Radioimmunoassayable Growth Hormone in the Rat Pituitary Gland: Effects of Age, Sex and Hormonal State

A sensitive radioimmunoassay for rat growth hormone (GH) has been modified and used to study pituitary content of GH in the Sprague-Dawley rat under varying conditions. Growth hormone does not appear in the rat fetal pituitary until the 19th day of gestation. Day-old rats have low GH content and concentration but GH rapidly accumulates with age. By puberty the male rat has more pituitary GH than the female rat. This difference increases as the rats grow older. Estrogen treatment of the male rat lowers GH concentration and causes an increase in pituitary size. Testosterone treatment of the female rat leads to an elevation of GH content and concentration. Castration of male rats results in levels of GH that are indistinguishable from those of female rats. These studies indicate that factors of age, sex and gonadal hormones interact to affect pituitary content of growth hormone in the rat. (Endocrinology81: 195,1967)