HORMONAL-REGULATION OF CONNEXIN-43 IN BABOON CORPORA-LUTEA

The synthesis and secretion of progesterone in the corpus luteum are r egulated by both endocrine and paracrine/autocrine factors which affec t the steroidogenic cells. Evidence suggests that these cells communic ate via cell-cell junctional proteins, the connexins. Previously we ha ve shown that connexin-43 is expressed ill both human and baboon (Papi o hamadryus anubis) corpora lutea, with differential expression throug hout luteal development, but is not detectable in corpora albicantia. We have examined the effect of human chorionic gonadotropin (hCG), oxy tocin, clomiphene citrate and the anti-progesterone onapristone on exp ression of connexin-43 protein in the early luteal phase 1-5 days afte r the mid-cycle luteinizing hormone (LH) surge (LH+ 1-5 days), the mid -luteal phase 6-10 days after the LH surge (LH+6-10 days), and the lat e luteal phase 11-15 days after the LH surge (LH+11-15 days) in corpor a lutea obtained from normal adult cycling females. Connexin-43 was lo calized by immunohistochemistry in cultured cells from all the three s tages. Western blot analysis of die treated cells indicated the presen ce of two bands at 43 and 45 kDa. The band at 45 kDa was found to be p hosphorylated connexin-43, indicating the presence of functional gap j unctions, hCG (10 IU/mL) stimulated the expression of connexin-43 thro ughout luteal development; however, maximum expression occurred in the early luteal phase with a significantly greater expression of the non -phosphorylated protein. In contrast, in the mid-luteal phase, the exp ression of the phosphorylated protein was predominant. Oxytocin (200 m U/ml) also stimulated connexin-43 expression throughout luteal develop ment with similar effects on the phosphorylated and non-phosphorylated protein in the early and mid-luteal phase; however, compared with hCG , oxytocin had a greater effect on mid-luteal phase connexin-43 expres sion. In the presence of both hCG and oxytocin, the expression of conn exin-43 was significantly higher than the control only in the late lut eal phase. Both clomiphene citrate and onapristone suppressed connexin -43 expression, and concomitant addition of hCG did not counteract the ir effect.. In the context of our previous studies, it is concluded th at, together with LH/hCG and the steroid hormones, oxytocin is involve d in cell-cell contact-dependent communication in the corpus luteum.