CHANGES IN EXPRESSION OF INHIBIN ACTIVIN-ALPHA, INHIBIN/ACTIVIN-BETA(A), AND INHIBIN/ACTIVIN-BETA(B) SUBUNIT MESSENGER RIBONUCLEIC-ACIDS FOLLOWING INCREASES IN SIZE AND DURING DIFFERENT STAGES OF DIFFERENTIATION OR ATRESIA OF NONOVULATORY FOLLICLES IN COWS/

Northern and slot blot analyses were used to examine the sizes, variab ility, and changes in amounts of alpha, beta(A) and beta(B) inhibin/ a ctivin subunit mRNAs following increases in size and during different stages of differentiation or atresia of bovine nonovulatory follicles. In Study I, a major 1.3-kb band and minor 2.2-, 3.3- and 6.4-kb bands of alpha mRNA; a major 6.4-kb band and minor 2.6 and 4.0 kb bands of beta(A); and major 3.5- and 4.6-kb bands of beta(B) mRNA were detected in total and/or poly(A)+ RNA isolated from pools of small (1-5 mm), m edium (6-10 mm), or large (> 10 mm) follicles. In Study II, 18 of 19 f ollicles had a 1.3-kb alpha mRNA, and amounts of 1.3 kb alpha mRNA inc reased with follicle size. However, 0 of 19, 9 of 19, and 3 of 19 foll icles had 2.2-, 3.3-, and 6.4-kb a mRNA bands. In Study III, the ratio of estradiol (E) to progesterone (P) in follicular fluid (FF) was use d to separate follicles into the following three stages of differentia tion and atresia: estrogen-active (EA; E>P in FF), atretic (P:E = 1-10 0), and highly atretic (P:E > 100). Total amounts of alpha and beta(A) mRNAs were 2.4- and 5.8-fold greater in EA follicles compared with sm all follicles. Alpha and beta(A) mRNAs and concentration of total inhi bin immunoactivity were 4.4-, 9.8- and 1.8-fold lower in highly atreti c follicles compared with EA follicles. Changes in amounts of follicul ar alpha and beta(A) mRNAs were highly positively correlated it with i ntrafollicular concentrations of E, ratio of E to P, and total inhibin immunoactivity, but negatively correlated with P. Ratio of amounts of alpha to beta(A) mRNAs was 3.9- and 6.5-fold greater in small and hig hly atretic follicles compared with EA follicles. Amounts of beta(B) s ubunit mRNAs were unchanged during follicular development and unrelate d to changes in follicular concentrations of E, P, or total inhibin im munoactivity. On the basis of these results, we concluded that 1) mult iple forms of each inhibin/activin subunit mRNA are expressed in folli cular tissue; 2) alpha and beta(A) subunit mRNAs and inhibin transient ly increase; 3) alpha and beta mRNAs are not co-regulated similarly; a nd 4) beta(B) mRNA is constitutively expressed during differentiation and atresia of nonovulatory follicles.