Vascular actions of octreotide in the portal hypertensive rat.

1 We have investigated the actions of the somatostatin analogue octreotide in the portal hypertensive Wistar rat in vivo and in rat small mesenteric artery and aorta in vitro. 2 In small mesenteric artery, octreotide (0.1–0.3 μM) failed to produce any direct contraction, nor did it affect contractions to noradrenaline (NA, 10 μM) or endothelium-dependent relaxations to acetylcholine. 3 In rat aorta, octreotide (0.3 μM) and somatostatin (1 μM) failed to affect contractions to NA (1 μM), or concentration-contractile response curves to NA. 4 In rat vas deferens, octreotide and somatostatin significantly reduced contractile responses to electrical stimulation with pD2 values (−log IC50) of 8.19±0.10 (n=4) and 8.16±0.26 (n=4), respectively. Hence, the lack of effect of these agents in aorta or mesenteric artery was not due to lack of efficacy or inappropriate choice of concentration. 5 In the anaesthetized portal hypertensive rat, intravenous injection of octreotide (1–100 μg kg−1) did not significantly affect systemic blood pressure, nor did it affect mesenteric vascular conductance as measured by laser doppler flow probes. However, octreotide (100 μg kg−1) significantly reduced vascular conductance to 74.2±7.7% of control (n=6) in porto-systemic shunt vessels as measured by laser doppler flow probes. 6 Phenylephrine (1 μg kg−1) significantly raised blood pressure and significantly decreased vascular conductance in both mesenteric (66.6±3.7% of control) and porto-systemic shunt vessels (58.7±10.0% of control). 7 It was concluded that octreotide has selective effects on porto-systemic shunt vessles in vivo in the portal hypertensive rat. British Journal of Pharmacology (1997) 122, 698–702; doi:10.1038/sj.bjp.0701444