Effects of nicotinamide on sinoatrial conduction time and sinus node recovery time in rabbit hearts

The effects of nicotinamide (Nic) on sinoatrial conduction time (SACT) and sinoatrial node recovery time (SNRT) were studied in anesthetized rabbits and the isolated sinoatrial preparation of rabbit hearts by right atrium pacing techniques. In vivo, SNRT and corrected sinoatrial node recovery time (SNRTc) were markedly shortened after Nic administration (0.6 g/kg, iv) 12% (p<0.01) and 30% (p<0.01) respectively. In vitro, when the preparation was overdriven at a frequency about 20-30% or 40-45% above the intrinsic firing rate, Nic (33 mmol/L) induced 20% (p<0.01) or 24% (p<0.01) shortening of SNRT and 32% (p<0.05) or 36% (p<0.01) shortening of SNRTc. SACT tended to be shortened but insignificantly (p>0.05).