Cellular Action of Vasopressin in Medullary Tubules of Mice with Hereditary Nephrogenic Diabetes Insipidus

Abstract

A B S T R A C T Our previous studies (1974. J. Clin. suggested that impaired metabolism ofcyclic AMP (cAMP) may be involved in the renal unresponsiveness to vasopressin (VP) in mice with hereditary nephrogenic diabetes insipidus (NDI). To localize such a defect to specific segments of the nephron, we studied the activities of VP-sensitive adenylate cyclase, cAMP phosphodiesterase (cAMP-PDIE), as well as accumulation of cAMP in medullary collecting tubules (MCT) The results of the present in vitro experiments suggest that the functional unresponsiveness of NDI mice to VP is perhaps mainly the result of the inability of collecting tubules to increase intracellular cAMP levels in response to VP. In turn, this inability to increase cAMP in response to VP is at least partly the result of abnormally high activity of cAMP-PDIE, a somewhat lower activity of VP-sensitive adenylate cyclase in MCT of NDI mice, and perhaps to a deficiency of some other as yet unidentified factors. The possible contribution of low VP-sensitive adenylate cyclase activity in MAL of NDI mice to the renal resistance to VP remains to be defined. INTRODUCTIONOne animal model that phenotypically closely resembles human hereditary nephrogenic diabetes insipidus (NDI)l is a strain of mouse (so-called DI +/+ severe) with an inherited, vasopressin (VP)-resistant urinary concentrating defect (1)(2)(3)(4). Because administration of VP to NDI mice fails to increase osmolality of hypotonic urine (2, 3), these functional features indicate that collecting tubules failed to increase water permeability in response to the hormone. It is well established that the hydroosmotic effect of VP in collecting tubules (5-8) is mediated by adenosine 3',5'-cyclic monophosphate (cAMP) (5-7), and we have previously investigated the possibility that unresponsiveness to VP in NDI mice might be the

Evidence for beta adrenoceptors in proximal tubules. Isoproterenol-sensitive adenylate cyclase in pars recta of canine nephron.

“…Tubular segments were microdissected from the canine kidney in a similar manner as in our other studies of nephrons from other mammalian species (20)(21)(22)(23)(24). Kidneys were taken from the mongrel dogs, anesthetized with pentobarbital, and immediately perfused with heparinized ice-cold collagenase medium.…”

“…After the perfusion with heparinized collagenase medium, the cortical tissue was sliced with a razor blade and the pieces of tissue were incubated in aerated collagenase medium at 350C for 50-70 min, which was similar to our previous studies (20)(21)(22). After incubation, the slices were thoroughly rinsed in ice-cold microdissection medium and transferred to Petri dishes for microdissection.…”

“…The total tubular length was measured using Dietzger planimeter from the drawn pictures of samples (21). The measured samples were either immediately frozen for storage at -80'C for AdC assay or kept at 0-40C before incubations to determine cAMP accumulation (21,22).…”

“…The assay for AdC was identical in every detail to that described originally by Morel et al (24) and used in our previous studies on microdissected nephron segments (20)(21)(22). AdC activity was expressed as femtomoles cAMP generated per 30 min/mm of tubule length (20)(21)(22).…”

“…Measurement of cAMP accumulation was conducted on freshly dissected tubules using the same procedure described in every detail in our previous studies on tubules of rat or mouse kidneys (20)(21)(22). Briefly, samples of freshly dissected tubule segments were incubated in modified Krebs-Ringer buffer (KRB) for 10 min at 30'C.…”