ANDROGENIC CONTROL OF PORPHYRIN IN THE HARDERIAN GLANDS OF THE MALE SYRIAN-HAMSTER IS MODULATED BY THE PHOTOPERIOD, WHICH SUGGESTS THAT THESEXUAL DIFFERENCES IN PORPHYRIN CONCENTRATIONS IN THIS GLAND ARE IMPORTANT FUNCTIONALLY

Background: The porphyrin concentrations of the Harderian glands of Sy rian hamsters show marked sexual differences, with male levels being m uch lower than those of females. Porphyrinogenesis is inhibited by and rogens, so orchidectomy leads to elevated male porphyrin concentration s; however, a number of other procedures (some of which also lower and rogen levels) prevent this. We studied the effects of short-day photop eriods and melatonin on Harderian porphyrin concentrations. Methods: I ntact, castrated, or pinealectomized hamsters of both sexes were expos ed to long-day or short-day photoperiods. Intact or castrated hamsters were given melatonin injections in the morning or the afternoon, or w ere given beeswax pellets containing melatonin. After a variable perio d, Harderian glands were dissected and porphyrins were measured. Resul ts: Prolonged short-day exposure (13 weeks) led to increased Harderian porphyrin concentrations and this rise was prevented by pinealectomy. The rise in Harderian porphyrins following short-day exposure was sma ll, compared with that following castration. Short-day photoperiods al so prevented the rise in porphyrin levels associated with castration a nd this effect was prevented by removal of the pineal. Melatonin injec tions, whether given in the morning or in the afternoon, had no effect on Harderian porphyrin concentration of castrated male hamsters. Cont inuous release melatonin pellets reduced the postcastrational rise in porphyrin levels in one experiment, while having no effect in another. In female hamsters, neither short photoperiods nor melatonin pellets influenced Harderian porphyrin concentrations. Conclusions: These resu lts suggested that a factor from the pineal gland helps maintain the l ow levels of porphyrin which are characteristic of male Harderian glan ds, despite the decrease in androgen levels which typically results fr om exposure to short days. Morning and afternoon injections of melaton in and continuous release melatonin pellets failed to resolve the ques tion of whether this pineal factor is melatonin. Our results demonstra ted that low male and high female porphyrin levels are maintained in S yrian hamsters, despite seasonal variations in the hormonal milieu, su ggesting that these sexual differences are important for the (still un established) function of the Harderian glands in this species. (C) 199 4 Wiley-Liss, Inc.