Growth hormone affects both adiposity and voluntary food intake in old and obese female rats

Abstract

OBJECTIVE: To investigate whether the promotion of breakdown of body fat and the increased energy expenditure associated with growth hormone (GH) affect the voluntary food intake of an obese organism. DESIGN: Wistar rats (15 months old) were first fed either a high-fat (HF) or a low-fat (LF) diet for 10 weeks. In the subsequent treatment period, two saline groups continued with either the HF or the LF diet, and rats of three other groups had their diet shifted from HF to LF and were treated with saline, human GH (hGH) or rat GH (rGH). hGH and rGH were given in a dose of 4 mg/kg per day. After 21 days of treatment and registration of food intake, rats were killed, blood was collected and tissues were excised. RESULTS: The HF diet produced a significant (P<0.05) increase in weight of fat pads compared with the LF diet: 69+/-5 g compared with 48+/-2 g. The switch from HF to LF diet combined with injections of saline alone decreased the intake of metabolizable energy, but fat pad weight did not decrease significantly (69+/-5 g compared with 63+/-6 g). The latter value was significantly (P<0.05) decreased (to 37+/-3 g) in groups treated with either hGH or rGH. Both GH treatments increased serum IGF-I and muscle weight, whereas the activity of adipose tissue lipoprotein lipase decreased significantly (P<0.01). During the first 9 days of treatment, food intake was significantly (P<0.01) depressed, from 27+/-1 g/kg per day in control rats to 14+/-2 and 16+/-4 g/kg per day in the hGH and rGH groups respectively. CONCLUSION: This study demonstrates that breakdown of adipose tissue and a transient decrease in voluntary food intake are parallel consequences of GH treatment in old and obese rats, and that the actions of hGH and rGH are very similar.