Background
During cerebral angiography, intracarotid infusion of sodium nitroprusside (SNP), an endothelium-independent nitric oxide donor, fails to increase cerebral blood flow (CBF) of human subjects. A confounding effect of intracranial pathology or that of radiocontrast could not be ruled out in these experiments. The authors hypothesized that, if nitric oxide was a significant regulator of CBF of primates, then intracarotid SNP will augment CBF of baboons.
Methods
In studies, CBF (intraarterial (133)Xe technique) was measured in healthy baboons during isoflurane anesthesia at (1) baseline and during (2) induced hypertension with intravenous phenylephrine, (3) concurrent infusions of intravenous phenylephrine and intracarotid SNP, and (4) intracarotid verapamil (positive control drug). In studies, the authors measured tissue cyclic guanosine monophosphate (cGMP) by radioimmunoassay after incubating vascular rings obtained from freshly killed baboons (1) with increasing concentrations of SNP and (2) after SNP exposure following preincubation with the radiocontrast agent, iohexhol.
Results
In the studies, coinfusion of intravenous phenylephrine and intracarotid SNP did not increase CBF. However, intracarotid verapamil significantly increased CBF (from 26 +/- 7 to 43 +/- 11 ml x 100 g(-1) x min(-1); P < 0.0001) without a change in mean arterial pressure. In the studies, incubation of intracranial arterial rings in SNP resulted in dose-dependent increases in cGMP concentrations. A similar increase in cGMP content was evident despite iohexhol preincubation.
Conclusions
Collectively, these results suggest that, in healthy baboons, intracarotid SNP does not decrease arteriolar resistance, although SNP could affect proximal arterial tone, as demonstrated by the increase in cGMP content of these vessels.
Reciprocal effects of interleukin‐4 and interferon‐γ on immunoglobulin E‐mediated mast cell degranulation: a role for nitric oxide but not peroxynitrite or cyclic guanosine monophosphate
