Mercurial diuretics

Diuretics. Use and misuse

It is apparent that the large number of diuretics available today enables the clinician to mobilize edema fluid from patients with heart failure or other fluid retention states, to control blood pressure effectively in many patients with hypertension, and to manage many nonedematous states more successfully. The potency of some of these agents and their varied effects on renal tubular transport necessitate a cautious approach based on an understanding of their mechanisms of action. By selectively choosing different diuretics or diuretic combinations, the clinician can achieve the desired diuretic effect and prevent many of the electrolyte and acid-base derangements that accompany diuretic therapy. Selectivity of usage based on knowledge of the practical clinical pharmacology of these agents will also minimize the occurrence of side effects and avoid undesirable drug interactions.

A comparison of the effects of glucose ingestion and NH4Cl acidosis on urinary calcium and magnesium excretion in man

Both glucose ingestion and NH(4)Cl acidosis have been reported to augment urinary calcium (U(Ca) V) and magnesium (U(Mg) V) excretion. Both also cause acidification of the urine and an increase in renal acid excretion. To examine whether a common mechanism of action was involved, the effects of glucose ingestion and NH(4)Cl acidosis on U(Ca) V and U(Mg) V were tested in the same subjects. Glucose ingestion caused significant increases in both U(Ca) V and U(Mg) V. During stable NH(4)Cl acidosis, U(Ca) V increased significantly, while U(Mg) V was unaffected. When a glucose load was given during acidosis, the separate effects of acidosis and glucose on U(Ca) V were additive, whereas U(Mg) V increased less than observed during normal acid-base balance. Although renal acid excretion increased and the urine was acidified after glucose in the normal steady state, when glucose was administered during NH(4)Cl acidosis urine pH rose and there was no change in renal acid excretion. We concluded that NH(4)Cl acidosis and glucose ingestion reduce the renal tubular reabsorption of magnesium and (or) calcium, but they act through separate mechanisms.

Effect of hypotonic expansion on sodium, water, and urea excretion in late pregnancy: the influence of posture on these results

Mineralocorticoid-treated, normotensive third trimester subjects positioned in lateral recumbency were studied before and during the infusion of 300 mEq of hypotonic saline. Urinary sodium excretion increased in all subjects from a mean value of 199 to 416 muEq/min. In 12 maximally hydrated subjects free water clearance (C(H2O)) and urine flow (V) increased from means of 7.54 and 9.50 to 11.6 and 14.5 ml/100 ml of glomerular filtrate (GFR) Also the ratio of urea to inulin clearance (C(urea)/C(inulin)) increased from 0.59 to 0.64. The changes in the renal handling of water and urea suggest that fractional sodium reabsorption decreased at proximal nephron sites. The subjects then assumed a supine position, and the results were compared to those obtained during the lateral recumbent control periods. Filtered sodium decreased in 11 experiments, but in five studies it remained up to 2.6 mEq/min above control values. There was only one instance in which a significant increase in sodium excretion occurred. It was concluded that supine recumbency blunts natriuresis despite volume expansion or an increase in the filtered load of sodium.Finally, in the 12 hydrated subjects supine recumbency reduced C(H2O) and V from a mean of 11.6 and 14.5 to 6.2 and 8.2 ml/100 ml of GFR. In eight of these experiments urine osmolality fell or did not change. Simultaneously, C(urea)/C(inulin) fell from 0.64 to 0.57. These data suggest that the antinatriuresis, which occurred when the volume-expanded subjects were positioned in supine recumbency, was accompanied by a decrease in the fractional reabsorption of sodium at proximal nephron sites.

Renin release: relation to renal sodium load and dissociation from hemodynamic changes

The relations between renin release and renal hemodynamics, renal sodium load, and sodium and water balance were studied during hyponatremia, hypernatremia, mercurial natriuresis, norepinephrine infusion, and reduction in renal perfusion pressure. Significant reciprocal relations were found between renin secretory activity and the renal arterial plasma sodium concentration, the filtered sodium load, and urinary sodium excretion; however, no significant, or even consistent, relations were found between renin release and any hemodynamic parameter or sodium or water balance. During bilateral stimulation of renin release, unilateral restoration of the filtered sodium load inhibited ipsilateral renin release, without demonstrable changes in hemodynamics, while renin release from the contralateral kidney continued unabated. However, this inhibition was not seen unless the filtered sodium load and urinary sodium excretion rose to control levels even though renal venous plasma sodium concentrations exceeded 170 mEq/liter. Thus, renin release can be dissociated from hemodynamics and sodium and water balance, but not from some function of the filtered sodium load. We propose that renin secretory activity is controlled by an intrarenal, but extravascular, sodium-sensitive mechanism and that the stimulus is a function of the sodium flux across the macula densa into the interstitium surrounding the contiguous juxtaglomerular cells.