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Kinetic Study of Atrial Natriuretic Peptide in Patients with Idiopathic Dilated Cardiomyopathy: Evidence for Resistance to Biologic Effects of the Hormone Even in Patients with Mild Myocardial Involvement

Atrial natriuretic peptide (ANP) kinetics was studied in 12 patients with idiopathic dilated cardiomyopathy at different sodium excretion (30-175 mmol/day) and variable degrees of hemodynamic dysfunction [New York Heart Association (NYHA) class range I-III] to investigate whether differences in renewal and distribution of this hormone (as compared with those of a control group) play a role in pathogenesis and evolution of heart failure. [125I]Labeled ANP was injected as a bolus, and a high-performance liquid chromatography (HPLC) procedure was used to purify the labeled hormone in venous plasma samples collected for < or = 50 min after injection; the main ANP kinetic parameters were then derived from the disappearance curve of the labeled hormone. As in controls, a positive linear regression between ANP metabolic clearance rate (MCR, ml/min/m2) values and daily urinary excretion of sodium (NaUE, mmol/day) was noted in patients. The different linear regression coefficients between normal subjects (MCR = 365 +/- 8.08 NaUE, r = 0.986, p < 0.0001) and patients (MCR = 497 + 18.5 NaUE, r = 0.867, p = 0.001) indicate that in patients a higher peptide clearance rate is needed to obtain the same biologic effect (sodium excretion) and suggest that resistance to biologic effects of the hormone exists in patients at an early stage of disease (NYHA class I). When the efficiency of the ANP system in excreting sodium was expressed as the ratio of NaUE to ANP production rate (PR = MCR x ANP plasma concentration, microgram/day/m2) patients showed significantly lower values (p = 0.0126) than normal volunteers, thus confirming resistance to the hormone effects. Significantly lower values for ANP total distribution volume (16.5 +/- 8.4 L/m2), mean residence time in the sampling space (4.04 +/- 1.14 min), mean residence time in the body (7.25 +/- 2.13 min), and fewer recycles through the initial (sampling) space (0.27 +/- 0.16) were noted in patients, indicating an altered mechanism regulating distribution of the hormone. The positive correlations between ANP MCR (L/min/m2) values and cardiac index (CI, L/min/m2) (MCR = -1.24 + 1.17 CI, r = 0.689, p = 0.0092) and between initial distribution volume (IDV, L/m2) and CI (IDV = -11.2 + 6.85 CI, r = 0.730, p = 0.0046) in all patients indicate that hemodynamic factors contribute to the progressive reduction in MCR and IDV values throughout the progression of myocardial involvement.(ABSTRACT TRUNCATED AT 400 WORDS)