Key result
Specific binding of [125I] Angiotensin II to rat anterior pituitary membranes indicated a single class of binding sites with a Kd of 0.49 nM and maximum binding capacity of 40 fmol/mg protein.
The study demonstrates the presence of specific, high-affinity Angiotensin II receptors in the rat anterior pituitary gland, suggesting a role for Angiotensin II in regulating anterior pituitary hormone secretion.
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Supports investigation of angiotensin II in pituitary regulation; leaves open human relevance or clinical implications from animal data alone.
Previous work from this laboratory (1) indicates that angiotensin II (AII) can affect release of several anterior pituitary hormones, both in vivo and in vitro. To ascertain whether specific receptors mediate the effects of AII on the anterior pituitary, specific binding as well as the kinetics of [125I] AII binding to rat anterior pituitary membranes were analyzed. Binding of [125I] AII was rapid, reaching equilibrium within 4 min at 37 C. Specific binding was approximately 90%. Increasing concentrations of ligand resulted in saturation of binding, with equilibrium attained at [125I] AII = 2 nM. Scatchard analysis of the data indicated a single class of binding sites, with an equilibrium dissociation constant, Kd = 0.49 nM, and a maximum binding capacity of 40 fmol/mg protein. Specific binding was directly proportional to membrane protein concentration (range 20-240 micrograms protein). Binding was competitively inhibited on an equimolar basis by (Sar1, Ala8) AII (Saralasin), a specific AII receptor antagonist. The decapeptide Angiotensin I was about 10-20-fold less potent in inhibiting specific AII binding. These studies demonstrate and characterize specific receptor sites for AII in the anterior pituitary gland and offer additional evidence for a role of AII in the regulation of anterior pituitary hormone secretion.
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Mukherjee et al. (1982) studied this question. [125I] Angiotensin II was evaluated on Specific binding and kinetics of [125I] AII binding to rat anterior pituitary membranes. Specific binding of [125I] Angiotensin II to rat anterior pituitary membranes indicated a single class of binding sites with a Kd of 0.49 nM and maximum binding capacity of 40 fmol/mg protein.
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