Levels of dynorphin-(1-13) immunoreactivity in rat neurointermediate pituitaries are concomitantly altered with those of leucine enkephalin and vasopressin in response to various endocrine manipulations.

Abstract

The levels of dynorphin-(1-13), leucine enkephalin, beta-endorphin and vasopressin immunoreactivity (ir-DYN, ir-1-ENK, ir-beta-END, ir-VP) have been determined in the anterior and in the neurointermediate lobes of the pituitary of rats subjected to a variety of manipulations. Dehydration of rats by 5 days enforced inhibition of a 2% solution of NaCl resulted in a significant decrease in the levels of ir-DYN, ir-1-ENK and ir-VP, but not in those of ir-beta-END in the neurointermediate lobe of the pituitary. In contrast, substitution of drinking water by a solution containing 20 microgram/ml dexamethasone for 5 days produced a significant increase in the neurointermediate pituitary content of ir-DYN, ir-1-ENK and ir-VP, whereas levels of ir-beta-END remained unaffected. This treatment, however, resulted in a significant fall in the ir-beta-END content of the adenopituitary without changing levels of ir-DYN in this structure. Adrenalectomy was associated with a significant decrease in the ir-DYN, ir-VP and ir-1-ENK content of the neurointermediate lobe of the pituitary and a pronounced elevation in the ir-beta-END but not ir-DYN content of the adenohypophysis. These observations are indicative that the regulation mechanisms of the functional state of particular endorphins differ between the anterior and neurointermediate lobes of the pituitary. The concomitant alterations in levels of ir-DYN, ir-1-ENK and ir-VP detected suggest that a common or similar mechanism of regulation may exist for these peptides. A common biosynthetic origin, however, appears to be unlikely, since Brattleboro rats which are unable to synthesize vasopressin possess unchanged ir-DYN- and ir-1-ENK- levels in the pituitary.