From the Totman Laboratory for Human Cerebrovascular Research (R.D.B.,
J.D., P.N., N.T.-T., T.W., J.A.B.); the Department of Pharmacology, Division
of Neurosurgery (P.L.P.), University of Vermont, Given Building, Burlington,
Vt; and Neurological Surgeons, Phoenix, Az (C.L.W.).
Correspondence to John A. Bevan, MD, Department of Pharmacology, University of Vermont, 303B Given Bldg, Burlington, VT 05405-0068.
Background and PurposeThe 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.
MethodsResponses to electrical activation of intramural nerves
and related features of fresh segments of human cephalic arteriesthe
pial (PA; 478±34 µm ID), middle meningeal (MMA; 540±41
µm ID), and superficial temporal (STA; 639±49 µm
ID)obtained from patients aged 15 to 82 years during surgical
procedures were studied on a resistance artery myograph.
ResultsThe 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 µm). All arteries dilated well to acetylcholine.
Possible explanations for the PA marginal neurogenic responses were
assessed. NE ED50 was 5.4±2.2x10-7 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
NG-monomethyl-L-arginine,
NG-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 µm from the closest smooth muscle cell.
ConclusionsWe 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.
Department
of Pharmacology,
Southern Illinois University School of Medicine,
Springfield, Illinois
© 1998 American Heart Association, Inc.
Original Contributions
Weakness of Sympathetic Neural Control of Human Pial Compared With Superficial Temporal Arteries Reflects Low Innervation Density and Poor Sympathetic Responsiveness
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