SEASONAL FLUCTUATIONS IN PITUITARY-GLAND AND PLASMA-LEVELS OF GONADOTROPIC-HORMONES IN RANA

Changes in plasma and pituitary levels of two gonadotropins, luteinizi ng hormone (LH) and follicle-stimulating hormone (FSH), in male and fe male Korean frogs (Rana dybowshii and Rana nigromaculata) were examine d. Plasma levels of LH and FSH were measured by radioimmunoassay using antibodies raised against bullfrog LH and FSH. In male and female R. dybowshii, plasma concentrations of LH were low in early hibernation ( October-January) and increased to high levels by late hibernation, whe n breeding occurs (late February-early March). Plasma FSH levels were also higher in the breeding period than during hibernation in male and female animals, but absolute levels of FSH were much lower than those of LH. In females, pituitary LH levels were higher in early hibernati on, whereas pituitary FSH in females and pituitary LH and FSH in males changed little during hibernation. Plasma LH levels of frogs having u terine eggs or in amplexus were much higher (> 25 ng/ml) than those of frogs with unovulated follicles (December) (<8 ng/ml) or frogs that h ad already spawned (<11 ng/ml). In R. nigromaculata, plasma LH and FSH levels of females collected during hibernation (October-May) were rel atively low; however, following hibernation, plasma LH and FSH levels were markedly elevated for a short period. Thus, these animals exhibit a clear gonadotropin surge prior to ovulation and spawning. Soon afte r spawning, however, gonadotropin levels dropped to basal levels. Foll owing spawning in females, levels of FSH increased steadily and rapid follicle growth occurred until August. By September, FSH had dropped t o basal levels. In males, a sharp elevation of LH and FSH levels occur red during the short breeding period followed by a second increase in August, when early stages of spermatogenesis were evident. (C) 1998 Ac ademic Press.