Comparative effects of homoplastic pituitary pars distalis homogenate (PDH), pregnant mare serum gonadotrophin (PMSG), human chorionic gonadotrophin (HCG), growth hormone (GH), PMSG + GH, and HCG + GH on oocyte recruitment and development in the long-term hypophysectomized frog, Rana cyanophlyctis (Schn)

Abstract

Follicular development and oocyte recruitment were studied in the ovaries of long-term (2 months) hypophysectomized frogs Rana cyanophlyctis during the postbreeding season (October/November). The effects of homoplastic pituitary pars distalis homogenate (PDH) (1 pituitary per frog), 40 IU pregnant mare serum gonadotrophin (PMSG), 40 IU human chorionic gonadotrophin (HCG), 10 μg growth hormone (GH), 40 IU PMSG + 10 μg GH, and 40 IU HCG + 10 μg GH in 0.2 ml saline on oocyte growth and recruitment were also studied in these frogs. Injections (ip) were given on alternate days for 30 days, with autopsy on the 31st day. The frogs were fed with minced thigh muscles of other frogs and injected twice a week with 0.02 IU adrenocorticotrophic hormone (ACTH) in 0.2 ml saline to maintain their health. One month after hypophysectomy there was a significant reduction in the weight of the ovaries and oviducts, mean diameter of the largest oocytes, and the total number of oocytes in the ovaries. Oogonial mitosis was not impaired. In 2-month hypophysectomized saline-treated frogs, oocyte growth occurred and as a result there was an increase in the mean size. Also, the total number of oocytes in the ovaries increased compared to 1-month hypophysectomized controls. HCG induced maximum recruitment of oocytes from first growth phase (FGP) to second growth phase (SGP) but the number of oocytes in the ovary remained unchanged. In contrast, PMSG induced the recruitment of FGP oocytes and to a lesser extent SGP oocytes. Thus, PMSG, unlike HCG, caused a significant increase in the total number of oocytes in the ovary. Bovine GH alone had no effect on the recruitment of FGP or SGP oocytes but it enhanced the gonadotrophic action of PMSG and HCG when given in combination. The PDH caused a greater stimulation of the ovary by inducing the recruitment of both FGP and SGP oocytes in the long-term hypophysectomized frogs. The percentage of oocytes undergoing atresia was considerably reduced following PDH, PMSG, HCG, and even GH treatment. The decrease in the weight of the oviduct caused by hypophysectomy was not overcome by any of the hormone treatments. The present findings suggest that in R. cyanophlyctis oogonial proliferation may be independent of hypophysial hormones and show that recruitment of FGP and SGP oocytes can be induced in long-term hypophysectomized frogs using PDH, PMSG, and HCG. These findings support the view that the recruitment of FGP oocytes is influenced by the ovarian condition (absence of SGP oocytes) and that there exists an intraovarian mechanism to regulate recruitment of FGP oocytes in anurans.