Splenic lobes from the pancreas of newborn rats (48-64) hr. were used for the in vitro investigation of cyclic AMP, glucose and amino acid interaction in hormonal secretion. The slight discrepancy found in glucagon relaease with radioimmunoassay and binding assay to specific receptors in liver does not affect the ratio of stimulated to control values. The insulin release due to gheophylline dibutyrl cyclic AMP (dbcAMP) or to arginine is glucose-dependent as in adult rats and provides an index for the validity of the preparations. Glucose alone is efficient in stimulating insulin release but does not affect glucagon secretion; however simultaneous addition of 10 mM arginine, alanine, and lysine (A.A.) or of arginine alone resulted in a higher glucagon release at 1.6 mM than at 16.7 mM GLUCOSE. Theophylline (5 mM)and dbcAMP (2mM) induced a 2=fold increase in glucagon release at low or hight glucose concentrations . Incubation of theophylline (10 mM) and A.A. or arginine resulted in a considerable increase in glucagon release. Potentation of the 3 A.A.-induced glucagon reby dbcAMP was about 1800% no matter what the glucose concentration; similar observations were made for insulin with a 700% potentiation of the 3 A.A.effect glucagon was released more effectively by dbcAMP than was insulin,whereas the reverse was observed with theophylline. These findings suggest that knowledge of the cyclic AMP content is essential when assessing the influence of substrates on glucagon release. The combination of substrates with cyclic AMP clearly demonstrated that potentiation of glucagon release occurs mainly with amino acids, whereas for insulin occurs mainly with amino acids, whereas for insulin release it is mainly glucose which potentiates release.

A B S T R A C T The purpose of the present study was to investigate the regulation of insulin biosynthesis during the perinatal period. The incorporation of [3H]leucine into total immunoreactive insulin (IRI) and into IRI fractions was measured by a specific immunoprecipitation procedure after incubation, extraction, and gel filtration in isolated 3-day-old rat pancreases without prior isolation of islets. IRI fractions were identified by their elution profile, their immunological properties, and their ability to compete with the binding of "I-insulin in rat liver plasma membranes. No specific incorporation of [3H]leucine was found in the IRI eluted in the void volume, making it unlikely that this fraction behaves as a precursor of (pro)insulin in this system. In all conditions tested, the incorporation of [8H]leucine was linearly correlated with time. Optimal concentration of glucose (11 mM cose and was not modified by any further increase in glucose concentrations up to 27.5 mM. Theophylline or dbcAMP at 10 mM concentration did not reverse the somatostatin inhibitory effect on either insulin biosynthesis or release. Somatostatin also inhibited both processes in isolated islets from the 3-day-old rat pancreas. High Ca"+ concentration in the incubation medium reversed the inhibitory effect of somatostatin on glucoseinduced insulin biosynthesis as well as release. In both systems the inhibitory effect of somatostatin on insulin biosynthesis and release correlated well. Glipizide (10-100 ,M) and tolbutamide (400 ELM) inhibited the stimulatory effect of glucose, dbcAMP, and theophylline on [8H]leucine incorporation into IRI. The concentrations of glipizide that were effective in inhibiting [3H]leucine incorporation into IRI were smaller than those required to inhibit the phosphodiesterase activity in isolated islets of 3-day-old rat pancreas.These data suggest the following conclusions: (a) the role of the cAMP-phosphodiesterase system on insulin biosynthesis is likely to be greater in newborns than in adults; (b) the greater effectiveness of glucose and the cAMP system on insulin biosynthesis than on insulin release might possibly be related to the rapid accumulation of pancreatic IRI which is observed in the perinatal period; (c) somatostatin, by direct interaction with the endocrine tissue, can inhibit glucose and cAMPinduced insulin biosynthesis as well as release; calcium reverses this inhibition; (d) sulfonylureas inhibit insulin biosynthesis in newborn rat pancreas an effect which has

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