β-Endorphin disrupts seasonal and FSH-induced ovarian recrudescence in the lizard Mabuya carinata

Abstract

Administration (ip) of an opioid peptide, β-endorphin (β-EP) (0.1, 0.5, or 1 μg β-EP/day/lizard for 30 days) during seasonal recrudescence phase of the ovarian cycle inhibited ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary in contrast to their presence in treatment controls in the lizard Mabuya carinata. In the germinal bed, treatment of 0.1 μg β-EP did not affect primordial follicles, whereas their mean number was significantly lower in lizards treated with 0.5 or 1 μg β-EP compared to those of treatment controls. There was also suppression of oviductal development as shown by a significantly lower relative weight of the oviduct and regressed oviductal glands in lizards treated with all the dosages of β-EP compared to treatment controls. In another experiment, administration of FSH (10 IU FSH/alternate day/lizard for 30 days) during the regression phase of the ovarian cycle induced development of vitellogenic follicles, whereas the treatment controls showed only previtellogenic follicles. In addition, there was a significant increase in the ovarian and oviductal weights compared to initial and treatment controls. However, simultaneous administration of similar dosage of FSH and β-EP (0.5 μg/day/lizard) did not induce ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary and significantly lower weight of the ovary and the oviduct and the mean number of oogonia, oocytes, and primordial follicles compared to those of FSH-treated lizards. The results indicate that β-EP inhibits seasonal as well as FSH-induced ovarian recrudescence. Inhibitory effect of β-EP on follicular development despite FSH administration implies its effect at the ovarian level in M. carinata. While adversely affecting the ovarian follicular development, β-EP did not affect the adrenal gland as there was no significant variation in the mean nuclear diameter of the adrenocortical cells of treatment controls and β-EP-treated lizards. Furthermore, administration of β-EP caused a significant decrease in the mean number of islands of white pulp of the spleen indicating its adverse effect on immunity.