CHARACTERIZATION OF A MAJOR SLOW OSCILLATION IN THE MESENTERIC CIRCULATION OF CONSCIOUS RATS

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Abstract
SUMMARY: 1. Little is known about spontaneous slow rhythms in regional circulations. The present study was aimed at characterizing low‐frequency (LF; 78–269 mHz) oscillations in the mesenteric and hindquarter circulations of conscious rats.2. Mean arterial pressure (MAP) and indices (pulsed Doppler technique) of mesenteric (n= 25) and hindquarter (n= 23) blood flows were recorded in conscious, freely moving rats during 1 h periods. Fast Fourier transform analysis was applied to beat‐to‐beat data after resampling at 10 Hz of consecutive 205 s time series.3. A major oscillation centred at 164±4mHz was present in the mesenteric, but not in hindquarter, circulation. Consequently, LF power accounted for approximately 43% of the overall variability of mesenteric blood flow. Cross‐spectral analysis performed between MAP and mesenteric blood flow indicated that fractional changes in flow were approximately two‐fold of those in MAP, in pressure, at the peak frequency.4. Acute blockade of the autonomic, renin‐angiotensin and vasopressin systems combined with noradrenaline infusion (n= 7) reduced the frequency of the mesenteric blood flow oscillation (115 ± 6 mHz) but did not change its contribution to overall flow variability (approximately 48%). A clear oscillation was still present after acute inhibition of nitric oxide (NO) synthesis with NG‐nitro‐l‐arginine methyl ester (n= 8), but was virtually absent in chronically guanethidine‐sympathectomized rats (n= 12).5. In conclusion, the mesenteric blood flow of conscious rats exhibits a major slow oscillation that originates in the mesenteric vasculature and is not secondary to the activity of the major pressor systems or to the cyclic release of NO. Because of the strong attenuation of the oscillation in sympathectomized rats, we suggest that adrenergic vasoconstrictor tone plays a permissive role in its genesis.