WEAKNESS OF SYMPATHETIC NEURAL CONTROL OF HUMAN PIAL COMPARED WITH SUPERFICIAL TEMPORAL ARTERIES REFLECTS LOW INNERVATION DENSITY AND POOR SYMPATHETIC RESPONSIVENESS

Background and Purpose-The primary goal of these studies was to unders tand and investigate the capacity of perivascular nerves to influence the tone of human pial arteries and to compare them with other human c ephalic arteries, the superficial temporal and middle meningeal. Metho ds-Responses to electrical activation of intramural nerves and related features of fresh segments of human cephalic arteries-the pial (PA; 4 78+/-33 mu m ID), middle meningeal (MMA; 540+/-41 mu m ID), and superf icial temporal (STA; 639+/-49 mu m ID)-obtained from patients aged 15 to 82 years during surgical procedures were studied on a resistance ar tery myograph. Results-The PA segment responses to electrical nerve ac tivation and to norepinephrine (NE; 10(-5) mol/L) were 1% and 21% of t issue maximum, respectively, compared with 6% and 33% for the MMA and 14% and 90% for the STA, Tissue maximum was defined as the force incre ase to 127 mmol/L KCl plus arginine vasopressin (1 mu m). All arteries dilated well to acetylcholine. Possible explanations for the PA margi nal neurogenic responses were assessed. NE ED50 was 5.4+/-2.2x10(-7) m ol/L and did not vary with age or diameter. NE responsiveness did not increase in vessels with spontaneous or raised potassium-induced tone. Relaxation to isoproterenol was variable and propranolol did not incr ease the neurogenic response, Neither N-G-monomethyl-L-arginine, N-G-n itro-L-arginine methyl eater, endothelium removal, nor indomethacin co nsistently influenced the contractions to NE or neurogenic reactivity. The weak PA neurogenic response is in keeping with its poor innervati on. As determined by catecholamine histofluorescence, innervation in t he PA is sparse, with density increasing in the order PA, MMA, and STA , The incidence of nerve structures in the PA adventitio-medial juncti on was only 3% of those in the STA, and these were situated more than 3 mu m from the closest smooth muscle cell, Conclusions-We conclude th at the weak neurogenic response of adult human pial artery reflects it s poor innervation and responsiveness to NE, implying that these featu res are not important in the regulation of its diameter.