Spermidine and cardiovascular control in nucleus tractus solitarii in rat.

Cardiovascular effects elicited by unilateral microinjection of polyamines into the nucleus tractus solitarii (NTS) were tested in anesthetized rats. Spermidine (50-900 pmol) produced dose-dependent depressor and bradycardiac responses that were similar to those elicited by N-methyl-D-aspartate (NMDA; 0.1-1.2 pmol). The polyamines, putrescine and spermine, did not produce significant cardiovascular responses. The cardiovascular responses induced by spermidine and NMDA were almost eliminated by prior injection of the noncompetitive NMDA antagonist MK801 into NTS. On the other hand, a competitive antagonist 2-amino-5-phosphonovaleric acid (APV) blocked responses to NMDA but only attenuated those to spermidine. These findings support an action of the polyamine spermidine at the NMDA receptor complex in NTS where it could participate in modulating cardiovascular activity.