Renal tubular excretion of the N4-acetyl metabolites of sulphasomidine and sulphadimethoxine in the dog.

To investigate whether dogs are able to excrete acetylated drugs by active transport, the plasma kinetics and renal excretion of the N4-acetyl metabolites of sulphasomidine and sulphadimethoxine were studied in the beagle dog after a rapid intravenous bolus injection. Two doses of N4-acetylsulphasomidine (1050 and 105 mg) and one dose of N4-acetylsulphadimethoxine (472 mg) were administered on separate occasions. The renal clearance (CLR) was as follows: N4-acetylsulphasomidine (1050 mg) 34 mL min-1; N4-acetylsulphasomidine (105 mg) 28 mL min-1; and N4-acetylsulphadimethoxine (472 mg) 24 mL min-1. CLR was higher than expected on the basis of the measured glomerular filtration rate, indicating that the N4-acetyl metabolites may be excreted by the renal tubules by active tubular transport. Saturation of the excretion process of N4-acetylsulphasomidine occurred with a transport maximum of 930 +/- 190 micrograms min-1 and a Michaelis-Menten constant of 37 +/- 10 micrograms mL-1. It may be concluded that the dog renal organic anion transport system is able to secrete acetylated sulphonamides.

Absorption of high dose furosemide (frusemide) in congestive heart failure.

To investigate the influence of the presence of oedema on the pharmacokinetics and pharmacodynamics of furosemide (frusemide) we selected 9 hospitalised patients (mean age 70.3 years, range 59 to 84 years) with severe congestive heart failure (NYHA III to IV) and an assessed amount of peripheral oedema of at least 5 kg. In these patients the absorption of a single oral dose of furosemide 250 mg was studied when their heart failure was decompensated and again, after intensive therapy, when it was clinically compensated. The mean (+/- SEM) weight loss after clinical treatment was 12.0 +/- 2.2 kg. Individual furosemide plasma concentration-time curves could be fitted adequately to a 1-compartment model with 1 first-order absorption and elimination process, in which absorption took place in 2 parts with different lag times. Comparing the decompensated state with the compensated state we did not find significant differences in pharmacodynamics, absorption half-life, elimination half-life, time to peak serum concentration, peak serum concentration itself and area under the plasma concentration-time curve. However, the relative amount of furosemide absorbed in the first fraction was significantly increased after compensation. We conclude that the presence of massive oedema in patients with congestive heart failure has a minor influence on the pharmacokinetics and pharmacodynamics of high dose oral furosemide.

Renal handling and effects of S(+)-ibuprofen and R(-)-ibuprofen in the rat isolated perfused kidney.

1. The renal handling and effects of S(+)- and R(-)-ibuprofen have been studied in the isolated perfused kidney (IPK) of the rat. 2. Both ibuprofen enantiomers were extensively reabsorbed and accumulated in the kidney in a concentration-dependent manner. No pharmacokinetic differences were observed between the two enantiomers. 3. S(+)-ibuprofen concentrations ranging from 0.25 to 25 micrograms ml-1 (1.2 to 120 microM) caused a decrease in urinary flow, glomerular filtration rate (GFR) and electrolyte excretion. Urinary pH and excretion of glucose were not influenced. R(-)-ibuprofen concentrations ranging from 2.5 to 25 micrograms ml-1 (12 to 120 microM) also decreased urinary flow and electrolyte excretion. This decrease, however, was less than observed with S(+)-ibuprofen. GFR, urinary pH and glucose excretion were not affected by R(-)-ibuprofen. Prostaglandin E2 (PGE2) concentrations of 133 ng ml-1 reversed the effects on renal function of both enantiomers. 4. Very high S(+)- and R(-)-ibuprofen concentrations (greater than 400 micrograms ml-1) resulted in an increase in urinary flow and fractional excretion of sodium, chloride, potassium, glucose and calcium. 5. It is concluded that the pharmacokinetic behaviour of ibuprofen in the kidney is not stereoselective. Relatively high concentrations of both enantiomers increased the urinary flow and electrolyte excretion in a nonstereoselective manner. Lower concentrations of S(+)-ibuprofen decreased urinary flow and electrolyte excretion. The pharmacologically inactive R(-)-ibuprofen was also able to affect renal function in a similar way, but at different concentrations. These effects on renal function are probably caused by inhibition of PGE2 synthesis.

