Ghrelin is a novel growth hormone-releasing peptide originally identified in the rat stomach as an endogenous ligand of the growth hormone (GH) secretagogue receptor. Recent work suggests that ghrelin plays an important role in reproductive function. In this study, prepubertal pig ovaries were used to examine ghrelin levels in the ovarian follicles. Ghrelin levels in the follicular fluid, follicular wall and culture medium were measured using an enzyme immunoassay (EIA). The ghrelin level in the follicular fluid (18 pg/ml) was the sum of the amounts found in the follicular wall (13.7 pg/ml) and the culture medium (4.6 pg/ml). In conclusion, the data presented in this paper suggest local production of this hormone in ovarian follicles.
Authors:Ewa L. Gregoraszczuk, Agnieszka Rak, Anna Wójtowicz, Anna Ptak, Tatiana Wojciechowicz and K. W. Nowak
Leptin (L) is recognised as an important regulator of puberty and a factor which controls reproduction. Whole pig ovarian follicles were incubated with different doses of leptin (2, 20 and 200 ng/ml) added alone or in combination with 100 ng/ml of GH or 50 ng/ml of IGF-I. The expression of the functional long form leptin receptor (Ob-Rb) mRNA was examined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in follicular cells cultured with GH or IGF-I. Both GH and IGF-I increased leptin receptor expression in prepubertal pig ovaries. In separate experiments, the action of leptin on ovarian follicular steroidogenesis and cell apoptosis was examined. After 24 h of incubation with leptin alone or in combination with GH or IGF-I, oestradiol (E2) levels were determined in the culture medium while follicular tissue was used for the estimation of caspase-3 activity. Leptin increased E2 secretion and significantly diminished caspase-3 activity at all doses used. Both GH and IGF-I stimulated oestradiol secretion and decreased caspase-3 activity. No differences were demonstrable in oestradiol secretion and caspase-3 activity between cells treated with GH plus leptin and GH alone or cells treated with IGF-I plus leptin as compared to cultures treated with GH or IGF-I alone. However, GH diminished leptin-stimulated oestradiol secretion while IGF-I was without effect on it. Both GH and IGF-I reversed the anti-apoptotic action of leptin. In conclusion, we infer that (1) leptin directly affects ovarian function in prepubertal animals by its action on oestradiol secretion and cell apoptosis, (2) GH and IGF-I modulate the action of leptin, and (3) at least in part, the direct effect of GH/IGF-I on leptin production is due to an action on leptin receptor expression.