Steroidogenesis in the Preovulatory Porcine Follicle1

Abstract

The expression of four major steroidogenic enzymes in porcine theca and granulosa cell layers of preovulatory follicles was related to the levels of steroids in follicular fluid and gonadotropin concentrations in peripheral serum at slaughter. Ovaries were collected during proestrus, early estrus, and late estrus as evidenced by behavioral signs. Follicles were dissected from the ovaries, and theca, granulosa, and follicular fluids were pooled for each of 24 sows. Cytochromes P450 17 alpha-hydroxylase/17-20 lyase (P450c17), aromatase (P450arom) and side-chain cleavage (P450scc), as well as 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), were subjected to Northern and Western immunoblot analyses. The concentrations of estradiol-17 beta, testosterone, androstenedione, and progesterone were determined in follicular fluid, and peripheral serum was assayed for estradiol-17 beta, LH, and FSH. Stages of preovulatory development were verified by plasma levels of LH, FSH, and estradiol-17 beta. Thecca expressed P450c17, P450arom, P450scc, and 3 beta HSD whereas granulosa expressed only P450arom and low levels of P450scc. Thecal P450c17, thecal P450arom, and granulosa P450arom expression decreased coincidentally as serum estradiol-17 beta and follicular fluid estradiol-17 beta, testosterone, and androstenedione levels declined after the presumed gonadotropin surge. Unlike P450c17 and P450arom P450scc and 3 beta HSD remained relatively constant in theca and granulosa. From these data, we suggest that the theca interna may be the primary steroidogenic compartment of the porcine follicle during its final stages of preovulatory development. Moreover, preovulatory estrogen secretion appears to be controlled by the coordinated expression of a triad of enzymes in the porcine follicle that includes theca P450c17, theca P450arom and granulosa P450arom.

Ca2+/Mg2+-Dependent Endonuclease but not Ca22+-Dependent, Mg2+-Dependent or Cation-lndependent Endonuclease is Involved in Granulosa Cell Apoptosis of Pig Atretic Follicles.

“…Follicular fluid progesterone and estradiol-17β concentrations, and progesterone/estradiol-17β ratios in healthy and atretic follicles of pigs are summarized in Table 2. The ranges of concentrations of estradiol-17β (1.5 to 23 ng/ml), and progesterone (116 to 335 ng/ml) in follicular fluid correspond well with previously reported values [12,17,18]. Follicular fluid progesterone concentration was 2.21-fold higher (P<0.001) in atretic than in healthy follicles.…”

“…In pigs, estradiol-17β production by atretic follicles is decreased, but production of progesterone is increased [18]. Thus, the progesterone/estradiol-17β ratio of follicular fluid in each follicle provides a good index of follicular atresia in pig ovaries [17,18]. The present study showed that there is a high correlation (r=0.892) between the Ca 2+ /Mg 2+ -dependent endonuclease activity of granulosa cell nuclei prepared from atretic follicles and the progesterone/estradiol-17β ratio of the follicular fluid.…”

“…Sex steroids are important for intraovarian regulation of follicle growth and atresia, and the profile of sex steroid production differs between healthy and atretic follicles [17,18]. In pigs, estradiol-17β production by atretic follicles is decreased, but production of progesterone is increased [18].…”

“…In pigs, estradiol-17β production by atretic follicles is decreased, but production of progesterone is increased [18]. Thus, the progesterone/estradiol-17β ratio of follicular fluid in each follicle provides a good index of follicular atresia in pig ovaries [17,18].…”

In vivo gene expression in granulosa cells during pig terminal follicular development

“…Moreover, the cytochrome P450 11A (CYP11A) and the STAR protein (STAR) genes, not present on our micro-arrays and whose expression was already known to increase during the terminal development of the follicle (Hatey et al 1992, Conley et al 1994 gave the expected results. GSTA1 gene expression, first ranked (score 222) with the RF analysis as a predictive marker for follicle size class with a relatively high expression fold change (2.58) between LF and SF, was examined by in situ hybridization (Fig.…”