Control of Secretory Lipid Droplets in the Harderian Gland by Testosterone and the Photoperiod: Comparison of Two Species of Hamsters

Harderian glands of mammals secrete lipid. They are markedly sexually dimorphic in Syrian (golden) hamsters ( Mesocricetus auratus); female glands consist almost entirely of one cell type (type I) with small lipid droplets, whereas glands of males have both type I and type II cells, with large lipid droplets. Siberian (Djungarian) hamsters ( Phodopus sungorus) have sexually monomorphic Harderian glands, with both type I and type II cells. We used a morphometric technique to quantify the proportions of small (type 1) and large (type 2) lipid droplets in these two species, in relation to the presence or absence of testosterone and to variations in the photoperiod. In Syrian hamsters, orchidectomy led to a marked increase in the proportion of type 1 lipid droplets in males kept in long (but not short)-day photoperiods. In contrast, treatment of females with testosterone led to an increase in type 2 lipid droplets. Short-day photoperiods in both sexes led to an increase in the proportion of type 2 lipid droplets and this was prevented by pinealectomy. In Siberian hamsters, on the other hand, castration or short photoperiods had no effect on Harderian gland morphology in either sex. These results suggest that some property of type 2 lipid droplets is important to Syrian hamsters during the autumn and winter. Syrian hamsters have a dimorphic Harderian gland and testosterone maintains the basic sexual dimorphism during the long days of spring and summer; a pineal-mediated mechanism, perhaps the drop in serum prolactin levels, leads to an increase in type 2 lipid droplets with the short days of autumn and winter. Siberian hamsters maintain levels of type 2 lipid droplets in both sexes and under all conditions of photoperiod, perhaps because of the colder conditions prevalent at all seasons of the year in their native Siberian habitat.