Adrenergic control of cAMP generation in rat inner medullary collecting tubule cells

Abstract

The adrenergic nervous system profoundly alters water excretion by both renal and extrarenal pathways. The effects of catecholamines on cultured rat inner medullary collecting tubule cells were studied. The beta-adrenergic agonist, isoproterenol, increases cAMP from 19.5 +/- 2.3 to 79.4 +/- 14.4 fm/micrograms protein, P less than 0.001. The response to arginine vasopressin (AVP) is also greater in the presence of isoproterenol, but the increment is unchanged when compared to that seen in the absence of AVP. The agonist effect of isoproterenol is blocked by propranolol but not by the specific beta 1 antagonist, atenolol. The effect of alpha-adrenergic stimulation was studied by the use of norepinephrine (NE) in the background of the beta blocker, propranolol. NE decreases AVP-stimulated cAMP generation from 190 +/- 11 to 117 +/- 10 fm/micrograms, P less than 0.001, N = 6. The specific alpha 2 antagonist, yohimbine, but not the alpha 1 antagonist, prazosin, prevents the NE-induced decrease as AVP-stimulated cAMP is restored to 187 +/- 19 fm/micrograms. Similarly the selective alpha 2 agonist, clonidine, significantly inhibits both AVP- and isoproterenol-mediated cAMP generation. To define the site of alpha 2 inhibition in the adenylate cyclase (AC) complex the effect of pertussis toxin (PT) was investigated. After pretreatment with PT (1-1000 ng/ml), AVP-stimulated cAMP was not inhibited by NE. The alpha 1 agonist, phenylephrine, fails to inhibit AC or to increase cytosolic Ca in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)