RESUMO
The effect of oxytocin (0.25 IU/100 g per day) on the adrenal medulla was examined in intact, intact estrogen-treated, castrated and castrated testosterone-treated adult male Wistar rats. Stereological analysis of the gland (N = 5 rats per group) revealed that in intact animals the number of chromaffin cells (x10(3)) was significantly increased after 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 administration. During 7 days of recovery after the 7-day treatment, the chromaffin cell number returned to the control level (saline: 491.4 +/- 12.6; oxytocin: 554.4 +/- 28.7). The effect of oxytocin on chromaffin cell number was also observed in rats simultaneously injected with estradiol (0.3 microg/100 g per day) for 10 days (estradiol: 454.3 +/- 32.8; estradiol + oxytocin: 576.1 +/- 25.0), as well as in 10-day castrated rats (saline: 594.7 +/- 22.7; oxytocin: 765.3 +/- 33.1). Testosterone replacement (0.6 mg/100 g per day) abolished the medullary response to oxytocin (testosterone + saline: 528.5 +/- 24.7; testosterone + oxytocin: 620.8 +/- 56.0). There was a 20 percent rise in adrenal dopamine content (from 0.236 +/- 0.015 to 0.283 +/- 0.015 microg per pair of glands; N = 9-12) in intact rats injected with oxytocin for 3 days. Oxytocin had no effect on any of the catecholamine levels in adrenal glands of rats exposed to stress induced by constant lighting. The present data indicate that the proliferative response of chromaffin tissue to oxytocin depends on the gonadal hormone level and the basal activity of the adrenal medulla.