Long-term octreotide treatment prevents vascular hyporeactivity in portal-hypertensive rats

Chronically portal-hypertensive rats show in vitro vascular hyporeactivity in large part mediated by the endothelium-derived vasodilator nitric oxide. We tested whether long-term octreotide treatment (15 micrograms/kg subcutaneously in 5% D/W, 8-hourly) corrects the in vitro vascular hyporeactivity. Increases in perfusion pressures (delta mm Hg) to potassium chloride (30-300 mmol/L) of in vitro perfused superior mesenteric arterial vascular beds of partial portal vein-ligated (PVL) rats were significantly (P < .05) higher in octreotide (n = 9) compared with placebo (n = 10, 5% D/W) treated animals. Octreotide significantly (P < .05) increased mean arterial pressure compared with placebo, the values being 129 +/- 3 and 117 +/- 4 mm Hg, respectively. Furthermore, a significant (P < .001) correlation was observed between in vitro vascular reactivity and mean arterial pressure. Incubation of separate vascular beds (n = 7 for both PVL and sham-operated rats) with octreotide (10(-6) mol/L) did not enhance pressure responses to 125 mmol/L potassium chloride, and failed to increase perfusion pressures in preconstricted vessel preparations (n = 6), excluding a direct inhibitory effect on NO. In summary, long-term octreotide treatment prevents in vitro vascular hyporeactivity in prehepatic portal-hypertensive rats, and octreotide does not exert its action through direct effects on endothelium-derived NO.