Evidence for Selective Expression of Angiotensin II Receptors on Atretic Follicles in the Rat Ovary: An Autoradiographic Study*

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Abstract
Ovarian angiotensin II (Ang II) receptors display a cyclical pattern of variation during the rat estrous cycle. Ang II receptors, estimated by the specific binding of the Ang II receptor antagonist [125I]iodo-[Sar1,Ile8] Ang II to ovarian membranes, were lowest at estrus [binding site density (Bmax) = 35 .+-. 2 fmol/mg; binding site affinity (KD) = 2.0 .+-. 0.2 nM] and highest at diestrus I (Bmax = 59 .+-. 3 fmol/mg; KD = 1.6 .+-. 0.1 nM). We have previously shown that Ang II receptors in the rat ovary predominantly exist on the granulosa cell layer of a subpopulation of follicles. Our present studies show that the Ang II receptor-containing follicles in the rat ovary are mainly atretic (.apprx.80%) or show signs of early atresia (.apprx.15%) during all stages of the estrous cycle. A small number of Ang II receptor-containing follicles were healthy (.apprx.5%). In contrast to the Ang II receptor-containing follicles, the FSH receptor-containing follicles were predominantly healthy (>90%). Follicles which contained both Ang II receptors and FSH receptors were mainly early atretic. Since Ang II receptor-containing follicles in the rat ovary were mainly atretic these studies suggest that in the rat Ang II may be a major factor in regulating the function of atretic ovarian follicles.