Effect of labetalol on adrenoceptors in the isolated perfused rat mesentery.
Isolated perfused rat mesentery has been used to define alpha- and beta-adrenoceptors. Norepinephrine was used as a reference substance to induce vasoconstrictor responses (increase in perfusion pressure). Log-dose response curves were obtained in the dose range between 0.3-10 mug. Labetalol, a known competitive inhibitor of both alpha- and beta-adrenoceptors, when administered as a single bolus injection (3 mug) initially induced predominant alpha-blockade lasting upto 75 min followed by potentiation of the vasoconstrictor responses to norepinephrine used at multiple dose levels. This potentiation was maximum between 150-195 min after injection of labetalol. This potentiating effect of labetalol observed in the later phase of the experiment might be related to its inhibitory mechanism of neuronal uptake.
D000818:Animals; D004983:Ethanolamines / Q000494:pharmacology*; D066298:In Vitro Techniques; D007741:Labetalol / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D013152:Splanchnic Circulation / Q000187:drug effects*; D014661:Vasoconstriction / Q000187:drug effects
D004983:Ethanolamines; D011941:Receptors, Adrenergic; D007741:Labetalol; D009638:Norepinephrine; D010646:Phentolamine