Contribution of nitric oxide and prostaglandins to reactive
hyperemia in the human forearm.
Engelke, Keith A., John R. Halliwill, David N. Proctor, Niki M. Dietz,
and Michael J. Joyner.
Departments of Anesthesiology and Physiology and Biophysics, Mayo
Clinic and Foundation, Rochester, MN 55905
APStracts 3:0292A, 1996.
We investigated the separate and combined contributions of nitric
oxide (NO) and vasodilating prostaglandins as mediators of reactive
hyperemia in the human forearm. Forearm blood flow (FBF) was measured
with venous occlusion plethysmography following five minutes of
ischemia. In one protocol (n = 12) measurements were made before and
after intra-arterial administration of the nitric oxide synthase
inhibitor NG-monomethyl L-arginine [L-NMMA] to one forearm. In a
separate protocol (n = 7) measurements were made before and after
systemic administration of the cyclooxygenase inhibitor ibuprofen and
again after L-NMMA. L-NMMA reduced baseline FBF at rest (2.7 +/- 0.4
to 1.6 +/- 0.2 ml.100ml-1.min-1; P < 0.05), and had a modest
effect on peak forearm vascular conductance (FVC) and flow (FVC =
31.1 +/- 3.1 vs. 25.7 +/- 2.5, P < 0.05; FBF = 26.6 +/- 2.9 vs.
22.8 +/- 2.6, P = 0.055). Total excess flow above baseline during
reactive hyperemia was unaffected by L-NMMA (14.3 +/- 3.0 to 13.1 +/-
2.3 ml.100ml-1; P < 0.05). Ibuprofen did not change FBF at rest,
reduced peak FBF from 27.6 +/- 1.9 to 20.3 +/- 2.7 ml.100ml-1.min-1
(P < 0.05), but had no effect on total excess flow above
baseline. Infusion of L-NMMA after ibuprofen reduced FBF at rest by
40%, had no effect on peak flow, but reduced total excess flow above
baseline from 12.0 +/- 2.5 to 7.6 +/- 1.3 ml.100ml-1 (P < 0.05).
These data demonstrate that NO synthase inhibition has a modest
effect on peak vasodilation during reactive hyperemia, but plays a
minimal role later. Prostaglandins appear to be important
determinants of peak flow. The effects of NO synthase inhibition
during reactive hyperemia may also be potentiated by concurrent
cyclooxygenase inhibition.
Received 9 November 1995; accepted in final form 13 May 1996.
APS Manuscript Number A1181-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96