Renal handling and effects of salicylic acid in the isolated perfused rat kidney.

The renal handling of salicylic acid (SA) and its effects on renal function were studied in the isolated perfused rat kidney (IPK). The renal handling of SA is dominated by reabsorption and only a small fraction of the filtered SA is excreted into the urine. Reabsorption is a passive process and is dependent on urinary pH. Because of the extensive reabsorption, no decrease in perfusate concentration can be observed in the course of the IPK experiment. SA accumulated slightly in the IPK and this accumulation is concentration dependent. Small amounts of SA were converted to salicyluric acid (SU), the glycine conjugate of SA. SA concentrations higher than 100 micrograms/ml caused an immediate increase in urinary flow and in fractional excretion of sodium, potassium, chloride and calcium. Fractional excretion of glucose increased gradually. Glomerular filtration rate, renal perfusion flow, renal pressure and fractional excretion of magnesium were not affected by SA. The effects were dependent on the SA concentration. Although SA is a classical non-steroidal antiinflammatory drug (NSAID), its influence on renal function appears to be different from other NSAIDs which are usually associated with a reduction in urinary flow and salt excretion.

Alterations of muscarinic acetylcholine receptors in the nasal mucosa of allergic patients in comparison with nonallergic individuals.

Cholinergic nasal hyperresponsiveness in nasal allergy may be due to changes of the characteristics in muscarinic cholinergic receptors. Radioligand receptor binding and in vitro autoradiographic studies of nasal mucosa in nonallergic (NA) and allergic patients were performed to investigate this hypothesis. The heterogeneous NA group was subdivided into control individuals and patients with chronic sinusitis and vasomotor rhinitis. The 3H-(-)-Quinuclidinylbenzilate binding to muscarinic receptors in human nasal mucosa membranes was saturable and of high affinity in all groups. No significant differences could be demonstrated between the subgroups of the NA patients. In allergic patients the dissociation constants and receptor densities were significantly decreased in comparison with those of NA and with those of control individuals. No differences in agonist binding or coupling of the muscarinic receptor to the effector system via the G protein could be observed in allergic patients. In vitro autoradiographic experiments demonstrated specific 3H-(-)-Quinuclidinylbenzilate labeling of the glandular acini in NA and allergic patients. No specific labeling could be observed in the epithelium, blood vessels, or connective tissue. In conclusion, the increased sensitivity and decreased muscarinic receptor number may reflect the cholinergic-induced hypersecretion in nasal allergy but are probably too small to explain the complex allergic reaction.

Alterations of adrenoceptors in the nasal mucosa of allergic patients in comparison with nonallergic individuals.

Nasal hyperreactivity in nasal allergy may be due to changes of the characteristics in adrenergic receptors. Radioligand receptor-binding studies with the antagonists, 3H-prazosin (alpha 1-adrenoceptor), 3H-rauwolscine (alpha 2-adrenoceptor), and 125I-(-)-Cyanopindolol (beta-adrenoceptor) were performed in homogenates of nasal mucosa of allergic and nonallergic (NA) patients to investigate this hypothesis. The heterogeneous NA group was subdivided into control individuals and patients with chronic sinusitis and vasomotor rhinitis. No significant differences in affinities or densities of alpha 1- and alpha 2-adrenoceptors could be demonstrated in allergic patients in comparison with NA and control individuals. The beta-adrenoceptor density was significantly reduced in allergic patients in comparison with that of control individuals. Neither changes in agonist binding or in the effect of Gpp(NH)p on the agonist binding to beta-adrenoceptors could be observed in allergic patients. The subtype selective antagonist, LK203-030, demonstrated the presence of a homogeneous population of beta 2-adrenoceptors in human nasal mucosa of both NA and allergic patients. In vitro, autoradiography demonstrated specific 125I-(-)-Cyanopindolol labeling of the epithelium in NA and allergic patients. In conclusion, no changes in characteristics of alpha 1- or alpha 2-adrenoceptors in the nasal mucosa could be demonstrated in nasal allergy. However, a decreased number of beta-adrenoceptors may reflect a beta-adrenergic abnormality in nasal allergy.

Effect of substituted benzoates on p-aminohippurate transport in dog renal membrane vesicles.

