Histamine H2-receptors in the human peripheral circulation

Area of Science:

• Pharmacology
• Physiology
• Vascular Biology

Background:

• Histamine is a key mediator in physiological responses, including vasodilation.
• Histamine exerts its effects through distinct histamine receptors (H1, H2, H3, H4).

Purpose of the Study:

• To investigate the specific histamine receptor subtypes involved in histamine-induced forearm vasodilation.
• To elucidate the roles of H1 and H2 receptors in the initiation and maintenance of increased forearm blood flow.

Main Methods:

• Histamine was infused into the brachial artery of participants at a rate of 10 mug/min for 3 minutes.
• Forearm blood flow was measured before, during, and after histamine infusion.
• The effects of mepyramine (H1 receptor antagonist) and metiamide (H2 receptor antagonist) on blood flow were assessed, both individually and in combination.

Main Results:

• Histamine infusion significantly increased forearm blood flow.
• Mepyramine reduced the histamine-induced increase in blood flow, particularly in the first minute.
• Metiamide did not affect the vasodilation during infusion but accelerated the return to baseline flow; the combined administration abolished the response.

Conclusions:

• Histamine-induced forearm vasodilation is primarily initiated by H1-receptor stimulation.
• Both H1 and H2 receptors contribute to the maintenance of this vasodilation.
• Sustained H2-receptor activity may be responsible for the prolonged elevation in forearm blood flow post-infusion.