Melatonin Effect on the Hamster Pituitary Response to LHRH1

Previous studies from this laboratory showed that, in the rat, melatonin can suppress the neonatal pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) responses to LH releasing hormone (LHRH). Since melatonin is a more potent antigonadotropic hormone in hamsters than in rats, the present study examined the action of the indole on the hamster LH response to LHRH. The following systems were used: 1) neonatal pituitary cells in culture, 2) cells from adult males maintained in long or short photoperiods, and 3) adult males early and late in the light phase of a long photoperiod. For in vitro studies, anterior pituitary glands from neonatal and adult Syrian hamsters were dissociated with collagenase and hyaluronidase. After overnight culture in serum containing medi-um, the cells were washed free of serum, distributed to culture dishes, and incubated for 3 h with LHRH (102 to i0 ’ M) emther alone or in the presence of melatonin (10- ’ to 106 M). For in vivo experiments, animals were injected s.c. in the nape of the neck with LHRH and melatonin. They were decapitated 15 mm later, and trunk blood was collected. Medium, cell lysate, and serum LH concentrations were measured by double antibody ovine;ovine RIA.