1. Blood volume, total exchangeable sodium and the effects of head-up tilt on plasma noradrenaline were studied in 10 normotensive and 11 hypertensive renal transplant recipients. The blood pressure and heart rate responses to infused noradrenaline and isoprenaline were measured.
2. Blood volume and total exchangeable sodium were significantly greater in hypertensive than in normotensive patients.
3. Resting plasma noradrenaline was significantly higher in both groups of transplantees than in normal subjects, but was similar in normotensive and hypertensive patients.
4. Plasma noradrenaline rose in normotensive but not hypertensive patients in response to head-up tilt.
5. The rise in blood pressure in response to infused noradrenaline was significantly greater in hypertensive than in normotensive transplantees. Both groups of patients showed similar responses to infused isoprenaline.
6. Extracellular fluid volume expansion associated with increased α-receptor sensitivity to noradrenaline may contribute to hypertension in renal transplant recipients.