Growth Hormone Secretion after Hypophysial Stalk Transection in Pigs

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Abstract
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 h, 2 days before surgery (Day -2) and 2 days after surgery (Day +2), and at 4-h intervals from Day +3 to Day +8. Mean overall serum concentrations of GH after hypophysial stalk transection remained similar (P > 0.05) to presurgical levels. These mean concentrations also were similar to those in sham-operated and unoperated controls. Hypophysial stalk transection significantly dampened (P < 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 2 control groups. Synthesis and secretion of GH continue in the absence of hypothalamic control in hypophysial stalk-transected gilts. The hypothalamus is required for regulation of both episodic release and the tonic inhibition of basal secretion of growth hormone in the pig.