Functional activity of the hypothalamo-pituitary complex in the rat after betamethasone treatment

Inhibition of corticotrophin releasing factor secretion in the pentobarbitone-morphine-treated rat

The concentrations of ACTH in the plasma and adenohypophysis and corticotrophin releasing factor (CRF) in the hypothalamus were determined and the functional capacities of the adenohypophysis and hypothalamus assessed in male rats treated with pentobarbitone and morphine. A single injection of morphine increased markedly the concentrations of ACTH in both the plasma and the adenohypophysis and the CRF content in the hypothalamus. When the opiate was given to rats injected 10 min previously with sodium pentobarbitone its effects were substantially reduced and the hypothalamo-pituitary-adrenocorticotrophic response to stress was abolished. The functional activity in vitro of pituitary tissue removed from control rats was not affected by the addition to the incubation medium of pentobarbitone and/or morphine. Pituitary glands of drug-treated rats also responded normally both in vivo and in vitro, with respect to ACTH secretion, to hypothalamic extracts prepared from control animals, CRF-41 and arginine vasopressin (AVP). On the other hand, hypothalami removed from pentobarbitone/morphine treated rats showed a marked reduction in their ability to secrete CRF in response to acetylcholine or 5-hydroxytryptamine as also did hypothalami from control animals after preincubation with pentobarbitone and/or morphine. The results suggest that the hypothalamus is an important site of action of pentobarbitone and morphine in modulating the functional activity of the hypothalamo-pituitary-adrenocortical system and are in accord with the view that the pentobarbitone/morphine-treated rat is suitable for the detection and quantification of potential corticotrophin releasing factors.

Effects of adrenalectomy and hypophysectomy on enkephalin content of the rat hypothalamus

1 Hypothalamic content of enkephalin in rats has been measured by bioassay against methionine-enkephalin on field-stimulated mouse vas deferens after acid extraction and purification using Amberlite XAD-2 resin.2 Surgical stress lowered hypothalamic enkephalin content initially but 6 days after operation the content was higher in sham-operated than in adrenalectomized animals.3 Corticosteroid replacement therapy showed that hypothalamic enkephalin content was not related directly to circulating corticosteroid levels and that it was increased by the stress of handling and injection.4 Hypothalamic enkephalin content of rats that had undergone hypophysectomy 11 days earlier did not differ from that of intact animals but surgical stress, which lowered content in intact rats and had no effect after adrenalectomy, produced a rise in content in these hypophysectomized animals.5 The ingestion of 0.9% saline, in place of water, by sham-adrenalectomized rats altered the effect of surgical stress on hypothalamic enkephalin content without affecting the resting levels.6 Of extracts from adrenalectomized rats, 10% contained a substance that behaved atypically on the mouse vas deferens, showing a slower onset and offset of action. The mol. wt. of the substance and sensitivity to naloxone reversal appeared to be similar to enkephalin, but it was resistant to carboxypeptidase-A and protease treatment.7 It is concluded that the enkephalin content of the hypothalamus is affected by activity in the hypothalamus-pituitary-adrenal system but that it is not related in a simple manner to the levels of corticotrophin releasing hormone, corticotrophin or corticosteroids.