0013.7227/92/1316-2603503.00/0 Endocrmology Copyright 0 1992 by The Endocrine
Vol. 131, No. 6 I’rinhd in (1 S A
Society
Inhibitory Effects of Ethanol on the Growth Hormone (GH)-Releasing Hormone-GH-Insulin-Like Growth Factor-I Axis in the Rat* PIOTR A. SOSZYNSKIt
AND
LAWRENCE
A. FROHMAN
Division of Endocrinology and Metabolism, Department College of Medicine, Cincinnati, Ohio 45267
of
Internal
Medicine,
University
of
Cincinnati
ABSTRACT Ethanol administration decreases GH secretion in humans and experimental animals. The mechanism of these inhibitory effects was investigated by evaluating the spontaneous secretory pattern of GH in chronically cannulated unanesthetized rats, plasma insulin-like growth factor-I (IGF-I) concentrations, and hypothalamic GH-releasing hormone (GHRH) and somatostatin, and pituitary GH mRNA levels. Body weight gain was reduced in ethanol (5%)-liquid diet-fed rats (n = 6) for 6 days compared to that in both isocalorically pair-fed controls (n = 6) and ad libitum-fed animals (n = 6). Spontaneous GH secretion was markedly decreased (by 75-90%) in ethanol-fed rats compared to that in pair-fed and ad lib&urn-fed groups, while pulsatile pattern of GH release was preserved, with secretory bursts occurring every 180220 min in all groups. Mean 6-h plasma GH levels in ethanol-, pair-,
and ad libitum-fed animals were: 18.8 + 4.5, 113.3 + 14.9, and 179.6 f 30.1 rig/ml, respectively (P < 0.01, ethanol us. each control). Plasma IGF-I concentrations were decreased in the ethanol-fed rats (338 f 16 rig/ml) compared to those in pair-fed (427 + 39 rig/ml; P < 0.05) and ad lib&urn-fed (769 + 25 rig/ml; P < 0.01) rats. Ethanol treatment decreased GHRH mRNA levels to 9% of those in ad libitum-fed (P < 0.01) and 20% of those in pair-fed (P < 0.05) animals, whereas it did not significantly alter somatostatin or GH mRNA levels. The results indicate that the effects of ethanol inhibit GH secretion primarily at the hypothalamic level, resulting in impaired GHRH gene expression. Since the GHRH-GH-IGF-I axis has an important role in growth regulation, the growth retardation seen in experimental models of alcohol abuse may be a consequence at least in part of the suppressive effects of ethanol on this axis. (Endocrinology 131: 2603-2608, 1992)
E
has been shown to decreaseserum insulin-like growth factorI (IGF-I) levels in some, but not all, studies (15-17), and this decreasemay affect GH concentrations by altering feedback regulation (18). Since the GH-releasing hormone (GHRH)GH-IGF-I axis plays an essentialrole in nutrient metabolism and growth (19), the effects of ethanol may have important physiological consequences. The present study was designed to investigate the effects of short term ethanol administration on the regulation of GH by measuring spontaneous GH secretion in conscious rats, plasma IGF-I concentrations, and pituitary GH mRNA and hypothalamic GHRH and somatostatin (SRIH) mRNA levels.
THANOL exerts multiple toxic effects on body growth and metabolism in humans. Chronic alcohol abuse is frequently associatedwith marked weight loss, which results primarily from malnutrition and liver disfunction, although other adverse metabolic effects of ethanol are also important (1,2). Animals fed ethanol-containing diets exhibit decreased growth even when food intake and other nutritional factors are controlled (2-4). In addition to its effects on organs directly involved in the control of metabolism, such as liver and brain, ethanol alters other physiological functions involved in growth homeostasis, such as endocrine system activity (5, 6). It is well documented that ethanol is capable of altering signal transduction pathways involved in hormone synthesis and release(7). Circulating GH levels decrease after both acute and chronic ethanol administration in humans and laboratory animals (8-12). The site of this effect has not been precisely determined, although most indirect evidence suggests an alteration of neurohormonal function within the central nervous system at the level of the hypothalamus (11-13). However, we have recently reported that ethanol may directly modify signal transduction in somatotrophs, resulting in reduced GH release (14). In addition, ethanol treatment Received May 4, 1992. Address all correspondence and requests for reprints to: Lawrence A. Frohman, M.D., Department of Medicine (M/C 787), University of Illinois at Chicago, 840 S. Wood Street, Chicago, IL 60612. * This work was supported in part by USPHS Grant DK-30667. t Visiting Scientist from Department of Endocrinology, Medical Center for Postgraduate Education (Warsaw, Poland), supported by a research fellowship from the Fogarty International Center.
