THE ANATOMICAL RECORD 232293-300 (1992) zy Female Syrian Hamster Harderian Gland: Development and Effects of High Environmental Temperature and Melatonin Injections on Histology and Porphyrin Deposits MARIA J. RODRIGUEZ-COLUNGA, COVADONGA FERNANDEZ, CARMEN RODRIGUEZ, DELI0 TOLIVIA, zyxwvu AND ARMAND0 MENENDEZ-PELAEZ zyxw Departamento de Morfologia y Biologia Celular, Uniuersidad de Ouiedo, Ouiedo, Spain zyxwv ABSTRACT We have investigated the development of the Harderian glands of female Syrian hamsters from birth to 8 months of age. The effects of melatonin injections on Harderian gland histology and porphyrin deposits of female hamsters exposed to two different temperatures were also studied. The morphology of the Harderian glands from 30-day-old female hamsters resembled those of sexually mature adult animals. The intraluminal area occupied by porphyrins increased significantly between 20 to 30 days of age. However, the relative number of mast cells per mm2 rose between 30 to 90 days. Both porphyrins and mast cell numbers appeared clearly reduced in the 8-month-old group. Secretory cells characterized by large lipid droplets (type I1 cells) were not observed. Daily afternoon injections of 25 pg of melatonin to female hamsters exposed to 22°C for 14 weeks resulted in the discontinuity of estrous cyclicity, a marked decrease in the intraluminal area occupied by porphyrins, a reduction of the num- ber of mast cells per mm2, and in a marked augmentation of the number of type I1 cells per mm2. Although the administration of similar dosages of melatonin to hamsters exposed to an environmental temperature of 32°C did not interrupt es- trous cycles, a clear reduction of the area occupied by porphyrins was observed. However, the number of mast cells and type I1 cells per mm2 was unaffected in these animals. Our results suggest that hormones other than ovarian steroids are involved in the regulation of the female hamster Harderian glands. The possible role of me- latonin on Harderian gland metabolism is discussed. Although the precise functions of the Harderian glands have not been determined, the hypothetical role of these orbital glands in thermoregulation (Thiessen, 1988) and their participation in a light-pineal-gonadal axis (Hoffman et al., 1985) is certainly possible. It is well documented that the Syrian hamster Harderian glands show a strong sexual dimorphism which seems to be under an androgenic control (Hoffman, 1971; Payne et al., 1977). Female hamsters contain in their Harderian glands much more porphyrins than male glands. The Harderian glands of female hamsters pos- sess a single secretory cell type (type I) which is char- acterized by minute lipid droplets whereas the Harde- rian glands from male hamsters show two secretory cell types, type I (similar to the female type cell) and a type I1 cell which is filled with large lipid vacuoles and has a swollen appearance (Hoffman, 1971). In addition, the Harderian glands from female hamsters contain an average of 40 times more mast cells within the connec- tive tissue than the male gland (Payne et al., 1982). Also, there are distinct ultrastructural differences be- tween the sexes (Bucana and Nadakavukaren, 1972; Lopez et al., 1990). It is clear that androgens alone can induce and main- tain the male-type gland in both male and female ham- zyxwv 0 1992 WILEY-LISS. INC. sters (Hoffman, 1971; Payne et al., 1977; Sun and Nadakavukaren, 1980). The fact that ovariectomy has little effect in changing the female-associated charac- teristics (Spike et al., 1986) described above suggests that ovarian steroids might not be important in the genesis and maintenance of the female-type character- istics. Nevertheless, interactions between the pineal gland and the ovaries regulating the porphyrin metab- olism and the morphology of female hamster Harde- rian glands have been also proposed (McMaster and Hoffman, 1984). Recently, it has been shown that me- latonin administration to female hamsters can modify porphyrin metabolism (Hoffman et al., 1989). The present studies address two major issues. First, we attempted to determine the precise age when the Harderian glands from developing female hamsters Received June 10, 1991; accepted July 18, 1991. Address reprint requests to Dr. Maria J. Rodriguez-Colunga, De- partamento de Morfologia y Biologia Celular, Facultad de Medicina, Universidad de Oviedo, 33006 Oviedo, Principado de Asturias, Spain. Part of this work was presented in the First International Sympo- sium on the Harderian Glands, October 1990, Barcelona, Spain.