Cardiorenal-endocrine dynamics during and following volume expansion

Role of atrial natriuretic peptide in mediating the blood pressure-independent natriuresis elicited by systemic inhibition of nitric oxide

While it is clearly recognized that increased intrarenal nitric oxide (NO) levels elicit natriuresis, confounding data showing that systemic nitric oxide synthase inhibition (NOSi) also increases sodium excretion (U_NaV) poses a conundrum. This response has been attributed to the associated increases in arterial pressure (AP); however, the increases in AP and in U_NaV are temporally dissociated. The changes in regional renal haemodynamics induced by NOSi could also contribute to the alterations of U_NaV. To evaluate the roles of AP and non-AP mechanisms mediating the natriuresis, N_ω-nitro-l-arginine methyl ester hydrochloride (L-NAME) was infused i.v. at doses ranging from 5 to 50 μg/kg/min in anaesthetized rats. U_NaV, perfusion of the cortex (cortical blood flow, CBF) and medulla (medullary blood flow, MBF) with laser-Doppler flowmetry and glomerular filtration rate (GFR) were measured. U_NaV increased from 0.6 ± 0.2 to 1.6 ± 0.1 μmol/kg/min (P < 0.05) with the lower nonpressor doses. With the higher doses, AP increased from 116 ± 4 to 122 ± 4 mmHg and U_NaV increased from 1.1 ± 0.3 to 3.3 ± 0.7 μmol/min/g (P < 0.002). U_NaV increased similarly in a group where renal AP was maintained at baseline levels. The associated reductions in CBF (17 ± 5 and 38 ± 5 %) and MBF (27 ± 6 and 52 ± 6 %) would be expected to attenuate rather than contribute to the natriuresis. Plasma atrial natriuretic peptide (ANP) concentrations increased significantly following NOSi. Anantin, a natriuretic peptide receptor-A blocker, prevented or reversed the L-NAME-induced natriuresis without altering the L-NAME-induced changes in AP or CBF. The results indicate that increased ANP and related natriuretic peptides mediate the AP-independent natriuresis, at least partly, elicited by systemic L-NAME infusion and help resolve the conundrum of natriuresis during systemic NOSi.

Plasma adrenomedullin concentration in dogs with myxomatous mitral valvular disease

Adrenomedullin (AM), a peptide identified to have vasodilating and natriuretic effects, is involved in the regulation of the cardiovascular system. To evaluate plasma AM concentration in dogs with myxomatous mitral valvular disease (MMVD), and to investigate the associations between the concentrations of plasma AM and natriuretic peptides and the echocardiographic data, we evaluated plasma AM concentrations in 31 healthy control dogs and 57 dogs with MMVD. Plasma AM concentrations in dogs with MMVD were higher than that in the control subjects. The plasma AM concentration increased in conjunction with the severity of heart failure according to the International Small Animal Cardiac Health Council (ISACHC). The AM concentrations were 25.1 ± 5.0 fmol/ml (ISACHC class Ia), 29.9 ± 11.0 fmol/ml (ISACHC class Ib), 43.4 ± 19.8 fmol/ml (ISACHC class II) and 73.5 ± 21.7 fmol/ml (ISACHC class III) and 7.5 ± 5.1 fmol/ml (control group), respectively. The receiver operating characteristic curve indicated an area of 0.93 (95% CI, 0.8801-0.9889; <0.0001), a cutoff value of 30.5 fmol/ml, a sensitivity of 87.1%, and a specificity of 82.5% for the determination of congestive heart failure. Plasma AM concentrations correlated with atrial natriuretic peptide concentrations, LA/Ao ratio, and left ventricular diameter. In conclusion, AM may be a potential diagnostic marker for canine MMVD and possibly plays a pathophysiological role in collaboration with the other neurohumoral factors such as natriuretic peptides.

Cardio-renal-endocrine dynamics during stepwise infusion of physiologic and pharmacologic concentrations of atrial natriuretic factor in the dog

Infusion of alpha-human atrial natriuretic factor (alpha-h-ANF) into pentobarbital anesthetized dogs (n = 10) at 0.0025, 0.005, 0.01, and 0.3 micrograms/kg/min was performed to differentiate the physiologic actions of atrial natriuretic factor from its pharmacologic actions. The lowest doses of atrial natriuretic factor infusion resulted in circulating levels that were previously produced by 0-10% saline volume expansion. At the lowest infusion rate, circulating ANF increased 31 +/- 3 pg/ml, resulting in a significant increase in absolute sodium excretion, fractional excretion of sodium, and fractional excretion of lithium, and a significant decrease in urine osmolality. A greater change in circulating atrial natriuretic factor (96 +/- 12 pg/ml) was required to significantly decrease right atrial pressure, cardiac output, and plasma renin activity, and to increase systemic vascular resistance and total and fractional excretion of potassium. The highest dose of atrial natriuretic factor infused was required to decrease arterial pressure and renal vascular resistance. The present study demonstrates that atrial natriuretic factor is natriuretic and diuretic at physiologic concentrations; at low concentrations, atrial natriuretic factor appears to decrease the whole kidney proximal tubular reabsorption of sodium and does not affect glomerular filtration rate; a greater (but physiologic) change in circulating atrial natriuretic factor is required to significantly decrease cardiac output, cardiac filling pressure, and plasma renin activity than is required to significantly increase sodium excretion; and a decrease in systemic arterial pressure and vascular resistance does not occur at physiologic concentrations of atrial natriuretic factor.