Immunolocalisation of adenosine A(1) receptors in the rat kidney.

The location of adenosine A(1) receptors in the rat kidney was investigated using immunolabelling with antibodies raised to a 15-amino-acid sequence near the C-terminus of the receptor (antibody I) and to a 14-amino-acid sequence in the second extracellular loop (antibody II). In the cortex, antibody I bound to adenosine A(1) receptors in mesangial cells and afferent arterioles, whilst antibody II bound to receptors in proximal convoluted tubules. In the medulla, both antibodies bound to receptors in collecting ducts and the papillary surface epithelium. These observations provide support for the diverse functional roles previously proposed for the adenosine A(1) receptor in the kidney. The labelling of distinct but different structures in the cortex by antibodies raised to different amino acid sequences on the A(1) receptor protein suggests that differing forms of the receptor are present in this region of the kidney.

Effects of adenosine receptor antagonists on the responses to contrast media in the isolated rat kidney.

Contrast media can induce both a decrease in renal blood flow and a reduction in glomerular filtration rate (GFR) when administered to both experimental animals and humans. In the present study we have examined the role of adenosine in mediating these effects using the isolated perfused rat kidney. Kidneys were perfused with a 6. 7%-(w/v)-albumin-based perfusate supplemented with glucose and amino acids (n=6 per group). They were exposed to diatrizoate [20 mg of iodine (mgI)/ml; osmolality 1650 mOsm/kg of water] or iotrolan (20 mgI/ml; osmolality 320 mOsm/kg of water) in the presence or absence of theophylline (10.8 microg/ml), or to diatrizoate in the presence or absence of a specific adenosine A(1) receptor antagonist (KW-3902; 2 microg/ml) or a specific A(2) receptor antagonist (KF17837; 6 microg/ml). Diatrizoate (n=6) produced a fall in GFR from 0.65+/-0.04 to 0.42+/-0.03 ml.min(-1).g(-1) (P<0.05); renal perfusate flow (RPF) also declined, from 36.5+/-3.8 to 22.0+/-3.2 ml. min(-1).g(-1) (P<0.05). Iotrolan (n=6) produced a fall in GFR from 0. 64+/-0.02 to 0.48+/-0.04 ml.min(-1).g(-1) (P<0.05) and in RPF from 33.3+/-3.8 to 24.0+/-3.0 ml.min(-1).g(-1) (P<0.05). Theophylline (10.8 microg/ml) prevented the fall in GFR caused by either diatrizoate (baseline, 0.63+/-0.05 ml.min(-1).g(-1); diatrizoate+theophylline, 0. 60+/-0.04 ml.min(-1).g(-1)) or iotrolan (baseline, 0.64+/-0.04 ml. min(-1).g(-1); iotrolan+theophylline, 0.67+/-0.05 ml.min(-1).g(-1)), but did not affect the decreases in RPF caused by either agent. KW-3902 (2 microg/ml) also prevented the fall in GFR produced by diatrizoate (baseline, 0.66+/-0.05 ml.min(-1).g(-1); diatrizoate+KW-3902, 0.61+/-0.05 ml.min(-1).g(-1)), while the fall in RPF remained unaffected. KF17837 (6 microg/ml) had no effect on the decreases in either GFR or RPF induced by diatrizoate (n=6 per group). The results suggest a role for adenosine acting at the A(1) receptor in mediating the decrease in GFR induced by contrast media. This effect is independent of a change in renal vascular resistance, and possibly secondary to mesangial cell contraction causing a decrease in the ultrafiltration coefficient.

Differential expression of renal adenosine A(1) receptors induced by acute renal failure.

