Cyclic Guanosine 3′,5′-Monophosphate in Mammalian Tissues and Urine

Abstract The occurrence of cyclic guanosine 3',5'-monophosphate (3',5'-cGMP) as a natural constituent of mammalian tissues was established, and details of a method for its quantitative determination in milligram amounts of liver, kidney, and brain or in microliter samples of urine are presented. In the analytical procedure 3',5'-cGMP partially purified from tissue extracts by thin layer chromatography or in urine samples (not subjected to any purification) was converted to 5'-GMP with the aid of cyclic nucleotide 3',5'-phosphodiesterase and then to GTP by the combined actions of ATPGMP phosphotransferase and pyruvate kinase. An enzymic cycling system composed of succinate thiokinase and pyruvate kinase was then used to generate proportionate concentrations of pyruvate equivalent to several thousand times the guanine nucleotide present. By measuring the pyruvate fluorometrically it was possible to detect 10-13 to 10-14 mole of 3',5'-cGMP in biological samples. Results are presented showing that 3',5'-cGMP excretion rates were constant in dogs during the infusion of hypertonic and hypotonic NaCl solution in spite of the fact that urinary concentrations of the cyclic nucleotide and urine volume varied almost 100-fold. Exogenous 3',5'-cGMP administered intravenously was rapidly cleared by the kidney and recoverable in the urine. Tissue levels of 3',5'-cGMP ranged from 4 x 10-8 mole per kg, wet weight, in rat kidney and liver to 1 to 2 x 10-7 mole per kg in cerebral tissue. Theophylline treatment of animals led to a 2-fold elevation of renal 3',5'-cGMP but produced no measurable alteration of hepatic levels. Glucagon, epinephrine, and alloxan-induced diabetes elevated concentrations of cyclic 3',5'-adenylate (3',5'-cAMP) in liver but had no effect on those of 3',5'-cGMP. Insulin administration (6 min) also had no influence. It was concluded that the formation of 3',5'-cAMP and 3',5'-cGMP is under separate hormonal and metabolic control and that specific enzymes (cyclases) are probably involved in their biosynthesis.