Effects of swim training alone and in combination with clonidine and rilmenidine on blood pressure, plasma electrolytes, vasopressin, and renin activity in spontaneously hypertensive rats.

Adaptations to the effects of clonidine (CL) and rilmenidine (R) were studied during a 12-week training program (swimming) in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Systolic blood pressure (SBP) was regularly measured during this period. Body weight (BW) was determined at the beginning and at the 12th week. Plasma parameters, cardiac determinations, vasopressin (pAVP), and plasma renin activity (PRA) were measured only at the end of the experiment. Both SBP and ponderal benefit were reduced by CL, R, and training. Contrary to beta-adrenoceptor blocking agents, we found no inhibition of the beneficial effect on SBP of training in combination with CL or R. Plasma and hypothalamic vasopressin were reduced by both drugs but only CL increased plasma renin activity (PRA) although its mechanisms of action are still not clearly understood. Our results suggest that CL and R as well as swim training can be considered as an effective countermeasure in SHR. Moreover, the heterogeneity of action of CL and R on some of the parameters tested is in favor of different pharmacological properties for these drugs.