IMMUNOHISTOCHEMICAL LOCALIZATION OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE AND P450 17-ALPHA-HYDROXYLASE DURING FOLLICULAR AND LUTEAL DEVELOPMENT IN PIGS, SHEEP, AND COWS

Follicular and luteal morphology and steroidogenic function were inves tigated by immunohistochemistry for cytochrome P450 17 alpha-hydroxyla se (P450(c17)) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) du ring the estrous cycle in pigs, sheep, and cows. The theca interna of all species expressed P450(c17) during follicular development. In the pig, this constituted a continuous layer of cells around the follicle, but a sheath of cells lining the basement membrane appeared not to ex press P450(c17). Neither was expression of P450(c17) in ovine and bovi ne follicles uniform throughout the theca interna. In these two specie s, a beaded appearance was given by P450(c17), since it was expressed in some regions but not in others. Therefore, staining for P450(c17) d efined functional sub-populations of cells within the theca interna of pigs, sheep, and cows. Ovulation was associated with a decrease in P4 50(c17) in all species, but some expression persisted in theca-derived cells of developing and mature porcine CL. Expression of 3 beta-HSD i n the preovulatory follicle was confined to the theca of the pig and s heep; in contrast, in the cow, it was highest in the granulosa. In gen eral, 3 beta-HSD expression appeared to be greater in porcine than ovi ne or bovine follicles, the physiological relevance of which is discus sed. Porcine and ovine theca continued to express 3 beta-HSD after owl ation, and granulosa-derived cells increased their 3 beta-HSD expressi on markedly as they luteinized in all three species. During early lute al development in pigs and sheep, theca-derived cells with high 3 beta -HSD encircled luteal lobules, but these cells appeared throughout the parenchyma of the mature CL. Luteal regression in sheep and cows was typified by the loss of many cells expressing 3 beta-HSD, whereas othe rs, adjacent to them, appeared to be intact without loss of enzyme exp ression. These data further define differences in steroidogenesis duri ng follicular and luteal development among the pig, sheep, and cow.