The distribution of renal adenosine A(1) receptors was investigated in rats with glycerol- or mercuric chloride (HgCl(2))-induced acute renal failure. Receptors were localised by autoradiography using [(3)H]8-cyclopentyl-1,3-dipropylxanthine ([(3)H]DPCPX), a selective A(1) adenosine receptor antagonist. In saline-injected control animals, significant labelling with [(3)H]DPCPX was detected in glomeruli, the inner stripe of outer medulla, and the inner medulla. Sixteen hours following induction of glycerol-induced acute renal failure (ARF), a 34% increase in labelling in glomeruli was noted compared to saline-injected controls, and by 48 hr, glomerular labelling had increased by 200%. In addition, 48 hr following glycerol injection, significant labelling was now detected in the cortical labyrinth and medullary rays whilst, in the inner medulla, labelling had decreased by 34%. By contrast to glycerol-induced ARF, the only significant change noted 48 hr following induction of HgCl(2)-induced ARF was a 39% decrease in labelling in the inner medulla. It is concluded that glycerol-induced ARF results in differential expression of renal adenosine A(1) receptors with increased expression in the cortex and reduced expression in the inner medulla. Increased density of A(1) receptors in glomeruli may account, at least in part, for the increased renal vasoconstrictor response to adenosine and depressed glomerular filtration rate noted previously in this type of acute renal failure.

Regulation of renal adenosine A(1) receptors: effect of dietary sodium chloride.

The influence of dietary NaCl on the regulation of renal adenosine A(1) receptors was investigated in the rat. Renal membranes from rats fed on a diet low (0.04%) in NaCl showed a 46% increase in B(max) for the binding of [3H]-1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX), a selective adenosine A(1) receptor antagonist, compared to membranes from rats fed on a normal diet (0.4% NaCl). Conversely, a high NaCl diet (4.0%) resulted in a 37% decrease in B(max). Levels of renal adenosine A(1) receptor mRNA were 65% lower in rats on a high salt diet. Autoradiographic studies showed that, for the inner medullary collecting ducts, a low NaCl diet resulted in a 30% increase in [3H]DPCPX binding with a 39% decrease noted in rats maintained on a high salt diet. The results indicate that changes in adenosine A(1) receptor density may represent a novel mechanism whereby the kidneys adapt to changes in salt load.

Role of K+ channels in A2A adenosine receptor-mediated dilation of the pressurized renal arcuate artery.

1. Adenosine A2A receptor-mediated renal vasodilation was investigated by measuring the lumenal diameter of pressurized renal arcuate arteries isolated from the rabbit. 2. The selective A2A receptor agonist CGS21680 dilated the arteries with an EC50 of 130 nM. The CGS21680-induced vasodilation was, on average, 34% less in endothelium-denuded arteries. 3. The maximum response and the EC50 for CGS21680-induced vasodilation in endothelium-intact arteries were not significantly affected by incubation with the K+ channel blockers apamin (100 nM), iberiotoxin (100 nM), 3,4-diaminopyridine (1 mM), glibenclamide (1 microM) or Ba2+ (10 microM). However, a cocktail mixture of these blockers did significantly inhibit the maximum response by almost 40%, and 1 mM Ba2+ alone or 1 mM Ba2+ in addition to the cocktail inhibited the maximum CGS21680-response by 58% and about 75% respectively. 4. CGS21680-induced vasodilation was strongly inhibited when the extracellular K+ level was raised to 20 mM even though the dilator response to 1 microM levcromakalim, a K(ATP) channel opener drug, was unaffected. 5. CGS21680-induced vasodilation was inhibited by 10 microM ouabain, an inhibitor of Na+/K(+)-ATPase, but ouabain had a similar inhibitory effect on vasodilation induced by 30 nM nicardipine (a dihydropyridine Ca2+ antagonist) or 1 microM levcromakalim. 6. The data suggest that K+ channel activation does play a role in A(2A) receptor-mediated renal vasodilation. The inhibitory effect of raised extracellular K+ levels on the A(2A) response may be due to K(+)-induced stimulation of Na+/K(+)-ATPase.

Functions of large conductance Ca2+-activated (BKCa), delayed rectifier (KV) and background K+ channels in the control of membrane potential in rabbit renal arcuate artery.

