Cardiovascular and catecholamine responses to acute haemorrhage in anaesthetized potassium-adapted rats

The experiments were designed to determine whether potassium-loaded rats have a deficient recovery of blood pressure after a rapid arterial haemorrhage. Potassium loading was achieved by providing a 0.75% KCl solution as drinking fluid for 14 days, while control rats had either distilled water or tapwater. MAP, HR, Hct, and plasma electrolytes were determined before and after 1 and 2% body weight haemorrhage in anaesthetized Sprague-Dawley rats. Potassium-loaded rats had significantly reduced blood pressure recovery within 20 min after haemorrhage. HR was significantly reduced within 5 min only after 2% haemorrhage in potassium-adapted rats. Haemorrhage induced significant hyperkalaemia which was greater and significantly prolonged after 2% haemorrhage. The significant fall in Hct after haemorrhage was not affected by the magnitude of haemorrhage. In an additional group of rats, the pressor response to intravenous infusion of vasopressin was unaffected by potassium loading, whereas that to noradrenaline and angiotensin II was significantly reduced throughout the 20 min of infusion. The peak increase in blood pressure after phenylephrine injection was, however, unaffected by potassium loading. Basal plasma catecholamines concentration as well as concentrations after 1% haemorrhage were unaffected by potassium loading. It is concluded that the reduced vascular response to noradrenaline and angiotensin contributed to the reduced recovery of blood pressure after haemorrhage in potassium-loaded rats. Furthermore, the result with phenylephrine suggest a mechanism that is unrelated to direct vascular effects of noradrenaline and angiotensin II.