Vasoactive transmitters in the coronary circulation

Coronary resistance can be modified by perivascular, endothelial and humoral vasoactive substances. A network of perivascular nerve fibres is present in the adventitia and at the adventitial-medial border of human coronary arteries and veins, and immunocytochemical studies have provided evidence that several neuropeptides are localized in subpopulations of afferent and efferent nerve fibres supplying the human coronary vasculature. Neuropeptide Y seems to be co-localized with noradrenaline in adrenergic perivascular nerve fibres and vasoactive intestinal peptide co-localized with acetylcholine in parasympathetic nerves, whereas sensory perivascular nerves contain immunoreactivity to substance P and calcitonin gene-related peptide. On the other hand, nitric oxide and endothelin are synthesized in coronary endothelial cells. Humoral substances like gonadal hormones are also likely candidates in the regulation of coronary resistance. The presence of different vasoactive substances in the coronary vasculature and the potential of these substances to affect coronary vessel tone, suggest that they have an important role in the regulation of coronary blood flow.