Estrus cycle-dependent action of leptin on basal and GH or IGF-I stimulated steroid secretion by whole porcine follicles.

Objective: To determine the levels of leptin in the follicular fluid and using culture of whole ovarian follicles, to test the hypothesis that leptin may directly influence GH and IGF-I stimulated ovarian function.

Methods: Porcine follicles were recovered from ovaries during early, middle, and preovulatory stage of the follicular phase of the estrus cycle. They were cultured in the presence of the recombinant ovine leptin (oLEP) added either alone or with oGH or hIGF-I. Steroid concentrations in the media were determined after 48 h of culture.

Results: The respective values for leptin in follicular fluid from small, medium and large follicles were 1.98, 2.18 and 1.96 ng/ml, respectively. Leptin added alone at a dose of 2 ng/ml had no effect on basal steroid secretion by small and medium follicles. However, in small follicles a synergic action of GH and IGF-I was noted. Leptin did not influence the secretion of progesterone by follicles collected during the early and middle follicular phases. In preovulatory follicles, leptin added alone to the culture media caused a decrease in basal estradiol secretion with a concomitant increase in progesterone secretion. Moreover, it acted synergistically with IGF-I and GH causing further stimulation of progesterone secretion.

Conclusions: The presented data show a direct, maturation dependent action of leptin on GH and IGF-I stimulated follicular steroidogenesis. During follicular growth they acted synergistically with GH and IGF-I in estradiol production, while in preovulatory follicles, they acted with both investigated hormones in luteinization process, which starts before follicular disruption.