achieve maximum release of GH. Concentrations of prolactin and GH in serum of heifers also appear to reach a plateau after intravenous administration of TRH (12). Despite the limited number of animals we conclude that large concentrations of TRH have biological activity after absorption from the gastrointestinal tract of cattle. In view of earlier reports that parenteral administration of TRH increased GH concentration of serum and potentiated growth of dairy calves (6) and lambs (3) we suggest that oral administration of TRH to young calves may stimulate growth. The proteolytic activity of the rumen microflora, however, may necessitate administration of T RH before a rumen is developed or protection of TRH from rumen microbial degradation. Journal of Dairy Science Vol. 60, No. 10
SMITH ET AL.
1628 REFERENCES
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Journal of Dairy Science Vol. 60, No. 10
prolactin and insulin in calves after thyrotropinreleasing hormone or 3-methyl-thyrotropin releasing hormone. J. Anita. Sci. 44:422. 7 Purchas, K., R. Macmillan, and H. Hafs. 1970. Pituitary and plasma growth hormone levels in bulls from birth to one year of age. J. Anita. Sci. 31:358. 8 Schams, D., U. Andreae, V. Reinhardt, and H. Karg. 1974. The influence of TRH on release of prolactin and lactation in the bovine. Acta Endocrinol. (Kbb) Suppl. 184:111. (Abstr.) 9 Smith, V. G., R. R. Hacker, and R. G. Brown. 1977. Effect of alterations in ambient temperatures on serum prolactin concentration in steers. J. Anim. Sci. 44:645. 10 Sokal, R. R., and F. J. Rohlf. 1969. Biometry. The principles and practice of statistics in biological research. W. H. Freeman and Co., San Francisco. 11 Tyson, J. E., H. G. Friesen, and M. S. Anderson. 1972. Human lactational and ovarian response to endogenous prolactin release. Science 177: 897. 12 Vines, D. T., H. A. Tucker, and E. M. Convey. 1976. Serum prolactin and growth hormone response to thyrotropin-releasing hormone in prepubertal heifers. J. Anim. Sci. 42:681.