Effects of growth hormone and triiodothyronine on insulin-induced progesterone production by granulosa cells from prepubertal gilts

Two experiments were performed using granulosa cells from medium-sized follicles (2–4 mm) derived from prepubertal gilts. Cells were cultured in a serum-free medium at a density of either 1 or 2 × 106 viable cells per well (experiments 1 and 2, respectively). For exp. 1, porcine growth hormone (pGH) (0 or 100 ng mL−1) was included in the culture medium from the time of plating, and low-density lipoprotein (LDL) (100 μg mL−1) was added at 72 h. For exp. 2, granulosa cells were plated in a culture medium containing either pGH (0 or 100 ng mL−1) or triiodothyronine (T3) (0 or 5 ng mL−1) or both pGH T3; LDL was not included. For both experiments, after 24 h of culture, bovine insulin at 0, 10, 100 or 1000 ng mL−1 was included in the medium. Hormones were replaced at 48 and 72 h, and the cultures were terminated at 96 h. Results from exp. 1 indicated that insulin increased (P < 0.01) progesterone production in a dose-dependent manner, both in the presence and absence of LDL. This response was augmented (P < 0.01) by co-culture with pGH. Results from exp. 2 confirmed the augmenting effect of pGH (P < 0.01). It was further observed that T3 increased (P < 0.01) progesterone production when cultured with insulin at 1000 ng mL−1, but at lower insulin-inclusion levels, results were equivocal. The progesterone production response was greatest (P < 0.01) when cells were cultured with both pGH and T3 at insulin levels of 100 or 1000 ng mL−1. There appeared to be little relationship between the media concentrations of insulin-like growth factor 1 and progesterone. The present results suggest that relatively high levels of pGH and T3 will enhance the in vitro steroidogenic capabilities of porcine granulosa cells. Key words: Granulosa cells, GH, T3, insulin