SEXUAL DIMORPHISM IN THE HARDERIAN-GLAND OF THE SYRIAN-HAMSTER IS CONTROLLED AND MAINTAINED BY HORMONES, DESPITE SEASONAL FLUCTUATIONS IN HORMONE LEVELS - FUNCTIONAL IMPLICATIONS

The Harderian gland of the Syrian hamster (Mesocricetus auratus) is un usual amongst rodents in the degree of dimorphism present. Other types of hamsters have Harderian glands which are apparently identical in m ale and female animals. Laboratory populations of Syrian hamsters are derived from very limited genetic stock, which makes one concerned les t they not be representative of wild populations; however, until wild stocks of M. auratus become available, we should assume that insights derived from studies of dimorphism in Syrian hamsters represent import ant considerations for the life of these animals. Two dimorphic featur es are the histology and the porphyrin content of the Harderian glands . About 95% of the lipid droplets in female glands are small (type 1), whereas only about 65% of those in males is type 1, with the other 35 % being type 2 (large droplets). Five weeks of castration of males led to an increase in type 1 droplets to 90%. On the other hand, 2 weeks treatment of females with testosterone led to a reduction in type 1 dr oplets to about 82%. Short day photoperiods led to a large increase in type 2 droplets in both males and females (to 52% in males, 35% in fe males after 8 weeks). These results suggest that the lipid contained i n type 2 droplets is important to hamsters of both sexes during the wi nter. Porphyrin concentrations are 100-1,000 times higher in females t han males, and this is largely controlled by testosterone as orchidect omy leads to increased male levels and testosterone treatment leads to reduced female levels. However, a number of treatments which also lea d to reduced testosterone levels do not lead to increased porphyrins a nd may, in fact, prevent the rise which would normally follow orchidec tomy. One of these antiporphyrinogenic treatments is exposure to short day photoperiods. Thus, the sexual differences in porphyrin levels in Syrian hamsters are maintained, despite seasonal fluctuations in horm one levels. This suggests that this dimorphism is important for the fu nction of the gland. (C) 1995 Wiley-Liss, Inc.