ABSTRACT
The effects of muscarinic M(1), M(2), and M(3) cholinergic receptor blockade on the regulation of chronotropic function of the heart were studied in vivo in 7-day-old rat pups. Intravenous injection of M(2) receptor blocker gallamine produced no changes in cardiac chronotropy. In contrast, M(1) receptor blocker pirenzepine and M(3) receptor blocker 4DAMP provoked bradycardia. These data attest to the involvement of M(1) and especially M(3) cholinergic receptors in the regulation of cardiac chronotropy in rat pups, which confirms the view on pronounced species-specific and age-related peculiarities in the heart control mechanisms.
Subject(s)
Heart Rate/drug effects , Heart Rate/physiology , Muscarinic Antagonists/pharmacology , Receptor, Muscarinic M1/antagonists & inhibitors , Receptor, Muscarinic M2/antagonists & inhibitors , Receptor, Muscarinic M3/antagonists & inhibitors , Animals , Animals, Newborn , Gallamine Triethiodide/pharmacology , Piperidines/pharmacology , Pirenzepine/pharmacology , Rats , Stimulation, Chemical , Vagus Nerve/physiologyABSTRACT
We compared the effects of blockade of α(1A)-, α(1B)-, and α(1D)-subtypes of α(1)-adrenoceptors on the cardiac rhythm in newborn rats. Different responses of the heart were observed after blockade of several subtypes of α(1)-adrenoceptors. Administration of WB 4101, a selective blocker of α(1A)-adrenoceptors, increased heart rate, while blockade of α(1AD)-adrenoceptors with BMY 7378 decelerated of heart rhythm. Blockade of α(1B)-adrenoceptors with chloroethylclonidine produced no significant effects on heart chronotropy.
