Life Sciences, Vol. 50, pp. 951-958
Pergamon Press
Printed in the USA
EFFECTS OF PASSIVE IMMUNIZATION OF GROWTH H O R M O N E - R E L E A S I N G HORMONE AND SOMATOSTATIN ON GROWTH HORMONE SECRETION U N D E R CONDITIONS OF HIGH S O M A T O S T A T I N TONE Bethany A. Janowski and W i l l i a m B. W e h r e n b e r g D e p a r t m e n t s of Health Sciences and Biological Sciences, U n i v e r s i t y of Wisconsin-Milwaukee, Milwaukee, WI (Received in final form January 22, 1992) Summary Pulsatile GH secretion decreases during foodd e p r i v a t i o n in the rat. It has been h y p o t h e s i z e d that this decrease is d u e to e l e v a t e d hypothalamic somatostatin secretion. This is b a s e d on the o b s e r v a t i o n that GH i n c r e a s e s in f o o d - d e p r i v e d rats f o l l o w i n g r e m o v a l of e n d o g e n o u s s o m a t o s t a t i n u s i n g passive immunization techniques. C o g n i z a n t of the important stimulatory e f f e c t s of g r o w t h h o r m o n e r e l e a s i n g hormone (GHRH) on GH secretion, we sought to determine if t h i s n e u r o p e p t i d e p l a y s a n y r o l e in m e d i a t i n g GH s e c r e t i o n in f o o d - d e p r i v e d rats. Male rats w e r e p r e p a r e d w i t h i n d w e l l i n g v e n o u s c a t h e t e r s using sodium pentobarbital anesthesia seven days prior to experimentation. Animals were food-deprived for 72 h, a f t e r w h i c h control blood samples were drawn from -60 to 0 min. One group was then treated with normal r a b b i t s e r u m (NRS), while a second group was t r e a t e d with GHRH antiserum (GHRHab). At 55 m i n all a n i m a l s r e c e i v e d s o m a t o s t a t i n a n t i s e r u m (SSab). No animal e x h i b i t e d any spontaneous GH peak during the one hour c o n t r o l p e r i o d or in the s u b s e q u e n t one h o u r p e r i o d following the administration of G H R H a b or N R S . A b s e n c e of GH p u l s a t i l i t y d u r i n g f o o d - d e p r i v a t i o n , coupled with no decrease in GH levels in f o o d - d e p r i v e d rats treated with GHRHab suggest that d i m i n i s h e d GHRH pulsatility is l i k e l y during food-deprivation. Subsequent treatment of t h e s e a n i m a l s w i t h S S a b r e s u l t e d in an i d e n t i c a l 2.5 f o l d i n c r e a s e in GH concentrations. This result suggests that GHRH is not i n v o l v e d in the GH r e b o u n d f o l l o w i n g s o m a t o s t a t i n w i t h d r a w a l in food-deprived rats. Pituitary growth hormone (GH) s e c r e t i o n in the rat is c h a r a c t e r i z e d by an u l t r a d i a n rhythm, with intermittent peaks and troughs at a p p r o x i m a t e l y three hour intervals (i). The p u l s a t i l e p a t t e r n of s e c r e t i o n r e s u l t s from the i n t e r a c t i o n b e t w e e n the s t i m u l a t o r y e f f e c t s of g r o w t h h o r m o n e - r e l e a s i n g h o r m o n e (GHRH) and the inhibitory effects of somatostatin (2-10). H i g h levels of s o m a t o s t a t i n m a i n t a i n low GH c o n c e n t r a t i o n s d u r i n g t r o u g h 0024-3205/92 $5.00 + .00 Copyright © 1992 Pergamon Press plc All rights reserved.
