Beta adrenergic receptors of rat tria and 19w3=isoproterenol mechanical were examined with the use of enantiomers of sioproterenol as agonists and mcehanical responses and adenosine 3',5' monophosphate (cyclic AMP) levels as measured effects. Assuming that stereoselectively reflects the unique asymmetry of receptors, potency differences between the enantiomers are excepted to provide a sensitive indication of ligand binding. All effects in each tissue were investigated under similar experimental conditions. Both isomers produced the same maximum effect on all measured responses. Enantiomeric potency differences (in log units) for positive chronotropic and inotropic responses and increases in cyclic AMP levels in atria were 3.31, 3.51 and 3.48, respectively. In uteri, the values for reduction of spontaneous contractile amplitude and increases in cyclic AMP were 2.90 and 2.79 log units, respectively. Even though these absolute values varied slightly with the experimental conditions, they were consistently smaller in uteri than in atria. In both tissues, dose response curves for production of mechanical effects were greater than 2 log units to the left of those for increases in cyclic AMP levels. Regardless of the interpretation of this phenomenon, the results show the following. The stereoselectivity for isoproterenol induced effects is different between the two tissues at both levels of response. Therefore, it is suggested that this reflects dissimilar beta adrenergic receptor types in rat atrium vs. rat uterus. The stereochemical selectivity for isoproterenol induced mechanical effects and increases in cyclic AMP is the same in rat atrium and in rat uterus. Therefore, the data support the postulate that cyclic AMP is formed from interaction of isoproterenol with a receptor that is similar to the one activated to produce a mechanical effect.
|Original language||English (US)|
|Number of pages||14|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Dec 1 1975|
All Science Journal Classification (ASJC) codes
- Molecular Medicine