Influence of repeated prazosin administration on cardiovascular responses in rats and rabbits.
Prazosin was injected i.v. at a dose of 50 micrograms/kg every 2 h for 8 h in conscious rats. Its hypotensive action significantly declined. A similar effect was also observed in rabbits pretreated with prazosin (40 micrograms/kg, i.v.) every 1 h for 4 h. In prazosin-treated rabbits, the total peripheral resistance became less responsive to phentolamine stimulation. Repeated prazosin administration abolished its ability to block receptors in a model of anococcygue muscle contraction after noradrenaline (NA) stimulation. The alpha-adrenoceptors in anococcygue muscle exhibited lower pD2 to NA and lower pA2 to prazosin in prazosin-treated rats. The results demonstrate that repeated prazosin administration reduces the effectiveness of alpha-adrenoceptors blockers.
Hui
S C
SC
School of Professional and Continuing Education, University of Hong Kong, Hong Kong.
Qiu
B S
BS
D000818:Animals; D000959:Antihypertensive Agents / Q000008:administration & dosage*; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects* / Q000503:physiopathology; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000008:administration & dosage*; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism
D000959:Antihypertensive Agents; D011942:Receptors, Adrenergic, alpha; D011224:Prazosin; D010646:Phentolamine