Detection of mRNA for inhibin α- and βA-subunits in bovine ovarian tissues and the effect of in vivo administration of GNRH

The aims of these studies were to determine which types of bovine ovarian tissue contain mRNA for inhibin/activin subunits and whether administration of GnRH influences concentration of these mRNAs. In experiment (exp.) one, cows in the luteal phase of the estrous cycle were given prostaglandin F 2α (PGF 2α) to induce luteal regression and injected after 40 hr with saline (n=5) or 100 μg GnRH (n=6). Ovaries were removed 6 hr later. In exp. two, unilaterally ovariectomized (OVX) heifers (n=33) in the luteal phase of their estrous cycle were given PGF 2α to induce luteal regression. Twelve heifers were OVX without injection of GnRH at 24 (n=6) or 40 hr (n=6) after PGF 2α. The remaining heifers (n=21) were given 100μg GnRH at 40 hr after PGF 2α injection and OVX 8 (n=4), 16 (n=5), 24 (n=6) or 48 (n=6) hr after GnRH injection. Total cellular RNA was isolated from large follicles (exp. one and two), small-medium follicles and stromal tissue (SMS) and corpora lutea (CL; exp. one) tissues and analyzed by dot blot and Northern blot techniques by hybridizing with cDNA probes for human inhibin/activin α- and β A-subunits. Large follicles were classified as steroidogenically active (EA) if follicular fluid (FF) concentration of estradiol-17β (E 2) was greater than progesterone (P 4), or if P 4 and E 2 concentrations in FF were greater than 100ng/ml, and estrogen inactive (EI) if FF concentration of E 2 and P 4 did not satisfy these criteria. In exp. one, mRNA for the α-subunit was primarily expressed in EA follicles, and detectable in EI follicles, SMS, and CL while β A-subunit mRNA was detected only in large EA follicles and a few SMS samples. The mRNA (x ± SEM fmoles/mg DNA) for both subunits of inhibin/activin was higher (P.10) between saline and GnRH treatments. In exp. two, the mRNA (fmol/mg DNA ± SEM) for the α-subunit decreased slightly 24 to 40 hr after PGF 2a injection from 112 ± 41 to 84 ± 15, increased (P