Additive Effects of Atrial Natriuretic Peptide and Angiotensin II on Luteinizing Hormone and Prolactin Release in Female Rats

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Abstract
The present experiments were designed to assess the effects of central administration of atrial natriuretic peptide (ANP), alone or in conjunction with angiotensin II (AII), on luteinizing hormone (LH) and prolactin release in ovarian steroid-primed female rats. Intracerebroventricular injection of ANP (200 ng/2 .mu.l over 1 min) induced an increase in plasma LH levels without significantly affecting prolactin release. Injection of AII (50 ng/2 .mu.l over 1 min) also resulted in an increase in LH levels and, in addition, reduced plasma prolactin titers. Coinjection of ANP and AII did not elevate LH levels beyond that achieved by either peptide alone, but produced a further suppression in prolactin levels than that seen with AII alone. Water intake induced by AII was attenuated by coadministration of ANP. In a second protocol utilizing lower doses of the peptides delivered by infusion, either ANP (800 ng/h; 13.3 ng/min) or AII (200 ng/h; 3.3 ng/min) alone produced 100% increases in LH levels. Coinfusion of the peptides induced an additive (250%) increase in plasma LH titers. In this protocol, the release of prolactin was unaffected by infusion of the peptides, either alone or as a comixture. Water intake induced by AII infusion was attenuated by coadministration of ANP. Taken together, these experiments demonstrate that, in contrast to the antagonistic interaction of ANP and AII on water intake, the peptides affect reproductive hormone secretion in the same direction and, under particular experimental conditions, display additive effects in stimulating LH and inhibiting prolactin release.

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