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Electrophysiological response of amiloride action on renal proximal tubule
THROMBOXAN RECEPTOR ANTAGONIST AGGRAVATES POSTiSCHEMIC RENALFAILURE M.__~.Lerki6,V.Veljkovid, D.Jovovi~, J.Varagi6, ~.. Mali~evi6, A. Lazarov, N. Ostoji6 and D. Sugi6 Institute for Medical Research, Dr. 8uboti6.a 4, PO Box 721, 11001 Belgrade, Yugoslavia It has been postulated that thromboxan A2 participates in the pathogenesis of acute renal failure. In order to examine this hypothesis, the effect of thromboxan receptor antagonist (BM !3.505, Boehringer) on the course of postischemic acute renal failure (ARF) was'investigated. The experimental group received BM. 13.505 (15 or 30 mg/kg b.w., through a gastric tube, 1 hour before induction of ARF), while controls received veehicle via the same~route. The right kidney was removed, and the left renal artery was clamped for 45 minutes. BM 13.505 in dose of 15 mg/kg b.w. did not affect the course of ARK However in rats which received higher dose (30 mg/kg b,w.) of BM 13.505 further deterioration of renal function was observed. Thus, when compared to controls, plasma urea and creatinine concentrations were significantly higher while urea and creatinine clearances were lower in rats treated with BM 15.505 four days after induction of ARF.The histological examination revealed that degree of tubular epithelial cell necrosis, tubular dilatation and mononuclear infiltration was significantly higher in rats treated with BM 15.505 four days after ARF than in controls. Two hours-after the administration of BM 15.505 plasma renin .activity (PRA) significantly increased from 4.98+1.45 ng Al/ml/h to 10.38+2.25 ng AUmL/h, and Subsequently decreased to 6.22+1.97 ng AVml/h 24 hours after BM 1:3.505. Our results indicated that thromboxan receptor antagonist stimulate the secretion of renin. We suggest that increased secretion of renin could cause deterioration of renal function in postisehemic ARF reaching the maximum four days after-effective inhibition of thromboxan receptors.
IELECTROPHYSIOLOGICAL RESPONSE OF AMILORIDE ACTION ON RENAL PROXIMAL TUBULE Ira Samar~i~a Dept of Pharmacology , Faculty of Pharmacy & Biochememistry University of Zagreb, Croatia The effect of potassium-sparing diuretic amiloride is based on the inhibition of sodium-channels in distal tubules. The drug, present in the primary urine, starts to act at micromolar concentration, when i t a r r i v e to the distal tubules. By this work it was observed a possible action of amiloride efficiency even in proximal tubules, but at higher concentration than micromolar. Cell membrane potential changes were measured on isolated perfused rabbit tubules. It was established that 1 mmol/L amiloride, a ~ d t ~ o the peritubular side~ depolarized'the cells by +13 +/-3 mV;(n=lO) because of blocking basolateral potassium-permeability. This alteration was omitted either in the presence of barium or by changing the pH of the perfused solution from 7.4 to 6.~ , which inhibits potassium conductance. However luminal perfusion with amiloride caused inhibition of Na/H-echanger and for this reason the cells hyperpolarized by -3 +/-1 mV (n=$). From these results it can be concluded that amiloride becomes a nonselective cation blocker Only at higher concentration level. That weeks not only on sodium transport pathways (sodium-channel, Na/H-exchanger), but also on potassium conductance (potassium-channel) in particular nephron segments~ where the drug interacts with a cation blnding site.
SEROTONERGIC MECHANISMS ON R E N A L BLOOD FLOW IN THE IN SITU AUTOPERFUSED RAT KIDNEY. J, A. Mor~n, C. Velasco, E. Martin, M.U Marffn and L. San l~om~ Lab. F a r m a c o g n o s i a y F a r m a c o d i n a m i a , Facultad de Farmacia, Universidad de Salamanca. 37007 SALAMANCA, Spain. This study was designed to define the serotonergic receptor subtypes of renal vascular beds in the rat kidney in vivo and to demonstrate the possible existence of a peripheral mechanisms which can be activated by exogenous 5hydroxytryptamine (5-HT) or 5-HT agonists. 5-HT and serotonergic agonists were injected directly intoartery (i.a.) of the left kidney in anaesthetized rats. A possible interaction between serotonergic mechanisms and sympathetic renal nerve stimulation in anaesthetized rat, also had been investigated. The local injection of 5-HT increased, in a dose dependent way, the perfusion pressure in the in situ autoperfused rat renal vascular beds. Similar results were obtained by i.a. administration of 1-(3-chlorophenyl)piperazine (m-CPP). The local vascular renal effects of both 5-HT or m-CPP, w a s c o m p l e t e l y antagonized by both ritanserin and enalapril and was not modified by propranolol, prazosin or indomethacin pretreatment. However, these agonists not modified the perfusion responses to electrical stimulation of the sympathetic renal nerves. Our results suggest a vasoconstrictor renal serotonergic effect mediated by a local 5-HT2 activation and by a increase of angiotensin 11.