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periods since passive immunization with somatostatin antiserum (SSab) increases basal GH c o n c e n t r a t i o n s but does not a l t e r the p u l s a t i l e p a t t e r n of GH secretion (8, 9). High c o n c e n t r a t i o n s of G H R H m a i n t a i n e l e v a t e d GH c o n c e n t r a t i o n s d u r i n g p e a k p e r i o d s since administration of G H R H a n t i s e r u m (GHRHab) completely i n h i b i t s the p u l s a t i l e s e c r e t i o n of GH (i0). That GHRH and s o m a t o s t a t i n are released in a p u l s a t i l e fashion is s u g g e s t e d by the f a c t t h a t at t h e t i m e of an a n t i c i p a t e d GH p u l s e , G H R H c o n c e n t r a t i o n s are e l e v a t e d and s o m a t o s t a t i n c o n c e n t r a t i o n s are d e p r e s s e d in h y p o t h a l a m i c - h y p o p h y s e a l portal blood (ii). GH pulses are depressed in r a t s u n d e r c o n d i t i o n s of f o o d - d e p r i v a t i o n or m a l n u t r i t i o n (12-14) , and plasma s o m a t o s t a t i n c o n c e n t r a t i o n s are increased (15). Indeed, a GH rebound has been r e p o r t e d in 72 h f o o d - d e p r i v e d rats u p o n the a d m i n i s t r a t i o n of somatostatin antiserum (16). These findings suggest that s o m a t o s t a t i n m e d i a t e s the s u p p r e s s i o n of GH s e c r e t i o n d u r i n g food-deprivation. It is possible, however, that s u p p r e s s e d GH is a l s o d u e to d e c r e a s e d G H R H s e c r e t i o n , a h y p o t h e s i s yet to be tested. S u p p o r t i n g this h y p o t h e s i s is an e a r l i e r s t u d y w h i c h s u g g e s t e d that h y p o t h a l a m i c GHRH c o n c e n t r a t i o n s d e c r e a s e during f o o d - d e p r i v a t i o n (17). In an effort to further c h a r a c t e r i z e the neuroregulation of GH s e c r e t i o n d u r i n g f o o d - d e p r i v a t i o n , we examined the contribution of G H R H in r e g u l a t i n g basal GH s e c r e t i o n and in c o n t r o l l i n g the m a g n i t u d e of the GH r e b o u n d following immunoneutralization of s o m a t o s t a t i n in 72 h f o o d - d e p r i v e d rats. Methods Animals: A l l a n i m a l s in t h e s e s t u d i e s w e r e a c q u i r e d , maintained, a n d u s e d in a c c o r d a n c e with the guidelines e s t a b l i s h e d by the N a t i o n a l I n s t i t u t e s of H e a l t h (18). Male S p r a g u e - D a w l e y rats (225-350 g) were m a i n t a i n e d in a t e m p e r a t u r e and h u m i d i t y - c o n t r o l l e d e n v i r o n m e n t and exposed to a 14 h light, I0 h dark lighting schedule (lights on at 0600 h). Surqical Preparation: Animals anesthetized with sodium p e n t o b a r b i t a l (NaPb, 40 mg/kg, ip) were o u t f i t t e d with a chronic indwelling venous c a t h e t e r one week prior to e x p e r i m e n t a t i o n (3). The c a t h e t e r was c o n n e c t e d to a single channel, fluid swivel to allow free m o v e m e n t of the rat following surgery. The rats were p l a c e d in isolation cages and received a constant infusion (0.08 ml/h) of h e p a r i n i z e d s a l i n e (i0 IU/ml) u n t i l t h e m o r n i n g of experimentation. Experimentation: F o o d - d e p r i v a t i o n was initiated four days after surgery and was continued for 72 h. B e g i n n i n g at 1200 h on t h e d a y of e x p e r i m e n t a t i o n , three control blood samples were d r a w n (0.35 ml), f o l l o w e d by an iv i n j e c t i o n of e i t h e r 0.5 ml n o r m a l r a b b i t s e r u m (NRS, n=7) or G H R H a b (n=ll). Subsequent b l o o d samples were drawn i0, 25 and 55 min following t r e a t m e n t . All animals then received 0.5 ml of SSab, iv, and blood samples w e r e d r a w n 5, i0, 15, 30 and 60 m i n f o l l o w i n g the i n j e c t i o n . Blood samples were centrifuged, plasma separated and then frozen for d e t e r m i n a t i o n of GH by RIA. The red blood cells were r e s u s p e n d e d in normal saline and returned to the animals.