1. The types of K+ channel which determine the membrane potential of arcuate artery smooth muscle cells were investigated by patch-clamp recording from isolated cells and lumenal diameter measurements from intact pressurized renal arcuate arteries. 2. Single cells had a mean resting potential of -38 mV and were depolarized by 130 mM K+ but not by the Cl- channel blocker 4,4'-diisothiocyanatostilbene-2, 2'-disulphonic acid (DIDS). 3. Iberiotoxin did not affect the resting potential but inhibited spontaneous transient hyperpolarizations. Iberiotoxin or 1 mM tetraethylammonium (TEA+) constricted intact arteries. 3,4-Diaminopyridine (3,4-DAP)-sensitive delayed rectifier K+ (KV) channel current was elicited by depolarization but 3,4-DAP did not affect the resting potential or induce constriction in the intact artery. 4. A voltage-independent K+ current was inhibited by >= 0.1 mM barium (Ba2+) and unaffected by iberiotoxin, glibenclamide, apamin, 3,4-DAP and ouabain. In six out of ten cells, 1 mM Ba2+ depolarized the resting potential, while in the other cells the potential was resistant to all of the K+ channel blockers and ouabain. Ba2+ (0.1-1 mM) constricted the intact artery, but 10 microM Ba2+, 1 microM glibenclamide or 100 nM apamin had no effect. 5. The data suggest that resting potential is determined by background K+ channels, one type being Ba2+ sensitive and voltage independent, and another type being poorly defined due to its resistance to any inhibitor. Large conductance Ca2+-activated K+ (BKCa) and KV channels do not determine the resting potential but have separate functions to underlie transient Ca2+-induced hyperpolarizations and to protect against depolarization past about -30 mV.

K(+)-induced dilation of a small renal artery: no role for inward rectifier K+ channels.

OBJECTIVE: To investigate the mechanism of K(+)-induced vasodilation in a small artery from the kidney, with a particular emphasis on the role of inward rectifier K+ channels. METHODS: Lumen diameter and isometric tension recordings have been made from rabbit renal arcuate artery using pressurised- and wire-myography respectively. In addition, conventional whole-cell and amphotericin-perforated patch whole-cell recordings have been made from single smooth muscle cells isolated from the vessel. RESULTS: Arcuate arteries dilated when the extracellular K+ concentration was raised to 8-10 mM from either zero or a normal physiological level of about 6 mM. The effect was not endothelium-dependent. Application of 0.01-1 mM Ba2+ to block inward rectifier K+ channels had no significant effect on K(+)-induced vasodilation in the arcuate artery, but under the same experimental conditions K(+)-induced dilation of the rat posterior cerebral artery was abolished by Ba2+. In the presence of 60 mM extracellular K+, inward rectifier K(+)-current was detectable in some single smooth muscle cells isolated from arcuate arteries but on average the current density was low (-1.44 pA pF-1 at -60 mV). K(+)-induced vasodilation of the arcuate artery was abolished by 10 microM ouabain and the half-effective concentration of K+ which induced vasodilation was 0.9-1.5 mM. CONCLUSIONS: The observations suggest that an increase in the extracellular K+ concentration (up to about 10 mM) dilates the rabbit renal arcuate artery and that the primary mechanism underlying the effect may be stimulation of Na(+)-K+ ATPase in the smooth muscle cell membrane. Inward rectifier K+ channels have a low average density in smooth muscle cells isolated from arcuate arteries and play no significant role in K(+)-induced vasodilation.

Adenosine receptor mRNA levels during postnatal renal maturation in the rat.

Adenosine may affect the pattern of intrarenal blood flow during renal development. It provides an angiogenic stimulus for the growth of new blood vessels and may be involved in compensatory renal growth. It is therefore of interest to investigate the expression of adenosine receptor genes during postnatal renal development. In the present study this was carried out by measuring adenosine receptor mRNA levels in rats aged between 2 and 60 days. The order of abundance of adenosine receptor mRNA levels in 60-day-old rats was A2A > A2B > or = A1 > A3. A1 receptor mRNA levels showed only small changes with increasing age although, by contrast, A3 receptor mRNA increased markedly with age with levels at 60 days twenty-fold greater than at 2 days. A2A receptor mRNA levels declined during renal maturation with transcript numbers four- to fivefold that at 12-18 days compared with numbers at 60 days. By contrast to the A2A receptor, there were no significant changes in the renal levels of A2B receptor mRNA during kidney maturation. During postnatal renal maturation, the levels of mRNA for A2A and A3 adenosine receptor subtypes undergo marked changes which may be related to functional maturation, morphological development, or both.

The haemodynamic effects of iodinated water soluble radiographic contrast media: a review.

