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.
Cardiovascular and catecholamine response to clonidine in obese subjects / G., Zizzo; DEL RIO, Graziano; Me, Bonati; Ia, Macdonald; Velardo, Antonino. - In: INTERNATIONAL JOURNAL OF OBESITY. - ISSN 0307-0565. - 19:(1995), pp. 475-479.