Alpha-adrenergic agonist and antagonist activity of dihydroergotoxine in rats.
The alpha-adrenergic activity of dihydroergotoxine had been studied in both pithed and urethane or pentobarbitone anaesthetized rats. In anaesthetized rats, blood pressure effects varied with the anaesthetic agent: hypotension with urethane, hypertension with pentobarbitone. This latter pressor response was a peripheral effect. In pithed rats, the vasopressor response to dihydroergotoxine was reduced competitively by yohimbine, and non-competitively by nifedipine, but not by prazosin or methysergide, showing that the vasoconstriction is mediated by alpha 2-adrenoceptors. Dihydroergotoxine decreases the tachycardia elicited by stimulation of the cardioaccelerator nerves, this effect being antagonized by yohimbine. It also reduced the pressor response to (-)-phenylephrine. These results indicated that, on the peripheral vascular system of the rat, dihydroergotoxine acts as an alpha 1-adrenoceptor blocker and an alpha 2-adrenoceptor agonist.
Roquebert
J
J
Demichel
P
P
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000758:Anesthesia; D000818:Animals; D004088:Dihydroergotoxine / Q000494:pharmacology*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004088:Dihydroergotoxine; D010656:Phenylephrine; D015016:Yohimbine; D009543:Nifedipine; D011224:Prazosin; D008784:Methysergide