Is histamine a human coronary vasospastic substance?

Mast cells in human coronary arteries; is there any correlation with luminal narrowing?

Histamine in the human coronary arteries is harboured in mast cells and possibly in a non-mast cell store. Upon histamine exposure atherosclerotic coronary arteries react differently than normal coronary arteries, and histamine has been proposed to provoke vasospasms, ischaemia and sudden cardiac death. Previous reports have indicated a correlation between the mast cell density and the histamine content on the one hand and the degree of atherosclerosis on the other hand. Since previous reports applied visual assessment of the luminal narrowing only, we reexamined these results utilising planimetric methods. The study was accomplished by examining coronary arteries from autopsy cases (50-70 years, N = 29) with a diagnosis of sudden death, myocardial infarction or a non-cardiac cause. The mast cell density was calculated as the ratio between the mast cell count and the adventitial area as seen by light microscopy, and was compared to the degree of luminal narrowing. We were not able to find any correlation between the mast cell density and the luminal narrowing. The myocardial infarction group had the most severe degree of luminal narrowing, but there was no significant difference in mast cell density between the groups. We therefore question the previous notion that there is a correlation between the adventitial mast cell density in the coronary arteries and the luminal narrowing. Earlier reports may have been biased by visual assessment and by erroneously treating several measurements from the same person as independent samples.

Nitric oxide-mediated neurogenic relaxation in monkey mesenteric veins

The purpose of this investigation was to determine if neurally induced vasodilatation is mediated by nitric oxide (NO) in monkey mesenteric veins. Helical strips of the monkey mesenteric vein were exposed to the bathing media for isometric tension recording, and perivascular nerves were stimulated by nicotine. Nicotine produced a contraction, which was potentiated by treatment with NG-nitro-L-arginine, a NO synthase inhibitor, the effect being reversed by L-arginine. The nicotine-induced contraction was reversed to a relaxation by prazosin. The relaxation was abolished by the NO synthase inhibitor, and it was restored by L-arginine. D-Enantiomers were without effect. The response was not influenced by timolol and indomethacin, but was abolished by hexamethonium and oxyhemoglobin. There were perivascular nerve fibers containing NO synthase immunoreactivity in the monkey vein. Neurally induced venous relaxations appear to be mediated by NO from perivascular nerves, as seen in dog and monkey mesenteric arteries. It is concluded that monkey mesenteric veins are innervated by nitroxidergic and adrenergic nerves, which may balance the vascular tone.

Histamine release during paediatric cardiopulmonary bypass

Histamine release is part of the general inflammatory response and occurs during surgery and cardiopulmonary bypass (CPB) in adults. Few data are available for children. Histamine release was studied in 23 children undergoing CPB with standard anaesthetic and CPB techniques. Blood sampling was performed in relation to specific anaesthetic and surgical events, e.g., start of CPB, removal of aortic clamps, reventilation of the lungs. Plasma histamine was determined by a single isotope radioenzymatic technique. There was no consistent histamine release in the study population although there was an increase in plasma histamine concentration in some subjects after initiation of CPB (P < 0.05) and on removal of the aortic cross-clamp (P < 0.05). No correlation was demonstrated between histamine concentration and systolic arterial pressure, temperature, duration of CPB or cross-clamp time. Histamine concentration was positively correlated with heart rate.

Effects of selective phosphodiesterase inhibitors on isolated coronary, lung and renal arteries from man and rat

The relaxant effects of some isozyme-selective phosphodiesterase inhibitors were evaluated in isolated human and rat coronary, lung and renal arteries. Milrinone and OPC 3911, inhibitors of a cGMP-inhibited cAMP phosphodiesterase (cGI-PDE), were shown to have distinct vasodilator actions. These agents were less potent as relaxants in rat lung and renal arteries than in the corresponding human tissues. OPC 3911, the more potent cGMP-inhibited cAMP phosphodiesterase inhibitor, was found to be the more potent vasorelaxant. Rolipram, a selective inhibitor of a cGMP-noninhibited cAMP phosphodiesterase, had small effects on coronary and lung arteries, but produced a slightly more pronounced relaxation of renal arteries from both man and rat. In human preparations contracted by 30 mM K+, milrinone and OPC 3911 had similar relaxant profiles, and were as potent in coronary as in renal arteries. These results do not support the notion that milrinone has reduced effects on renal vessels in man and show that there may be species differences in vascular responsiveness to cGMP-inhibited cAMP phosphodiesterase inhibitors.

Interaction between neutrophils and pig coronary artery increases histamine contractions

In the present study we investigated the possible role of neutrophils and the endothelium in the induction of hyperreactivity of pig coronary arteries to histamine. Histamine caused a dose-dependent contraction of isolated pig coronary arteries. The maximal contraction to histamine was reduced in preparations from which the endothelium had been removed. Pre-incubation of intact coronary arteries with isolated neutrophils had no influence on the contractile response to histamine. However, when the same experiments were performed with coronary arteries without endothelium, the maximal contraction to histamine was increased. Incubation with scavengers and inhibitors of the enzymes, lipoxygenase or cyclo-oxygenase, provided evidence for a role of lipoxygenase products in the induction of hyperreactivity to histamine by neutrophils in the pig coronary artery.

Neutrophils increase histamine contractions in pig coronary artery: a role for lipoxygenase products

The possible role of neutrophils and the endothelium in the induction of hyperreactivity of the pig coronary artery to histamine was studied. In pig isolated coronary arteries histamine caused a concentration-dependent contraction; maximal contraction to histamine, however, was reduced in endothelium-denuded arteries. Pre-incubation of intact coronary arteries with isolated neutrophils did not affect the contractile response to histamine, while pre-incubation of endothelium-denuded arteries induced a hyperreactivity to histamine. This induction of hyperreactivity to histamine by neutrophils in pig coronary arteries seems to be mediated by lipoxygenase products, since it could be prevented by pre-incubation of the preparations with lipoxygenase inhibitors, but not with inhibitors of cyclo-oxygenase or with scavengers.