OBJECTIVE This study evaluated the dependence of portal and mesenteric blood flow and plasma glucagon levels on octreotide dosage and its mode of application. METHODS Two groups of 10 individuals each received octreotide either subcutaneously (placebo, 100 and 200 microgram) or intravenously (100- microgram bolus i.v., 25 and 100 microgram/h) in a double-blind, random order. Using Doppler ultrasound, we examined portal and mesenteric blood flow and measured plasma glucagon levels at regular intervals within a 4-hour period under fasting conditions. RESULTS Contrary to placebo, octreotide caused a decrease in portal blood flow (PVF) and in superior mesenteric artery blood flow (SMAF) together with an increase in the mesenteric pulsatility index (PI). The same total dose of 100 microgram octreotide caused a similar PVF response, averaged over 4 h, given either subcutaneously (-28.0 +/- 4.8%), intravenously (-29.4 +/- 4.3%) or as a continuous infusion (-29.3 +/- 4.6%). As concerns intravenous infusions, 100 microgram/h was more effective than 25 microgram/h (-37.8 +/- 6.2 vs. -29.3 +/- 4.6%). The PVF reduction remained constant during intravenous infusion, whereas glucagon levels decreased progressively over the entire observation time. CONCLUSIONS The decrease in PVF is dependent on the octreotide dose. However, this is not constantly paralleled by a decrease in plasma glucagon concentration.