Effects of 4-aminopyridine on cat blood pressure in relation to the sympathetic nervous system.
The pressor effect of 4-aminopyridine (4-AP) was studied in anesthetized cats and in isolated cat aortic ring preparations. A significant increase in blood pressure (38.9 +/- 11.4 mmHg) was observed following intravenous administration of 4-AP (0.3 mg/kg). The elevated blood pressure lasted for 1.3 h and returned to the control level after 1.5 h. The pressor effect of 4-AP was not blocked by prior administration of phentolamine (2 mg/kg i.v.) or by pretreatment with reserpine (2 mg/kg i.m., once a day for two consecutive days). In vitro, a dose-dependent tonic contraction of aortic ring was noted after addition of 4-AP into the bathing fluid. The ED50 of 4-AP was significantly greater than that of norepinephrine (NE) (8 X 10(-4) M vs. 10(-7) M). Phentolamine (10(-6) M) antagonized the contractile response to NE but not that to 4-AP, whereas verapamil (10(-5) M) attenuated the 4-AP induced contractile response. A diminished contractile effect was also obtained when aortic ring preparations were bathed in calcium-free solution. These data suggest that the sympathetic nervous system plays a minor role in the pressor effect of 4-AP and that the increased calcium influx may account, at least partially, for the vasoconstricting effect of 4-AP.
D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D002118:Calcium / Q000502:physiology; D002317:Cardiovascular Agents / Q000494:pharmacology*; D002415:Cats; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D012110:Reserpine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology
D000631:Aminopyridines; D002317:Cardiovascular Agents; D012110:Reserpine; D015761:4-Aminopyridine; D014700:Verapamil; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine