Contents
The present studies were undertaken to examine the influence of μ (β‐endorphin, DAMGO, FK 33‐824), δ (met‐enkephalin, leu‐enkephalin, DPLPE) and κ opioid receptor agonists (dynorphin A, dynorphin B, U 50488) used at different doses (1–1000 nm) alone and in combination with LH (100 ng/ml) on steroidogenesis in porcine granulosa cells derived from large follicles. The effects of μ, δ and κ receptor agonists on both basal and LH‐induced progesterone (P~4~) secretion were negligible. Agonists of μ opioid receptors reduced basal androstenedione (A~4~), testosterone (T) and oestradiol (E~2~) release. Co‐treatment with LH entirely abolished the inhibitory effect of these agonists on A~4~ and E~2~ secretion and resulted in an increase in T release. The addition of δ receptor agonists was followed by a decrease in basal A~4~, T and E~2~ secretion. The cells incubated in the presence of LH increased the androgen production and abrogated the inhibitory effect of δ agonists on E~2~ output. Basal A~4~, T and E~2~ release was also suppressed by κ receptor agonists. The presence of LH in culture media extended the inhibitory effect of these opioids on E~2~ output and caused either abolition of the inhibitory influence of κ agonists or even augmentation of both androgen release in response to the opioids. In conclusion, these data support the involvement of three major types of opioid receptors in the regulation of porcine granulosa cell steroidogenesis.