All classes of iodinated water-soluble radiographic contrast media (RCM) are vasoactive with the iso-osmolar dimers inducing the least changes in the vascular tone. The mechanisms responsible for RCM-induced changes in the vascular tone are not fully understood and could be multifactorial. A direct effect on the vascular smooth muscle cells causing alterations in the ion exchanges across the cell membrane is thought to be an important factor in RCM-induced vasodilatation. The release of the endogenous vasoactive mediators adenosine and endothelin may also play a crucial role in the haemodynamic effects of RCM particularly in the kidney. In addition, the effects of RCM on blood rheology can cause a reduction in the blood flow in the microcirculation. The purpose of this review is to discuss the pathophysiology of the haemodynamic effects of RCM and to offer some insight into the biology of the endothelium and vascular smooth muscle cells as well as the pharmacology of the important vasoactive mediators endothelin and adenosine.

Renal adenosine A1 receptor binding characteristics and mRNA levels during the development of acute renal failure in the rat.

1. The binding characteristics and mRNA levels for renal adenosine A1 receptors were investigated in normal rats and rats with acute renal failure (ARF) induced by either glycerol or HgCl2. 2. Saturation isotherms determined from the binding of [3H]-1,3-dipropyl-8-cyclopentylxanthine ([3H]-DPCPX), a selective adenosine A1 antagonist, to renal membranes of untreated rats gave values of 0.62 nM for the equilibrium dissociation constant (Kd) and 19.9 fmol mg-1 protein for the density of binding sites (Bmax). No saturable binding was observed with [3H]-2-(p-(carboxylethyl)-phenylethylamino)-5'-N-ethylcar box amido adenosine ([3H]-CGS 21680), a selective adenosine A2a agonist. 3. By contrast to time-matched controls, renal membranes obtained from rats 16 and 48 h following the induction of ARF with glycerol, showed statistically significant increases (2-4 fold) in both Bmax and Kd for the binding of [3H]-DPCPX. No significant changes in the binding characteristics of [3H]-DPCPX were noted with membranes from rats 48 h following the production of ARF with HgCl2. 4. Adenosine A1 receptor mRNA levels were significantly elevated 0.5, 16 and 48 h following induction of ARF with glycerol, whilst no change was noted in mRNA levels for beta-actin at the same time points. No statistically significant changes in adenosine A1 receptor or beta-actin mRNA levels were noted 48 h after the induction of ARF with HgCl2. 5. This study indicates that glycerol-induced ARF in the rat is associated with an increase in renal adenosine A1 receptor density which appears to result from increased transcription of the gene for this receptor. An increase in adenosine A1 receptor density in renal resistance vessels may explain, at least in part, the enhanced renal vasoconstrictor response to adenosine in glycerol-induced ARF that was noted in a previous study.

Amelioration of cisplatin nephrotoxicity with glycine: dose dependency in rats.

The effects of glycine (0.1-1.0 g kg-1, i.v.) on the acute changes in renal haemodynamics and nephrotoxicity produced by cisplatin (6.0 mg kg-1, i.v.) were investigated in the rat. Cisplatin produced decreases of 50% in the clearance of [3H] inulin (CIN) and renal blood flow (RBF), 110 min following its injection. Glycine at a dose of 0.1 g kg-1 produced no attenuation of the cisplatin-induced decrease in CIN or RBF. Furthermore, this dose of glycine provided no significant protection of renal function over a 7-day period following cisplatin injection. By contrast, glycine at a dose of either 0.5 or 1.0 g kg-1 markedly attenuated cisplatin-induced falls in CIN and RBF, with the highest dose completely preventing any falls in these indices during the course of the experiment. Treatment with these higher doses of glycine produced prominent protection from the nephrotoxic actions of cisplatin, as evidenced by improvements in a range of indices of renal function which included plasma urea and creatinine concentrations, urine output, sodium excretion, CIN and the clearance of [14C] p-aminohippurate. The results of experiments with an intermediate dose of 0.25 g kg-1 glycine revealed some degree of amelioration of acute renal haemodynamic effects of cisplatin, particularly with regard to CIN; whilst in the nephrotoxicity study, 0.25 g kg-1 glycine produced a modest but significant reduction in cisplatin-induced acute renal dysfunction. The results have revealed a clear association between the acute renal haemodynamic effects produced by glycine in cisplatin-injected rats with the longer-term renal protective effects of glycine in cisplatin nephrotoxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal haemodynamic responses to adenosine in acute renal failure.