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Antibody Preparation: Antiserum a g a i n s t rat G H R H w a s p r e p a r e d by i m m u n i z i n g r a b b i t s w i t h a m i x t u r e of s y n t h e t i c rat GHRH and methylated BSA emulsified in F r e u n d ' s a d j u v a n t as d e s c r i b e d p r e v i o u s l y (19). This a n t i s e r u m is s p e c i f i c for rat GHRH. It does not cross-react with GHRH from other species nor with p e p t i d e s that have considerable sequence h o m o l o g y with GHRH s u c h as s e c r e t i n , v a s o a c t i v e i n t e s t i n a l p e p t i d e and g l u c a g o n . The antibody d i l u t i o n required to bind a p p r o x i m a t e l y 50% of a rat GHRH-II25 labeled trace was 1:80,000. The dose a d m i n i s t e r e d was based on our observations that 0.5 ml of GHRHab is e f f e c t i v e in neutralizing e n d o g e n o u s G H R H as e v i d e n c e d by an a b s e n c e of p u l s a t i l e GH secretion (20). The SSab was p r e p a r e d by i m m u n i z i n g sheep w i t h s y n t h e t i c somatostatin. C o m p l e t e c h a r a c t e r i z a t i o n of t h e s o m a t o s t a t i n a n t i b o d y has b e e n p u b l i s h e d (21). Briefly, the antibody was partially purified by ammonium sulfate purification. It is d i r e c t e d toward the m i d - p o r t i o n of somatostatin. RIA s e n s i t i v i t y w a s 14 p g / t u b e at a f i n a l d i l u t i o n of 1 / 2 5 , 0 0 0 . The dose a d m i n i s t e r e d was based on our observations that 0.5 ml of SSab is effective in n e u t r a l i z i n g endogenous s o m a t o s t a t i n (22). R a d i o i m m u n o a s s a y Procedures: Plasma GH c o n c e n t r a t i o n s were d e t e r m i n e d in d u p l i c a t e by a d o u b l e a n t i b o d y p r o c e d u r e u s i n g materials s u p p l i e d by t h e N a t i o n a l P i t u i t a r y A g e n c y of t h e N a t i o n a l I n s t i t u t e s of Health. Blood s a m p l e s w e r e a s s a y e d in a l i q u o t s of e i t h e r i0 or 50 ~i. G r o w t h hormone c o n c e n t r a t i o n s are e x p r e s s e d in t e r m s of t h e r a t G H - R P - 2 s t a n d a r d . Assay sensitivity was approximately 0.08 ng/tube. Withinand b e t w e e n - a s s a y v a r i a t i o n s averaged less than 10%. Statistical Analyses: Significant t r e a t m e n t effects on GH c o n c e n t r a t i o n s were detected by analysis of v a r i a n c e for repeated m e a s u r e s (23). Since the variances of the mean GH c o n c e n t r a t i o n s were not homogenous, t h e d a t a w e r e f i r s t s u b j e c t e d to log transformation. E v a l u a t i o n of the overall GH response during the e x p e r i m e n t involved analyzing the area under the GH curve (AUC). The e x p e r i m e n t w a s s e p a r a t e d i n t o t h r e e d i f f e r e n t t r e a t m e n t periods. The control period was designated as -60 to 0 min, the N R S / G H R H a b period from 0 to 55 min, and SSab p e r i o d from 55 to 115 min. Less than 1% of the total number of blood samples to be drawn were missed due to technical problems during the experiment. In t h e s e i n s t a n c e s the GH v a l u e was e s t i m a t e d by c a l c u l a t i n g the average GH concentration from the p r e c e d i n g and following blood sample. All data are expressed as mean + SEM. Results Effects of F o o d - D e p r i v a t i o n : Seventy-two h o u r s of f o o d - d e p r i v a t i o n resulted in a 14-17% loss in total body weight. Pulsatile GH secretion was inhibited and baseline GH c o n c e n t r a t i o n s were elevated during the 60 min control p e r i o d in all animals (Fig. i). Although the control p e r i o d was too short to c o m p l e t e l y e v a l u a t e GH p u l s a t i l i t y , it has p r e v i o u s l y b e e n established that GH pulses are absent and baseline GH c o n c e n t r a t i o n s are elevated in food-deprived animals as c o m p a r e d to n o r m a l ones (3, I0, 13, 24). In addition to a l t e r i n g these e n d o c r i n e p a r a m e t e r s , f o o d - d e p r i v a t i o n a l s o m a d e the a n i m a l s agitated, restless and aggressive.
