Srivastava R K, Luu-The V, Marrone B L, Harris-Hooker S, Sridaran R
Department of Physiology, Morehouse School of Medicine, Atlanta, GA 30310-1495.
J Steroid Biochem Mol Biol. 1994 May;49(1):73-9. doi: 10.1016/0960-0760(94)90303-4.
Previous studies from this laboratory have demonstrated that the administration of a gonadotropin-releasing hormone agonist (GnRH-Ag) in vivo in early or mid-pregnancy to rats induces antifertility effects by suppressing the luteal production of progesterone (P4) within 24h with a concomitant increase in luteal lipid droplets and decreases in the luteal cytochrome P450 side chain cleavage (P450scc) enzyme and its mRNA content. These observations suggest a direct inhibitory effect of GnRH-Ag on the corpus luteum. Here we demonstrate a suppressive effect of GnRH-Ag in vitro on the basal P4, pregnenolone (P5) and 20 alpha-dihydroprogesterone (20 alpha-DHP) production by luteal cells obtained during early pregnancy in rats. We further studied its effect on two key enzymes, namely P450scc and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), which participate in the conversion of cholesterol to P5 and conversion of P5 to P4, respectively. We observed that two doses of GnRH-Ag, 10(-4) and 10-7 M, suppress the basal P4 production in vitro after 12 h of incubation by luteal cells; P4 remained suppressed after 48 h of incubation. Basal P5 production was also suppressed after luteal cells were incubated for 12 h with 10(-4) M and 10(-7) M GnRH-Ag, but incubation for 48 h with GnRH-Ag failed to alter P5 production by these cells. 20 alpha-DHP production was suppressed after incubating the luteal cells with both doses of GnRH-Ag for 12 h. GnRH-Ag inhibited P450scc activity after 12 h of incubation and 3 beta-HSD protein content at all time periods measured. These results suggest that GnRH exerts a direct inhibitory effect on luteal steroidogenesis. This inhibition is due to its suppressive effect on P450scc and/or 3 beta-HSD and not due to an increase in P4 metabolites.
该实验室之前的研究表明，在大鼠妊娠早期或中期对其进行促性腺激素释放激素激动剂（GnRH-Ag）体内给药，可通过在24小时内抑制黄体生成孕酮（P4）来诱导抗生育作用，同时黄体脂质滴增加，黄体细胞色素P450侧链裂解酶（P450scc）及其mRNA含量降低。这些观察结果提示GnRH-Ag对黄体有直接抑制作用。在此我们证明，GnRH-Ag在体外对大鼠妊娠早期获得的黄体细胞基础P4、孕烯醇酮（P5）和20α-二氢孕酮（20α-DHP）的产生有抑制作用。我们进一步研究了其对两种关键酶的影响，即P450scc和3β-羟基类固醇脱氢酶（3β-HSD），它们分别参与胆固醇向P5的转化以及P5向P4的转化。我们观察到，10⁻⁴和10⁻⁷ M这两种剂量的GnRH-Ag在黄体细胞孵育12小时后可抑制体外基础P4的产生；孵育48小时后P4仍受到抑制。在用10⁻⁴ M和10⁻⁷ M GnRH-Ag孵育黄体细胞12小时后，基础P5的产生也受到抑制，但用GnRH-Ag孵育48小时未能改变这些细胞的P5产生。在用两种剂量的GnRH-Ag孵育黄体细胞12小时后，20α-DHP的产生受到抑制。GnRH-Ag在孵育12小时后抑制P450scc活性，并在所有测量时间段抑制3β-HSD蛋白含量。这些结果表明，GnRH对黄体类固醇生成有直接抑制作用。这种抑制是由于其对P450scc和/或3β-HSD的抑制作用，而不是由于P4代谢产物的增加。
