Cardiovascular effects of different schedules of nicotine administration on spinal rats: influence of pentobarbital

This work examined the cardiovascular effects of different schedules of i.v. nicotine administration with respect to doses and timing in non-anesthetized and pentobarbital-treated spinal rats. For this purpose, complete nicotine dose-response curves were made for mean arterial pressure and heart rate. In non-anesthetized spinal rats, tachyphylaxis was not found for the pressor effects; moreover, consecutive doses, given at short intervals, produced additive actions. Furthermore, nicotine produced a biphasic heart rate response: an initial and brief bradycardia followed by a longer lasting tachycardia. In pentobarbital-treated rats, the sensitivity of the cardiovascular system to nicotine was decreased; in these rats, consecutive nicotine doses did show tachyphylaxis for the pressor and tachycardiac responses. The present series of experiments, using different schedules of administration for single and consecutive nicotine doses, demonstrated opposite tachyphylactic effects in non-anesthetized and in pentobarbital-treated spinal rats.