Hypothalamic Somatostatin and LH-RH after Hypophysectomy,in Hyper- or Hypo-Thyroidism,and during Anesthesia in Rats

Abstract

Summary

Twenty-four days after hy-pophysectomy both hypothalamic somatostatin and LH-RH contents decreased to 1/3 of the control values in male rats. The LH-RH remained unchanged thereafter, whereas the somatostatin continued to fall until 2.5 months after hypophysectomy. The hypothalamic somatostatin and LH-RH contents in 117 day old rats (24.5 and 6.0 ng, respectively) were significantly lower than those in 59-day-old rats (49 and 9.1 ng, respectively).

Thyroidectomy and excess of T₄ did not modify the hypothalamic somatostatin in LH-RH content. On the other hand, an injection of Nembutal or urethane altered the hypothalamic somatostatin content, but not the LH-RH content. After urethane injection the somatostatin content did not change at 5 min as compared with the level at 0 time, but showed a decrease at 10 min. This was associated with a rapid fall of serum GH level which remained low thereafter. The hypothalamic somatostatin then increased stepwise. Nembutal caused a decrease of the hypothalamic somatostatin content at 5 and 10 min and an increase at 60 min. The pattern of change in the hypothalamic somatostatin levels resembled a mirror image of the patterns of change in the serum GH levels.