Adrenergic innervation and cyclic adenosine 3':5'-monophosphate levels in response to norepinephrine in stomach of postnatal rats.

Changes in receptor function, innervation and cyclic adenosine 3':5'-monophosphate (cAMP) levels in response to norepinephrine were investigated in the stomach of postnatal developing rats. We found that although the beta adrenergic receptor function and responsiveness of cAMP-generating system to norepinephrine are present in the early postnatal stage (3-day-old), these systems are not fully developed at birth and that increase in sensitivity comes with age. Adrenergic innervation is present at birth in Auerbach's plexus but not in smooth muscle, during the 1st postnatal week. Direct adrenergic innervation to smooth muscle appears 1 week after birth and matures during the first 4 weeks. This maturation of direct adrenergic innervation runs in parallel with the increased sensitivity of beta receptors and is accompanied by an elevated responsiveness of the cAMP-generating system to norepinephrine.