Release of 3H2O from 1β,2β[3H]androstenedione by equine granulosa cells

Granulosa cells were harvested from mares at various stages of the oestrous cycle and incubated in Krebs-Ringer bicarbonate buffer with 1 beta,2 beta[3H]androstenedione as substrate. The release of 3H2O expressed as CPM/h/mg protein varied from 44000 to 768000 in follicles from 7 mares. The release of 3H2O was not significantly altered by luteinizing hormone, follicle stimulating hormone or pregnant mare's serum gonadotrophin. There was a significant negative correlation between the release of 3H2O and the concentration of progesterone in the follicular fluid. Based on the assumption that the release of 3H2O represent total aromatization, these data suggest that the equine granulosa cells have a very active aromatizing enzyme system.