Comparison of the natriuresis and chloruresis associated with glomerular hyperfiltration induced by atrial natriuretic factor or glucagon

A 4-h hyperglycaemic excursion induces rapid and slow changes in major electrolytes in blood in healthy human subjects

Hyperglycaemia is well known to cause reductions in plasma Na(+) levels or even hyponatraemia due to an osmotically induced dilution of the interstitium and blood. It is, however, unclear whether this dilution is significantly counteracted by ion regulatory homeostatic mechanism(s) or not. Furthermore, the effects of moderate hyperglycaemia on other major ions are less well known. To further clarify these questions, we measured the changes in blood osmolarity and concentrations of Na(+), K(+), Cl(-), Mg(2+) and Ca(2+) during a 4-h-long experimental hyperglycaemia in healthy subjects rendered temporarily insulin deficient using the hyperglycaemic clamp. Hyperglycaemia, 16.8 mM, was rapidly imposed from a baseline of 4.4 mM by intravenous somatostatin and glucose infusions in 19 healthy subjects (10 m, 9 f; age 36 ± 5 years (mean ± SD); BMI 22.7 ± 2.9 kg/m(2)). Subsequently, glycaemia was returned to basal and measurements continued until all dynamic changes had stopped (at ~8 h). Osmolarity increased from 281.8 ± 0.7 to 287.9 ± 0.7, while Na(+) decreased from 143.9 ± 0.3 to 138.7 ± 0.2, Cl(-) from 101.7 ± 0.2 to 99.5 ± 0.1, Ca(2+) from 1.98 ± 0.04 to 1.89 ± 0.02 and Mg(2+) from 0.84 ± 0.01 to 0.80 ± 0.00 mM. All these changes were rapidly reaching stable levels. K(+) increased from 4.02 ± 0.02 to 4.59 ± 0.02 mM (P < 0.0001) also reaching stable levels but with some delay. Na(+), Cl(-), Mg(2+) and Ca(2+) are essentially determined by blood dilution, and their values will remain diminished as long as the hyperglycaemia lasts. Partial suppression of insulin-stimulated Na(+)/K(+) pumping lead to increased K(+) levels. The combination of elevated K(+) and decreased Mg(2+) and Ca(2+) levels may lead to an altered excitability, which is particularly relevant for diabetic patients with heart disease.

Cellular basis for blunted volume expansion natriuresis in experimental nephrotic syndrome

Experimental nephrotic syndrome results in sodium retention, reflecting, at least in part, an intrinsic defect in renal sodium handling in the distal nephron. We studied the relationships among plasma atrial natriuretic peptide (ANP) concentration, sodium excretion (UNaV), and urinary cyclic GMP excretion (UcGMPV) in vivo, and the responsiveness of isolated glomeruli and inner medullary collecting duct (IMCD) cells to ANP in vitro, in rats with adriamycin nephrosis (6-7 mg/kg body weight, intravenously). 3-5 wk after injection, rats were proteinuric and had a blunted natriuretic response to intravenous infusion of isotonic saline, 2% body weight given over 5 min. 30 min after onset of the infusion, plasma ANP concentrations were elevated in normals and were even higher in nephrotics. Despite this, nephrotic animals had a reduced rate of UcGMPV after the saline infusion, and accumulation of cGMP by isolated glomeruli and IMCD cells from nephrotic rats after incubation with ANP was significantly reduced compared to normals. This difference was not related to differences in binding of 125I-ANP to IMCD cells, but was abolished when cGMP accumulation was measured in the presence of 10(-3) M isobutylmethylxanthine or zaprinast (M&B 22,948), two different inhibitors of cyclic nucleotide phosphodiesterases (PDEs). Infusion of zaprinast (10 micrograms/min) into one renal artery of nephrotic rats normalized both the natriuretic response to volume expansion and the increase in UcGMPV from the infused, but not the contralateral, kidney. These results show that, in adriamycin nephrosis, blunted volume expansion natriuresis is associated with renal resistance to ANP, demonstrated both in vivo and in target tissues in vitro. The resistance does not appear related to a defect in binding of the peptide, but is blocked by PDE inhibitors, suggesting that enhanced cGMP-PDE activity may account for resistance to the natriuretic actions of ANP observed in vivo. This defect may represent the intrinsic sodium transport abnormality linked to sodium retention in nephrotic syndrome.