Developmental changes in adenylate cyclase activity in canine myocardium.

Basal and epinephrine-induced adenylate cyclase activity in homogenates of dog myocardium increased significantly from birth to adulthood, without further change with advancing age. The stimulatory effect of epinephrine (i.e. the net increase over basal activity), however, increased (p less than 0.05) during the first week after birth only and then remained constant. While fluoride-stimulated activity increased, 5'-guanylyl imidodiphosphate [Gpp(NH)p]-stimulated activity declined gradually during development (p less than 0.05). In the presence of Gpp(NH)p and epinephrine at concentrations producing a maximal effect, the enzyme activities in all dogs, except in the 1-day-old, were not significantly different and were comparable to that of fluoride-stimulated activity in adult dogs. The results suggest that age-related alterations in the characteristics of the guanine nucleotide regulatory protein may account, at least in part, for the changes in adenylate cyclase activity occurring during development.