Effects of starvation on pituitary and plasma growth hormone in rats

The present experiments were undertaken to study the effect of complete food removal on body weight, pituitary growth hormone (GH), plasma GH and glucose concentration in male and female Wistar rats. Plasma and pituitary GH levels were measured by means of a specific radioimmunoassay. Plasma glucose concentration decrease during the initial 60 h fasting in males and 72 h in females, and remained fairly constant thereafter in both groups. Pituitary GH content was unchanged in males and females by 36 h and 60 h, respectively, after the onset of starvation. Thereafter, pituitary GH decreased progressively with increase of the starvation period. In spite of the changes in pituitary GH, plasma GH concentration in fasted male and female rats was similar to or higher than in controls. In fact, during an initial period, up to 72 h in males and 96 h in females, plasma GH levels in fasting rats were similar to control values. With longer starvation periods, plasma GH concentration rose above control values. After 24 h of refeeding 102 h fasted rats, plasma GH concentrations were comparable to control levels. In addition, after an initial loss of 10 g after 24 h fasting, body weight of both male and female animals decreased, and by the end of the starvation period it was about 50% of control weight. From these results it seems that complete food removal has a direct effect on pituitary GH. Furthermore, the fact that changes in plasma GH concentrations were evidentiated just before the period when plasma glucose was maintained at constant levels in fasted rats of both sexes supports the hypothesis that growth hormone plays a physiological role in the regulation of glucose homeostasis during starvation.