Autonomic nervous system and adrenergic receptors in chronic hypotensive haemodialysis patients.

increased plasma catecholamine levels induced an a 2 and b 2 -adrenoceptor downregulation. This downregulBackground. The pathophysiology of chronic hypotension (CH ) in uraemia is not elucidated. The possible ation may play a role in the reduced cardiovascular responses to adrenergic stimuli reported in hypotensive role of autonomic nervous system dysfunction and adrenoceptor alterations in the pathophysiology of CH HD patients. in uraemia was evaluated in this study. Methods. Seventeen hypotensive haemodialysis ( HD) ceptors; chronic hypotension; chronic renal failure; patients, 17 normotensive HD patients, and 17 control haemodialysis subjects were studied. We evaluated the integrity of the baroreflex arc ( Valsalva manoeuvre), the parasympathetic eerent pathway (‘deep-breathing test’) and the sympathetic eerent pathway (‘hand-grip test’). We Introduction also evaluated platelet a 2 -adrenoceptor and lymphocyte b 2 -adrenoceptor densities (radioligand binding Hypertension is a common manifestation of chronic assay), and b 2 -adrenoceptor response (intracellular renal failure (CRF ), and is a major risk factor for the cAMP generation after isoproterenol stimulation in excessive cardiovascular morbidity and mortality in lymphocytes). uraemic patients. In contrast, a small subset of dialysis Results. Responses to the Valsalva manoeuvre and the patients develop chronic hypotension, defined as a deep-breathing test were altered in all HD patients systolic blood pressure lower than 100 mmHg between (P<0.05). Valvalva ratio was lower in hypotensive dialysis sessions. Although the pathophysiology of patients than in normotensive patients (P<0.01), chronic hypotension in uraemic patients is unknown, whereas the pressor response to the hand-grip test was several mechanisms have been implicated: the autoreduced only in hypotensive HD patients (P<0.01). nomic neuropathy often present in uraemia [1], an In haemodialysed patients, basal mean blood pressure impaired vascular adrenoceptor function [2 ], or a ( MBP) correlated with MBP increases during the hand- decreased vascular response to angiotensin II (AII ) grip exercise (r=0.59, P<0.01). infusion secondary to a reduced AII receptor number Plasma catecholamine levels were elevated in both [3], and others. groups of patients (P<0.025). Plasma adrenaline levels An autonomic nervous system (ANS ) dysfunction were higher in hypotensive HD patients than in normo- has been widely recognized in patients with CRF tensive patients (P<0.05). a 2 - and b 2 -adrenoceptor undergoing haemodialysis ( HD) [4]. This autonomic densities and b 2 -adrenoceptor response were reduced neuropathy is more pronounced in uraemic patients in hypotensive patients (P<0.05 vs normotensive with chronic hypotension, suggesting that the autopatients). MBP correlated with a 2 -adrenoceptor nomic dysfunction is involved in the pathophysiology (r=0.46, P<0.01) and b 2 -adrenoceptor (r=0.43, of this disorder [1 ]. On the other hand, plasma catechoP<0.025) densities in HD patients. lamine levels are increased in haemodialysed patients Conclusions. Normotensive haemodialysed patients [2,5], suggesting that the sympathetic activity is have increased plasma catecholamine levels with pre- increased in these patients. Although plasma catecholaserved a 2 - and b 2 -adrenoceptor numbers, as well as b 2 - mine levels in uraemic patients cannot be considered a adrenoceptor responses. In hypotensive patients, reliable index of sympathetic activity, recent studies plasma adrenaline levels were even higher; the using microneurographic techniques confirmed that