Acute regulation of lymphocyte beta 2-adrenoceptors is altered in patients with essential hypertension

Abstract

The effects of acute stimulation of the sympathetic activity by dynamic exercise on lymphocyte beta 2-adrenoceptor density [assessed by (-)-125iodocyanopindolol (ICYP) binding] and responsiveness [10 mumol/l isoprenaline-induced cyclic adenosine monophosphate (cAMP) increases] were studied in 10 normotensive (Pdiast < 90 mmHg) volunteers and in 10 patients with established essential hypertension (Pdiast > 95 mmHg). In normotensives, dynamic exercise on a bicycle (80% of maximum heart rate) for 15 min led to an increase in lymphocyte beta 2-adrenoceptor density from 1080 +/- 77 to 2033 +/- 152 ICYP binding sites/cell; concomitantly isoprenaline-induced increase in lymphocyte cAMP was enhanced. This effect appears to be mediated by beta 2-adrenoceptor stimulation, since the exercise-induced increase in beta 2-adrenoceptor density was markedly attenuated by pretreatment of the volunteers with propranolol (5 mg intravenously 45 min before exercise), but not by pretreatment with the beta 1-selective antagonist bisoprolol (2.5 mg intravenously 30 min before exercise). In patients with essential hypertension, lymphocyte beta 2-adrenoceptor density (1512 +/- 101 ICYP binding sites/cell) was significantly higher than in controls (P < 0.05); the same held true for isoprenaline-induced cAMP increases. In these patients, however, dynamic exercise caused only a slight increase in lymphocyte beta 2-adrenoceptor density (to 1859 +/- 154 ICYP binding sites/cell) and in isoprenaline-induced cAMP increases. From these results it is concluded that in essential hypertension acute regulation of the beta-adrenoceptor/adenylate cyclase system is impaired.