PHOTOPERIOD AND THE PINEAL-GLAND REGULATE THE MALE PHENOTYPE OF THE HARDERIAN GLANDS OF MALE SYRIAN-HAMSTERS AFTER ANDROGEN WITHDRAWAL

The Harderian glands of Syrian hamsters exhibit a marked sexual dimorp hism in cell types and porphyrin production. The glands of male hamste rs have two secretory cell types (Type I and II) while the glands of f emales consist of a single secretory cell type (female Type I) and lar ge intraluminal deposits of porphyrins. Besides androgens, there is ev idence that the pineal gland, through the secretion of melatonin, cont ributes to the maintenance of the ''male'' and ''female'' phenotypes. In this study, we investigated the effects of castration, short photop eriods, and pinealectomy on the distribution of secretory cells and po rphyrin deposits in the Harderian glands of male Syrian hamsters. Two groups of animals were maintained in long days (14 hr light/day). Hams ters in one group were left intact and those in the other were castrat ed. Another three groups were maintained in short days (8 hr light/day ); these animals were either left intact, castrated, or both castrated and pinealectomized. The duration of the experiment was 5 weeks. Cast ration of long photoperiod-exposed animals resulted in a significant d rop in the number of Type II cells and a large increase in the porphyr in deposits (P < 0.01). However, castrated animals exposed to short ph otoperiod showed a significant smaller change in both parameters compa red with those exposed to long days (P < 0.05). Pinealectomy prevented the effects of short days in castrated animals. No significant change s were observed in the relative number of mitotic figures or in the nu mber of cell nuclei, indicating that the changes observed were due in part to a transformation of Type II into Type I cells. In a second exp eriment, male hamsters were injected daily either with 25 mu g of mela tonin late in the afternoon or with the saline for 8 weeks. The admini stration of melatonin resulted in a significant (P < 0.05) increase in the percentage of Type II cells. We conclude that when circulating an drogens are very low or absent, pineal melatonin maintains the male ph enotype in the Syrian hamster Harderian gland.