Effects of histamine on vascular sympathetic neuroeffector transmission
Powell, J.R.
Journal of Pharmacology and Experimental Therapeutics 208(3): 360-365
1979
ISSN/ISBN: 0022-3565 PMID: 219175 Document Number: 152317
Histamine is contained in high quantities in sympathetic nerves and vascular tissues. The functional significance of the histamine stores is not known but suggests a possible interaction between histamine and sympathetic nerves controlling blood vessels. Experiments were conducted in anesthetized dogs to determine whether histamine influences sympathetic vasoconstriction. The vascularly isolated gracilis muscle was perfused with blood at a constant flow rate by a pump. Perfusion pressure was measured as a reflection of vascular resistance. Electrical stimulation of the lumbar sympathetic chain caused vasoconstriction as did intra-arterial norepinephrine. Histamine infused at 1.0 .mu.g/min did not affect resting vascular resistance but reduced vasoconstriction caused by sympathetic nerve stimulation. Vasoconstriction caused by injected norepinephrine was not reduced by histamine indicating a prejunctional site of action. The inhibitory effect of histamine was prevented by treatment with metiamide and mimicked by dimaprit, a H2-receptor agonist, suggesting mediation by H2-receptors. Similar experiments were conducted in the perfused hindpaw where histamine inhibited vasoconstriction caused by both nerve stimulation and injected norepinephrine suggesting a postjunctional site of action. In the hindpaw the inhibitory effect of histamine was blocked by metiamide but not by mepyramine. Apparently histamine can modulate sympathetic vasoconstriction by pre- and postjunctional mechanisms through an interaction with H2-receptors.