The effects of new diuretics on net ion movements in sodium-rich smooth muscles

Pharmacokinetics of furosemide in anephric patients and in normal subjects

The pharmacokinetics of furosemide 40 mg i.v. were compared in 7 anephric patients and in 7 normal subjects. The average serum clearance was 66 ml/min in the patients and 219 ml/min in the normal subjects, and the corresponding weight corrected clearances were 1.33 ml/min . kg and 2.96 ml/min . kg. Binding to serum proteins was significantly decreased in the anephric subjects, in whom a significant negative correlation was found between the percentage binding and the volume of distribution VDSS. In the patients, but not in the normal subjects, there was a significant positive correlation between VDSS and serum clearance. Both in normal and anephric individuals 4-chlor-5-sulphamoyl-anthranilic-acid (CSA) was found, but there was no evidence of special accumulation either of CSA or anthranilic acid in the anephric patients. In the patients the initial increase in serum concentration of sodium and protein followed by a more conspicuous decrease were more pronounced, but none of the changes were statistically significant.

Effect of frusemide on the reactivity of rat portal vein

Short lengths of rat portal vein were suspended in Krebs bicarbonate solution. Contractile responses to noradrenaline and angiotensin II and the parameters of spontaneous contractions were determined before and after addition of frusemide at 10–6 and 10–4 g/ml. Frusemide at 10–6 g/ml slightly suppressed the amplitude of spontaneous contractions and slightly decreased the responses to noradrenaline and angiotensin II. At 10–4 g/ml the drug had a much greater inhibitory effect on endogenous and exogenous stimulation. The concentrations used appear to be similar to those achieved during effective diuretic and hypotensive treatment. It is postulated that frusemide may have a direct inhibitory action on the reactivity of vascular smooth muscle mrticularlv in the capacitance vessels.

The effects of transport inhibitors on sodium outflux and influx in red blood cells: evidence for exchange diffusion

Active sodium transport (outflux or efflux) in red blood cells generally has been measured by assessing the amount of outflux inhibited by digitalis glycosides (outflux-fraction I). The presence of a ouabain-uninhibited sodium outflux (outflux-fraction II) attributable either to a second active transport mechanism or to exchange diffusion has been the subject of recent investigations. In the present study a variety of transport inhibitors, including ouabain, ethacrynic acid, furosemide, oligomycin, and amiloride, were studied for their effects on these components of sodium transport in RBC. In the presence of ouabain both ethacrynic acid and furosemide exerted similar effects on sodium outflux, inhibiting approximately 0.5 mmoles/L of cells per hr. This component of sodium outflux has been called outflux-fraction II. Ethacrynic acid showed no inhibitory potency when ouabain and furosemide were present, thereby suggesting that the same outflux component (fraction II) was affected by ethacrynic acid and by furosemide. In addition, furosemide reduced sodium influx to the same extent that it reduced sodium outflux. Outflux-fraction II, as defined by furosemide, did not contribute a net sodium outflux. These results of sodium outflux and influx experiments confirm the existence of a transport pathway which does not contribute to net flux and which fits the definition of exchange diffusion. The inhibitory effect of furosemide on outflux-fraction II remained despite the use of a sulfhydryl protective reagent, whereas the effect of ethacrynic acid was obliterated. No combination of inhibitors was found which affected the residual or uninhibited sodium outflux (0.4-0.5 mmoles/liter of cells per hr). Oligomycin possessed an inhibitory potency less than that of ouabain, and it exerted no effect on sodium outflux if it was superimposed upon ouabain inhibition. Amiloride proved to be a very weak inhibitor of sodium outflux in human erythrocytes.

Ion movements in human red cells independent of the sodium pump

1. A study was made of the dependence on external Na of the movements of Na and K in human red cells. Special attention was given to ouabain-insensitive movements. The effect of internal Na on Na influx, and the influence of some sulphydryl inhibitors on ion movements and metabolism was also investigated.2. External Na stimulated ouabain-insensitive Na efflux and K influx. There was also a ouabain-insensitive component of Na influx that was raised on increasing the internal Na concentration. Exchange diffusion of Na appears to occur in the presence of ouabain and external K.3. Net transport of Na and K in the presence of ouabain was independent of external Na, as was also lactate production.4. Ethacrynic acid partially inhibited the Na pump; the Na-dependent components of Na efflux and K influx in the presence of ouabain were completely inhibited by ethacrynic acid. Both ouabain-sensitive and ouabain-insensitive adenosinetriphosphatase activities were inhibited by ethacrynic acid indicating a non-specific effect of this compound. Iodoacetamide decreased only the ouabain-insensitive ATPase activity.5. The results suggest that when the Na pump is blocked by ouabain, part of the residual ion movements can be attributed to exchange diffusion.

The action of ethacrynic acid on sodium efflux from single toad oocytes

1. Ethacrynic acid (10(-3)M) at pH 7.4 caused approximately 83% inhibition of Na efflux from single dissected toad oocytes.2. Less inhibition was found at concentrations below 10(-3)M but higher concentrations did not cause greater inhibition.3. At an external pH of 7.0 the onset of inhibition was more rapid than at pH 7.4.4. Ouabain (10(-3)M) produced only 30% inhibition of the Na efflux, and the subsequent application of ethacrynic acid largely inhibited the remaining efflux.5. Application of ouabain, after ethacrynic acid had produced some 80% inhibition, caused only a further 9% drop in efflux.6. In uninhibited cells, Na efflux was found to be greater at pH 8.0, and less at pH 7.0 than at 7.4.

Redistribution of renal blood flow produced by furosemide and ethacrynic acid

Outer medullary blood flow ( 85 Kr method) is markedly reduced by furose-mide and ethacrynic acid injected into the renal artery of unanesthetized dogs; juxtamedullary cortical flow is also decreased. Anatomic localization of the redistribution was verified by autoradiography and by silastic injection studies. The injected specimens demonstrated a relative increase in the resistance of the peritubular capillaries of the juxtamedullary cortex and outer medulla, the blood supply of the juxtamedullary tubules, Henle's loops and collecting ducts; the vasa recta were dilated. Total renal blood flow (Doppler Flowmeter) decreased 10% 1 min after injection, and then gradually began to increase at 2 to 3 min, reaching levels 25 to 30% above control as cortical blood flow increased. The vasodilatation in the cortex is probably localized in the pars radiata. The onset of the diuresis coincided with the decrease in renal blood flow, and persisted after total renal blood flow returned to control value. Thus, the time course of the dicresis correlated more closely with the sustained decrease in juxtameduiary and outer medullary blood flow.