Very low frequency blood pressure variability is modulated by myogenic vascular function and is reduced in stroke-prone rats.

BACKGROUND

Cerebrovascular myogenic function, which protects the brain from hemorrhagic stroke, is impaired in stroke-prone spontaneously hypertensive rats. Furthermore, myogenic function contributes to very low frequency blood pressure variability and dynamic autoregulation of cerebral blood flow is most effective at very low frequency in rats. Therefore, we hypothesized that very low frequency blood pressure variability is reduced in stroke-prone spontaneously hypertensive rats compared with stroke-resistant spontaneously hypertensive rats. In addition, we investigated if myogenic function also contributes to very low frequency blood pressure variability in conscious dogs.

METHODS

In 8-week-old normotensive Wistar-Kyoto rats, 8-week-old and 15-week-old stroke-prone spontaneously hypertensive rats and stroke-resistant spontaneously hypertensive rats, and dogs, blood pressure variability was studied during control conditions, inhibition of myogenic function (nifedipine) and hypotension induced by sodium nitroprusside. In dogs, transfer function analysis between blood pressure and total peripheral resistance was performed to study the contribution of myogenic function to blood pressure variability.

RESULTS

Inhibition of myogenic function, but not hypotension induced by sodium nitroprusside, significantly reduced very low frequency variability of systolic blood pressure (rats: 0.02-0.2 Hz; dogs: 0.02-0.075 Hz) in conscious rats and dogs. In dogs, the gain of the transfer function was high (0.28 +/- 0.04 min/l) in the very low frequency band and was decreased to 0.11 +/- 0.01 min/l (P < 0.05) by nifedipine but not by sodium nitroprusside (0.26 +/- 0.02 min/l). Very low frequency blood pressure variability was significantly smaller in stroke-prone spontaneously hypertensive rats than in stroke-resistant spontaneously hypertensive rats (8 weeks of age: 7.8 +/- 1.1 vs. 13.1 +/- 2.2 mmHg; P < 0.05; 15 weeks of age: 7.1 +/- 1.2 vs. 16.5 +/- 3.6 mmHg; P < 0.05).

CONCLUSION

Myogenic function affects very low frequency blood pressure variability in conscious rats and dogs. The smaller very low frequency blood pressure variability in stroke-prone spontaneously hypertensive rats compared with stroke-resistant spontaneously hypertensive rats suggests that impaired cerebrovascular myogenic function is reflected in reduced very low frequency blood pressure variability.