Estradiol-induced changes in progesterone secretion by rabbit corpora lutea are associated with quantitative ultrastructural changes in luteal cells

Expression and regulation of 17beta-hydroxysteroid dehydrogenase 7 in the rabbit

We cloned partial cDNA sequences of rabbit 17beta-hydroxysteroid dehydrogenase 1 (17beta-HSD1) and 17beta-HSD7. We analyzed the tissue distribution of 17beta-HSD7 as well as the expression in corpus luteum and endometrium during pseudopregnancy. The obtained cDNA sequence of 17beta-HSD7 coded for all functional regions of the protein and showed 86 and 81% similarity to human and rodent sequences, respectively. The partial sequence of rabbit 17beta-HSD1 was 76 and 82% similar to rodent and human sequences. By Northern analysis 17beta-HSD7 expression was predominantly found in reproductive organs like ovary, oviduct, endometrium, placenta and mammary gland. Substantial expression was also apparent in the heart, stomach and cerebellum. The 17beta-HSD1 could be detected in placenta by reverse transcriptase-polymerase chain reaction (RT-PCR), so far. During rabbit pseudopregnancy 17beta-HSD7 expression was found to be regulated in corpus luteum as well as in endometrium. In the corpus luteum, strongest expression occurred from d10 to d14 of pseudopregnancy (p. hCG) and was downregulated on d16 p. hCG. In endometrium strongest expression of 17beta-HSD7 was found on d6 p. hCG, when the endometrium was differentiated to its implantation permissive status.

Quantitative changes in steroidogenic organelles in the corpus luteum of the pregnant rat in relation to progestin secretion on day 16 and in the morning and afternoon of day 22

The present study was carried out to determine whether the major steroidogenic organelles of luteal cells quantitatively reflect variations in ovarian steroid secretion rates during pregnancy in the rat. Assessments were made on day 16 and in the morning (AM) and afternoon (PM) of day 22 (term is day 23). Ovarian steroidogenesis differs both quantitatively and qualitatively between these stages of pregnancy, so together they provide an ideal physiological model to study structural-functional relationships in the ovary. Corpora lutea of five rats were examined at each stage after progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP) secretion rates had been determined by a venous outflow technique. Total progestin secretion (progesterone plus 20 alpha-OHP) fell from 32.5 +/- 5.2 to 9.8 +/- 1.2 micrograms/hr per ovary (mean +/- SEM) between day 16 and day 22 AM but then increased to 22.6 +/- 1.4 micrograms/hr per ovary by day 22 PM. The total volume of luteal cell cytoplasm was slightly greater at day 22 AM and PM than at day 16. Similarly, the volumes of smooth endoplasmic reticulum (SER), lipid droplets, and membrane-bound granules all increased, but the volume of mitochondria decreased slightly. In contrast, the surface areas of SER and the inner and outer mitochondrial membranes did not change between day 16 and day 22 AM but then increased substantially by day 22 PM. Therefore, steroid secretion rates per unit area of steroidogenic membrane showed no consistent pattern over the stages examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Leydig cell differentiation during maturation of the rat testis: a stereological study of cell number and ultrastructure

In an effort to further understand the basis for the changes in steroidogenesis known to occur during sexual maturation in the rat, we examined by quantitative morphologic methods the number and ultrastructure of Leydig cells in fetal rats (days 18-20 of gestation) and in rats from days 2 to 3 of age through adult. Quantitative light microscopic analyses indicated that Leydig cell number, when expressed per unit volume of testis, was very high in fetal rat testes, fell significantly in testes of days 2 to 3 rats, and subsequently rose significantly. When Leydig cell number was expressed per testis rather than per unit volume of testis, the results indicated that testes of fetal rats and rats of days 2 to 3 contained the same number of Leydig cells; after the neonatal period, significant increases in Leydig cell number per testis occurred in concert with increases in testis weight. Quantitative electron microscopic studies revealed significant differences in the ultrastructure of fetal and adult populations of Leydig cells. For example, Leydig cells of fetal and neonatal rats contained abundant lipid, whereas Leydig cells of weeks 7 to 8 and adult rats contained little. Stereological analyses also revealed dramatic changes in smooth endoplasmic reticulum and inner mitochondrial membrane surface areas during sexual maturation, both per cell and per testis. These findings are discussed with respect to the steroidogenic capacity of the testis during sexual maturation.

Corpus luteum: animal models of possible relevance to reproductive toxicology

The presence of a normally functioning corpus luteum is an essential requirement for the maintenance of gestation in mammals. The chief function of the corpus luteum in all species is to synthesize the steroid hormone progesterone that is necessary for implantation and for the subsequent development of the fetoplacental unit. Activation and maintenance of luteal function involve pituitary, placental, and ovarian hormones. Perturbation in the secretion and/or action of any of these luteotropins by exogenous compounds can profoundly affect the steroidogenic capacity of the corpus luteum. Abnormal luteal function causes failure of implantation and embryonic wastage. Both in vitro and in vivo models for assessing luteal function are available; while the former are more convenient, the model of choice for toxicological studies is one in which in vitro findings can be easily confirmed in whole animals in vivo. This article is concerned primarily with the techniques used in basic research that might be useful for the evaluation of luteal function in reproductive toxicology.