Dehydration-induced vasopressin secretion in humans: involvement of the histaminergic system

In rats, the hypothalamic neurotransmitter histamine participates in regula tion of vasopressin secretion and seems to be of physiological importance, because blockade of the histaminergic system reduces dehydration-induced va sopressin secretion. We investigated whether histamine is also involved in regulation of vasopressin secretion during dehydration in humans. We found that 40 h of dehydration gradually increased plasma osmolality by 10 mosmol /kg and induced a fourfold increase in vasopressin levels. Pretreatment wit h the H-2-receptor antagonists cimetidine or ranitidine significantly reduc ed the dehydration-induced increase in vasopressin levels similar to 40% af ter 34 and 37 h of dehydration, whereas this was not the case with the H-1- receptor antagonist mepyramine. Dehydration reduced aldosterone secretion b y similar to 50%. This effect of dehydration was reduced by both H-1 and H- 2-receptor blockade after 16 and/or 34 h of dehydration. We conclude that v asopressin secretion in response to dehydration in humans is under the regu latory influence of histamine and that the effect seems to be mediated via H-2-receptors. In addition, the regulation of aldosterone secretion during dehydration also seems to involve the histaminergic system via H-1 and H-2 receptors.