CHANGES IN CONCENTRATIONS OF FOLLICULAR INHIBIN-ALPHA AND BETA-A SUBUNIT MESSENGER RIBONUCLEIC-ACIDS AND INHIBIN IMMUNOACTIVITY DURING PREOVULATORY MATURATION IN THE PIG

Ovarian tissues were collected from 5 pigs on each of days 1, 3, 5, and 7 after withdrawal of an orally active progestin to determine changes in follicular inhibin subunit mRNAs during preovulatory maturation. Follicles (N = 146) were aspirated for fluid and homogenized in guanidinium isothiocyanate for RNA isolation. Follicular RNA and inhibin alpha and beta(A) subunit mRNA standards were dot-blotted, hybridized with [P-32]-cDNA probes, and quantified by densitometry. Mean concentrations of a mRNA (pg/mug of RNA) increased (p less-than-or-equal-to 0.05) by 140% as healthy follicles grew from medium (3-5 mm) to large (>5 mm). Inhibin immunoactivity was greater (p less-than-or-equal-to 0.05) in large than medium follicles. In contrast, mean concentrations of inhibin beta(A) subunit mRNA did not differ between healthy medium and large follicles. However, both alpha mRNA and beta(A) mRNA increased (p less-than-or-equal-to 0.05) linearly as follicular diameter increased from 3 to 5 mm on Day 1 and from 3 to 9 mm on Day 3. On Day 5, a mRNA remained elevated, but was not significantly correlated with diameter. In contrast, beta(A) mRNA decreased linearly (p < 0.05) as increased from 6 to 11 mm on Day 5. The molar ratio of mRNA to beta(A) mRNA was 20:1 in healthy, large follicles on Days 3 and 5. Mean concentration of alpha mRNA in large follicles decreased (p < 0.05) by 72% between Days 5 and 7, while beta(A) mRNA decreased to non-detectable levels on Day 7. Mean concentration of immunoactive inhibin in large follicles increased (p < 0.05) between Days 3 and 7. Results indicate that 1) inhibin alpha and beta(A) subunit mRNA increased in follicles selected for ovulation and decreased during luteinization, and 2) inhibin alpha subunit peptide increased progressively during preovulatory maturation.