Supersensitivity to isoprenaline induced in rats by prolonged isolation.

1 The effect of isoprenaline on diastolic blood pressure and heart rate was determined in anaesthetized male rats which had been housed individually for 6-8 weeks after weaning, and compared with its effect in group-housed litter-mate controls.2 Isoprenaline caused a significantly greater fall in diastolic pressure in isolated rats and a greater increase in heart rate.3 Low doses of noradrenaline (5-10 ng) caused vasodepressor responses in isolated, but not in group-housed rats.4 The pressor response to noradrenaline, which was smaller in isolated rats, was increased to the level of group-housed controls by (+/-)-propranolol.5 Prolonged isolation of rats may bring about an increase in sensitivity of beta-adrenoceptors to isoprenaline and noradrenaline.