Measurement of Cyclic AMP and Cyclic GMP in Xenopus Oocytes Stimulated with Angiotensin II and Atrial Natriuretic Factor

Angiotensin type-1 receptors (AT₁ receptors) mediate various physiological actions of angiotensin (Ang II) via multiple-signal transduction pathways (1 ). In addition to the phospholipase C pathway and dihydropyridine-sensitive voltage-dependent calcium channels, AT₁ receptors can couple to inhibition of adenylate cyclase via the guanine nucleotide binding protein Gi. Beside acting directly through G_i , AT₁ receptors can modulate levels of cyclic AMP (cAMP) indirectly through receptor crosstalk. cAMP is a major second messenger of many G protein coupled receptors. One group of receptors (e.g., (3-adreno-receptors, A₂ adenosine, D₁ dopamine, H₂ histamine, and some prostanoid receptors) elevate cAMP by activating adenylate cyclase through G_s , whereas a second group (a₂ adrenoreceptors, A1 adenosine, D₂ dopamine, 5HT₁ metabotropic glutamate, and i opioid receptors) reduce cAMP levels by inhibiting adenylate cyclase via G_i . Accumulating evidence indicates that signaling crosstalk can occur between AT receptors and receptors for atrial natriuretic factor (ANF) (2 ), bradykinin (3 ), catecholamines (4 ), adrenocorticotropin releasing hormone (5 ), vasopressin (6 ), and dopamine (7 ). Ang II is also found to indirectly modulate cyclic GMP (cGMP) levels via nitric oxide (8 ,9 ).