title: Interaction between presynaptic facilitatory angiotensin II receptors and inhibitory muscarinic cholinoceptors on 3H-noradrenaline release in the rabbit heart.
abstract: The existence of a functional interaction between presynaptic receptors modulating the release of noradrenaline was studied in the rabbit heart. Isolated right atria were prelabelled with 3H-noradrenaline and the overflow of tritium was induced by field stimulation (2 Hz, 0.1 ms duration, supramaximal voltage for a total of 180 pulses). In atria superfused with Krebs' solution containing 10 mumol/l cocaine and 30 mumol/l corticosterone, angiotensin II (10 nmol/l) increased the stimulation-evoked overflow of 3H-transmitter by 2.8-fold. The addition of atropine (0.3 mumol/l) to the perfusion medium, either in the presence or in the absence of uptake inhibitors, further enhanced the facilitatory effect of angiotensin II (3H-transmitter release increased by 3.5-fold). Exposure to 1 mumol/l carbachol decreased by 65% the stimulation-evoked release of 3H-transmitter while the facilitatory effect of angiotensin II determined in the presence of the muscarinic cholinoceptor agonist was enhanced (3H-transmitter release increased by 6.6-fold). Conversely, during sustained activation of presynaptic angiotensin receptors producing a 2.5-fold increase in the release of 3H-transmitter, the inhibitory effect of carbachol remained unchanged. These results suggest a functional interaction between presynaptic inhibitory muscarinic cholinoceptors and the presynaptic facilitatory angiotensin receptor which modulate the release of noradrenaline from cardiac noradrenergic nerves.
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D003345:Corticosterone / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D011817:Rabbits; D011945:Receptors, Angiotensin / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*
chemical_list: D011945:Receptors, Angiotensin; D011956:Receptors, Cell Surface; D011976:Receptors, Muscarinic; D000804:Angiotensin II; D001285:Atropine; D002217:Carbachol; D003042:Cocaine; D003345:Corticosterone; D009638:Norepinephrine