Renal vascular reactivity was studied in rats with acute renal failure (ARF) to investigate whether changes in sensitivity to the renal haemodynamic effects of adenosine can explain why adenosine plays a significant role in some but not all forms of ARF. Experiments involved rats with glycerol-induced ARF in which adenosine antagonists have been shown previously to have beneficial effects and rats with HgCl2-induced ARF which was not ameliorated by treatment with the selective A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (0.1 mg/kg). Close renal arterial injections of adenosine (0.1-10 micrograms) or noradrenaline (0.003-0.1 microgram) produced falls in renal blood flow in rats with HgCl2-induced ARF which were not statistically different from controls. Adenosine evoked falls in renal blood flow in rats with glycerol-induced ARF which were significantly greater 16 and 48 h, but not 30 min after glycerol injection. The enhanced responsiveness to adenosine's renal constrictor effects was most pronounced 48 h following glycerol injection when, for example, a dose of 10 micrograms produced a fall of 60 +/- (SEM) 5% (n = 8) in renal blood flow in comparison to a fall of 27 +/- 5% (n = 8) in controls. By contrast to the renal vascular response to adenosine, the falls in renal blood flow induced by noradrenaline in rats 48 h following glycerol injection were not statistically different from the decreases in renal blood flow recorded in control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of arginine on cisplatin-induced acute renal failure in the rat.

The effect of arginine on the nephrotoxicity produced by cisplatin (6.0 mg/kg i.v.) was investigated in the rat. Intravenous administration of L-arginine at doses of 0.26-2.63 g/kg at the time of cisplatin injection produced significant protection of renal function as evidenced by reductions in plasma urea and creatinine concentrations, decreased polyuria and increases in the plasma clearance of [3H]inulin and [14C]-p aminohippurate. Administration of D-arginine (2.63 g/kg i.v.) also significantly ameliorated the renal dysfunction induced by cisplatin although this protective effect was not as great as produced by the same dose of L-arginine. D-arginine, by contrast to its L-isomer, is reported to have little or no effect on renal haemodynamics. Consequently, the results of this study indicate that the protective effect of L-arginine in cisplatin nephrotoxicity involves both haemodynamic and nonhaemodynamic components.

Diuretic effect of NG-nitro-L-arginine methyl ester in the rat.

Intravenous infusion of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester, L-NAME (10 micrograms kg-1 min-1), to anaesthetized rats produced a diuresis and natriuresis. By contrast, infusion of the same dose of NG-nitro-D-arginine methyl ester had no effect on either urine output or sodium excretion. The effects of L-NAME were first evident 120 min after the start of infusion and by 170 min a fivefold increase in urine volume and sodium excretion was recorded. L-NAME also produced a transient fall in inulin clearance and a persistent decline in renal blood flow. These renal effects of L-NAME were associated with a gradual elevation of mean arterial blood pressure, although this only attained statistical significance, in comparison with saline-infused animals, 170 min after the start of infusion. The findings indicate the diuresis and natriuresis evoked by L-NAME in the rat is a result of a direct tubular action together with a pressure diuresis.

The protective effect of glycine in cisplatin nephrotoxicity: inhibition with NG-nitro-L-arginine methyl ester.

