Smith C J, Richards J S, Yasin K, Sangster J N, Sridaran R
Department of Physiology, Morehouse School of Medicine, Atlanta, Georgia 30310-1495.
Biol Reprod. 1991 Feb;44(2):382-91. doi: 10.1095/biolreprod44.2.382.
Previous studies have demonstrated that plasma progesterone levels decrease in pregnant rats treated in vivo with a gonadotropin-releasing hormone agonist (GnRH-Ag), without changes in testosterone or estradiol levels in ovarian vein plasma. The objective of this study was to determine the loci of GnRH-Ag disruption of progesterone synthesis by examining luteal mitochondria, lipid droplets, cellular composition, and P450 side-chain cleavage (P450scc) enzyme and mRNA content in the pregnant rat. On Day 7 or 11 of pregnancy, osmotic minipumps containing GnRH-Ag were implanted into 5-7 rats. Sham operations were performed on 5-6 controls at each time period. Five micrograms per day of GnRH-Ag were released for about 24 h, after which corpora lutea and jugular vein plasma were collected. The corpora lutea were prepared for microscopy or analyzed for P450scc enzyme and mRNA content. Plasma progesterone levels were measured by RIA. In those rats treated with GnRH-Ag, progesterone levels had decreased, and within the luteal cells, there was an increase in the number of lipid droplets and a decrease in the number of tubular cristae within the mitochondria. Concomitantly, P450scc enzyme and mRNA content decreased on both Day 8 and Day 12 of pregnancy. Also, GnRH-Ag treatment decreased the ratio of large to small steroidogenic luteal cells on Day 8 of pregnancy, but did not alter cellular ratios on Day 12 of pregnancy. These observations suggest that treatment with GnRH-Ag inhibits progesterone synthesis by decreasing the amount of P450scc mRNA and enzyme content, which may alter the mitochondrial cristae structure on Day 8 and Day 12 of pregnancy. The reduction in tubular cristae and P450scc enzyme in the mitochondria may account for the increase in lipid droplets, as less cholesterol is converted to pregnenolone. An additional mechanism of inhibition may be the reduction in the number of large steroidogenic luteal cells, which appear to be the major source of progesterone in the rat corpus luteum on Day 8 of pregnancy.
先前的研究表明，用促性腺激素释放激素激动剂（GnRH-Ag）对妊娠大鼠进行体内处理后，其血浆孕酮水平会降低，而卵巢静脉血浆中的睾酮或雌二醇水平没有变化。本研究的目的是通过检查妊娠大鼠黄体的线粒体、脂滴、细胞组成以及P450侧链裂解酶（P450scc）和mRNA含量，来确定GnRH-Ag对孕酮合成的破坏位点。在妊娠第7天或第11天，将含有GnRH-Ag的渗透微型泵植入5-7只大鼠体内。在每个时间段，对5-6只对照大鼠进行假手术。每天释放5微克GnRH-Ag，持续约24小时，之后收集黄体和颈静脉血浆。将黄体制备用于显微镜检查或分析P450scc酶和mRNA含量。通过放射免疫分析法测定血浆孕酮水平。在用GnRH-Ag处理的那些大鼠中，孕酮水平降低，并且在黄体细胞内，脂滴数量增加，线粒体内管状嵴的数量减少。同时，在妊娠第8天和第12天，P450scc酶和mRNA含量均降低。此外，GnRH-Ag处理在妊娠第8天降低了大、小类固醇生成黄体细胞的比例，但在妊娠第12天未改变细胞比例。这些观察结果表明，GnRH-Ag处理通过降低P450scc mRNA和酶的含量来抑制孕酮合成，这可能会在妊娠第8天和第12天改变线粒体嵴的结构。线粒体中管状嵴和P450scc酶的减少可能解释了脂滴的增加，因为较少的胆固醇被转化为孕烯醇酮。另一种抑制机制可能是大的类固醇生成黄体细胞数量减少，这些细胞在妊娠第8天似乎是大鼠黄体中孕酮的主要来源。
