Intrathecal somatostatin in the guinea pig: effects on spinal cord blood flow, histopathology and motor function

In the present investigation, the vasoconstrictive, motor and neurodegenerative effects of intrathecal somatostatin (SST) were assessed in guinea pigs implanted with lumbar intrathecal catheters. Five consecutive dose increments of SST (5, 10, 15, 30 and 60 micrograms) to a total of 120 micrograms during the period of 16 +/- 3 min, resulted in a moderate (< 20%), gradual decrease of the spinal blood flow monitored with the laser-doppler method. A subsequent injection of clonidine (50 micrograms) or norepinephrine (10 micrograms) resulted in a more pronounced decrease of spinal blood flow (35% and 79%, respectively). Three consecutive, daily intrathecal injections of 30 or 60 micrograms SST did not cause any loss of weight support or paralysis of the hind limbs. There were no histopathological changes in the white or gray matter of the thoracic and lumbar sections of the spinal cords. It is concluded that SST, in the doses studied, is not neurodegenerative in guinea pigs. These findings are in contrast to those previously seen in rats. The implication of this study may be the necessity to use several alternate animal species in order to evaluate the antinociceptive and neurodegenerative properties of the peptides administered by the intrathecal route and the choice of dose to be compared across species.