USE OF NONLINEAR METHODS TO ASSESS EFFECTS OF CLONIDINE ON BLOOD-PRESSURE IN SPONTANEOUSLY HYPERTENSIVE RATS

In spontaneously hypertensive rats (SHR), chronic infusion of clonidin e failed to decrease blood pressure and blood pressure variability. We used nonlinear methods to get a deeper insight on the effects of clon idine on blood pressure dynamics. For 24 h and 4 wk, clonidine (0.1 mg .kg(-1).day(-1) sc) was infused by minipumps in the conscious SHRs, an d, for comparison, a vehicle was infused in SHRs and in Wistar-Kyoto r ats. Blood pressure was recorded for 30 min before and after treatment s. We used the Lyapunov exponent, approximated by the inverse of the l (max) index derived from the recurrence plot method, to characterizcha racterize nonlinear dynamics. Before treatment, l(max) index of blood pressure was lower (P < 0.01) in the SHRs than in the Wistar-Kyoto rat s. Clonidine significantly increased l(max) (P < 0.01) to the level ob served in normotensive rats, at 24 h and up to 4 wk after infusion. We conclude that clonidine has a significant chronic effect on blood pre ssure dynamics, as evidenced by nonlinear methods. Our study also sugg ests that the mechanisms governing blood pressure variations are nonli near.