Somatostatin causes vasoconstriction, reduces blood flow and increases vascular permeability in the rat central...

Using radiolabeled microspheres, spinal cord blood flow was measured after spinal subarachnoid injections of 3.1- to 12.5-nmol doses of somatostatin through either indwelling i.t. catheters or acutely inserted intervertebral needles. With either injection technique, somatostatin caused significant dose-dependent reductions in thoracic and lumbosacral blood flow that could be partially blocked by a 5-min preinjection of the somatostatin receptor antagonist cyclo[7-aminoheptanoyl-Phe-D-Trp-Lys-Thr(Bzl)], which has previously been shown to block the hindlimb flaccidity produced by these doses of somatostatin in conscious rats. The duration of these blood flow changes were appreciably less in the rats injected through indwelling i.t. catheters. Somatostatin-induced reductions in spinal cord perfusion were accompanied by transient pressor responses, reduced cardiac output, 3-fold increases in spinal cord cerebrospinal fluid lactic acid concentrations and breakdown of the blood-spinal cord barrier, as reflected by significantly increased extravasation of [125I]bovine serum albumin. By 24 hr postinjection, a 12.5-nmol dose of somatostatin caused appreciable spinal cord cellular injury, as evidenced by significant elevations in cerebrospinal fluid concentrations of lactate dehydrogenase. After topical application to exposed pial vessels of the parietal cortex, comparable doses of somatostatin caused immediate intense dose-related arteriolar vasospasm and subsequent extravasation of the visible macromolecular tracer Evans blue dye. We conclude that somatostatin has significant vasoconstrictory effects on the blood vessels of the brain and spinal cord of the rat that must be recognized and appreciated when studying its neuropharmacological actions in vivo.