HIGH-AFFINITY ANGIOTENSIN II RECEPTORS IN THE BOVINE OVARY ARE DIFFERENT FROM THOSE PREVIOUSLY IDENTIFIED IN OTHER TISSUES

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Abstract
Scatchard analysis of angiotensin II (A II) binding data revealed different effects of dithiothreitol (DTT) on high-affinity A II receptors in the bovine adrenal and ovary. Dithiothreitol predominantly inhibited 125I-A II binding capacity of adrenal membranes by decreasing the number of the high-affinity binding sites (Bmax = 265 .+-. 25 fmol/mg of protein without DTT; Bmax = 26 .+-. 5 fmol/mg of protein with 100 mM DTT) without significant change in A II binding affinity (Kd = 0.49 .+-. 0.02 nM vs. Kd = 0.37 .+-. 0.10 nM). By contrast, in the ovary the agent stimulated 125I-A II binding capacity up to 3-fold by increasing A II binding affinity of the high-affinity receptors (Kd = 0.22 .+-. 0.04 nM vs. Kd = 0.041 .+-. 0.015 nM for 0 mM and 100 mM DTT, respectively) with no change in the number of binding sites (Bmax = 72 .+-. 13 vs. 85 .+-. 8 fmol/mg of protein). These results suggest the existence of two distinct subtypes of A II receptors between the two tissues.