Acute changes in noradrenaline levels do not alter lymphocyte -adrenergic receptor concentrations in man

Abstract

Physiological means of elevating plasma catecholamines were characterised with respect to their effect on β-adrenergic catecholamine receptors in man. The noradrenaline content of plasma was determined by the single isotope enzyme method on blood samples from which lymphocytes were also isolated by centrifugation on ficol-hypaque density gradients. β-adrenergic catecholamine receptors were quantified by specific binding of (−)-[3H]-dihydroalprenolol to these cells, in which noradrenaline acts by stimulating β-adrenergic receptors. Nine subjects had supine blood pressure measurements and blood samples drawn every 20 min for 24 h for measurement of plasma noradrenaline (NA). Six of these subjects had blood samples collected for measurement of lymphocyte β-adrenergic receptor concentration over a 14 h period (0800 to 2200 h). Mean recumbent plasma NA levels were lowest at 0400 to 0600 h (126 to 150 pg·ml−1), rose sharply prior to awakening and reached peak concentrations at 0800 to 1100 h (280 to 340 pg·ml−1). There was also a rather sharp drop in plasma NA from 1600 h to 2200 h (290 to 210 pg·ml−1). There was an excellent correlation between blood pressure and plasma levels of NA throughout the 24 h of study. Despite periodic circadian changes in plasma NA over the 14 h sampling period (210 to 360 pg·ml−1) β-adrenergic receptor concentration of lymphocytes did not vary. In addition, basal supine NA levels and lymphocyte β-adrenergic receptor concentrations and their response to 2 h upright posture were examined in six normal volunteers. Plasma NA levels were significantly elevated after 10 min, reached peak levels two-fold greater than basal levels at 30 min, and remained elevated throughout 2 h of upright posture. During the 2 h of upright posture, lymphocyte β-adrenergic receptor concentration did not change. These results suggest that acute variations in plasma catecholamines over a physiological range are not associated with changes in receptor number.