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Role of endothelin 1 in steroid production by ovine granulosal cells collected from large preovulatory follicles

Abstract:

For this experiment it was hypothesized that endothelin 1 (END1) acting through its receptors, endothelin receptor type A (ENDRA) and/or endothelin receptor type B (ENDRB), on granu-losal cells (GC) of ovine preovulatory follicles would inhibit steroid production, and therefore, prevent the premature luteinization of granulosal cells of those follicles. The ovaries of 17 Suffolk ewes were removed by mid-ventral laparotomy after two doses of PGF 2α (5 mg; three h apart). Granulosal cell were harvested under sterile conditions from the two or three largest follicles. Ali-quots of 15 μL of GC suspension from each presumed preovulatory follicle were cultured in 96-well plates containing a solution of 185 μL of Ham's F12 supplemented medium and treatments (single and combined effects of LH, END1, ENDRA and ENDRB). According to estradiol (E 2) concentration in follicular fluid (FF), presumed preovulatory follicles were categorized in estrogen-active and estrogen-inactive follicles. Data from 20 estrogen-active follicles (collected from 13 ewes) challenged to 10 different treatments were examined by analysis of variance. Accumulation of E 2 and progesterone (P 4) by cultured GC was not affected by either LH or END1 or the END receptor blockers. Granulosal cells from follicles with the greatest concentration of E 2 in FF produced on the average significantly more E 2 and P4 than follicles with lower concentrations of E 2 in FF (P<0,0001). In conclusion, under the experimental conditions of this study, END1 did not affect steroid production by GC from preovulatory follicles in sheep, and therefore the working hypothesis was not supported.