ARTERIAL SPONTANEOUS RHYTHMIC CONTRACTILE ACTIVITY IN HUMANS AND RATS- SPECTRAL-ANALYSIS AND REGULATORY MECHANISMS

Objective: Many experimental observations have demonstrated the presen ce of spontaneous cyclic vasomotor activity (CVA) in large and small a rteries. This study aimed to evaluate the characteristics of spontaneo us CVA in rat and human resistance arteries, and to investigate its po ssible interference with the evaluation of sympathetic activity by mea ns of spectral analysis of blood pressure in vivo. Design and results: In study 1 we examined small mesenteric arteries of spontaneously hyp ertensive rats and Wistar-Kyoto rats, as well as smalt omental arterie s of normotensive subjects and hypertensive patients (Mulvany and Halp ern technique). CVA was enhanced by the agonists of nitric oxide relea se, and was abolished by the inhibitors of nitric oxide or cyclic GMP synthesis. A potassium channel, which is barium- and zinc-sensitive an d tetraethylammonium-insensitive, seems to play a crucial role in the genesis of CVA. In rats and in humans the frequency of CVA fell exactl y in the frequency band ('low frequencies') of power spectral analysis of blood pressure usually considered to be an 'index of sympathetic a ctivity'. In study 2, a power spectral analysis of blood pressure vari ability before and after intra-arterial infusion of noradrenaline or a cetylcholine was performed in 18 patients with mild-to-moderate hypert ension. The absolute and normalized spectral power of the low-frequenc y systolic blood pressure peak increased remarkably after noradrenalin e and acetylcholine infusion, while its central frequency shifted from 0.10 Hz to approximately 0.06 Hz, exactly the frequency of CVA observ ed in vitro. Conclusions: A potassium channel appears to be involved i n the genesis of CVA. Also, CVA might contribute to the blood pressure variability independently of the autonomic nervous system activity, a nd thus probably plays a role in the genesis of the low-frequency peak in the rat and in humans.