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Estradiol Inhibition of Ovine Luteal Progesterone Synthesis In Vitro^{1, 2,}

Oregon State University,³ Corvallis 97331

Abstract

The effect of 17β-estradiol on the in vitro conversion of pregnenolone-4-¹⁴C to progesterone by luteal slices of mature ewes on days 6 and 13 of the estrous cycle (first day of estrus=day zero of the cycle) was studied. Luteal slices were incubated in 3 ml of Krebs Ringer bicarbonate with 0.3, 1.0 or 10 µg/ml of 17β-estradiol and 0.2 µCi of pregnenolone-4-¹⁴C for 1.5 hr. at 37 C under an atmosphere of 95% O₂-5% CO₂. Luteal slices of ewes on day 6 of the cycle converted more labeled pregnenolone to progesterone than luteal slices of ewes on day 13 (P<.05). Estradiol (10 µg/ml) inhibited the conversion of labeled pregnenolone to progesterone by luteal slices of ewes at both stages of the cycle studied (P<.01). Stage of the cycle or estradiol concentration was without significant effect on the mass of luteal progesterone synthesized.

¹ Technical Paper No. 3283, Oregon Agricultural Experiment Station.

² Appreciation is expressed to Susan K. Martin for technical assistance.

³ Department of Animal Science.