Neurotensin-induced contractions in venous smooth muscle

Synthetic neurotensin was shown to be a powerful contractant of the isolated rat portal vein. Concentration-dependent increases in basal tension and frequency of spontaneous contractions were obtained in response to single dose (10-1000 nM, final bath concentrations). The responses reached maxima within 2 min and differed in this respect from comparable responses to angiotensin II, substance P and bradykinin, which were maximal after 2-4 min. The "apparent affinity" for neurotensin (pD2 = 7.5 +/- 0.3, S.D., n = 10) was about 10 times less than for angiotensin II while higher than for both the other peptides and for norepinephrine. The "intrinsic activity" was 0.75 (+/- 0.13, S.D., n = 6) relative to angiotensin II during the first 2 min of the response. A pronounced degree of tachyphylaxis was observed; repetition of the neurotensin dose at the lower range of concentrations (1-10 nM) within 2-4 min was completely ineffective. The results suggest that there is a specific neurotensin receptor in the tissue and that neurotensin-induced contractions may play a part in redistributing the blood flow in the gastrointestinal region following release of this peptide from the ileum into the portal circulation.