1: Am J Physiol. 1999 Apr;276(4 Pt 2):R1087-94. 

Contribution of endogenous carbon monoxide to regulation of diameter in
resistance vessels.

Kozma F, Johnson RA, Zhang F, Yu C, Tong X, Nasjletti A.

Department of Pharmacology, New York Medical College, Valhalla, New York 10595,
USA.

Endogenous carbon monoxide was proposed to subserve vasodepressor functions. If
so, inhibition of heme oxygenase may be expected to promote vascular
contraction. This hypothesis was examined in large and small arteries and in
isolated first-order gracilis muscle arterioles of rat. The heme oxygenase
inhibitors chromium mesoporphyrin (CrMP) and cobalt protoporphyrin (0.175-102
micromol/l) decreased the diameter of pressurized (80 mmHg) gracilis muscle
arterioles, whereas magnesium protoporphyrin, a weak heme oxygenase inhibitor,
did not. CrMP also elicited development of isometric tension in the muscular
branch of the femoral artery but not in the aorta or femoral artery. Arteriolar
constrictor responses to CrMP varied in relation to the intravascular pressure,
were blunted in preparations exposed to exogenous carbon monoxide (100
micromol/l), and were unaffected by an endothelin receptor antagonist.
Importantly, CrMP amplified the constrictor response to increases of pressure in
gracilis arterioles. Accordingly, the constrictor effect of heme oxygenase
inhibitors is attributable to magnification of myogenic tone due to withdrawal
of a vasodilatory mechanism mediated by endogenous carbon monoxide. The study
suggests that the vascular carbon monoxide system plays a role in the regulation
of basal tone in resistance vessels.

PMID: 10198389 [PubMed - indexed for MEDLINE]