The stimulation by catecholamines of guanylate cyclase activity in a cell-free system

Cytosolic guanylate cylase activity in cell-free preparations of the rabbit renal cortex was increased 3- to 5-fold by catecholamines. The plasma membrane-bound enzyme was not activated, although hormone receptors were present. Stimulation was augmented by NaN3, which by itself had little effect on the soluble enzyme activity. With a partially purified enzyme, activity was enhanced by 0.1 muM 1-epinephrine and activated half-maximally by about 1 muM. In decreasing potency, epinephrine greater than isoproterenol greater than norepinephrine greater than dopamine greater than catechol. Phenylephrine and metanephrine did not stimulate. 1-Epinephrine-stimulation of the enzyme was reversed by dialysis and the deactivated enzyme was reactivatable by a second exposure to the catecholamine. Activation by catecholamines was not stereospecific. Epinephrine-stimulated guanylate cyclase activity in the crude cytosolic fraction was partially inhibited by alpha-adrenergic antagonists, but neither alpha- nor beta-blockers inhibited when the partially purified enzyme was used; thus, leaving open the question of a role for typical alpha- or beta-adrenergic mechanisms in this regulation of the soluble enzyme. Adrenochrome was the most potent activator of the partially purified guanylate cyclase, being approximately 10-times more effective than epinephrine. Epinephrine and adrenochrome activated in the presence of reducing agents, i.e., ascorbate, DTT and N2, although the enzyme in a more SH-reduced form and in an oxygen-deficient medium had a decreased sensitivity to both effectors. Epinephrine activated soluble guanylate cyclase in several tissues, including cerebrum, cerebellum, brain stem, lung, heart, liver, ductus deferens and colon. Although the precise mechanism by which low concentrations of catecholamines stimulated guanylate cyclase activity is unknown and the physiological significance of the activation remains to be established, these findings direct attention to an interesting interaction of catecholamines with the cytosolic enzyme system and stress the need for further studies.