NICORANDIL AFFECTS DIURNAL RHYTHMS OF BODY-TEMPERATURE, HEART-RATE AND LOCOMOTOR-ACTIVITY IN RATS

The effects of nicorandil, a K+ channel opener with a potent vasodilat or action, on diurnal rhythms of body temperature, heart rate and loco motor activity were assessed in rats. Transmitters were intraperitonea lly implanted under ether anaesthesia. After recovery from surgery, bo dy temperature, heart rate and locomotor activity were recorded during control, saline or nicorandil (10 mg.kg(-1) administered orally) trea tment and for 5 days after treatment. For each period, Fourier analysi s determined the predominant rhythmicity for body temperature, heart r ate and locomotor activity while cosinor analysis assessed the corresp onding mesors, acrophases and amplitudes and maxima and minima were di rectly plotted from raw data. The results indicated: (1) loss of the d iurnal rhythmicity for all three rhythms after implantation; (2) stres s-induced modifications of almost all the characteristics of the three rhythms after saline and (3) a loss of diurnal rhythmicity of heart r ate after nicorandil, an effect that was not observed after saline and which was reversed when nicorandil administration was stopped. In con clusion, nicorandil perturbed the diurnal rhythmicity of heart rate wh ile the rhythmicity of body temperature and locomotor activity was not affected. (C) 1998 Elsevier Science B.V.