Somatotropin treatment reduces energy intake without altering protein intake in pigs selecting between high and low protein diets

Effects of growth hormone-releasing hormone gene targeted ablation on ghrelin-induced feeding

Impairment of growth hormone (GH) signaling has been associated with increased feeding and adiposity. The gastric hormone ghrelin, in addition to its GH-secretagogue effects, stimulates food intake after both central and peripheral administration. In the present study we further investigated the feeding regulatory role of the ghrelin-GH axis in a mouse model of isolated GH deficiency due to targeted ablation of the GH-releasing hormone (GHRH) gene [GHRH knockout (GHRHKO)]. We evaluated the effects of intracerebroventricular ghrelin administration on feeding behavior, related hypothalamic neuropeptides and neurotransmitters, and serum ghrelin levels in mice homozygous for GHRHKO allele (-/-) and heterozygous (+/-) control animals. Vehicle-treated GHRHKO mice showed increased food intake compared to heterozygotes, associated with increased circulating ghrelin levels. Moreover, -/- mice showed elevated hypothalamic levels of neuropeptide Y (NPY), agouti-related peptide (AgRP) mRNAs and norepinephrine (NE) and decreased corticotropin-releasing hormone (CRH) mRNA levels. Ghrelin treatment significantly augmented food intake in both genotypes, but the relative increase compared to vehicle-treated animals was higher in -/- than +/- mice. In the hypothalamus, ghrelin increased AgRP and decreased CRH gene expression only in heterozygous mice, while it induced a significant reduction in proopiomelanocortin (POMC) mRNA levels in -/- mice. Ghrelin treatment also decreased hypothalamic serotonin (5-hydroxytriptamine, 5-HT) and dopamine (DA) levels in both genotypes. Additionally, we observed increased DA metabolism induced by ghrelin in both genotypes. In conclusion, dysregulation of the ghrelin-GHRH-GH axis in GHRHKO mice could lead to increased feeding secondary to elevated circulating levels of ghrelin, and the obesogenic phenotype is likely mediated by elevated NPY and AgRP, and decreased CRH gene expression in the hypothalamus.

Effect of Long-Term Somatotropin Treatment on Body Composition and Life Span in Aging Obese Zucker Rats

The objective of this work was to test the hypothesis that a somatotropin (STH)-induced reduction in body fat would prolong the life span of the obese Zucker rat. Two experiments were conducted. In the first experiment, male and female, lean and obese Zucker rats were treated with STH (0 or 2 mg/d bovine STH) for 4 weeks, beginning at 7 months of age. Across phenotypes, STH treatment increased the growth rate by 159%, muscle weights by 14%, and circulating insulin-like growth factor (IGF)-1 by 23%, and decreased carcass fat by 21% (P < 0.05). The second experiment was a longevity trial to determine whether these changes in body composition would increase the life span of the obese rat. Beginning at 7 months of age, individually housed, male and female, lean and obese rats were assigned to daily STH treatments (0 or 2 mg/d). Rats were monitored daily, and sick or moribund rats were euthanized and necropsied to determine existing pathologies. The average life span of the lean rats was 661 days and was unaffected by STH treatment (639 days, NS) or gender. Average life span of the vehicle-injected obese rats (435 days) was less than that of the lean group (P < 0.001). STH treatment of the obese rats resulted in a further reduction of life span (349 days, P < 0.02). The predominant pathology observed across the treatment groups was renal disease, characterized by progressive glomerulonephropathy. Thus, although exogenous STH was able to reduce carcass lipid and to increase lean tissue mass in obese rats, there was no improvement in longevity. In contrast to the hypothesis, STH actually reduced the life span of the obese rat. It is likely that STH treatment accelerated the development of progressive glomerulonephropathy in the obese rat.

Effects of isolated GH deficiency on adipose tissue, feeding and adipokines in mice

OBJECTIVE

Growth hormone deficiency (GHD) leads to growth failure and changes in body composition including increased fat accumulation and reduced lean body mass in both humans and rodents. The aim of this study was to characterize the consequences of isolated GHD (IGHD) on adiposity, total body weight (TBW), and food intake in a mouse model of autosomal recessive IGHD due to targeted ablation of the GH-releasing hormone (GHRH) gene [GHRH knockout (GHRHKO)]. Animals were also analyzed with respect to leptin, adiponectin and visfatin circulating levels and gene expression in both intra-abdominal and subcutaneous fat.