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Neuroregulation of GH in Food-deprived Rats
60 ~"
50
0 NRS • GHRHab
40 I:~ C"
All Receive SSab
Vol. 50, No. 13, 1992
:kT-I
30
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20
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100
-60-30
0
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60
90 120
Time (min) FIG. 1 Mean plasma GH concentrations in 72 h f o o d - d e p r i v e d rats. NRS (n=7) o r G H R H a b (n=ll) w a s a d m i n i s t e r e d after the 0 min blood sample. All animals received SSab after t h e 55 m i n b l o o d sample• Baseline GH concentrations were elevated compared to previously e s t a b l i s h e d v a l u e s for n o r m a l r a t s ( c r o s s - h a t c h e d area, r e f s 3, i0, 24). GH concentrations did not change following NRS or GHRHab treatment• GH concentrations in b o t h N R S - a n d G H R H a b - t r e a t e d r a t s w e r e s i g n i f i c a n t l y e l e v a t e d a f t e r S S a b t r e a t m e n t (p
Pergamon Press
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EFFECTS OF PASSIVE IMMUNIZATION OF GROWTH H O R M O N E - R E L E A S I N G HORMONE AND SOMATOSTATIN ON GROWTH HORMONE SECRETION U N D E R CONDITIONS OF HIGH S O M A T O S T A T I N TONE Bethany A. Janowski and W i l l i a m B. W e h r e n b e r g D e p a r t m e n t s of Health Sciences and Biological Sciences, U n i v e r s i t y of Wisconsin-Milwaukee, Milwaukee, WI (Received in final form January 22, 1992) Summary Pulsatile GH secretion decreases during foodd e p r i v a t i o n in the rat. It has been h y p o t h e s i z e d that this decrease is d u e to e l e v a t e d hypothalamic somatostatin secretion. This is b a s e d on the o b s e r v a t i o n that GH i n c r e a s e s in f o o d - d e p r i v e d rats f o l l o w i n g r e m o v a l of e n d o g e n o u s s o m a t o s t a t i n u s i n g passive immunization techniques. C o g n i z a n t of the important stimulatory e f f e c t s of g r o w t h h o r m o n e r e l e a s i n g hormone (GHRH) on GH secretion, we sought to determine if t h i s n e u r o p e p t i d e p l a y s a n y r o l e in m e d i a t i n g GH s e c r e t i o n in f o o d - d e p r i v e d rats. Male rats w e r e p r e p a r e d w i t h i n d w e l l i n g v e n o u s c a t h e t e r s using sodium pentobarbital anesthesia seven days prior to experimentation. Animals were food-deprived for 72 h, a f t e r w h i c h control blood samples were drawn from -60 to 0 min. One group was then treated with normal r a b b i t s e r u m (NRS), while a second group was t r e a t e d with GHRH antiserum (GHRHab). At 55 m i n all a n i m a l s r e c e i v e d s o m a t o s t a t i n a n t i s e r u m (SSab). No animal e x h i b i t e d any spontaneous GH peak during the one hour c o n t r o l p e r i o d or in the s u b s e q u e n t one h o u r p e r i o d following the administration of G H R H a b or N R S . A b s e n c e of GH p u l s a t i l i t y d u r i n g f o o d - d e p r i v a t i o n , coupled with no decrease in GH levels in f o o d - d e p r i v e d rats treated with GHRHab suggest that d i m i n i s h e d GHRH pulsatility is l i k e l y during food-deprivation. Subsequent treatment of t h e s e a n i m a l s w i t h S S a b r e s u l t e d in an i d e n t i c a l 2.5 f o l d i n c r e a s e in GH