Spontaneous variations in arterial blood pressure, heart rate and sympathetic nerve activity in conscious normotensive and spontaneously hypertensive rats.

In the present study we have recorded spontaneous variations in mean arterial blood pressure (MAP), heart rate (HR) and mean rectified splanchnic nerve activity (SNA) in conscious undisturbed normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The variability in blood pressure was not significantly different but HR variability tended to be lower in SHR. The variability in SNA expressed as % change from mean value was not significantly different between SHR and WKY. By computer techniques the correlation between HR, MAP and SNA could be calculated during spontaneous variations of these parameters. The slope of the regression line correlating HR and SNA was significantly steeper in SHR than in WKY (0.73, 0.47 resp.). Thus a certain change in HR was associated by a greater change in SNA in SHR compared with WKY. Spontaneous changes in SNA could be divided in principally two different patterns. One typical pattern was a rise in SNA in parallel with a drop in MAP. This pattern was most likely triggered by the arterial baroreceptors and was called a "baroreceptor-pattern". Marked spontaneous excitations in SNA and HR was also observed during natural behaviours such as eating, drinking and explorative behaviour, a so called "centrally mediated pattern".