Autoregulation during pressor response elevates wall shear rate in
arterioles.
Kurjiaka, David T., and Steven S. Segal.
The John B. Pierce Laboratory and Departments of Epidemiology &
Public Health and of Cellular & Molecular Physiology, Yale
University School of Medicine, New Haven, Connecticut 06519; and Noll
Physiological Research Center, Pennsylvania State University,
University Park, Pennsylvania 16802
APStracts 2:0437A, 1995.
Autoregulation of blood flow implies reciprocal changes in vessel
diameter and red blood cell velocity (Vrbc) when perfusion pressure
is altered. We tested two hypotheses: (1) blood flow will be
autoregulated throughout arteriole networks during a pressor
response; and (2) wall shear rate (WSR; proportional to
Vrbc/diameter) will increase during autoregulation. Male hamsters
(n=22; 109 3 g) were anesthetized (pentobarbital, 60 mg/kg) and the
cremaster muscle prepared for intravital video microscopy. Internal
diameter and Vrbc were monitored in first- (1A) through fourth- (4A)
order arterioles; WSR and blood flow were calculated. Data were
acquired at rest and at the peak of diameter responses to bilateral
carotid artery occlusion (CAO). At rest: (i) mean arterial and 1A
transmural pressures were 100 5 and 59 4 mmHg respectively; (ii) as
branch order increased, arteriole diameter, Vrbc, and blood flow
decreased (p < 0.05); (iii) WSR and resting tone increased (p
< 0.05) with branch order. During pressor responses to CAO: (i)
arterial and 1A pressures increased to 145 +/- 7 and 89 5 mmHg
(p<0.05); (ii) 1A branches dilated while 2A, 3A, and 4A branches
constricted (p<0.05); (iii) Vrbc and WSR increased (p<0.05)
in all branches; (iv) blood flow increased in 1A and 2A branches
(p<0.05), yet was unchanged (i.e., was autoregulated) in 3A and
4A branches. Arteriolar constrictions during CAO were not affected by
-adrenoceptor blockade with phentolamine (10-6 M). We conclude that
autoregulation of muscle blood flow during a pressor response
involves myogenic constriction of arterioles with concomitant
elevation of WSR.
Received 1 July 1994; accepted in final form 15 September 1995.
APS Manuscript Number A652-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95