The effect of substituted benzoates on the transport of p-aminohippurate (PAH) was studied in basolateral (BLMV) and brush border membrane vesicles (BBMV) isolated from dog kidney cortex. For both membranes, kinetic analysis of [3H]PAH transport in the presence of a fixed concentration of two different benzoates, respectively, revealed an increase in the apparent Km for PAH, while the transport capacity (Vmax) was unaffected. This is compatible with competitive inhibition of a common transport pathway. A range of 19 monosubstituted benzoates were then tested as potential inhibitors by measuring the probenecid-sensitive fraction of 100 mumol/l PAH uptake into BLMV and BBMV in the presence of 5 mmol/l benzoate, and apparent inhibition constants (Ki) were calculated. For all benzoates the inhibitory potency in BBMV was lower than in BLMV, but the pattern of inhibition was similar; the most pronounced inhibition was found for 3-Cl- and 4-Cl-benzoate, while the least pronounced inhibition was found for the 3-NH2 and 4-NH2 substitutes. The inhibitory potency, expressed as logKi, correlated significantly with the relative hydrophobicity of the benzoates determined by reversed phase HPLC, whereas a poor correlation was found between pKa and logKi. This indicates that hydrophobic and electronic parameters are the main determinants of affinity for the PAH transport system. It is suggested that the PAH transport system present in the proximal tubules is responsible for the active secretion of benzoates by the mammalian kidney.

Indometacin: renal handling and effects in the isolated perfused rat kidney.

We investigated renal handling and effects of indometacin on renal function in the isolated perfused rat kidney (IPK). Indometacin concentrations less than 2.5 ng/ml did not influence renal function, while higher concentrations caused a decrease in urinary flow and electrolyte excretion. The presence of 133 ng/ml prostaglandin E2 (PGE2) in the perfusate fully opposed these effects on kidney function. Only a small fraction of the filtered indometacin is excreted into the urine, indicating extensive reabsorption of the compound. This is probably a passive process, dependent on the tubular load, urinary pH and urinary flow. Indometacin accumulates extensively in the IPK, causing a kidney to perfusate ratio between 5 and 9. Accumulation decreased with increasing perfusate concentration. This can be explained by active secretion: increasing the perfusate concentration leads to a saturation of the active secretion and a decrease in the relative accumulation. We conclude that indometacin accumulates extensively in the IPK, that it affects kidney function and that this influence is probably caused by the inhibition of PGE2 synthesis.

Renal disposition and effects of naproxen and its l-enantiomer in the isolated perfused rat kidney.

Renal handling, metabolism and effects on kidney function of naproxen and its l-enantiomer were examined in the isolated perfused rat kidney (IPK). Urinary excretion rate of naproxen was much lower than the filtration rate, indicating extensive reabsorption. Naproxen is accumulated considerably in the IPK. This accumulation is concentration-dependent and is probably the result of active secretion of naproxen. Considerable amounts of desmethyl-naproxen were formed in the IPK. The kinetic behavior of the l-enantiomer of naproxen did not differ from naproxen. Addition of 37.5 to 3750 micrograms naproxen caused a decrease in urinary flow, glomerular filtration rate and fractional excretion of sodium, chloride, potassium, magnesium and calcium. The presence of prostaglandin E2 in the perfusate fully opposed the effects of naproxen on kidney function. Addition of 375 micrograms l-enantiomer of naproxen did not influence kidney function. Addition of very high doses (1 x 10(5) micrograms) of naproxen and its l-enantiomer to the IPK caused diuresis and increased the fractional excretion of sodium, chloride, potassium, glucose and calcium. We conclude that the pharmacokinetic behavior and the metabolism of naproxen in the IPK is probably not stereoselective; that relatively low doses of naproxen exert a specific, stereoselective effect on kidney function caused by inhibition of the prostaglandin E2 synthesis and that high doses of naproxen exert a nonstereoselective effect on kidney function.

Isolated perfused rat kidney as a tool in the investigation of renal handling and effects of nonsteroidal antiinflammatory drugs.

