AROMATASE-ACTIVITY OF OVINE FOLLICULAR WALLS - TECHNICAL VALIDATION AND PHYSIOLOGICAL CONTROL

Since aromatase activity quickly disappears in cultured sheep granulos a cells, its control is poorly understood. As a result, an aromatase a ssay was developed using cultures of follicular walls and measuring th e amount of (H2O)-H-3 generated from H-3-testosterone. Chromatography and mass spectrometry analysis demonstrated that (H2O)-H-3 production was indeed associated with the production of oestradiol-17 beta. Optim ization of the assay demonstrated: (1) a steady increase in the amount of (H2O)-H-3 produced over at least 12 h; and (2) highly significant correlations between the amounts of (H2O)-H-3 measured and the weight of the follicular wall or the amount of H-3-testosterone provided. Fur thermore, a highly significant correlation (r = 0.82) was observed bet ween the amount of (H2O)-H-3 produced and the concentration of oestrad iol in the same samples. The effects of follicle-stimulating hormone ( FSH), luteinizing hormone (LH) and oestradiol on aromatization by foll icles at two specific stages of maturation (recruitment, 12 h after lu teolysis; dominance, 36 h after luteolysis) were then assessed. At rec ruitment and dominance, FSH was able to modulate aromatase activity si milarly, increasing and decreasing the activity at low concentrations and high concentrations respectively. At recruitment and dominance, oe stradiol had no stimulatory effect on basal aromatase activity and eve n blocked the stimulatory effects of FSH on aromatase at recruitment. LH significantly inhibited the FSH-stimulated aromatase activity of do minant follicles. It is concluded that: (1) FSH may induce the recruim ent of follicles by increasing aromatase activity; and (2) neither oes tradiol nor LH stimulate the aromatase activity of follicles which cou ld explain maintenance of the dominant follicle.