Effects of ethacrynic acid on electrolyte and fluid transport by the guinea pig gallbladder

Intracerebroventricular injection of ethacrynic acid induces status epilepticus

The intracerebroventricular (i.c.v.) injection of ethacrynic acid to mice at a dose of more than 25 micrograms induced repeated tonic-clonic convulsions with subsequent death. Ethacrynic acid was more potent than other loop diuretics such as furosemide and bumetanide. Diazepam and 2-amino-5-phosphonovaleric acid notably reduced both the incidence of convulsion and the lethality seen after ethacrynic acid administration. Both phenobarbital and ketamine suppressed the incidence of convulsions but not the lethality. Without effects on the incidence of convulsions or lethality, dextromethorphan prolonged, while phenytoin or atropine shortened, the time to the onset of convulsion. Neither ethosuximide, carbamazepine, nor muscimol had a significant effect on the responses to ethacrynic acid. The present findings indicate that i.c.v. injected ethacrynic acid shows strong convulsive activity, probably due to impairment of Cl- transport processes, concomitant with enhancement of excitatory amino acid activity in the brain.

Influence of serosal hydrostatic pressure on net water and electrolyte transport across the isolated rat colonic mucosa exposed to different secretagogues

The influence of 2 cm and 7 cm hydrostatic pressure applied upon the serosal side on net water and electrolyte transport and paracellular permeability was investigated in everted sacs of stripped rat colon mucosa exposed to different secretagogues. A 2 cm pressure abolished net fluid absorption in the presence of deoxycholic acid, bisacodyl, ethacrynic acid and rhein and reduced absorption in the tissue pretreated with cholera toxin. The paracellular permeability was increased by deoxycholic acid, bisacodyl and ethacrynic acid and diminished under the influence of rhein and cholera toxin. At a pressure of 7 cm H2O fluid movement was directed toward the mucosal side parallel to the increase of the paracellular permeability. The fluid appearing at the mucosal side was isotonic in the presence of deoxycholic acid, ethacrynic acid and rhein but hypotonic when the tissue was pretreated with cholera toxin. From the pressure-induced net water flow and the composition of the transferred fluid secretagogues acting predominantly on paracellular pathway can be distinguished from secretagogues acting on basis of other mechanisms.

Ethacrynic acid facilitates gentamicin entry into endolymph of the rat

Influence of ethacrynic acid (EA) upon gentamicin kinetics in perilymph and endolymph was studied in rats that were given a constant-infusion of gentamicin (150 micrograms/min) and EA (140 micrograms/min). Inner ear fluids and plasma were sampled up to 5 h. The purity of the endolymph was ensured by measurement of sodium and potassium concentrations. Gentamicin assay was done with a modified radioimmunoassay. Results show that EA facilitates the entry of gentamicin into endolymph, while it does not affect the kinetics of the drug in perilymph. Although the mechanism of this facilitation remains unclear, this result may account for the ototoxic potentiation reported between EA and aminoglycoside antibiotics.

Effect of "high ceiling" diuretics on active salt transport in the cortical thick ascending limb of Henle's loop of rabbit kidney. Correlation of chemical structure and inhibitory potency

The group of "high ceiling" diuretics consists of a variety of chemically different potent diuretic and saluretic substances. Appart from a few exemptions direct evidence for an action of these substances in the thick ascending limb of the loop of Henle (TAL) is still lacking. For furosemide, we have reported recently that it inhibits most likely the Na+-2 Cl--K+ cotransport system present in the lumen membrane of the TAL. The present study tests: 1. whether other "high ceiling" diuretics have a similar site and mode of action, and 2. how modifications of the furosemide molecule alter the inhibitory potency. Isolated cortical TAL (cTAL) segments (n = 185) of rabbit kidneys were perfused in vitro. The equivalent short circuit current (Isc = transepithelial PD/transepithelial resistance), as a measure of active salt transport was correlated to the dose of 64 substances. Several diuretics, such as 2-aminomethyl-4-(1,1-dimethyl-ethyl)-6-iodophenol hydrochloride (MK 447), hydrochlorothiazide, muzolimine, etozoline, tizolimide, amiloride, and triamterene were ineffective both from the lumen and basolateral side at concentrations as high as 10(-4) - 10(-3) mol X 1(-1). The phenoxyacetic acids ethacrynic acid, indacrinone (MK 196), and to less an extend tienilic acid were inhibitory active. They differed from furosemide in one or more of the following criteria: delayed onset, incomplete reversibility, stronger action from the bath, different slope of the dose response curve. Similarly, 1-ozolinone acted stronger from the bath. In contrast, the diuretics of the furosemide type and related compounds (bumetanide and piretanide) showed rapid onset and complete reversibility of inhibition. These substances acted stronger from the lumen. The individual positions in the benzyl ring of the diuretics were differently affected by substitutions, leading to parallel shifts in the dose response curves with halfmaximal inhibition at concentrations ranging between 8 X 10(-8) to greater than 10(-4) mol X 1(-1). For these substances the calculated Hill coefficients were close to unity: 0.96 +/- 0.05. We conclude that the so called "high ceiling" or "loop" diuretics consist of at least 3 groups: 1. drugs that do not interfere with the active salt transport in the cTAL segment, 2. drugs that interfere by so far not characterised mechanisms, and 3. drugs of the furosemide type which inhibit the Na+-2 Cl--K+ cotransport system in the lumen membrane of the cTAL segment.

Electron microscopy of the stria vascularis and its response to etacrynic acid. A study using electron-dense tracers and extracellular surface markers

Lanthanum nitrate (La3+), ruthenium red (RR) and tannic acid (TA) have been used to examine the cell coat and permeability pathways in thin sections of the stria vascularis of normal and etacrynic-acid (EA)-treated guinea pigs. The tight junctions around the stria, at both endolymphatic and spiral ligament sides, excluded tracers even when EA-associated oedema was well advanced. La3+ was also unable to enter oedematous stria from the capillaries. A dense fibrillar coat was revealed on the endolymphatic marginal cell surface. This coat was disorganised during EA intoxication. Both RR and TA crossed the apical membrane and produced enhanced contrast in some, but not all, marginal cells in EA-treated animals. The results suggest that EA may affect the structure of the apical membrane of the marginal cells and that there is heterogeneity amongst the marginal cell population. These possibilities are discussed.