Size and site-dependent heterogeneity of human vascular responses in vitro

Ring segments of splanchnic, peripheral, coronary, pulmonary and uterine conduit arteries obtained during surgery were studied in tissue baths. Resistance arteries dissected from various sites were studied in a myograph. Both conduit and resistance vessels contracted in response to the α1-agonist phenylephrine (10 to 10 mol/l), an effect that was antagonized by the α1-antagonist doxazosin (10 to 10 mol/l). However, the α2-agonists BHT 933 (10 to 10 mol/l) and UK 14304 (10 to 10 mol/l) only contracted the resistance vessels and not the conduit arteries. The response to BHT 933 was competitively antagonized by the α2-antagonist yohimbine (3.10 to 3.10 mol/l) and the magnitude of the contractile response was inversely related to vessel size. Similarly, neuropeptide Y (10 to 10 mol/l) contracted only the resistance vessels, and induced marked tachyphylaxis. Atrial natriuretic peptide (ANP; 10 to 10 mol/l) produced concentration-dependent relaxation in all conduit arteries studied, being ineffective in resistance arteries from subcutaneous or omental sites, but relaxed those from renal tissue and skeletal muscle. Calcitonin gene-related peptide (10 to 10 mol/l) and vasoactive intestinal peptide (10 to 10 mol/l) relaxed both conduit and resistance arteries. This response was dependent on the integrity of the endothelium in the systemic conduit but not the resistance vessels. These results indicate that the receptors for adrenergic agonists and vasoactive peptides are varyingly distributed throughout the human vasculature. The physiological relevance of these observations is not yet clear, but it is clearly important to the investigation of the sites of action of vasodilator drugs.