Cardiovascular and catecholamine response to clonidine in obese subjects

OBJECTIVE: To investigate central alpha-2 adrenergic activity, one of the main inhibitory factors affecting norepinephrine secretion, in human obesity. DESIGN: Cardiovascular and catecholamine responses to clonidine (300 mu g per os) were evaluated in a group of obese subjects. SUBJECTS: 10 obese men (OM) and 14 obese women (OW). MEASUREMENTS: Mean arterial pressure, pulse rate, plasma norepinephrine (NE) and epinephrine (E) before and 120', 130', 140' after clonidine (CL) administration. RESULTS: The mean arterial pressure decreased after CL administration in obese patients (from 92 +/- 12 to 79 +/- 2 mmHg; P < 0.001) with no significant differences between OM and OW. The values of pulse rate were reduced in obese patients after clonidine (60 +/- 1 b/min vs 65 +/- 1 b/min before clonidine; P < 0.01) with no differences between OM and OW. Plasma E was not affected by the administration of clonidine and no sex related differences were found in the basal (OM: 0.23 +/- 0.03 vs OW: 0.15 +/- 0.03 nmol/L; P = NS) and in the post-CL E levels (OM: 0.22 +/- 0.02 vs OW: 0.14 +/- 0.03 nmol/L; P = NS). Basal plasma NE values were not different between OM (1.32 +/- 0.15 nmol/L) and OW (1.03 +/- 0.11 nmol/L; P = NS). Plasma NE decreased after CL in obese patients (from 1.20 +/- 0.10 to 0.59 +/- 0.08 nmol/L; P < 0.001) and a significant difference was found in the post-CL values between OM and OW (0.74 +/- 0.11 vs 0.40 +/- 0.06 nmol/L respectively; P < 0.01). The decrease in plasma NE was strongly correlated with the basal value of NE (r = 0.70; P < 0.001). The sex-related differences in plasma NE responses to clonidine in obese subjects did not differ with those previously observed in control subjects (P = NS). CONCLUSION: The cardiovascular and catecholamine response to CL in obese patients were similar to that previously observed in normal subjects, indicating a normal alpha-a adrenergic activity. The sex related difference in the NE response to CL, previously reported in normal subjects, was maintained in obese patients.