Patterns of development of adenyl cyclase activity and norepinephrine responsiveness in the rat.

Abstract

Extract: The present studies were done to delineate developmental patterns of the adenyl cyclase system and its responsiveness to norepinephrine. Investigations were performed in four tissues of the rat: brain, brown fat, heart, and liver. The general developmental patterns of adenyl cyclase in brown fat, heart, and liver are similar. In all three tissues, adenyl cyclase activity reaches a nadir at approximately 14 days of age. Heart, brown fat, and liver also show similar responses to norepinephrine, which increases adenyl cyclase activity to 2–4 times that of basal levels at all ages. The adenyl cyclase activities in the late gestational and early infant brain are relatively low compared with later ages, but are comparable to those of the other tissues in the neonatal period. Activity in cerebrum rises steadily until about 21 days of age. There is responsiveness to sodium fluoride stimulation of adenyl cyclase in all tissues examined at all ages, with values 5–20 times basal levels in brown fat, liver, and heart. In cerebrum, sodium fluoride causes stimulation of adenyl cyclase activity to about 2 times basal levels at all ages. Speculation: Adenyl cyclase activity in brown fat in the rat is at high levels in the neonate. This may be related to the high metabolic activity and active lipolysis occurring in that tissue in the perinatal period. In the brain, adenyl cyclase activity is at very low levels in the neonate compared with the adult, rising rapidly in the 2nd and 3rd weeks of life. This pattern of development of the adenyl cyclase system in the rat brain may be related to concurrent biochemical and structural changes.