Anterior Pituitary Growth Hormone and the Composition of Growth

Abstract

The effect of the growth hormone of the anterior pituitary upon the gain in weight and upon the composition of the gain was determined in rats under a paired-feeding regimen. Twelve pairs, each composed of litter-mates of the same sex, initial body weight and length were used. The food consumption in each pair was kept the same for control and treated members. After 8 to 11 weeks the animals were killed and their carcasses analyzed. Their compositions at the beginning of paired-feeding and treatment were estimated from the analyses of other litter-mates killed at that time. The twelve controls showed the characteristic changes in body composition with age that would be expected. These changes were statistically significant decreases in the proportion of water, nitrogen, fat-free dry tissue, and ash, and increases in the percentage of fat and in the heat value of the tissue. They gained a total of 764 gm. in body weight and 18.2 cm. in length. The twelve treated animals retained almost exactly their initial composition in all constitutents and in the heat value of their tissue. Their excess gains over their control mates, on the same food intake, were: live weight, 531 gm; body length, 15 cm.; water, 447 gm.; fat-free dry tissue, 173 gm.; nitrogen, 22.5 gm.; ash, 22.4 gm.; fat, -119 gm.; energy, -341 calories. The composition of their gains thus differed markedly from that of the controls, but was closely similar to the initial composition of the animals themselves. The nitrogen and ash balances determined indirectly by analyses of food, urine and feces corroborate the direct findings from carcass analysis. The weekly excess nitrogen retention in the treated rats paralleled closely the weekly excess gain in weight, and indicates that even the excess gain in weight for the first week constituted true growth. The energy expenditure was 1.7 times as great for the controls as for the treated animals per gram of weight gained, and 2.4 times as great per gram of protein gained. The treated animals burned more fat and less protein than did the controls. Two treated animals on ad libitum feeding gave responses the same qualitatively, but greater in amount than did their treated mates on paired-feeding. Statistical analysis of the data indicates that nitrogen and fat-ash-free dry tissues were the constituents most specifically influenced by the hormone.