Effects of tilting in the anaesthetized and mechanically ventilated rat: a model of orthostatic hypotension.

The main of the present study was to determine the experimental conditions for an animal model of orthostatic hypotension based on tilting in rats. Blood pressure, heart rate and plasma catecholamine levels were measured before and after tilting in conscious and anaesthetized rats either breathing spontaneously or mechanically ventilated. In conscious rats, tilting did not alter arterial blood pressure, but increased heart rate and plasma catecholamine levels. In anaesthetized rats, tilting induced a drop in arterial blood pressure without any modification in plasma catecholamine concentrations. Mechanical ventilation significantly increased the postural hypotension and the percentage of rats showing a decrease in heart rate. Tyramine infusion increased plasma noradrenaline levels, and reduced or counteracted the postural hypotension and bradycardia. The results show that anaesthetized mechanically ventilated rats might constitute an appropriate model of orthostatic hypotension.