DESIGN

We studied 8 male mice homozygous for GHRHKO allele (-/-) and 8 heterozygous (+/-) animals as controls. Feeding and TBW data were collected weekly from 3 through 5 months of age. Animals were then euthanized for measurement of body length and intra-abdominal (epididymal and retroperitoneal) and subcutaneous (interscapular, axillary, gluteal and inguinal) fat weights, and for blood collection for leptin, adiponectin and visfatin measurement. Gene expression of leptin, adiponectin and visfatin in adipose tissue was evaluated by real-time reverse transcription polymerase chain reaction.

RESULTS

GHRHKO mice had significantly increased relative intra-abdominal (P<0.01) and subcutaneous (P<0.0001) fat, accompanied by significantly increased food intake per TBW (P<0.01), whereas - despite 40% higher food consumption--TBW change was not different from controls over the 2 month period. Adiponectin and visfatin mRNA levels were decreased in both intra-abdominal (P<0.001) and subcutaneous fat (P<0.0001), while leptin mRNA levels were not different from controls. Conversely, serum adiponectin levels were higher in GHRHKO mice (P<0.0001), whereas serum visfatin and leptin did not significantly differ from controls.

CONCLUSIONS

IGHD due to targeted ablation of the GHRH gene in mice is associated with increased relative subcutaneous and intra-abdominal fat mass and higher food consumption which is not related to changes in circulating leptin.

Treatment of Obesity Using GH

The obesity epidemic calls for complementary treatment possibilities in addition to lifestyle changes. One of the important regulators of lipid homeostasis is growth hormone (GH). Clinical trials have tested if GH can reduce obesity in humans. The mechanisms underlying the response to GH administration have also been investigated in animal models of human obesity. A literature search yielded 19 randomized placebo-controlled clinical studies and several animal studies investigating chronic GH treatment of obesity. Significant effects were found in some of the larger trials. One clinical trial showed significantly increased weight loss due to GH treatment, and in seven trials, a significant reduction of fat mass was found. The improvements observed were modest, but even minor improvements have been shown to be beneficial, especially if the reduction in fat mass includes visceral adipose tissue, as was reported in three of six trials. In principle, animal data support the clinical observations although the reduction of fat mass was more dramatic than observed in humans. The mechanisms resulting in lipid mobilization most likely include adipose tissue lipo-protein lipase (LPL) inhibition and antagonization of the anti-lipolytic activity of insulin. By feeding a restricted amount of a high fat diet to GH exposed rats hyper-insulinemia was avoided, loss of body fat was accelerated and metabolic markers were improved. Provision of a diet suitable for the metabolic conditions during GH treatment shows promise for improving metabolic control and can perhaps increase the efficacy and/or widen the therapeutic window of GH.

Hepatic vagotomy disrupts somatotropin-induced protein selection

Rats treated with somatotropin (STH) and allowed to self-select between diets varying in protein content will consume more of the high-protein diet. The objective of this study was to determine the role of the hepatic vagus nerve in this ability to select protein. Female Sprague-Dawley rats (n=40) received a hepatic vagotomy (HVAGX) or a sham surgery. Postsurgery, the rats were maintained on pelleted diets for 2 weeks, after which the rats were adapted to selecting between powdered diets with 5% casein and 30% casein. After a 7-day adaptation to diet selection, rats in each surgical treatment group were treated with STH (4 mg/day) or physiological saline for 14 days. Body weight and intake were recorded daily. STH treatment increased growth rate to a similar degree in both sham and HVAGX groups. Despite causing an increase in total food intake, there was no effect of HVAGX alone on body weight. Relative to the sham-saline group, sham-STH in treated rats had greater total food intake that was accounted for entirely by increased consumption of the 30% protein diet and no change in intake of the 5% diet. In contrast, HVAGX+STH rats exhibited 20-30% increases in consumption of both the 5% and 30% protein diets. Thus, the HVAGX+STH rats recognized an increased need for protein, but were unable to distinguish between the high- and low-protein diets and selected more of both. The data suggest that the ability to alter diet selection in response to a stimulation of protein accretion is at least partially mediated through the liver and hepatic branch of the vagus nerve.

