Measurement of cAMP in the cardiac conduction system of rats.
To characterize differences in regional cAMP production in the cardiac conduction system, 18 rats were anesthetized with pentobarbital (65 mg/kg IP) and randomized into a control (n = 9) and a stimulated group (n = 9). The stimulated group received aminophylline (20 mg/kg SC) and isoproterenol (16 micrograms/kg SC). The concentration of cAMP in freeze-dried, micro dissected pieces (1-3 micrograms) of cardiac tissue was measured using a new microanalytical method. The cAMP contents in right atrium, atrioventricular node, His bundle, and left ventricle (fmol/microgram dry weight, mean +/- SE) were 38.9 +/- 2.5, 39.0 +/- 4.3, 46.4 +/- 6.1, and 41.4 +/- 3.3 in controls and 72.9 +/- 6.7, 86.1 +/- 2.9, 115.0 +/- 11.5, and 79.5 +/- 7.3 in the stimulated group, respectively. Basal cAMP levels were similar throughout the heart, whereas isoproterenol increased cAMP levels in all regions (p < 0.01). Furthermore, cAMP levels in His bundle, after isoproterenol, were higher than in any other region (p < 0.05). These results demonstrate that: (a) cAMP can be measured in discrete portions of the cardiac conduction system; (b) there are significant regional differences of beta-adrenergic control in the cardiac conduction system; and (c) cAMP production after beta-adrenergic stimulation was lower than expected in the AV nodal region, based on previously described beta-adrenoceptor density measurements.
Sugiyama
A
A
Department of Medicine, University of Minnesota, Minneapolis, USA.
McKnite
S
S
Wiegn
P
P
Lurie
K G
KG
D000628:Aminophylline / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000032:analysis*; D006329:Heart Conduction System / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015290:Second Messenger Systems
D000628:Aminophylline; D000242:Cyclic AMP; D007545:Isoproterenol