Central bromocriptine-induced tachycardia is reversed to bradycardia in conscious, deoxycorticosterone acetate-salt hypertensive rats.
A central dopaminergic origin has been demonstrated for the bromocriptine-induced tachycardia in conscious, normotensive rats. The present study investigated the effect of bromocriptine on heart rate and the principal site of action of this agonist in conscious, deoxycorticosterone acetate-salt hypertensive rats, in which altered central dopaminergic activity has been previously reported. Intravenous administration of bromocriptine (150 microg/kg) increased heart rate (49+/-5 beats/min.) in uninephrectomized control rats, while it induced a significant bradycardia (50+/-6 beats/min.) in deoxycorticosterone acetate-salt hypertensive rats. In the latter animals, intravenous (500 microg/kg) or intrathecal (40 microg/rat at T9-T10) pretreatment with domperidone, a selective dopamine D2 receptor antagonist that does not cross the blood-brain barrier, reduced partially, but significantly, the bradycardiac responses to bromocriptine (reduction of about 44% and 48% of the maximal effect, respectively). In contrast, the bromocriptine-induced bradycardia was fully abolished by intravenous pretreatment with metoclopramide (300 microg/kg), a dopamine D2 receptor antagonist that crosses the blood-brain barrier, or by combined pretreatment with intravenous and intrathecal domperidone. These results indicate that, in deoxycorticosterone acetate-salt hypertensive rats, bromocriptine decreases rather than increases heart rate, an effect that is mediated partly through a peripheral D2 dopaminergic mechanism and partly through stimulation of spinal dopamine D2 receptors. They further support the concept that, in normotensive, conscious rats, the central tachycardia of bromocriptine appears to predominate and to mask the bradycardia of this agonist at both peripheral and spinal dopamine D2 receptors.
Lahlou
S
S
Department of Physiology and Pharmacology, Center of Biological Sciences, Federal University of Pernambuco, Recife, Brazil. lahlou@npd.ufpe.br
D000818:Animals; D001012:Aorta, Abdominal / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D001919:Bradycardia / Q000209:etiology; D001971:Bromocriptine / Q000008:administration & dosage / Q000494:pharmacology*; D003900:Desoxycorticosterone / Q000008:administration & dosage / Q000494:pharmacology*; D004294:Domperidone / Q000008:administration & dosage / Q000494:pharmacology*; D018491:Dopamine Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects*; D006973:Hypertension / Q000139:chemically induced / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D008787:Metoclopramide / Q000008:administration & dosage / Q000494:pharmacology; D009392:Nephrectomy; D051381:Rats; D017208:Rats, Wistar; D013610:Tachycardia / Q000139:chemically induced*; D013997:Time Factors
D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D001971:Bromocriptine; D003900:Desoxycorticosterone; D004294:Domperidone; D008787:Metoclopramide