Abstract
The blood pressure responses of normotensive (WKY) and hypertensive (SHR) rats to histamine injections were compared before and during pregnancy. A series of increasing doses of intravenous histamine was given before histamine receptor blockade, after H1 (pyrilamine) block, and after combined H1 and H2 (cimetidine) block. In both WKY and SHR nonpregnant rats, histamine caused dose-dependent decreases in blood pressure which were partially dependent on H1 and H2 receptors. In late pregnancy, the magnitudes of the hypotensive effects of histamine were significantly reduced and blocked only by combined H1 and H2 treatment but not by H1 treatment alone. Thus, the blood pressure effects of exogenous histamine in normotensive and hypertensive rats are modified in a similar way during late pregnancy with diminished hypotensive effects which are more dependent on H2 receptors than the effects in nonpregnant rats. This change in histamine responsiveness may play a role in the cardiovascular adjustments of pregnancy.
Published Version
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