An isolated perfused rat kidney (IPK) preparation is described in which renal perfusion flow, perfusion pressure, urinary flow, urinary pH, and glomerular filtration rate (GFR) are recorded continuously during the perfusion experiment. The usefulness of this IPK system in studying the renal handling and the effects of non-steroidal antiinflammatory drugs (NSAIDs) is shown using salicyluric acid (SU), salicylic acid (SA), and naproxen (NA). Excretion of SU involves glomerular filtration, active secretion, and passive reabsorption. The excretion rates of SA and NA were both much lower than their filtration rate, indicating extensive reabsorption. All three drugs accumulate in the IPK but at different levels. SU accumulates much more than either SA or NA. The effects on renal function were different for the three drugs studied. SU had no effect on kidney function. SA perfusate concentrations greater than 100 micrograms/mL caused diuresis and natriuresis, while SA concentrations less than 100 micrograms/mL did not influence kidney function. NA perfusate concentrations ranging from 0.16 to 25 micrograms/mL caused a decrease in urinary flow and sodium excretion. Very high NA concentrations (greater than 500 micrograms/mL) caused an increase in urinary flow and sodium excretion. We conclude that the IPK is a suitable preparation for characterizing and comparing renal handling and effects of NSAIDs.

Pharmacokinetic properties of the antimuscarinic drug [3H]-hexahydro-sila-difenidol in the rat.

The pharmacokinetics of tritiated hexahydro-sila-difenidol [( 3H]-HHSiD) were examined in rats. Furthermore, the distribution of radioactivity was studied by means of whole body autoradiography. After i.v. administration of 2.9 mg/kg HHSiD plus [3H]-HHSiD to anaesthetized rats bearing a catheter implanted in the ductus choledochus and receiving a mannitol infusion, HHSiD was rapidly distributed and metabolized. Only 5% of the radioactivity was recovered in blood after 23 s and 0.4% after 2.5 h. 64% of the plasma radioactivity could be extracted with hexane from the samples taken 23 s after administration. 52% of the radioactivity was eliminated within 2.5 h, 13% by urinary and 39% by biliary excretion. Following oral administration of 8.6 mg/kg HHSiD plus [3H]-HHSiD there was an absorption of approximately one fourth of the administered radioactivity within 4 h. By means of whole body autoradiography (i.v. injection) as well as by tissue distribution measurement the highest levels of radioactivity were found in bile, urine, lung, kidney, adrenals, liver and pancreas. Thus, after i.v. administration to rats HHSiD is rather quickly distributed, metabolized and excreted. This explains its low antimuscarinic potency in vivo.

Biochemical and autoradiographic analysis of beta-adrenoceptors in rat nasal mucosa.

The specific binding of 125I-(-)-cyanopindolol (125I-(-)-CYP) to homogenates and cryostat sections of rat nasal mucosa was saturable, stereoselective and of high affinity (Kd = 5.0 +/- 0.4 pM. Bmax = 204 +/- 12 fmol/mg protein and Kd = 7.2 +/- 0.7 pM; Bmax = 15 +/- 1 fmol/mg protein respectively). The subtype-selective antagonists, LK203-030 and ICI118,551, inhibited specific 125I-(-)-CYP binding according to a two-binding site model, indicating the presence of 57 and 45% beta 1-adrenoceptors in homogenates and cryostat sections, respectively. Competition of isoprenaline for antagonist binding to homogenates demonstrated 30 +/- 3% high-affinity agonist binding sites. A steepening of the curve was observed in presence of guanine nucleotides. In vitro labelling of cryostat sections of rat nasal mucosa was combined with autoradiography. The autoradiographs generated after incubation with 20 pM 125I-(-)-CYP showed specific labelling of the epithelium and glandular excretory ducts. It appeared from autoradiographs generated with subtype-selective antagonists in addition to the radioligand that beta 1- and beta 2-adrenoceptors were present in both structures.

Alpha 2-adrenoceptors in homogenates of rat nasal mucosa.

The specific binding of [3H]rauwolscine to rat nasal mucosa membranes was saturable, stereoselective and of high affinity. The Scatchard plot pointed to a homogeneous population of binding sites (Kd = 3.6 +/- 0.6 nM; Bmax = 5.1 +/- 0.7 pmol/g). The non-specific binding appeared to be non-linear, probably due to filter binding. Inhibition of [3H]rauwolscine binding with the subtype-selective antagonist, prazosin, suggested the presence of alpha 2-adrenoceptor subclasses in rat nasal mucosa. The (-)-epinephrine inhibition curves demonstrated high- and low-affinity agonist binding sites. A monophasic (-)-epinephrine inhibition curve was obtained in the presence of guanine nucleotides.

Age-dependent pharmacokinetics of phenylbutazone in calves.

