EXPRESSION OF DIFFERENT MOLECULAR-MASS FORMS OF INHIBIN IN ATRETIC AND NONATRETIC FOLLICLES DURING THE EARLY LUTEAL-PHASE AND ALTRENOGEST-SYNCHRONIZED FOLLICULAR PHASE IN PIGS

This experiment characterized changes in amounts and proportions of di fferent molecular forms of inhibin in porcine follicular fluid as rela ted to stage of follicular development. Thirty-seven follicles (2-4 pe r pig) were dissected from 12 pigs during early luteal phase of the es trous cycle on Days 5, 6, and 7 of the estrous cycle, whereas 34 folli cles (2-4 per pig) were dissected from 11 pigs on Days 1, 3, 5, and 7 of a follicular phase synchronized by altrenogest. Follicles were desi gnated atretic if incidence of apoptotic granulosa cells was greater t han or equal to 10% as determined by DNA fluorescence flow cytometry, Porcine follicular fluid was fractionated on 12% SDS-PAGE gels under n on-reducing conditions and electroblotted to Immobilin P membranes. In hibin forms were detected by immunoblot analysis using a mink anti-bov ine inhibin alpha(C)(1-26)gly tyr antiserum and quantified. Immunoblot s detected seven bands corresponding to inhibin forms of 44, 49, 58, 6 9, 121, 227, and > 227 kDa in > 91% of porcine follicular fluid sample s. Three additional forms of 27, 29, and 32 kDa were detectable in onl y 52%, 64%, and 48% of samples,respectively. Forms greater than or equ al to 69 kDa represented 83% of total inhibin immunoblot activity. The 121-kDa form was most abundant, with 39% of the total immunoblot acti vity in nonatretic follicles. The proportions of individual forms and total immunoblot activity pooled over days did not differ between earl y luteal and follicular phase follicles. Total inhibin immunoblot acti vity was 59% less in atretic than in nonatretic follicles. Amounts of the 44-, 49-, 69-, 121-, and 227-kDa forms were 50-80% lower (p less t han or equal to 0.05) in atretic than in nonatretic follicles. Total i nhibin immunoblot activity in nonatretic follicles decreased (p less t han or equal to 0.05) by 60% during the early luteal phase but did not change significantly during the follicular phase. In nonatretic folli cles, the 121-kDa form decreased (p < 0.05) during the early luteal an d follicular phases. During the early luteal phase, amounts of the oth er forms did not change, whereas during the follicular phase the 44-kD a form increased (p < 0.05) 10-fold. In atretic follicles, neither amo unt nor proportion of inhibin forms differed among days. We conclude t hat follicular production and/or intracellular processing of inhibin d imer and/or inhibin alpha subunits changes during different phases of follicular development, supporting the notion of physiological roles C ar these peptides.