Peripheral injection of growth hormone stimulates protein intake in aged male and female Lou rats

It is well established that growth hormone (GH) induces growth rate and foo d efficiency and stimulates protein accretion in young mammals. Senescence is characterized by metabolic and hormonal disorders, particularly a decrea se in protein turnover, which could be correlated to a decrease in GH and i nsulin-like growth factor I (IGF-I) secretion. We have shown that body weig ht, protein intake, and IGF-I plasma levels are greatly decreased with agin g in Lou/C rats, particularly in males. In order to specify the GH effect o n protein intake during aging, males and females (6, 19, and 24 mo) placed on a self-selection regimen were injected daily with a physiological dose o f human GH (0.023 mg/rat sc). No GH effect on caloric intake was observed. Nevertheless, GH treatment stimulated body weight in older rats; It also in creased protein intake in females and older males (19-24 mo). This stimulat ing effect was positively Correlated with the degree of weight loss in sene scent rats, suggesting that the decrease in protein intake observed with ag ing could be a marker of senescence.