On the patterns of blood pressure, heart rate, and blood levels of noradrenaline and adrenaline during haemorrhage in the rat.

Mean arterial blood pressure (MAP), heart rate (HR), and blood levels of noradrenaline (NA) and adrenaline (A) were studied in Sprague-Dawley rats during haemorrhage. The bleeding was performed in different ways towards complete exsanguination or into a reservoir kept at a constant pressure of 35 mmHg. Awake, unstressed rats or rats anaesthetized with different anaesthetics were examined. Four different phases in the reaction patterns were observed during bleeding. The first phase with the parameters studied expected to be at steady state, was found to be very shortlasting. Only very small blood volumes could be drawn without giving signs of interference with sympathetic activity. The second phase with signs of increased sympathetic activity, as increased HR, also was very shortlasting. Thereafter the marked third phase followed with signs of evident sympathetic inhibition, involving marked decreases in MAP, HR, and blood levels of NA. The last period, phase four, showed signs of a second period of increased sympathetic activity with increased HR and blood levels of NA (and A). On bleeding into a reservoir for 4 h signs of all four phases could be observed.