Restoration of growth hormone secretion in prolonged food-deprived rats depends on the level of nutritional intake and dietary protein

Reverse feeding suppresses the activity of the GH axis in rats and induces a preobesogenic state

Reversed feeding (RF) is known to disrupt hormone rhythmicity and metabolism. Although these effects may be mediated in part by phase inversion of glucocorticoid secretion, the precise mechanism is incompletely characterized. In this study, we demonstrate that acute nocturnal food deprivation in male rats suppressed the amplitude of spontaneous GH secretion during the dark phase by 62% (P < 0.001), without affecting baseline secretion. Prolonged RF, which reduced pituitary weight (by 22%; P < 0.05), also suppressed GH pulse height sufficiently to reduce skeletal growth (by 4-5%; P < 0.01) and terminal liver weight (by 11%; P < 0.001). Despite this suppression of the GH axis, proportionate adiposity was not elevated, probably due to the accompanying 16% reduction in cumulative food intake (P < 0.01). We demonstrate that RF also resulted in phase inversion of core clock gene expression in liver, abdominal white adipose tissue (WAT) and skeletal muscle, without affecting their expression patterns in the suprachiasmatic nucleus. In addition, RF resulted in phase inversion of hepatic peroxisome proliferator-activated receptor γ2 mRNA expression, a 3- to 5-fold elevation in fatty acid synthase mRNA in WAT in both light- and dark-phase samples (P < 0.01) and an elevation in muscle uncoupling protein 3 mRNA expression at the beginning of the light phase (P < 0.01). Consumption of a high-fat diet increased inguinal (by 36%; P < 0.05) and retroperitoneal WAT weight (by 72%; P < 0.01) only in RF-maintained rats, doubling the efficiency of lipid accumulation (P < 0.05). Thus, RF not only desynchronizes central and peripheral circadian clocks, and suppresses nocturnal GH secretion, but induces a preobesogenic state.

Change of the growth hormone–insulin-like growth factor-I axis in patients with gastrointestinal cancer: related to tumour type and nutritional status

Changes in the growth hormone (GH)–insulin-like growth factor-I (IGF-I) axis, especially acquired GH resistance, develop in many severe illnesses, including cachexia. To study changes in the GH–IGF-I axis in patients with cancer cachexia, biochemical markers and body composition parameters were measured in eighty-eight gastric cancer patients, thirty colorectal cancer patients (subclassified according to the presence or absence of cachexia) and twenty-four healthy control subjects. Fifty-nine patients were defined as cachectic, based on the percentage of weight loss compared with their previous normal weight. The remaining fifty-nine patients were defined as non-cachectic. Measurements were repeated in twenty-seven patients (sixteen with gastric cancer and eleven with colorectal cancer) 3 months after radical operation. Compared with the controls, the cachectic gastric cancer patients had high GH levels (1·36 v. 0·32 ng/ml; P=0·001), a trend towards high IGF-I levels (223·74 v. 195·15 ng/ml; P=0·128 compared with non-cachectic patients) and a low log IGF-I/GH ratio (2·55 and 2·66 v. 3·00; P=0·002), along with a decreased BMI; the cachectic colorectal cancer patients showed the biochemical characteristics of acquired GH resistance: high GH (0·71 v. 0·32 ng/ml; P=0·016), a trend towards decreased IGF-I levels (164·18 v. 183·24 ng/ml; P=0·127) and a low log IGF-I/GH ratio (2·54 v. 2·99; P=0·005), with increased IGF-I levels following radical surgery (200·49 v. 141·91 ng/ml; P=0·046). These findings suggest that normal GH reaction and sensitivity occur in gastric cancer patients, controlled by nutritional status, whereas acquired GH resistance develops in cachectic colorectal cancer patients, which may be caused by tumour itself.

Nutritional status in the neuroendocrine control of growth hormone secretion: the model of anorexia nervosa

Growth hormone (GH) plays a key role not only in the promotion of linear growth but also in the regulation of intermediary metabolism, body composition, and energy expenditure. On the whole, the hormone appears to direct fuel metabolism towards the preferential oxidation of lipids instead of glucose and proteins, and to convey the energy derived from metabolic processes towards the synthesis of proteins. On the other hand, body energy stores and circulating energetic substrates take an important part in the regulation of somatotropin release. Finally, central and peripheral peptides participating in the control of food intake and energy expenditure (neuropeptide Y, leptin, and ghrelin) are also involved in the regulation of GH secretion. Altogether, nutritional status has to be regarded as a major determinant in the regulation of the somatotropin-somatomedin axis in animals and humans. In these latter, overweight is associated with marked impairment of spontaneous and stimulated GH release, while acute dietary restriction and chronic undernutrition induce an amplification of spontaneous secretion together with a clear-cut decrease in insulin-like growth factor I (IGF-I) plasma levels. Thus, over- and undernutrition represent two conditions connoted by GH hypersensitivity and GH resistance, respectively. Anorexia nervosa (AN) is a psychiatric disorder characterized by peculiar changes of the GH-IGF-I axis. In these patients, low circulating IGF-I levels are associated with enhanced GH production rate, highly disordered mode of somatotropin release, and variability of GH responsiveness to different pharmacological challenges. These abnormalities are likely due not only to the lack of negative IGF-I feedback, but also to a primary hypothalamic alteration with increased frequency of growth hormone releasing hormone discharges and decreased somatostatinergic tone. Given the reversal of the above alterations following weight recovery, these abnormalities can be seen as secondary, and possibly adaptive, to nutritional deprivation. The model of AN may provide important insights into the pathophysiology of GH secretion, in particular as regards the mechanisms whereby nutritional status effects its regulation.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Impaired secretion of growth hormone in experimental uremia: relevance of caloric deficiency

To evaluate the impact of uremia and associated caloric restriction on physiologically pulsatile growth hormone (GH) release, we used deconvolution analysis of spontaneous plasma GH profiles in 5/6-nephrectomized male rats (NX, N = 9). Three different normal renal function sham-operated groups were used: rats fed a normal diet ad libitum (SAL, N = 9); NX pair-fed rats (SPF, N = 6); NX rats pair-fed for protein ingestion but calorically supplemented up to the energy intake of SAL (SPF+, N = 8). Severe renal failure was confirmed by much higher (P < 0.001) BUN in NX than sham groups. NX rats were growth retarded as shown by reduced (P < 0.01) weight and length gains as compared with sham animals. Deconvolution analysis (mean +/- SEM) of plasma samples obtained every 10 minutes over 6 hours, and 14 to 16 days after second stage nephrectomy showed that NX rats had a longer GH t(1/2) (17.0 +/- 1.8 vs. 11.6 +/- 0.8 min), less GH mass secreted per burst (48 +/- 15 vs. 95 +/- 16 ng/ml/pulse), lower secretory pulse amplitude (1.9 +/- 0.5 vs. 5.8 +/- 0.9 ng/ml/min), and a reduced total GH secretion (240 +/- 69 vs. 400 +/- 56 ng/ml/6 hr) than SAL rats. Corresponding data were not significantly different between NX and SPF, or between SAL and SPF+ groups. In summary, stunted rats with chronic renal failure exhibit a prolonged GH t(1/2) and suppression of GH secretory pattern burst mass. Control data from rats with normal renal function suggest that the amplitude-specific depression of GH secretion may be attributed, at least in part, to chronic renal failure-associated calorie deficiency.

Effects of hyper- and hypoglycemia on blood growth hormone level in free-feeding rats with anterolateral deafferentation of the medial basal hypothalamus

In rats with anterolateral deafferentation of the medial basal hypothalamus, the growth hormone (GH) level in the blood showed irregular and small fluctuations instead of the usual high bursts and low trough level, and the baseline GH level was higher than that in sham-operated rats. Continuous infusion of a glucose solution to operated rats increased the baseline level, GH pulse and pulse amplitude. I.v. bolus injection of the glucose solution resulted in a significant but transient increase in GH level. Insulin-induced hypoglycemia decreased the blood GH level in operated rats more effectively than in sham-operated ones and that was prevented by simultaneous infusion of glucose. Since SS influence on GH secretion had been largely eliminated in rats with anterolateral deafferentation of the medial basal hypothalamus, it is highly unlikely that the effects of hyperglycemia or hypoglycemia on GH secretion were the consequence of altered SS secretion.

Caloric intake stimulates growth hormone secretion in food-deprived rats with anterolateral deafferentation of the medial basal hypothalamus or administered antiserum to somatostatin

In rats, food deprivation inhibits episodic growth hormone (GH) secretion. On the basis of previous studies, we hypothesized that during a recovery from prolonged fasting, caloric intake stimulates the release of GH-releasing factor (GRF) and this process does not depend on the specific macronutrients in the meal, while protein in the meal acts to restore characteristic ultradian rhythmicity of GH secretion. To test this hypothesis, the effect of caloric intake on GH secretion was examined in fasted adult male Wistar rats devoid of somatostatin (SS) influence on GH secretion either by anterolateral deafferentation (ALC) of the medial basal hypothalamus (MBH) or administration of anti-SS goat serum (ASS). Rats were provided with an indwelling right atrial cannula and were deprived of food for 72 h. ALC was performed 2 weeks prior to the study. ASS was given i.v. 8 h and 7 h prior to refeeding, respectively. Serial blood specimens were collected every 10 min. In rats with ALC (ALC rats) or rats given ASS (ASS rats), the blood GH level revealed irregularly occurring small fluctuations, instead of the usual high bursts and low trough level. The baseline GH level and the mean GH level of fasted ALC rats or fasted ASS rats were significantly lower than those of fed ALC rats or fed ASS rats. Feeding the isocaloric mixed meal, the protein meal or the protein-deficient meal increased the GH pulse frequency, the pulse amplitude, the baseline GH level and the mean GH level in 72-h fasted ALC rats. These changes in GH secretory pattern persisted during the period of observation and were independent of the type of meal ingested. Following feeding the mixed meal, similar changes in the GH secretory pattern demonstrated in 72-h fasted ALC rats were also observed in 72-h fasted ASS rats, suggesting that the stimulation of GH secretion following caloric intake is not limited to ALC rats. Since the influence of SS on GH secretion has been largely eliminated in ALC or ASS rats, it is highly unlikely that the augmentation of GH secretion following feeding after prolonged food deprivation was the consequence of inhibition of SS secretion. Although GRF measurement was not performed, it is conceivable that the signal of caloric intake is conveyed to the MBH and acts to stimulate GRF release.