ALTERED GONADAL HORMONE LEVEL AND CONSTANT LIGHT-INDUCED STRESS INTERFERE WITH THE RESPONSE OF THE ADRENAL-MEDULLA TO OXYTOCIN

The effect of oxytocin (0.25 IU/100 g per day) on the adrenal medulla was examined in intact, intact estrogen-treated, castrated and castrat ed testosterone-treated adult male Wistar rats. Stereological analysis of the gland (N = 5 rats per group) revealed that in intact animals t he number of chromaffin cells (x10(3)) was significantly increased aft er 3-day (saline: 467.6 +/- 27.4; oxytocin: 567.6 +/- 28.9) or 7-day ( saline: 486.2 +/- 39.1; oxytocin: 618.7 +/- 36.8) oxytocin administrat ion. During 7 days of recovery after the 7-day treatment, the chromaff in cell number returned to the control level (saline: 491.4 +/- 12.6; oxytocin: 554.4 +/- 28.7). The effect of oxytocin on chromaffin cell n umber was also observed in rats simultaneously injected with estradiol (0.3 mu g/100 g per day) for 10 days (estradiol: 454.3 +/- 32.8; estr adiol + oxytocin: 576.1 +/- 25.0), as well as in 10-day castrated rats (saline: 594.7 +/- 22.7; oxytocin: 765.3 +/- 33.1). Testosterone repl acement (0.6 mg/100 g per day) abolished the medullary response to oxy tocin (testosterone + saline: 528.5 +/- 24.7; testosterone + oxytocin: 620.8 +/- 56.0). There was a 20% rise in adrenal dopamine content (fr om 0.236 +/- 0.015 to 0.283 +/- 0.015 mu g per pair of glands; N = 9-1 2) in intact rats injected with oxytocin for 3 days. Oxytocin had no e ffect on any of the catecholamine levels in adrenal glands of rats exp osed to stress induced by constant lighting. The present data indicate that the proliferative response of chromaffin tissue to oxytocin depe nds on the gonadal hormone level and the basal activity of the adrenal medulla.