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Control of the Adenosine 3',5'-Monophosphate-Adenyl Cyclase System in the Livers of Developing Rats¹

McArdle Laboratory for Cancer Research, Medical Center, University of Wisconsin, Madison, Wisconsin 53706

Full-term rats were delivered surgically and were maintained away from their mothers at 37° for times up to 12 hr. Under these conditions, the hepatic levels of glycogen decreased and tyrosine aminotransferase (EC 2.6.1.5) and cyclic AMP levels increased. The injection of glucose delayed the changes in all 3 parameters described above. If the rats were delivered naturally and were maintained under conditions comparable to those for the above studies or if they were left with their mothers, the hepatic cyclic AMP levels increased. However, the greatest changes in tyrosine aminotransferase were observed for the fasted group (i.e., 4-fold increase above the zero group for the fasted set, compared with a 2-fold increase for the fed group). The available data suggest that cyclic AMP may be involved in the postnatal increase in tyrosine aminotransferase. However, it is also suggested that another factor, in addition to cyclic AMP, was involved in the marked increase of tyrosine aminotransferase observed for the fasted animals.

In vitro determinations of hepatic adenyl cyclase and the effects of glucagon or isoproterenol, as well as in vivo determinations of hepatic levels of cyclic AMP before and after injection of either glucagon or isoproterenol, demonstrated that the adenyl cyclase-cyclic AMP system of developing rat liver was present and was responsive to either glucagon or isoproterenol as early as 4 days before birth (earlier times were not examined).

The magnitude of the response of hepatic adenyl cyclase to glucagon or isoproterenol was dependent on the age of the rat. The same was true for the effects of glucagon or isoproterenol on the hepatic levels of cyclic AMP.

A close parallel between the age-dependent effect of glucagon on the cyclic AMP levels and induction of tyrosine aminotransferase as well as on the transport of -aminoisobutyrate was observed.

¹ Financial support was provided in part by Department Grant CA-07175 and Training Grant CRTY-5002 from the National Cancer Institute.

² Recipient of Postdoctoral Fellowship CA-43800. Present address: Division of Biological and Medical Sciences, Brown University, Providence, R. I. 02912.

³ To whom requests for reprints should be sent.

Received 2/28/72. Accepted 6/19/72.