Histamine H2-receptors in the human peripheral circulation.

Histamine (10 mug/min for 3 min) infused into the brachial artery caused an increase in forearm blood flow which was reduced by mepyramine (25 mg). This effect was most marked in the first minute of the infusion. Metiamide (25 mg) had no effect on the dilatation during the infusion but caused a quicker return of flow to the resting level. The response was abolished when both drugs were given in combination. It is concluded that the response is initiated mainly by stimulation of H1-receptors and maintained by H1- and H2-receptors; continued activity of H2-receptors may account for the slow return of flow to the pre-infusional level.