title: Alpha 2-agonist activity of the dopamine DA2-agonist LY171555.
abstract: LY171555 is the active enantiomer of the racemate LY141865, a selective DA2-receptor agonist. LY171555 (10(-7)-10(-4) M) inhibited the twitch response to field stimulation in the adrenergically innervated rat vas deferens, a response due to activation of alpha 2-receptors as evidenced by total blockade with yohimbine (10(-6) M). The dopamine receptor antagonist sulpiride (10(-5) M) produced a small shift in the concentration-response curve to LY171555, consistent with the modest alpha 2-antagonist activity of sulpiride. LY171555 (10(-10)-10(-8) M) inhibited prolactin release from the anterior pituitary in vitro, a response due to activation of DA2-receptors as indicated by total blockade with sulpiride (10(-6) M). Thus, in addition to its predominant DA2-agonist activity, LY171555 can activate alpha 2-receptors in concentrations similar to those necessary for activation of histamine H2-receptors. Such concentrations were approximately 2,250-fold higher than necessary for DA2-receptor activation.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004873:Ergolines / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects; D011388:Prolactin / Q000378:metabolism; D019257:Quinpirole; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects*; D013469:Sulpiride / Q000494:pharmacology; D014649:Vas Deferens / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D004873:Ergolines; D011954:Receptors, Dopamine; D019257:Quinpirole; D015016:Yohimbine; D013469:Sulpiride; D011388:Prolactin; D003000:Clonidine