Materials Animals
and experimental
and Methods protocol
Male Sprague-Dawley rats (Harlan, Inc., Indianapolis, IN), weighing 225-250 g, were used for the experiments. Animals were maintained under constant environmental conditions (temperature, 23 f 1 C; lights on, 0600-1800 h), with water and food provided ad libitum. An iv cannula was implanted into the right atrium under sodium pentobarbital anesthesia, as previously described (20). Animals were then placed in individual cages, handled and weighed daily by the same investigator, and adapted to the specific blood-sampling procedures. When body weight returned to the preoperative levels (usually 5-6 days), rats were divided into three groups. The first group (n = 6) was fed a liquid diet (Bio-Serv, Frenchtown, NJ) containing 5% ethanol (wt/vol), which contributed 35% of the total calories. During first 2 days, animals were given a diet containing half of the ethanol content, after which a full ethanol-liquid diet was administered for 4 days (3). The second group of animals (n = 6) was pair-fed with an isocaloric liquid diet in which alcohol was replaced by dextro-maltose (3). The volume of each of the diets was measured daily, and the caloric value was determined. The
2603
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 17 November 2015. at 21:17 For personal use only. No other uses without permission. . All rights reserved.
EFFECTS OF ETHANOL
2604
third group of animals (n = 6) served as ad libitum-fed controls and was provided regular rat chow (Harlan Tekland, Bartonville, IL) ad libitum. The caloric
Vol. 131, No. 6 I’rinhd in (1 S A
Society
Inhibitory Effects of Ethanol on the Growth Hormone (GH)-Releasing Hormone-GH-Insulin-Like Growth Factor-I Axis in the Rat* PIOTR A. SOSZYNSKIt
AND
LAWRENCE
A. FROHMAN
Division of Endocrinology and Metabolism, Department College of Medicine, Cincinnati, Ohio 45267
of
Internal
Medicine,
University
of
Cincinnati
ABSTRACT Ethanol administration decreases GH secretion in humans and experimental animals. The mechanism of these inhibitory effects was investigated by evaluating the spontaneous secretory pattern of GH in chronically cannulated unanesthetized rats, plasma insulin-like growth factor-I (IGF-I) concentrations, and hypothalamic GH-releasing hormone (GHRH) and somatostatin, and pituitary GH mRNA levels. Body weight gain was reduced in ethanol (5%)-liquid diet-fed rats (n = 6) for 6 days compared to that in both isocalorically pair-fed controls (n = 6) and ad libitum-fed animals (n = 6). Spontaneous GH secretion was markedly decreased (by 75-90%) in ethanol-fed rats compared to that in pair-fed and ad lib&urn-fed groups, while pulsatile pattern of GH release was preserved, with secretory bursts occurring every 180220 min in all groups. Mean 6-h plasma GH levels in ethanol-, pair-,
and ad libitum-fed animals were: 18.8 + 4.5, 113.3 + 14.9, and 179.6 f 30.1 rig/ml, respectively (P < 0.01, ethanol us. each control). Plasma IGF-I concentrations were decreased in the ethanol-fed rats (338 f 16 rig/ml) compared to those in pair-fed (427 + 39 rig/ml; P < 0.05) and ad lib&urn-fed (769 + 25 rig/ml; P < 0.01) rats. Ethanol treatment decreased GHRH mRNA levels to 9% of those in ad libitum-fed (P < 0.01) and 20% of those in pair-fed (P < 0.05) animals, whereas it did not significantly alter somatostatin or GH mRNA levels. The results indicate that the effects of ethanol inhibit GH secretion primarily at the hypothalamic level, resulting in impaired GHRH gene expression. Since the GHRH-GH-IGF-I axis has an important role in growth regulation, the growth retardation seen in experimental models of alcohol abuse may be a consequence at least in part of the suppressive effects of ethanol on this axis. (Endocrinology 131: 2603-2608, 1992)
E
has been shown to decreaseserum insulin-like growth factorI (IGF-I) levels in some, but not all, studies (15-17), and this decreasemay affect GH concentrations by altering feedback regulation (18). Since the GH-releasing hormone (GHRH)GH-IGF-I axis plays an essentialrole in nutrient metabolism and growth (19), the effects of ethanol may have important physiological consequences. The present study was designed to investigate the effects of short term ethanol administration on the regulation of GH by measuring spontaneous GH secretion in conscious rats, plasma IGF-I concentrations, and pituitary GH mRNA and hypothalamic GHRH and somatostatin (SRIH) mRNA levels.