The effect of glycine on the acute changes in renal haemodynamics and nephrotoxicity produced by cisplatin was investigated in the rat. Cisplatin (6.0 mg kg-1, i.v.) injection in anaesthetized rats produced, over a period of 2 h, falls of approximately 50% in renal blood flow (RBF) and the clearance of [3H]inulin (CLIN), effects which were prevented by co-administration of glycine (1.0 g kg-1). Infusion of the nitric oxide (NO) synthase-inhibitor NG-nitro-L-arginine methyl ester, L-NAME (10 micrograms min-1 kg-1, i.v.), abolished glycine's ability to maintain RBF in cisplatin-injected rats whilst partially inhibiting the ability of glycine to preserve CLIN. Treatment of cisplatin-injected rats with glycine (1.0 g kg-1, i.v.) significantly ameliorated the nephrotoxic effects of cisplatin (6.0 mg kg-1) as judged by improvements in a range of indices of renal function which included plasma urea and creatinine concentrations, urine output, sodium excretion, CLIN and the clearance of [14C]p-aminohippurate. Administration of L-NAME (1.0 mg kg-1, i.v.) to rats which received cisplatin and glycine significantly inhibited the reno-protective effect of glycine. However, L-NAME administration to rats which were treated only with cisplatin did not result in any potentiation of cisplatin nephrotoxicity. The findings of this study suggest that glycine can block the acute falls in RBF and CIN produced by cisplatin by a mechanism which involves the production of NO. Furthermore, the results indicate that these renal haemodynamic actions of glycine are responsible, at least in part, for the ability of this amino acid to ameliorate cisplatin nephrotoxicity.

Effect of the selective A1 adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine on acute renal dysfunction induced by Escherichia coli endotoxin in rats.

The effect of the selective A1 adenosine antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX), on Escherichia coli endotoxin-induced acute renal dysfunction was determined in anaesthetized rats. Bolus administration of endotoxin at doses of either 1 or 20 mg kg-1 evoked decreases in inulin clearance, renal blood flow, urine flow and excretion of sodium, potassium and chloride. The changes in renal function produced by 20 mg kg-1 endotoxin were more severe than those noted with 1 mg kg-1 toxin and, by contrast to this lower dose, renal function showed no signs of recovery. Intravenous administration of CPX (0.1 mg kg-1) elicited a statistically significant, although modest, attenuation of the decline in inulin clearance, renal blood flow, urine output and electrolyte excretion induced by 20 mg kg-1 endotoxin. By contrast, treatment with 0.1 mg kg-1 CPX resulted in statistically significant protection against the falls in excretory function evoked by 1 mg kg-1 endotoxin but not against the reductions in renal blood flow and inulin clearance produced by the lower dose of toxin. These results suggest that adenosine may play a role, albeit not a major one, in the pathophysiology of endotoxaemic acute renal failure.

The diuretic action of 8-cyclopentyl-1,3-dipropylxanthine, a selective A1 adenosine receptor antagonist.

1. The diuretic effect of the selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (CPX), was investigated in anaesthetized rats. 2. CPX (0.1 mg kg-1, i.v.) produced significant increases in urine flow, and the excretion rate and fractional excretion of both sodium and chloride. By contrast, CPX administration did not result in any significant change in the excretion of potassium. 3. The diuretic effect of CPX was accompanied by a transient increase in inulin clearance although p-amino-hippurate clearance was unaffected, indicating the CPX induced a temporary elevation of glomerular filtration rate but no change in renal blood flow. 4. The fractional excretion of lithium (a marker of delivery of fluid out of the proximal tubule) was also significantly increased by CPX. However, other measures of tubular function derived from lithium clearance indicated that there were no changes in the handling of sodium or water in the distal regions of the nephron. 5. CPX did not significantly alter the relationship between either free water reabsorption or free water clearance and the distal delivery of sodium, which suggests that CPX does not affect the renal concentration/dilution mechanism. 6. The results of this study show that the diuresis and increased excretion of sodium and chloride induced by CPX (0.1 mg kg-1) in the rat, occurs with only transient elevation in glomerular filtration rate and no change in renal blood flow. The primary reason for the diuresis appears to be inhibition of sodium reabsorption in the proximal tubule. Furthermore, the results provide evidence that production and release of endogenous adenosine modifies renal excretory function via stimulation of the A1 receptor subtype.

Cardiac function in rats with acute renal failure.

