metiamide and Hyperemia

Direct, in vivo microcirculatory experiments were undertaken with anesthetized rats to determine whether prostaglandin (PG)-like compounds and histamine may mediate post-occlusion hyperemia in single mesenteric arterioles. Superfusion of the mesenteric vasculature with two structurally different PG synthetase inhibitors, indomethacin and 5,8,11,14-eicosatetraynoic acid (ETA), was found to markedly inhibit postocclusion vasodilator responses in arterioles 20-22 micrometer i.d. Superfusion of mesentery with an H2-histamine receptor antagonist, metiamide, resulted in a 40% inhibition of the postocclusion vasodilator responses in arterioles. Superfusion of the mesenteric vasculature with a combination of indomethacin and metiamide resulted in a 95% suppression of the postocclusion dilator responses. Administration of either the PG synthetase inhibitors, metiamide, or a combination of both types of drugs did not, however, influence resting arteriolar tone or responsiveness to PGE1 or epinephrine. Although the results of these experiments implicate a role for PG-like substances and histamine in reactive or postocclusion hypermia, they do not provide evidence for a role of these humoral substances in the normal moment-to-moment regulation of arteriolar tone.

Topics: 5,8,11,14-Eicosatetraynoic Acid; Animals; Arteries; Arterioles; Cyclooxygenase Inhibitors; Histamine; Hyperemia; Indomethacin; Male; Mesenteric Arteries; Metiamide; Prostaglandins; Rats; Vasodilation

The authors studied the effect of pretreatment of monkeys with antihistamines on hyperemia observed in the lateral funiculus of the spinal cord after severe experimental spinal cord trauma. After administration of Chlorpheniramine and Metiamide, the spinal cords were traumatized with a 600 gm-cm injury. Blood flow in the lateral funiculus at the injury site was then determined hourly for 6 hours. The blood flow at this site remained in the normal range at all times in all animals. Neither a hyperemia nor an ischemia could be demonstrated. This finding reaffirms the authors' previous observation that ischemia does not exist in the lateral funiculus after severe experimental spinal cord trauma, and explains the previous observation of hyperemia as a histamine-related phenomenon, easily blocked by the administration of Chlorpheniramine and Metiamide, potent antihistamines which together block both the H1 and H2 receptor sites.

Topics: Animals; Blood Pressure; Chlorpheniramine; Haplorhini; Histamine; Hyperemia; Macaca mulatta; Metiamide; Regional Blood Flow; Spinal Cord; Spinal Cord Injuries; Syndrome