Cardiovascular effects of clonidine-like drugs in pithed rabbits.
Administration (3 to 100 microg/kg IV) of clonidine, rilmenidine, and an imidazoline derivative, 2-(2-chlorophenylamino)imidazoline, in pithed nonstimulated rabbits caused a dose-dependent increase in mean arterial pressure without affecting heart rate. Prazosin (0.1 mg/kg IV) almost abolished the pressor responses to 2-(2-chlorophenylamino)imidazoline, partially inhibited those induced by clonidine, but failed to affect those elicited by rilmenidine. In contrast, yohimbine (1 mg/kg IV) blunted the pressor responses of the 3 drugs. In sympathetically stimulated pithed rabbits, 2-(2-chlorophenylamino)imidazoline induced only pressor effects, whereas clonidine and rilmenidine caused a transient pressure increase followed by a dose-dependent depressor effect. Yohimbine abolished the depressor effect of both drugs, which may have involved presynaptic alpha(2)-adrenoceptors. In conclusion, peripheral effects of 2-(2-chlorophenylamino)imidazoline and clonidine involved at least alpha(1)- and alpha(2)-adrenoceptor activation, whereas pressor and depressor effects of rilmenidine were mediated by alpha(2)-adrenoceptors.
Pompermayer
K
K
Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
Salgado
M C
MC
Feldman
J
J
Bousquet
P
P
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002320:Cardiovascular Physiological Phenomena; D003000:Clonidine / Q000494:pharmacology*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D010080:Oxazoles / Q000494:pharmacology*; D011817:Rabbits; D000077769:Rilmenidine; D013564:Sympathetic Nervous System / Q000502:physiology*; D009435:Synaptic Transmission
D000959:Antihypertensive Agents; D007093:Imidazoles; D010080:Oxazoles; C029899:imidazole; D003000:Clonidine; D000077769:Rilmenidine