Feed intake and protein skeletal muscle in growing mice treated with growth hormone: time course effects

The exogenous recombinant human growth hormone (rhGH) administration on gastrocnemius muscle growth performance and its contribution to body growth of male and female BALB/c mice fed a 12 % protein diet from 25 to 50 days of age, as well as the mechanism of utilization of feed intake to the lean muscle deposition were studied. Male and female weaning mice (21 days of age) were injected subcutaneously for 29 days with rhGH (74 ng x g(-1)) or saline vehicle (control). Feed intake and body weight (BW) were measured daily. At 25, 30, 35, 40, 45 and 50 days of age twenty mice were killed by cervical dislocation and the gastrocnemius muscle was isolated, weighed and the protein content was measured. The rhGH administration caused a biphasic response of BW and muscle growth as a consequence of age-specific feed intake changes. The initial feed intake fall induced the allometric proportion decreases in both muscle growth versus body growth and protein muscle versus muscle growth. That effect was due to ineffient utilization of energy and protein intake on protein muscle store. Later on, the self-controlled increase of feed intake leads to the recovery of muscle weight to control values, through nutrient partitioning toward non protein tissue showing a compensatory muscle growth. This suggests that a higher dietary protein level should be necessary for promoting the protein anabolic effect of GH during weaning.

The growth hormone axis, feeding, and central allocative regulation: lessons from giant transgenic growth hormone mice

Lifetime consumption rates of male transgenic growth hormone (GH) mice and normal controls were measured on either a 38% protein diet (HP), the standard rodent diet (STD) (23.5% protein), or the standard diet supplemented with a free choice of sucrose (CARB). On STD, daily intake of normal mice increased little at sizes greater than 20 g, but larger transgenic mice ate progressively more. Both kinds of mice showed declining daily mass-specific consumption with increasing age. Transgenic mice consistently ate 13.3% less food than normal mice on a mass-specific basis across all ages. On the self-selective CARB diet, normal mice exhibited increasing age-specific daily consumption, whereas transgenic mice exhibited a trend towards age-related decline in mass-specific feeding that proved significant on the basis of body mass. Transgenic mice ingested more sucrose than standard chow and this did not vary with age. In contrast, normal mice ate less sucrose than chow and chose a declining proportion of sucrose with age. Transgenic and normal mice showed a unitary relationship of daily intake of HP in relation to body mass, resulting in constant mass-specific feeding across all ages. Transgenic GH animals, including livestock, show numerous defects that we have attributed to relative energetic stress associated with excessive allocation to lean growth. This is exacerbated by failure to offset increased demands of growth by increasing mass-specific feeding. Results presented here document altered feeding regulation in transgenic GH mice and suggest underlying mechanisms.

Effects of intracerebroventricularly administered leptin on protein selection in the rat

The effect of centrally administered rat leptin on selection of 5 and 30% protein diets was investigated in male Sprague-Dawley rats with indwelling i.c.v. cannulas. Leptin (0 vs 2.5 microg/day) was administered for 4 consecutive days, followed by an 8-day withdrawal period. Total intake was reduced to approximately 50% of that in the vehicle injected group during each day following leptin administration. Intake of both the 5 and 30% diets was reduced. Vehicle-treated rats selected a 13-15% CP diet. Diet selection in leptin-treated rats was not different during the first day, but on Days 2-4, leptin-treated rats selected a 10% CP diet. Intake began to normalize within 24-48 h after the last treatment, and was not different by Day 3 of the withdrawal period. Body weight was reduced by leptin treatment, and despite the normalization of food intake, did not recover during the withdrawal period. Rats were sacrificed at the end of the 8-day withdrawal period. Despite the reduction in body and carcass weights, liver, kidney, heart, and soleus muscle weights were not different between control and leptin-treated groups when expressed on an absolute or relative basis. However, epididymal and retroperitoneal fat pad weights were still reduced 56 and 78%, respectively, in rats that had been previously treated with leptin for 4 days and then not treated for 8 days. In addition, circulating T3 levels remained elevated in rats that had been treated with leptin. Centrally administered leptin has little effect on muscle mass, but had potent effects on intake of nonobese rats and a sustained effect on adipose tissue mass, thyroid hormone status, and body weight after withdrawal. Results from rats selecting between diets varying in protein content suggest that leptin may cause avoidance of protein.