The receptor mechanisms for histamine actions in proximal portion differ from those in distal portion in human coronary artery.

Abstract

While most distal human coronary arteries markedly relaxed in response to histamine, nearly half the proximal ones contracted only. Thus, we investigated the receptor mechanisms for those heterogeneous histamine actions. After a combination of cimetidine-treatment and endothelial removal, but neither one alone, proximal and distal rings contracted to histamine to the same degree. It is suggested that histamine hypercontractility in proximal human coronary artery is due to a lack of both direct (H2-receptor) and endothelial-mediated (H1-receptor) relaxant actions.human coronary artery ; histamine Proximal human coronary arteries have been reported to be more sensitive to histamine than distal ones (Ginsburg et al. 1984). On the other hand, histamine induces a reduction of coronary vascular resistance (Vigorito et al. 1986). Recently, three different histamine receptor mechanisms have been reported in the human coronary artery (Toda 1987). If these three components differ depending on the size of the coronary vessel, previously conflicting data are conceivable. The purpose of this study, therefore, is to investigate how responses of proximal arteries to histamine differ from those of distal ones and, if any, to clarify their histamine receptor mechanisms.Proximal (diameter of 3-5 mm) and distal (diameter of 1 mm) segments of right epicardial coronary arteries were isolated at autopsy from 28 noncardiac patients, and cut into 2.5 mm wide rings. For isometric tension recording (Shinkoh U-Gage, UL-20, Tokyo), each ring was suspended in a tissue bath filled with Krebs-Ringer solution saturated with 95% 02 and 5% CO2 at 3TC.. During a 90 min equilibration, the resting tension of proximal and distal rings was adjusted to 1.5 and 1.0 g, respectively. Histamine (10-8-10-4 M) was added in a cumulative fashion to the ring contracted with 50 mM KC1 under several interventions ; first in a control series, second, after treatment with 10-5 M pyrilamine, an H1-receptor antagonist, or 10-4 M cimetidine, an H2-receptor antagonist, or without endothelium, and third, a combination of the latter two.While almost all distal rings (53/57) relaxed markedly in response to histamine, proximal rings responded variously, ranging from relaxation to contraction. Proximal rings (40/83) which only contracted to histamine were used as hypercontracted arteries in

Regulation of Human Umbilical Artery Contractility By Different Serotonin and Histamine Receptors

“…39 The importance of the H 1 receptor to trigger vascular contractility in some arteries is also supported by other authors working with human radial and coronary arteries. 40,41 In agreement with other studies, 42 our data indicate that H 2 receptors are also expressed in HUA smooth muscle. The activation of these receptors stimulates adenylate cyclase, increasing cAMP intracellular levels, 20 a nucleotide which is related to artery vasorelaxation.…”

Histamine: metabolism, physiology, and pathophysiology with applications in veterinary medicine

“…Conversely, in distal segments of the coronary arteries the main action is vasodilatation resulting from direct activation of smooth muscle H2Rs. 49,50 A similar pattern has been demonstrated in dogs. 51 In pigs and cattle, histamine-induced vasoconstriction predominates in most segments of isolated coronary arteries via H1Rs on smooth muscle cells.…”

“…51 In pigs and cattle, histamine-induced vasoconstriction predominates in most segments of isolated coronary arteries via H1Rs on smooth muscle cells. 49 Histamine affects the function of the cardiovascular system not only directly but indirectly through the central histaminergic neurons. The cell bodies of all histamine containing neurons in the CNS are localized to the posterior hypothalamus.…”