Short-term and long-term blood pressure and heart rate variability in the mouse

Knowledge on murine blood pressure and heart rate control mechanisms is Lim ited. With the use of a tethering system, mean arterial pressure (MAP) and pulse interval (PI) were continuously recorded for periods up to 3 wk in Sw iss mice. The day-to-day variation of MAP and PI was stable from 5 days aft er surgery. Within each mouse (n = 9), MAP and PI varied by 21 +/- 6 mmHg a nd 17 +/- 4 ms around their respective 24-h averages (97 +/- 3 mmHg and 89 +/- 3 ms). Over 24-h periods, MAP and PI were bimodally distributed and clu stered around two preferential states. Short-term variability of MAP and PI was compared between the resting (control) and active states using spectra l analysis. In resting conditions, variability of MAP was mainly confined t o frequencies <1 Hz, whereas variability of PI was predominantly linked to the respiration cycle (3-6 Hz). In the active state, MAP power increased in the 0.08- to 3-Hz range, whereas PI power fell in the 0.08- to 0.4-Hz rang e. In both conditions, coherence between MAP and PI was high at 0.4 Hz with MAP leading the PI fluctuations by 0.3-0.4 s, suggesting that reflex coupl ing between MAP and PI occurred at the same frequency range as in rats. Sho rt-term variability of MAP and PI was studied after intravenous injection o f autonomic blockers. Compared with the resting control state, MAP fell and PE increased after ganglionic blockade with hexamethonium. Comparable resp onses of MAP were obtained with the alpha-blocker prazosin, whereas the bet a-blocker metoprolol increased PI similarly. Muscarinic blockade with atrop ine did not significantly alter steady-state levels of MAP and PI. Both hex amethonium and prazosin decreased MAP variability in the 0.08- to l-Hz rang e. In contrast, after hexamethonium and metoprolol, PI variability increase d in the 0.4- to 3-Hz range. Atropine had no effect on MAP fluctuations but decreased those of PI in the 0.08- to 1-Hz range. These data indicate that , in mice, blood pressure and its variability are predominantly under sympa thetic control, whereas both vagal and sympathetic nerves control PI variab ility. Blockade of endogenous nitric oxide formation by N-G-nitro-L-arginin e methyl ester increased MAP variability specifically in the 0.08- to 0.4-H z range, suggesting a role of nitric oxide in buffering blood pressure fluc tuations.