AGE-RELATED POSTRECEPTOR MECHANISMS - CHANGES IN ADENYLATE-CYCLASE BUT NOT PHOSPHODIESTERASE IN ISOLATED MOUSE RENAL MEDULLARY COLLECTING DUCTS

Urine concentrating ability declines with increasing age, partly due t o an impaired response of kidney medullary collecting ducts to the ant idiuretic hormone, vasopressin. We investigated this change in isolate d mouse medullary collecting ducts by measuring the activity of adenyl ate cyclase and phosphodiesterase, which catalyse the formation and hy drolysis of cAMP, respectively, Adenylate cyclase activity was measure d in the presence of vasopressin (which stimulates adenylate cyclase v ia the receptor) or forskolin (which directly stimulates the catalytic subunit), We showed an age-related decrease in the catalytic subunit of adenylate cyclase, and no difference in the activity of phosphodies terase, indicating that a reduction in the catalytic subunit of adenyl ate cyclase contributes towards the age-related decrease in cyclic AMP response of kidney to vasopressin.