THANOL exerts multiple toxic effects on body growth and metabolism in humans. Chronic alcohol abuse is frequently associatedwith marked weight loss, which results primarily from malnutrition and liver disfunction, although other adverse metabolic effects of ethanol are also important (1,2). Animals fed ethanol-containing diets exhibit decreased growth even when food intake and other nutritional factors are controlled (2-4). In addition to its effects on organs directly involved in the control of metabolism, such as liver and brain, ethanol alters other physiological functions involved in growth homeostasis, such as endocrine system activity (5, 6). It is well documented that ethanol is capable of altering signal transduction pathways involved in hormone synthesis and release(7). Circulating GH levels decrease after both acute and chronic ethanol administration in humans and laboratory animals (8-12). The site of this effect has not been precisely determined, although most indirect evidence suggests an alteration of neurohormonal function within the central nervous system at the level of the hypothalamus (11-13). However, we have recently reported that ethanol may directly modify signal transduction in somatotrophs, resulting in reduced GH release (14). In addition, ethanol treatment Received May 4, 1992. Address all correspondence and requests for reprints to: Lawrence A. Frohman, M.D., Department of Medicine (M/C 787), University of Illinois at Chicago, 840 S. Wood Street, Chicago, IL 60612. * This work was supported in part by USPHS Grant DK-30667. t Visiting Scientist from Department of Endocrinology, Medical Center for Postgraduate Education (Warsaw, Poland), supported by a research fellowship from the Fogarty International Center.
Materials Animals
and experimental
and Methods protocol
Male Sprague-Dawley rats (Harlan, Inc., Indianapolis, IN), weighing 225-250 g, were used for the experiments. Animals were maintained under constant environmental conditions (temperature, 23 f 1 C; lights on, 0600-1800 h), with water and food provided ad libitum. An iv cannula was implanted into the right atrium under sodium pentobarbital anesthesia, as previously described (20). Animals were then placed in individual cages, handled and weighed daily by the same investigator, and adapted to the specific blood-sampling procedures. When body weight returned to the preoperative levels (usually 5-6 days), rats were divided into three groups. The first group (n = 6) was fed a liquid diet (Bio-Serv, Frenchtown, NJ) containing 5% ethanol (wt/vol), which contributed 35% of the total calories. During first 2 days, animals were given a diet containing half of the ethanol content, after which a full ethanol-liquid diet was administered for 4 days (3). The second group of animals (n = 6) was pair-fed with an isocaloric liquid diet in which alcohol was replaced by dextro-maltose (3). The volume of each of the diets was measured daily, and the caloric value was determined. The
2603
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 17 November 2015. at 21:17 For personal use only. No other uses without permission. . All rights reserved.
EFFECTS OF ETHANOL
2604
third group of animals (n = 6) served as ad libitum-fed controls and was provided regular rat chow (Harlan Tekland, Bartonville, IL) ad libitum. The caloric
