Altered release of growth hormone and thyrotropin induced by endotoxin in the rat

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Abstract
Plasma growth hormone (GH) and thyrotropin (TSH) levels were measured in freely behaving rats for 6 h on 3 consecutive days. On the 1st and 3rd days there was no treatment, and on the 2nd day endotoxin (150 mg/kg) was administered i.v. Endotoxin causes a biphasic temperature response: an initial hypothermia persisting for 1 h, followed by hyperthermia evident from 5-8 h after injection. Normal pulsatile GH release observed on the 1st day was abolished on the 2nd day by the endotoxin treatment. On the 3rd day GH secretion was greater than on the initial control day. TSH release was also suppressed by endotoxin and showed a rebound release on the subsequent day. The suppression of GH secretion by endotoxin was reversed in all animals by antisomatostatin serum, and the suppression of TSH secretion by endotoxin was reversed in some animals. Evidently, endotoxin is a potent stimulus for hypothalamic somatostatin release in the rat. Endotoxin profoundly alters adenohypophyseal hormone release.