Weakness of sympathetic neural control of human pial compared with superficial temporal arteries reflects low innervation density and poor sympathetic responsiveness.
OBJECTIVE
The primary goal of these studies was to understand and investigate the capacity of perivascular nerves to influence the tone of human pial arteries and to compare them with other human cephalic arteries, the superficial temporal and middle meningeal.


METHODS
Responses to electrical activation of intramural nerves and related features of fresh segments of human cephalic arteries-the pial (PA; 478+/-34 microm ID), middle meningeal (MMA; 540+/-41 microm ID), and superficial temporal (STA; 639+/-49 microm ID)-obtained from patients aged 15 to 82 years during surgical procedures were studied on a resistance artery myograph.


RESULTS
The PA segment responses to electrical nerve activation and to norepinephrine (NE; 10[-5] mol/L) were 1% and 21% of tissue maximum, respectively, compared with 6% and 34% for the MMA and 14% and 90% for the STA. Tissue maximum was defined as the force increase to 127 mmol/L KCl plus arginine vasopressin (1 microm). All arteries dilated well to acetylcholine. Possible explanations for the PA marginal neurogenic responses were assessed. NE ED50 was 5.4+/-2.2 X 10(-7) mol/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 increase the neurogenic response. Neither N(G)-monomethyl-L-arginine, N(G)-nitro-L-arginine methyl ester, endothelium removal, nor indomethacin consistently influenced the contractions to NE or neurogenic reactivity. The weak PA neurogenic response is in keeping with its poor innervation. As determined by catecholamine histofluorescence, innervation in the PA is sparse, with density increasing in the order PA, MMA, and STA. The incidence of nerve structures in the PA adventitio-medial junction was only 3% of those in the STA, and these were situated more than 3 microm from the closest smooth muscle cell.


CONCLUSIONS
We conclude that the weak neurogenic response of adult human pial artery reflects its poor innervation and responsiveness to NE, implying that these features are not important in the regulation of its diameter.
Bevan
R D
RD
Totman Laboratory for Human Cerebrovascular Research, Department of Pharmacology, University of Vermont, Burlington 05405-0068, USA.
Dodge
J
J
Nichols
P
P
Penar
P L
PL
Walters
C L
CL
Wellman
T
T
Bevan
J A
JA
D000109:Acetylcholine / Q000494:pharmacology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001127:Arginine Vasopressin / Q000494:pharmacology; D001158:Arteries / Q000294:innervation; D002452:Cell Count; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004547:Elastic Tissue / Q000294:innervation; D004558:Electric Stimulation; D004730:Endothelium, Vascular / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005453:Fluorescence; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008576:Meningeal Arteries / Q000294:innervation*; D008875:Middle Aged; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology; D010841:Pia Mater / Q000098:blood supply*; D011189:Potassium Chloride / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology; D013565:Sympatholytics / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D013699:Temporal Arteries / Q000294:innervation*; D017540:Tunica Media / Q000294:innervation; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology; D014666:Vasomotor System / Q000033:anatomy & histology / Q000502:physiology*
D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D013565:Sympatholytics; D013566:Sympathomimetics; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D001127:Arginine Vasopressin; D011189:Potassium Chloride; D011433:Propranolol; D019001:Nitric Oxide Synthase; D007545:Isoproterenol; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine; D007213:Indomethacin