Angiotensin Ii Receptor Density in Bovine Ovarian Follicles Relates to Tissue Renin and Follicular Size

The purpose of this study was to investigate angiotensin II (AII) receptors in isolated bovine ovarian follicles and the relationship of their density to follicular concentrations of prorenin, active renin, oestradiol and progesterone. 2. Displacement of [125I]-[Sar1-Ile5-Ile8]-AII binding by the AII receptor antagonists PD 123319 and Losartan (DuP 753) confirmed that follicular AII receptors are of subtype 2 (AT2 receptor). 3. The dissociation constant (Kd) for [Ile5]-AII (human AII) was 0.84 (range 0.51-1.47) nmol/L. The receptor density varied between 90 and 5990 (mean 1640) fmol/mg membrane protein. 4. The follicular AII receptor density correlated positively with follicular diameter (Spearman's rho = 0.518; P < 0.003) and tissue weight (Spearman's rho = 0.636; P < 0.0001), and negatively with the active renin concentration in the follicular wall (Spearman's rho = -0.399; P < 0.02). The AII receptor density did not correlate with the follicular fluid concentrations of prorenin, active renin, oestradiol (E2), progesterone (P4) or the E2/P4 ratio. The follicular fluid concentrations of prorenin correlated negatively with the E2/P4 ratio (Spearman's rho = -0.716; P < 0.0001). 5. The inverse relationship between AII receptor density and the high active renin concentrations in the follicular wall suggests an active regulated tissue renin-angiotensin system. A high AII receptor density is a general feature of large bovine ovarian follicles.