EFFECTS OF D-AMPHETAMINE ON THE FREQUENCY OF THE SPONTANEOUS CONTRACTION OF THE PORTAL-VEIN IN RAT

1. Effects of d-amphetamine on the frequency of spontaneous contractio n of the longitudinal muscle of the portal vein were studied in Wistar rats. Its effects on the circular muscles of the pulmonary artery and stomach also were tested, 2. d-Amphetamine increased the frequency of the spontaneous contraction of the portal vein. The ratio of the freq uency of the spontaneous contraction of the portal vein before and aft er d-amphetamine treatment also was increased. The effect was not affe cted in the presence of prazocin, (+)-lysergic acid diethylamide, atro pine and haloperidol. These results suggested that the d-amphetamine-e licited response was not due mainly to the activation of adrenergic, s erotoninergic (5-HT), cholinergic or dopaminergic receptors. 3. Increa sing extracellular calcium or sodium ion concentrations decreased the frequency of the spontaneous contraction of the portal vein. However, the ratios of the frequency of the spontaneous contraction of the rat portal vein before and after d-amphetamine treatment in media containi ng different extracellular calcium or sodium concentrations were not s ignificantly altered. Tetrodotoxin did not alter the effect of d-amphe tamine on the frequency of spontaneous contractions. It appeared that calcium and sodium ions may not take part in the effects of d-amphetam ine on the frequency of the portal vein. 4. An increase in extracellul ar potassium ion concentrations increased the frequency of the spontan eous contractions of the portal vein. In addition, the ratios of the f requency of the spontaneous contractions of the rat portal vein before and after d-amphetamine treatment in media containing different extra cellular potassium ion concentrations were significantly altered. Tetr aethylammonium chloride (TEA) and 4-aminopyridine (4-AP) increased the spontaneous contractions of the portal vein. However, TEA and 4-AP di d not increase the d-amphetamine elicited increasing effect on the fre quency of spontaneous muscle contractions. 5. Levochromakalim, a potas sium channel opener, decreased the frequency of the spontaneous contra ctions of the portal vein. Levochromakalim also decreased the effect o f d-amphetamine on the frequency of spontaneous contractions of the mu scle. It appeared that potassium ion may be associated with the effect s of d-amphetamine on the activity of the portal vein. 6. d-Amphetamin e potentiated, whereas prazosin decreased, the noradrenaline-elicited contracture of the rat pulmonary artery in a dose-dependent manner. 7. d-Amphetamine elicited contracture of the circular muscle of rat stom ach, whereas it did not alter the frequency of the spontaneous contrac tion of the muscle. 8. Both 5-HT and d-amphetamine elicited the contra cture of the circular muscle of rat stomach. Ketanserin decreased the 5-HT-elicited response, whereas it did not alter the d-amphetamine-eli cited response in the muscle. d-Amphetamine did not alter the frequenc y of the spontaneous contraction of the stomach. 9. It is concluded th at d-amphetamine has different effects on the frequency of spontaneous smooth muscle contractions. It increased the frequency in the portal vein, but it did not alter the frequency in stomach circular muscle. ( C) 1998 Elsevier Science Inc.