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Dispersed pinealocytes have been used to study the role of adenosine 3',5'-monophosphate (cyclic AMP) in the "turnoff" of N-acetyltransferace activity. Activity was first stimulated 100-fold by treating cells with 1-norepinephrine. 1-Propranolol acted stereospecifically to rapidly reverse this, resulting in a 70 percent loss of enzyme activity within 15 minutes. An even more rapid 1-propranolol-induced decreased in cyclic AMP also occurred. This together with the observation that the inhibitory effect of 1-propranolol on N-acetyltransferase was blocked by dibutyryl cyclic AMP and phosphodiesterase inhibitors indicate that an abrupt decrease in cyclic AMP may be the signal for the rapid decrease in pineal N-acetyltransferase activity.

Immunocytochemistry shows that early during phagocytosis of zymosan, adenosine 3',5'-monophosphate (cyclic AMP) appears on the cell surface before the phagosome is internalized. The appearance of cyclic AMP on the cell surface is coincident with that of granule products and regulatory subunit of type I cyclic AMP-dependent protein kinase. Guanosine 3',5'-monophosphate is not associated with the initiation site of phagocytosis, but is observed throughout the granular cytoplasmic region. This sharply localized accumulation of cyclic AMP may serve as a signal for the initiation of phagocytosis.

Carbamylcholine (30 micronM) increased the concentration of guanosine 3',5'-monophosphate (cyclic GMP) in guinea pig pancreatic lobules about eight-to tenfold over the basal concentration in 30 seconds with a concomitant increase in the rate of amylase secretion. The concentration of cyclic GMP rapidly declined to a plateau value of about 16 percent of the peak level in 10 minutes. Cellular cyclic GMP decreased, mostly because the nucleotide was secreted into medium; cellular adenosine 3',5'-monophosphate (cyclic AMP), however did not change, nor was this nucleotide secreted into the medium. An immunocytochemical technique showed that cyclic GMP was distributed in the apical plasmalemma membrane and lumen of the pancreas. Carbamylcholine increased the cyclic GMP fluorescence in tha apical plasmalemma membrane within 30 seconds, and in zymogen granules and the plasma membrane in the apical part of acinar cells in 10 minutes. The islets of Langerhans did not show any change in cyclic GMP. Fluorescence of cyclic AMP in pancreatic lobules was not altered by carbamylcholine and was localized along the apical portion of plasmalemma and cytoplasm. Cyclic GMP may thus participate either in the process of exocytosis or in the activation of enzymes secreted from the pancreas.