RATS TREATED WITH SOMATOTROPIN SELECT DIETS HIGHER IN PROTEIN

It was previously shown that somatotropin (STH) increases growth rate, improves food efficiency and stimulates protein accretion. In rats, S TH also increases food intake. This study examined the effect of exoge nous STH on rats' selection of diets varying in protein content. It wa s hypothesized that the increase in food intake in response to STH is driven by an increased protein requirement. Rats were allowed to selec t between two diets varying in casein (5 and 30%) or given a diet of a single casein level (20%). In each diet group, rats were treated with 0 or 4 mg of porcine STH/d. Rats treated with STH showed greater food intake (20%) and protein accretion (125%), regardless of;diet. Howeve r, the greater food intake in rats allowed to select was due to greate r consumption of the high protein diet. Diet selecting, STH-treated ra ts consumed 75% more of the 30% casein diet than did the saline-treate d controls, while consuming a similar amount of 5% casein diet. Total protein intake (g/d) was 22 and 53% greater in rats injected with STH consuming the 20% casein diet and selection diets, respectively. The r esults indicate that rats injected with somatotropin select a diet gre ater in protein when compared with those not receiving somatotropin. I t is suggested that the STH-induced increase in protein accretion resu lts in a greater demand for essential amino acids. The mechanism where by animals are able to monitor this greater need is not clear.