Ng inactivating MR mutations andMironova et al.10098 | www.pnas.org/cgi/doi/10.1073/pnas.AS deficiency, which require sodium supplementation to survive (4, 8, 9, 33). Clearly the hormonal state, and thus phenotype, of loss-offunction of MR or AS do not completely overlap that of adrenalectomy. With MR dysfunction, the RAAS is up-regulated (13). With AS dysfunction, aldosterone is absent, but the levels of other adrenal steroids capable of mineralocorticoid action–in particular, corticosterone–are increased (9, 32, 33). In Adx mice, there is no aldosterone or other adrenal steroids and catecholamines; thus, these animals receive no input from the adrenal gland to ENaC. Moreover, akin to adrenal insufficiency, removal of the adrenal glands, as shown here and by others (27?9), causes marked increases in plasma AVP levels. Increases in AVP are not present with Wuningmeisu C supplement either MR or AS dysfunction (25). Usually, AVP release is primarily controlled by plasma osmolality. Elevated AVP release in adrenal-insufficient states (that lack both glucocorticoids and mineralocorticoids) results from two events. There is loss of negative-feedback regulation by glucocorticoids of the hypothalamic ituitary axis controlling AVP release. There also is strong nonosmotic stimulation of AVP release, resulting from volume depletion due to sodium and water wasting by the kidney (27, 28). It is recognized that adrenal insufficiency and central diabetes insipidus are counterpoints when considering the equilibrium distribution of sodium and water: The pattern of sodium and water distribution in either deficiency depends in part on the activity of the remaining gland. As such, the hyponatremia of adrenal insufficiency is absent when combined with neurohypophyseal deficiency and in the Brattleboro rat, which has central diabetes insipidus (22, 27, 29, 34). Thus, the hyponatremia of adrenal insufficiency is dependent on elevated AVP release. As we (14) and others (15, 16) have demonstrated, AVP stimulates renal Na+ reabsorption in the ASDN by increasing ENaC activity. The current results demonstrating that AVP increases ENaC activity are consistent with these earlier findings. Akin to its regulation of aquaporin 2 water channels, AVP stimulates ENaC in principal cells via the V2 receptor (14). The current findings that AVP levels are increased in Adx mice and that inhibition of the V2 receptor decreases ENaC activity in ASDN from these mice to levels that are identical to those observed in control animals demonstrates that elevated AVP is the driving force maintaining ENaC activity high in Adx mice. Moreover, the findings that all three ENaC subunits are expressed in the ASDN of Adx mice and that V2 receptor antagonism in these animals does not overtly affect ENaC subunit expression are consistent with AVP stimulating ENaC via a posttranslational mechanism. The current electrophysiology results enable elaboration of the SCIO-469 chemical information mechanism by which elevated AVP levels in Adx mice increase ENaC activity. We find that ENaC Po is clamped and N is elevated in these mice resulting from the new balance between stimulation by AVP as countered by loss of stimulation by a dearth of aldosterone. Both aldosterone and AVP increase ENaC Po and N with the major, long-term effect of AVP being an increase in N (10, 11, 14, 21). Irrespective of the exact molecular mechanism, a consequence of adrenalectomy is that ENaC is no longer regulated in a normal manner by feedback signaling in response to change.Ng inactivating MR mutations andMironova et al.10098 | www.pnas.org/cgi/doi/10.1073/pnas.AS deficiency, which require sodium supplementation to survive (4, 8, 9, 33). Clearly the hormonal state, and thus phenotype, of loss-offunction of MR or AS do not completely overlap that of adrenalectomy. With MR dysfunction, the RAAS is up-regulated (13). With AS dysfunction, aldosterone is absent, but the levels of other adrenal steroids capable of mineralocorticoid action–in particular, corticosterone–are increased (9, 32, 33). In Adx mice, there is no aldosterone or other adrenal steroids and catecholamines; thus, these animals receive no input from the adrenal gland to ENaC. Moreover, akin to adrenal insufficiency, removal of the adrenal glands, as shown here and by others (27?9), causes marked increases in plasma AVP levels. Increases in AVP are not present with either MR or AS dysfunction (25). Usually, AVP release is primarily controlled by plasma osmolality. Elevated AVP release in adrenal-insufficient states (that lack both glucocorticoids and mineralocorticoids) results from two events. There is loss of negative-feedback regulation by glucocorticoids of the hypothalamic ituitary axis controlling AVP release. There also is strong nonosmotic stimulation of AVP release, resulting from volume depletion due to sodium and water wasting by the kidney (27, 28). It is recognized that adrenal insufficiency and central diabetes insipidus are counterpoints when considering the equilibrium distribution of sodium and water: The pattern of sodium and water distribution in either deficiency depends in part on the activity of the remaining gland. As such, the hyponatremia of adrenal insufficiency is absent when combined with neurohypophyseal deficiency and in the Brattleboro rat, which has central diabetes insipidus (22, 27, 29, 34). Thus, the hyponatremia of adrenal insufficiency is dependent on elevated AVP release. As we (14) and others (15, 16) have demonstrated, AVP stimulates renal Na+ reabsorption in the ASDN by increasing ENaC activity. The current results demonstrating that AVP increases ENaC activity are consistent with these earlier findings. Akin to its regulation of aquaporin 2 water channels, AVP stimulates ENaC in principal cells via the V2 receptor (14). The current findings that AVP levels are increased in Adx mice and that inhibition of the V2 receptor decreases ENaC activity in ASDN from these mice to levels that are identical to those observed in control animals demonstrates that elevated AVP is the driving force maintaining ENaC activity high in Adx mice. Moreover, the findings that all three ENaC subunits are expressed in the ASDN of Adx mice and that V2 receptor antagonism in these animals does not overtly affect ENaC subunit expression are consistent with AVP stimulating ENaC via a posttranslational mechanism. The current electrophysiology results enable elaboration of the mechanism by which elevated AVP levels in Adx mice increase ENaC activity. We find that ENaC Po is clamped and N is elevated in these mice resulting from the new balance between stimulation by AVP as countered by loss of stimulation by a dearth of aldosterone. Both aldosterone and AVP increase ENaC Po and N with the major, long-term effect of AVP being an increase in N (10, 11, 14, 21). Irrespective of the exact molecular mechanism, a consequence of adrenalectomy is that ENaC is no longer regulated in a normal manner by feedback signaling in response to change.
