Catecholamine-responsive adenylate cyclase activity in human endomyocardial biopsies. Individual sensitivity to isoproterenol stimulation and propranolol inhibition.

In the present study we have examined adenylate cyclase (AC) activity, the stimulation by isoproterenol and inhibition by propranolol, in endomyocardial biopsies from eleven patients with suspected cardiomyopathy. Biopsies were obtained by heart catheterization from the right endomyocardial surface of the interventricular septum. Three biopsies were taken from each patient (mean weight, 2.1 mg; range, 1.2-4.0 mg). One biopsy was studied by light microscopy. The two other biopsies were homogenized and AC activity in the homogenates was determined in the presence of different concentrations of isoproterenol and isoproterenol (5 micrograms/ml) combined with different concentrations of propranolol. Thus stimulation and inhibition curves were established for a pair of biopsies from each patient. Appropriate biopsy material was obtained in triplicate from only seven patients. In these patients the variance in maximal receptor stimulation (by isoproterenol) and inhibition (by propranolol) was significantly smaller in pairs of biopsies compared to the variance between all biopsies (p values from less than 0.05 to less than 0.025). Hence it is possible to determine AC activity, and adrenergic receptor function, in very small endomyocardial biopsies. New diagnostic possibilities could thereby be introduced.