Molecular Mechanism of Mercuric Chloride Inhibiting Progesterone Secretion in Ovarian Granulosa Cells of Laying Hens

This study investigated the effect of mercury (Hg) on progesterone secretion in ovarian granulosa cells of laying hens. The gene expressions of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD), cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway and intracellular calcium ion (Ca ) were further investigated to uncover the molecular mechanism. Results revealed that the cell viability was gradually decreased after Hg exposure from 0 to 24 hr. Besides, progesterone secretion was significantly decreased (p < 0.05) as the concentration of Hg increased from 0 to 4 μM followed by a plateau in 6 μM Hg group at 12-hr time point. Compared with 0 μM Hg group, 4 and 6 μM Hg for 48 hr had significantly decreased progesterone secretion (p < 0.05), while Hg exposure for 6 and 24 hr had no apparent effect on progesterone secretion. In addition, positive correlations occurred among intracellular progesterone, cAMP, PKA, mRNA expressions of StAR, P450scc and 3β-HSD at 12-h and 24-h time points. On the contrary, intracellular Ca level was negatively related to cAMP level at 6 time point and was negatively correlated with progesterone and PKA level at 48 time point. It could be concluded that Hg dose- and time-dependently inhibited progesterone secretion by means of attenuating cAMP-PKA signal pathway, gene expressions of StAR, P450scc and 3β-HSD and enhancing intracellular Ca in ovarian granulosa cells of laying hens.