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Severe Histaminosis and Cardiac Effects:
Cardiac effects of histamine include stimulation of sinus rate and ventricular contractile force, impairment of atrioventricular conduction and increase in ventricular automaticity. Atrioventricular block and increase in ventricular automaticity are common features of digitalis toxicity.
C5H9N3 (Histamines), produced by decarboxylation of histidine, found in all body tissues. It induces capillary dilation, which increases capillary permeability and lowers blood pressure; contraction of most smooth muscle tissue; increased gastric acid secretion; and acceleration of the heart rate. It is also a mediator of immediate hypersensitivity. There are three types of cellular receptors of histamine. H1 receptors mediate contraction of smooth muscle and capillary dilation and H2 receptors mediate acceleration of heart rate and promotion of gastric acid secretion. Both H1 and H2 receptors mediate the contraction of vascular smooth muscle. H3 receptors are believed to play a role in regulation of the release of histamine and other neurotransmitters from neurons.
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