The pharmacokinetics of phenylbutazone (PBZ) in relation to age was studied in calves. The drug was applied intravenously to calves (dose 22 mg/kg), which were divided, depending on age, into three groups. Heparinised blood samples were taken in defined intervals. The concentrations of phenylbutazone and two of its metabolites were determined in plasma by high performance liquid chromatography. The pharmacokinetic data derived from 1-month-old calves revealed a longer persistence (elimination half-lives twice as long, total body clearance 40-50% lower) of PBZ in the body than in the other two groups of calves aged 3-6 months. With respect to the long elimination half-lives (mean values 39-94 h), caution is needed in case of repeated doses (accumulation).

Binding characteristics of the muscarinic receptor subtype in rabbit pancreas.

The muscarinic receptor in the rabbit pancreas was characterized with the use of the labeled ligand (3H)-(-)-quinuclidinyl-benzylate ((3H)-(-)-QNB). Specific binding of (3H)-(-)-QNB to pancreatic acini was found to be reversible and of high affinity, with an equilibrium dissociation constant (KD) of 68 pmol/l and a receptor density (RT) of 170 fmol/mg protein. Agonist binding behaviour was investigated by displacement of (3H)-(-)-QNB binding by eight agonists like arecoline, arecaïdine-propargylester (APE) and carbachol, yielding only low affinity binding sites. The inhibition of (3H)-(-)-QNB binding by the selective antagonists pirenzepine, hexahydrosiladifenidol (HHSiD) and (11-[2-[diethyl-amino)-methyl)-1-piperidinyl]acetyl)-5,11-dihydro-6H-pyr ido (2,3-b) (1,4) benzodiazepin-6-one) (AF-DX 116) confirmed the M3 nature of the rabbit pancreatic receptor.

Comparison of the diuretic effect and absorption of a single dose of furosemide and free and the fixed combinations of furosemide and triamterene in healthy male adults.

The absorption and diuretic effect of furosemide 40 mg alone (F), and of the free (F + T) and the fixed (FT) combinations of furosemide 40 mg and triamterene 50 mg have been compared in 12 healthy young men. A slight reduction in the area under the concentration-time curve (AUC) of plasma furosemide was found for the fixed combination (AUC480) F2.58 micrograms.h.ml-1; F + T 2.46 micrograms.h.ml-1; FT 1.97 micrograms.h.ml-1. There was a significant reduction in the AUC480 of plasma triamterene (F + T 204.9 micrograms.h.l-1; FT 130.2 micrograms.h.l-1). Sodium excretion after F + T and FT was more pronounced than after F (F + T 302 mmol; FT 311 mmol; F259 mmol). When compared to F alone, there was a reduction in the 24-hour potassium excretion after F + T as well as after FT (F 121 mmol; F + T 104 mmol; FT 107 mmol). It is concluded that the absorption of triamterene was significantly reduced after ingestion of the fixed combination tablet. However, in healthy male adults this had no influence on its natriuretic and potassium-sparing effect as compared to the free combination.

Renal handling of salicyluric acid in the isolated perfused rat kidney: evidence for accumulation in tubular cells.

The renal handling of salicyluric acid (SU) was studied over a broad concentration range (0-400 micrograms/ml) in the isolated perfused rat kidney (IPK). The accumulation of SU was determined by difference calculations between the SU dose given and the SU amount present in the perfusate and excreted into the urine. SU accumulates highly in the IPK and this accumulation is concentration-dependent. At low perfusate concentrations (5-20 micrograms/ml) there is a sharp increase in the accumulation (100-400 micrograms/g), whereas at higher concentrations (20-100 micrograms/ml) a small increase (400-500 micrograms/g) is seen. The largest part of the accumulation is probably caused by accumulation of SU in the tubular cells. This is a result of the active uptake of SU over the basolateral membrane followed by facilitated diffusion over the brush-border membrane. As a result of the saturation of the active SU uptake, accumulation reaches a maximal value. Excretion of SU in the IPK involves glomerular filtration, active secretion and reabsorption. Reabsorption is probably a passive process, dependent on the urinary flow and pH. The apparent Michaelis-Menten constant of the excretion is 18.7 +/- 1.8 micrograms/ml and the maximum transport capacity is 69.8 +/- 1.4 micrograms/min. The pharmacokinetic parameters of the excretion of SU were in good agreement with previously reported in vivo values.