Plasma cyclic nucleotides and plasma catecholamines before and after prolonged treatment with clonidine in hypertensive patients.
The effect of standing and physical exercise and catecholamines and cyclic nucleotides in plasma was measured in 8 patients with essential hypertension under standardized conditions before and after prolonged treatment with clonidine. Before clonidine medication noradrenaline, adrenaline and cyclic AMP (cAMP) increased in response to standing and bicycling for 20 min. No significant correlation was found between their absolute levels nor was the increase in cAMP following exercise correlated to the increase in noradrenaline. Standing and physical exercise were without effect on cyclic GMP (cGMP). Clonidine reduced the plasma noradrenaline concentration in supine position and the noradrenaline and the adrenaline response to standing and exercise. Plasma cAMP was uneffected by clonidine under basal conditions but the response to exercise was slightly reduced initially. During clonidine there was a positive correlation between the plasma levels of cAMP and noradrenaline following work. Clonidine produced an increase in plasma cGMP in supine position, immediately prior to bicycling and after 5 min of exercise.