| Title | Effects of the nitric oxide synthase inhibitor L-NMMA on cerebrovascular and cardiovascular responses to hypoxia and hypercapnia in humans. | | Author(s) | Ide K, Worthley MI, Anderson TJ, Poulin MJ | | Institution | University of Calgary. | | Source | J Physiol 2007 Aug 2. | | Abstract | Objective: Cerebral blood flow is highly sensitive to alterations in arterial PO2 and PCO2. In humans, the extent to which nitric oxide (NO) is involved in this regulation is unclear. We hypothesized that the NO synthase (NOS) inhibitor, L-NMMA, attenuates the sensitivity of middle cerebral artery blood velocity (VP) to isocapnic hypoxia (end-tidal PO2 = 50 Torr) and euoxic hypercapnia (end-tidal PCO2 = +9 Torr above resting values) in 10 volunteers (age=28.7+/-1.3 years, height=179.2+/-2.4 cm, weight=78.0+/-3.7 kg; mean+/-SEM).
Methods: The techniques of transcranial Doppler ultrasound and dynamic end-tidal forcing were used to measure VP, and control end-tidal PO2 and end-tidal PCO2, respectively.
Results: At baseline (isocapnic euoxia), following intravenous administration of L-NMMA, mean arterial blood pressure (MAP) increased (76.3 +/-7.3 to 86.2+/-9.4 mmHg) and heart rate (HR) decreased (59.5+/-9.0 to 55.2+/-9.5 beats min-1) but VP was unchanged. Hypoxia-induced increases in MAP, HR and VP were similar with and without L-NMMA (5.0+/-0.7 vs 7.1+/-1.0 mmHg, 11.5+/-1.4 vs 12.4+/-1.5 beats min-1, 6.5+/-0.8 vs 6.6+/-0.8 cm s(-1) for DeltaMAP, DeltaHR, DeltaVP, respectively). Hypercapnia-induced increases in MAP, HR and VP were similar with and without L-NMMA (7.4+/-3.1 vs 8.1+/-2.2 mmHg, 10.4+/-4.6 vs 10.0+/-4.2 beats min(-1), 16.5+/-1.5 vs 17.6+/-1.5 cm s(-1) for DeltaMAP, DeltaHR, and DeltaVP, respectively) but the sensitivity of the of VP response at the removal of hypercapnia was attenuated with L-NMMA.
Conclusion: In young healthy humans, pharmacological blockade of nitric oxide synthesis does not affect the increases in cerebral blood flow with hypoxia and hypercapnia, suggesting that nitric oxide is not required for the cerbrovascular responses to hypoxia and hypercapnia. | | Language | ENG | | Pub Type(s) | JOURNAL ARTICLE
| | PubMed ID | 17673507 |
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