Adrenaline and stress-induced increases in blood pressure in rats

Stress was induced by immobilizing the hind limbs of rats for 12 days and housing the rats in individual cages. Control rats were housed in groups without immobilization. Blood pressure and heart rate were measured through an indwelling carotid cannula. After 10 and 12 days of immobilization and isolation, the stressed rats had significantly higher blood pressures (ca. 10 mmHg) and higher cardiac adrenaline levels (ca. 90%). After adrenal medullectomy cardiac adrenaline levels were markedly reduced in both stressed and control rats. Furthermore, the stressing procedure did not cause a rise in blood pressure in adrenal-medullectomized rats. Desipramine HCl (2 mg/kg per day), administered orally to block the neuronal uptake of adrenaline, prevented the elevation in blood pressures and cardiac adrenaline levels. Propranolol HCl (2.8 mg/kg per day), orally, also prevented the rise in blood pressure. The results are consistent with the hypothesis that activation of facilitatory prejunctional beta-adrenoceptors on sympathetic nerves by neuronally-released adrenaline may be responsible for the raised blood pressure.