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.