Cardiovascular and abdominal motor responses evoked by intravenous neurotensin in guinea pigs.

The intravenous (IV) infusion of neurotensin (NT) in anesthetized guinea pigs was found to elicit dose-dependent increases of systemic blood pressure (BP) and of heart rate (HR), accompanied by abdominal motor responses consisting in transient, twitch-like contractions of the abdominal wall (TAWC), and a slowly developing, relatively sustained increase of the basal abdominal wall tension (AWT). The TAWC responses were inhibited in animals pretreated with pancuronium, morphine, clonidine, and CP-96,345 [a neurokinin (NK) antagonist], were potentiated by naloxone, but were not modified by atropine or prior (30 s) intraperitoneal (IP) injection of lidocaine. The BP increases caused by IV NT were reduced by clonidine and by IP lidocaine only. The HR increases were attenuated by morphine and clonidine only. Increases of the basal AWT were resistant to all drug treatments and were attributed to a passive stretch of the abdominal wall caused by cecal distension. No defecation was observed in any of the animals given IV NT. These results were interpreted as an indication that the pressor and TAWC responses to IV NT represent an integrated nociceptive response likely to be triggered in part by NT-induced activation of abdominal visceral afferents. A NK acting through NK-1 receptors may participate in TAWC responses to IV NT.