Effects of d-Amphetamine on the Frequency of the Spontaneous Contraction of the Portal Vein in Rat

Abstract

1. Effects of d-amphetamine on the frequency of spontaneous contraction 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 frequency of the spontaneous contraction of the portal vein before and after d-amphetamine treatment also was increased. The effect was not affected in the presence of prazocin, (+)-lysergic acid diethylamide, atropine and haloperidol. These results suggested that the d-amphetamine-elicited response was not due mainly to the activation of adrenergic, serotoninergic (5-HT), cholinergic or dopaminergic receptors. 3. Increasing 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 containing different extracellular calcium or sodium concentrations were not significantly altered. Tetrodotoxin did not alter the effect of d-amphetamine on the frequency of spontaneous contractions. It appeared that calcium and sodium ions may not take part in the effects of d-amphetamine on the frequency of the portal vein. 4. An increase in extracellular potassium ion concentrations increased the frequency of the spontaneous contractions of the portal vein. In addition, the ratios of the frequency of the spontaneous contractions of the rat portal vein before and after d-amphetamine treatment in media containing different extracellular potassium ion concentrations were significantly altered. Tetraethylammonium chloride (TEA) and 4-aminopyridine (4-AP) increased the spontaneous contractions of the portal vein. However, TEA and 4-AP did not increase the d-amphetamine-elicited increasing effect on the frequency of spontaneous muscle contractions. 5. Levochromakalim, a potassium channel opener, decreased the frequency of the spontaneous contractions of the portal vein. Levochromakalim also decreased the effect of d-amphetamine on the frequency of spontaneous contractions of the muscle. It appeared that potassium ion may be associated with the effects of d-amphetamine on the activity of the portal vein. 6. d-Amphetamine 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 stomach, whereas it did not alter the frequency of the spontaneous contraction of the muscle. 8. Both 5-HT and d-amphetamine elicited the contracture of the circular muscle of rat stomach. Ketanserin decreased the 5-HT-elicited response, whereas it did not alter the d-amphetamine-elicited response in the muscle. d-Amphetamine did not alter the frequency of the spontaneous contraction of the stomach. 9. It is concluded that 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.