In vitro steroidogenesis by granulosa cells from equine pre-ovulatory follicles
Tucker, K.E.; Henderson, K.A.; Duby, R.T.
Journal of Reproduction and Fertility. Supplement 44: 45-55
1991
ISSN/ISBN: 0449-3087 PMID: 1795289 Document Number: 367719
23 follicles were collected from 14 mares during early (group 1), mid (group 2) and late (group 3) oestrus. Isolated granulosa cells from each follicle were cultured for 48 h in Eagle's Minimum Essential Medium, and medium plus horse LH (300 ng/ml), horse FSH (300 ng/ml) or both hormones, in the presence or absence of 0.5 micro M testosterone. The medium was replaced after 24 h of culture. There was no effect of adding gonadotropins on steroid secretion by granulosa cells from any group, so these values were pooled and averaged. Steroid concentrations were expressed as ng/ml per 1000 cells. Progesterone was the predominant steroid secreted by cells from all groups without added testosterone after 24 h of culture, and its concentration was highest for group 3 (7.86+or-1.19), greater (P<0.001) than the concentration for group 1 (0.02+or-0.004) and group 2 (0.15+or-0.03). Androstenedione was the predominant androgen secreted, but its concentration did not change among groups. Oestradiol and testosterone levels were similar in medium from group 1 (0.003+or-0.0004 and 0.003+or-0.0009 resp.), but oestradiol was highest in group-2 medium (0.17+or-0.11; P<0.001) and testosterone in group-3 medium (0.02+or-0.003; P<0.005). For cells incubated with testosterone, oestradiol increased in medium from all groups (P<0.0001). Oestradiol levels for group 1 (0.52+or-0.12) and group 3 (0.57+or-0.09) were similar, but were lower than in group 2 (2.15+or-0.29; P<0.01). After 48 h, progesterone concentration was higher in all groups than after 24 h (P<0.0001); progesterone was the predominant steroid secreted by group-3 cells. Progesterone levels were not affected by the addition of testosterone. Androstenedione increased in group-3 medium (P<0.001), whereas oestradiol and testosterone remained unchanged. The results suggest that the pattern of steroid secretion by horse granulosa cells changes as follicular maturation proceeds. Previous results showed that granulosa cells from oestrous follicles contain an active aromatase system, but later in oestrus they become primarily progesterone-secreting cells. This suggests that in the mare, granulosa cells luteinize prior to ovulation.