EFFECT OF PHONEUTRIA-NIGRIVENTER SPIDER VENOM ON GASTRIC-EMPTYING IN RATS

The effect of Phoneutria nigriventer spider venom (PNV) on the gastric emptying of liquids was studied in 240 young adult Wistar rats (2-3 m onths of age) divided into subgroups of 8 animals each, The study was performed in 3 stages. Initially, PNV was injected into rats at doses of 0, 19, 0.38 or 0.76 mg/kg and the effect on gastric emptying was as sessed 30 min later. In the second stage, a time-course study was perf ormed by injecting 0.76 mg PNV/kg and measuring the effect on gastric emptying 15, 60 and 120 min post-venom In the last stage, in order to investigate the possible mechanisms of PNV influence on gastric emptyi ng, one group of rats underwent subdiaphragmatic vagotomy and then rec eived 0.76 mg PNV/kg while three other groups were pretreated iv with either prazosin (0.4 mg/kg), domperidone (1.0 mg/kg) or propranolol (0 .6 mg/kg) and then given 0.38 or 0.76 mg PNV/kg. In this last stage, g astric retention was measured 30 min post-venom. Each animal received a saline test meal solution containing phenol red as a marker (60 mu g /ml). Ten min after administering the test meal by gavage, gastric ret ention was determined by measuring the residual test meal marker conce ntration and the animals were sacrified. PNV (0.76 mg/kg) provoked a s ignificant delay in gastric emptying of liquids 15, 30 and 60 min afte r its administration, Propranolol partially interfered with gastric em ptying in rats that had received 0.38 and 0.76 mg PNV/kg. Vagotomy and pretreatment of the rats with prazosin and domperidone had no effect. We conclude that the delay in the liquid gastric emptying observed in severely envenomed rats was probably due, at least in part, to a veno m-stimulated release of catecholamines which inhibited gastric motilit y by activating smooth muscle beta-adrenergic receptors.