concentrations. This result suggests that GHRH is not i n v o l v e d in the GH r e b o u n d f o l l o w i n g s o m a t o s t a t i n w i t h d r a w a l in food-deprived rats. Pituitary growth hormone (GH) s e c r e t i o n in the rat is c h a r a c t e r i z e d by an u l t r a d i a n rhythm, with intermittent peaks and troughs at a p p r o x i m a t e l y three hour intervals (i). The p u l s a t i l e p a t t e r n of s e c r e t i o n r e s u l t s from the i n t e r a c t i o n b e t w e e n the s t i m u l a t o r y e f f e c t s of g r o w t h h o r m o n e - r e l e a s i n g h o r m o n e (GHRH) and the inhibitory effects of somatostatin (2-10). H i g h levels of s o m a t o s t a t i n m a i n t a i n low GH c o n c e n t r a t i o n s d u r i n g t r o u g h 0024-3205/92 $5.00 + .00 Copyright © 1992 Pergamon Press plc All rights reserved.
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periods since passive immunization with somatostatin antiserum (SSab) increases basal GH c o n c e n t r a t i o n s but does not a l t e r the p u l s a t i l e p a t t e r n of GH secretion (8, 9). High c o n c e n t r a t i o n s of G H R H m a i n t a i n e l e v a t e d GH c o n c e n t r a t i o n s d u r i n g p e a k p e r i o d s since administration of G H R H a n t i s e r u m (GHRHab) completely i n h i b i t s the p u l s a t i l e s e c r e t i o n of GH (i0). That GHRH and s o m a t o s t a t i n are released in a p u l s a t i l e fashion is s u g g e s t e d by the f a c t t h a t at t h e t i m e of an a n t i c i p a t e d GH p u l s e , G H R H c o n c e n t r a t i o n s are e l e v a t e d and s o m a t o s t a t i n c o n c e n t r a t i o n s are d e p r e s s e d in h y p o t h a l a m i c - h y p o p h y s e a l portal blood (ii). GH pulses are depressed in r a t s u n d e r c o n d i t i o n s of f o o d - d e p r i v a t i o n or m a l n u t r i t i o n (12-14) , and plasma s o m a t o s t a t i n c o n c e n t r a t i o n s are increased (15). Indeed, a GH rebound has been r e p o r t e d in 72 h f o o d - d e p r i v e d rats u p o n the a d m i n i s t r a t i o n of somatostatin antiserum (16). These findings suggest that s o m a t o s t a t i n m e d i a t e s the s u p p r e s s i o n of GH s e c r e t i o n d u r i n g food-deprivation. It is possible, however, that s u p p r e s s e d GH is a l s o d u e to d e c r e a s e d G H R H s e c r e t i o n , a h y p o t h e s i s yet to be tested. S u p p o r t i n g this h y p o t h e s i s is an e a r l i e r s t u d y w h i c h s u g g e s t e d that h y p o t h a l a m i c GHRH c o n c e n t r a t i o n s d e c r e a s e during f o o d - d e p r i v a t i o n (17). In an effort to further c h a r a c t e r i z e the neuroregulation of GH s e c r e t i o n d u r i n g f o o d - d e p r i v a t i o n , we examined the contribution of G H R H in r e g u l a t i n g basal GH s e c r e t i o n and in c o n t r o l l i n g the m a g n i t u d e of the GH r e b o u n d following immunoneutralization of s o m a t o s t a t i n in 72 h f o o d - d e p r i v e d rats. Methods Animals: A l l a n i m a l s in t h e s e s t u d i e s w e r e a c q u i r e d , maintained, a n d u s e d in a c c o r d a n c e with the guidelines e s t a b l i s h e d by the N a t i o n a l I n s t i t u t e s of H e a l t h (18). Male S p r a g u e - D a w l e y rats (225-350 g) were m a i n t a i n e d in a t e m p e r a t u r e and h u m i d i t y - c o n t r o l l e d e n v i r o n m e n t and exposed to a 14 h light, I0 h dark lighting schedule (lights on at 0600 h). Surqical Preparation: Animals anesthetized with sodium p e n t o b a r b i t a l (NaPb, 40 mg/kg, ip) were o u t f i t t e d with a chronic indwelling venous c a t h e t e r one week prior to e x p e r i m e n t a t i o n (3). The c a t h e t e r was c o n n e c t e d to a single channel, fluid swivel to allow free m o v e m e n t of the rat following surgery. The rats were p l a c e d in isolation cages and received a constant infusion (0.08 ml/h) of h e p a r i n i z e d s a l i n e (i0 IU/ml) u n t i l t h e m o r n i n g of experimentation. Experimentation: F o o d - d e p r i v a t i o n was initiated four days after surgery and was continued for 72 h. B e g i n n i n g at 1200 h on t h e d a y of e x p e r i m e n t a t i o n , three control blood samples were d r a w n (0.35 ml), f o l l o w e d by an iv i n j e c t i o n of e i t h e r 0.5 ml n o r m a l r a b b i t s e r u m (NRS, n=7) or G H R H a b (n=ll). Subsequent b l o o d samples were drawn i0, 25 and 55 min following t r e a t m e n t . All animals then received 0.5 ml of SSab, iv, and blood samples w e r e d r a w n 5, i0, 15, 30 and 60 m i n f o l l o w i n g the i n j e c t i o n . Blood samples were centrifuged, plasma separated and then frozen for d e t e r m i n a t i o n of GH by RIA. The red blood cells were r e s u s p e n d e d in normal saline and returned to the animals.
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Neuroregulation of GH in Food-deprived Rats
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Antibody Preparation: Antiserum a g a i n s t rat G H R H w a s p r e p a r e d by i m m u n i z i n g r a b b i t s w i t h a m i x t u r e of s y n t h e t i c rat GHRH and methylated BSA emulsified in F r e u n d ' s a d j u v a n t as d e s c r i b e d p r e v i o u s l y (19). This a n t i s e r u m is s p e c i f i c for rat GHRH. It does not cross-react with GHRH from other species nor with p e p t i d e s that have considerable sequence h o m o l o g y with GHRH s u c h as s e c r e t i n , v a s o a c t i v e i n t e s t i n a l p e p t i d e and g l u c a g o n . The antibody d i l u t i o n required to bind a p p r o x i m a t e l y 50% of a rat GHRH-II25 labeled trace was 1:80,000. The dose a d m i n i s t e r e d was based on our observations that 0.5 ml of GHRHab is e f f e c t i v e in neutralizing e n d o g e n o u s G H R H as e v i d e n c e d by an a b s e n c e of p u l s a t i l e GH secretion (20). The SSab was p r e p a r e d by i m m u n i z i n g sheep w i t h s y n t h e t i c somatostatin. C o m p l e t e c h a r a c t e r i z a t i o n of t h e s o m a t o s t a t i n a n t i b o d y has b e e n p u b l i s h e d (21). Briefly, the antibody was partially purified by ammonium sulfate purification. It is d i r e c t e d toward the m i d - p o r t i o n of somatostatin. RIA s e n s i t i v i t y w a s 14 p g / t u b e at a f i n a l d i l u t i o n of 1 / 2 5 , 0 0 0 . The dose a d m i n i s t e r e d was based on our observations that 0.5 ml of SSab is effective in n e u t r a l i z i n g endogenous s o m a t o s t a t i n (22). R a d i o i m m u n o a s s a y Procedures: Plasma GH c o n