INFLUENCE OF SELECTED ENDOGENOUS AND EXOGENOUS COMPOUNDS ON CALCIUM OXALATE PRECIPITATION L. Saso~ S. Posta, G. Valentini, R. Guglielmi, L. Paris, and B. Silvestrini. Institute of Pharmacology and Pharmacognosy, University of Rome "La Sapienza', P.le A. Moro 5, 00185 Rome, Italy. In a previous communication [Saso et al., (1994). Effects o f some urine components on calcium oxalate precipitation, XXVII National Congress of Pharmacology, Torino, Italy] we reported that citrate, sulphate, magnesium, albumin and selected bile salts inhibit precipitation of calcium oxalate (CaOx) in vitro. In this work we extended the screening to other urine components as well as exogenous compounds. The effect of sodium chloride on CaOx precipitation was studied over a 30 min period after the preparation of supersaturated solutions of CaOx (0.0125 M and 0.005 M), observing that NaCI concentrations >0.1 increased CaOx solubility. Several carboxylic and di-carboxylic acids, like formic, acetic, propionic, pyruvic, gluconic, malonic, maleic, malic, succinic and tartaric acid, were tested, but none of them appeared more active than citric acid, that is already used in the therapy of certain forms of nephrolithiasis. Amino acids like Ala, Arg, Asp, Glu, Gly, and Ser, which are known to bind calcium, showed little activity. Biological buffers as CAPS, MES, CHES and bicine, which form soluble complexes with Ca2+, were less active than citrate in preventing CaOx precipitation. Work is in progress to search for new compounds potentially useful in the treatment of nelahrolithiasis.
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IELECTROPHYSIOLOGICAL RESPONSE OF AMILORIDE ACTION ON RENAL PROXIMAL TUBULE Ira Samar~i~a Dept of Pharmacology , Faculty of Pharmacy & Biochememistry University of Zagreb, Croatia The effect of potassium-sparing diuretic amiloride is based on the inhibition of sodium-channels in distal tubules. The drug, present in the primary urine, starts to act at micromolar concentration, when i t a r r i v e to the distal tubules. By this work it was observed a possible action of amiloride efficiency even in proximal tubules, but at higher concentration than micromolar. Cell membrane potential changes were measured on isolated perfused rabbit tubules. It was established that 1 mmol/L amiloride, a ~ d t ~ o the peritubular side~ depolarized'the cells by +13 +/-3 mV;(n=lO) because of blocking basolateral potassium-permeability. This alteration was omitted either in the presence of barium or by changing the pH of the perfused solution from 7.4 to 6.~ , which inhibits potassium conductance. However luminal perfusion with amiloride caused inhibition of Na/H-echanger and for this reason the cells hyperpolarized by -3 +/-1 mV (n=$). From these results it can be concluded that amiloride becomes a nonselective cation blocker Only at higher concentration level. That weeks not only on sodium transport pathways (sodium-channel, Na/H-exchanger), but also on potassium conductance (potassium-channel) in particular nephron segments~ where the drug interacts with a cation blnding site.
SEROTONERGIC MECHANISMS ON R E N A L BLOOD FLOW IN THE IN SITU AUTOPERFUSED RAT KIDNEY. J, A. Mor~n, C. Velasco, E. Martin, M.U Marffn and L. San l~om~ Lab. F a r m a c o g n o s i a y F a r m a c o d i n a m i a , Facultad de Farmacia, Universidad de Salamanca. 37007 SALAMANCA, Spain. This study was designed to define the serotonergic receptor subtypes of renal vascular beds in the rat kidney in vivo and to demonstrate the possible existence of a peripheral mechanisms which can be activated by exogenous 5hydroxytryptamine (5-HT) or 5-HT agonists. 5-HT and serotonergic agonists were injected directly intoartery (i.a.) of the left kidney in anaesthetized rats. A possible interaction between serotonergic mechanisms and sympathetic renal nerve stimulation in anaesthetized rat, also had been investigated. The local injection of 5-HT increased, in a dose dependent way, the perfusion pressure in the in situ autoperfused rat renal vascular beds. Similar results were obtained by i.a. administration of 1-(3-chlorophenyl)piperazine (m-CPP). The local vascular renal effects of both 5-HT or m-CPP, w a s c o m p l e t e l y antagonized by both ritanserin and enalapril and was not modified by propranolol, prazosin or indomethacin pretreatment. However, these agonists not modified the perfusion responses to electrical stimulation of the sympathetic renal nerves. Our results suggest a vasoconstrictor renal serotonergic effect mediated by a local 5-HT2 activation and by a increase of angiotensin 11.
INFLUENCE OF SELECTED ENDOGENOUS AND EXOGENOUS COMPOUNDS ON CALCIUM OXALATE PRECIPITATION L. Saso~ S. Posta, G. Valentini, R. Guglielmi, L. Paris, and B. Silvestrini. Institute of Pharmacology and Pharmacognosy, University of Rome "La Sapienza', P.le A. Moro 5, 00185 Rome, Italy. In a previous communication [Saso et al., (1994). Effects o f some urine components on calcium oxalate precipitation, XXVII National Congress of Pharmacology, Torino, Italy] we reported that citrate, sulphate, magnesium, albumin and selected bile salts inhibit precipitation of calcium oxalate (CaOx) in vitro. In this work we extended the screening to other urine components as well as exogenous compounds. The effect of sodium chloride on CaOx precipitation was studied over a 30 min period after the preparation of supersaturated solutions of CaOx (0.0125 M and 0.005 M), observing that NaCI concentrations >0.1 increased CaOx solubility. Several carboxylic and di-carboxylic acids, like formic, acetic, propionic, pyruvic, gluconic, malonic, maleic, malic, succinic and tartaric acid, were tested, but none of them appeared more active than citric acid, that is already used in the therapy of certain forms of nephrolithiasis. Amino acids like Ala, Arg, Asp, Glu, Gly, and Ser, which are known to bind calcium, showed little activity. Biological buffers as CAPS, MES, CHES and bicine, which form soluble complexes with Ca2+, were less active than citrate in preventing CaOx precipitation. Work is in progress to search for new compounds potentially useful in the treatment of nelahrolithiasis.
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