Crosstalk between the heart and peripheral organs in heart failure

Mediators from peripheral tissues can influence the development and progression of heart failure (HF). For example, in obesity, an altered profile of adipokines secreted from adipose tissue increases the incidence of myocardial infarction (MI). Less appreciated is that heart remodeling releases cardiokines, which can strongly impact various peripheral tissues. Inflammation, and, in particular, activation of the nucleotide-binding oligomerization domain-like receptors with pyrin domain (NLRP3) inflammasome are likely to have a central role in cardiac remodeling and mediating crosstalk with other organs. Activation of the NLRP3 inflammasome in response to cardiac injury induces the production and secretion of the inflammatory cytokines interleukin (IL)-1β and IL-18. In addition to having local effects in the myocardium, these pro-inflammatory cytokines are released into circulation and cause remodeling in the spleen, kidney, skeletal muscle and adipose tissue. The collective effects of various cardiokines on peripheral organs depend on the degree and duration of myocardial injury, with systematic inflammation and peripheral tissue damage observed as HF progresses. In this article, we review mechanisms regulating myocardial inflammation in HF and the role of factors secreted by the heart in communication with peripheral tissues.

Biphasic effects of ANP infusion in conscious, euvolumic rats: roles of AQP2 and ENaC trafficking

Atrial natriuretic peptide (ANP) acutely promotes water and sodium excretion, whereas subchronic effects involve water retention. Renal hemodynamics, water and sodium excretion, and aquaporin-2 (AQP2) and epithelial Na channel (ENaC) subcellular trafficking were determined in response to continuous ANP infusion in conscious rats, where body sodium and fluid balance was constantly maintained. ANP (0.5 μg·kg−1·min−1) evoked a transient (peak at 10 min) fivefold diuresis followed by reduced urine production to control levels (30- to 90-min period). The fractional distal water excretion was significantly increased initially and then decreased in response to ANP. There was no change in the subcellular localization of AQP2 and AQP2 phosphorylated in PKA consensus site S256 (p-AQP2) 10 min after ANP infusion. In contrast, after 90 min a marked increase in apical labeling of AQP2 and p-AQP2 was observed in the inner and outer medullary collecting ducts but not in cortical collecting ducts. In support of this, ANP induced plasma membrane targeting of AQP2 in transiently AQP2-transfected cells. ANP infusion evoked an instant increase in renal sodium excretion, which persisted for 90 min. Ten minutes of ANP infusion induced no changes in the subcellular localization of ENaC subunits, whereas a marked increase in apical targeting of α- and γ-subunits was observed after 90 min. In conclusion, 1) ANP infusion induced a sustained natriuresis and transient diuresis; 2) there were no changes in the subcellular localization of AQP2 and ENaC subunits after 10 min of ANP infusion; and 3) there was a marked increase in apical targeting of AQP2, p-AQP2, and α- and γ-ENaC after 90 min of ANP infusion. The increased targeting of ENaC and AQP2 likely represents direct or compensatory effects to increase sodium and water reabsorption and to prevent volume depletion in response to prolonged ANP infusion.

Taurine modulates arginine vasopressin-mediated regulation of renal function

Taurine has been implicated in the regulation of arginine vasopressin (AVP) secretion, and we have previously shown altered renal excretory function in the taurine-depleted rat. To further elucidate the role of taurine in AVP-mediated renal responses, the effects of an antagonist for renal AVP receptors were examined in four groups of conscious rats: control, taurine-supplemented, taurine-depleted, and taurine-repleted. Control and taurine-supplemented rats displayed similar and significant AVP receptor antagonist-induced elevations in fluid excretion, sodium excretion, and free water clearance but a marked reduction in urine osmolality. These effects are consistent with inhibition of endogenous AVP activity. By contrast, in the taurine-depleted rats, the magnitude and the time course of drug-induced renal excretory responses lagged behind those of the control and taurine-supplemented groups. Further, baseline urine osmolality was significantly higher in the taurine-depleted compared with the control or taurine-supplemented groups. However, after administration of the antagonist, taurine-depleted rats manifested a delayed but more marked reduction in urine osmolality, thereby eliminating the baseline differential that existed between the taurine-depleted rats and control or taurine-supplemented groups. Consistent with these observations, plasma AVP was significantly increased in the taurine-depleted compared with the control rats. Interestingly, taurine repletion shifted all responses closer to the control group. Analysis of the data suggests that the effect of the antagonist on renal excretory function is related primarily to altered tubular reabsorption activity. These observations suggest that taurine modulates renal function, and, thereby, body fluid homeostasis, through an AVP-dependent mechanism.