c e n t r a t i o n s were d e t e r m i n e d in d u p l i c a t e by a d o u b l e a n t i b o d y p r o c e d u r e u s i n g materials s u p p l i e d by t h e N a t i o n a l P i t u i t a r y A g e n c y of t h e N a t i o n a l I n s t i t u t e s of Health. Blood s a m p l e s w e r e a s s a y e d in a l i q u o t s of e i t h e r i0 or 50 ~i. G r o w t h hormone c o n c e n t r a t i o n s are e x p r e s s e d in t e r m s of t h e r a t G H - R P - 2 s t a n d a r d . Assay sensitivity was approximately 0.08 ng/tube. Withinand b e t w e e n - a s s a y v a r i a t i o n s averaged less than 10%. Statistical Analyses: Significant t r e a t m e n t effects on GH c o n c e n t r a t i o n s were detected by analysis of v a r i a n c e for repeated m e a s u r e s (23). Since the variances of the mean GH c o n c e n t r a t i o n s were not homogenous, t h e d a t a w e r e f i r s t s u b j e c t e d to log transformation. E v a l u a t i o n of the overall GH response during the e x p e r i m e n t involved analyzing the area under the GH curve (AUC). The e x p e r i m e n t w a s s e p a r a t e d i n t o t h r e e d i f f e r e n t t r e a t m e n t periods. The control period was designated as -60 to 0 min, the N R S / G H R H a b period from 0 to 55 min, and SSab p e r i o d from 55 to 115 min. Less than 1% of the total number of blood samples to be drawn were missed due to technical problems during the experiment. In t h e s e i n s t a n c e s the GH v a l u e was e s t i m a t e d by c a l c u l a t i n g the average GH concentration from the p r e c e d i n g and following blood sample. All data are expressed as mean + SEM. Results Effects of F o o d - D e p r i v a t i o n : Seventy-two h o u r s of f o o d - d e p r i v a t i o n resulted in a 14-17% loss in total body weight. Pulsatile GH secretion was inhibited and baseline GH c o n c e n t r a t i o n s were elevated during the 60 min control p e r i o d in all animals (Fig. i). Although the control p e r i o d was too short to c o m p l e t e l y e v a l u a t e GH p u l s a t i l i t y , it has p r e v i o u s l y b e e n established that GH pulses are absent and baseline GH c o n c e n t r a t i o n s are elevated in food-deprived animals as c o m p a r e d to n o r m a l ones (3, I0, 13, 24). In addition to a l t e r i n g these e n d o c r i n e p a r a m e t e r s , f o o d - d e p r i v a t i o n a l s o m a d e the a n i m a l s agitated, restless and aggressive.
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Neuroregulation of GH in Food-deprived Rats
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Vol. 50, No. 13, 1992
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Time (min) FIG. 1 Mean plasma GH concentrations in 72 h f o o d - d e p r i v e d rats. NRS (n=7) o r G H R H a b (n=ll) w a s a d m i n i s t e r e d after the 0 min blood sample. All animals received SSab after t h e 55 m i n b l o o d sample• Baseline GH concentrations were elevated compared to previously e s t a b l i s h e d v a l u e s for n o r m a l r a t s ( c r o s s - h a t c h e d area, r e f s 3, i0, 24). GH concentrations did not change following NRS or GHRHab treatment• GH concentrations in b o t h N R S - a n d G H R H a b - t r e a t e d r a t s w e r e s i g n i f i c a n t l y e l e v a t e d a f t e r S S a b t r e a t m e n t (p
