Growth hormone secretion after hypophysial stalk transection in pigs.

The level and pattern of growth hormone (GH) secretion were investigated in mature ovariectomized gilts after hypophysial stalk transection and sham operation. A nylon disk was inserted between severed ends of the stalk to prevent vascular regeneration. Blood samples were collected via indwelling jugular catheters at 15-min intervals for 3 hr, 2 days before surgery (Day -2) and 2 days after surgery (Day +2), and at 4-hr intervals from Day +3 to Day +8. Mean overall serum concentrations of GH after hypophysial stalk transection remained similar (P greater than 0.05) to presurgical levels. These mean concentrations also were similar to those in sham-operated and unoperated controls. However, hypophysial stalk transection significantly dampened (P less than 0.05) the episodic secretion of GH and resulted in elevated basal blood concentrations of the hormone as compared with either presurgical levels or those in the two control groups. These results indicate that synthesis and secretion of GH continue in the absence of hypothalamic control in hypophysial stalk-transected gilts. Thus, the hypothalamus is required for regulation of both episodic release and the tonic inhibition of basal secretion of growth hormone in the pig.