Vasopressin reverses mesenteric hyperemia and vasoconstrictor hyporesponsiveness in anesthetized portal hypertensive rats.

We recently reported that vasopressin analogues correct the in vitro vascular hyporeactivity to adrenergic vasoconstrictors in portal hypertensive rats. The aim of the present study was to determine whether vasopressin reduces splanchnic blood flow in portal vein-ligated (PVL) rats by restoring vasoconstrictor responsiveness in vivo. The ultrasonic transit time-shift technique was used for blood flow measurements. At basal conditions, blood flow through the superior mesenteric artery was elevated 1.6-fold in PVL rats as compared with sham-operated (SHAM) control rats. PVL rats also exhibited blunted mesenteric constrictor responses to the adrenoceptor agonist, phenylephrine (0.03-1 micromol x min(-1) x kg(-1)). Terlipressin (2-20 microg x k(-1)) and arginine vasopressin (3-300 pmol x min(-1) x kg(-1)) dose-dependently reduced, and at the highest doses, even abolished, the difference in mesenteric blood flow (MBF) between PVL and SHAM rats. When expressed as percent changes relative to baseline, mesenteric arterial responses to terlipressin and arginine vasopressin were found to be enhanced in PVL rats as compared with SHAM rats. Moreover, pretreatment with terlipressin (20 microg x kg(-1)) reversed the mesenteric hyporesponsiveness to phenylephrine of PVL rats. These vasopressin effects were independent of the nitric oxide (NO) pathway, because they were not mimicked by inhibition of NO synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME) (0.1-10 mg x kg(-1)). These data indicate that pharmacological doses of vasopressin reverse the splanchnic hyperemia by restoring the responsiveness to adrenergic vasoconstrictors in portal hypertensive rats.