During the perinatal period, norepinephrine (NE)-stimulated adenylyl cyclase activity increased in interscapular brown adipose tissue (IBAT) membranes and then declined to adult levels by 23 days postpartum. The developmental patterns of NE- and NaF-stimulated activities were identical, indicating that the developmental increase in transmitter-stimulated activity resulted from the increased interaction of alpha-subunit of guanine nucleotide-binding stimulatory protein of adenylyl cyclase (G(s-alpha)) with the catalytic subunit (C). This increased G(s-alpha)-C interaction was the result of an increase in G(s-alpha) specific activity, as assessed in cyc- reconstitution assays, as well as an increased C activity, as assessed by forskolin-Mn2+-stimulated adenylyl cyclase activity. Although adenylyl cyclase activity increased during the perinatal period, total G(s-alpha) levels significantly declined because of the loss of the small-molecular-mass form of G(s-alpha). Thus the ratio of large to small form of G(s-alpha) increased threefold and might have contributed to the perinatal increase in activity. G(i-alpha)-like proteins, as assessed by pertussis toxin-catalyzed [P-32]ADP ribosylation, declined dramatically after birth. However, this loss of G(i-alpha) did not contribute to developmental changes in adneylyl cyclase activity because pertussis toxin treatment failed to alter NE-stimulated activity. In contrast to G-alpha subunits, there were no changes in membrane levels of G-beta subunits.
