Effects of octreotide and morphine on the clearance rate of indium-111-pentetreotide from the epidural space

In this study we aimed to evaluate the possible mechanisms by which somatostatin acts when given epidurally. Twenty male New Zealand rabbits were randomly separated into four groups and various drugs were administered via a caudal epidural catheter. Group 1 received a bolus of 3.7 MBq indium-111 ((111)In)-pentetreotide, group 2 received 200 microg octreotide and after 15 min a bolus of 3.7 MBq (111)In-pentetreotide, group 3 received 0.1 mg morphine and after 15 min a bolus of 3.7 MBq (111)In-pentetreotide, and group 4 received a bolus of 3.7 MBq technetium-99m (99Tc(m))-diethylene triamine pentaacetic acid (DTPA). Dynamic images of 60 min' duration were obtained from the posterior projection. T(1/2), fast and T(1/2) total clearance half-times were calculated. When unlabelled octreotide was given to block somatostatin receptors, clearance of (111)In-pentetreotide was found to be faster. Epidural morphine administration did not change the clearance rate of (111)In-pentetreotide. All these findings are in favour of octreotide binding to its probable own specific receptors present in the epidural space.