Inotropic responses of isolated cardiac preparations from rats with glycerol-induced acute renal failure (ARF) were recorded, following a range of cardiac stimulants. Left atria of rats with ARF showed diminished inotropic responses only to the calcium agonist Bay K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyl-phenyl)-pyridine-5 -carboxylate) whilst right ventricular strips exhibited reduced responses to isoprenaline, 3-isobutyl-1-methylxanthine, Ca2+ and Bay K 8644. Investigations of cardiac mitochondrial respiration indicated that there is a site-unspecific 'pseudo' uncoupling of oxidative phosphorylation in ARF but that electron transport is unaffected. This uncoupling of oxidative phosphorylation did not have any detectable effect on either levels of total adenine nucleotides and creatine phosphate or cellular energy charge. Measurements were also made of the activity of pyruvate dehydrogenase which provides an index of mitochondrial Ca2+ levels. The proportion of pyruvate dehydrogenase in its active form was threefold higher following isoprenaline injection in hearts of rats with ARF compared with controls. The results suggest that in hearts of rats with ARF there is a change in the number, affinity, efficacy or coupling of the dihydropyridine receptor on the L-type calcium channel. Moreover, in the ventricle, a defect in cellular Ca2+ control, resulting in an increase in mitochondrial Ca2+ uptake, may contribute to the depression of inotropic response to the range of cardiac stimulants tested.

A comparison of drug binding sites on mammalian albumins.

The fluorescent probes warfarin and dansylsarcosine are known to selectively interact with binding sites I and II, respectively, on human albumin. This paper investigates whether similar binding sites exist on bovine, dog, horse, sheep and rat albumins. Binding sites on albumins were studied by: (1) displacement of warfarin and dansylsarcosine by site I (phenylbutazone) and site II (diazepam) selective ligands; (2) the effects of non-esterified fatty acids (carbon chain lengths: C5-C20) and changes in pH (6-9) on the fluorescence of warfarin and dansylsarcosine; and (3) the ability of site selective ligands to inhibit hydrolysis of 4-nitrophenyl acetate. For bovine, dog, horse, human and sheep albumins the fluorescence of bound warfarin and dansylsarcosine was selectively decreased by phenylbutazone and diazepam, respectively. For these albumins medium chain fatty acids (C1-C12) reduced the fluorescence of dansylsarcosine (maximum inhibition with C9) whereas long chain acids (C12-C20) enhanced the fluorescence of warfarin (maximum increases with C12). In addition, changes in pH from 6 to 9 increased the fluorescence of warfarin and although site I ligands (warfarin/phenylbutazone) had no pronounced effects on 4-nitrophenyl acetate hydrolysis, site II ligands (dansylsarcosine/diazepam) significantly inhibited this reaction. Rat albumin behaved differently from the other albumins studied in that the C12-C20 fatty acids and changes in pH did not enhance the fluorescence of warfarin. Moreover, the differential effects of site I and site II ligands on the fluorescence of warfarin/dansylsarcosine and hydrolysis of 4-nitrophenyl acetate were less apparent with rat albumin. The results suggest bovine, dog, horse and sheep albumins have binding sites for warfarin and dansylsarcosine with similar properties to sites I and II on human albumin. By contrast, the warfarin binding site and to a lesser degree the dansylsarcosine site, of rat albumin have different characteristics from these sites on the other albumins studied.

Further characterization of the protective effect of 8-cyclopentyl-1,3-dipropylxanthine on glycerol-induced acute renal failure in the rat.

In the rat, treatment with the alkylxanthine 8-cyclopentyl-1,3-dipropylxanthine (CPX) at a dose of 0.1 mg kg-1 antagonizes adenosine-induced falls in renal blood flow and reduces the severity of glycerol-induced acute renal failure. Treatment of glycerol-injected rats with 0.03 mg kg-1 of CPX resulted in no significant improvements in a range of indices of renal function. However, treatment with 0.1 or 0.3 mg kg-1 doses of CPX did significantly ameliorate acute renal failure although there were no significant differences in the degree of protection of renal function afforded by these two doses. In glycerol-injected rats, 0.1 or 0.3 mg kg-1 CPX administered either as a single dose or repeated doses every 12 h for two days did not inhibit renal phosphodiesterase. Thus the beneficial effects of CPX can be produced by doses that have no effect on renal phosphodiesterase activity whereas 0.1 mg kg-1 of CPX has been shown previously to antagonize the actions of adenosine. The findings provide further evidence that the beneficial effect of CPX in glycerol-induced acute renal failure is a consequence of adenosine antagonism and not phosphodiesterase inhibition.