Penetration of amoxycillin into the respiratory tract tissues and secretions in pigs

The pharmacokinetic properties of amoxycillin, and its penetration into respiratory tract tissues (alveolar macrophages, bronchial secretions, bronchial mucosa, lung tissue and lymph nodes), were determined in 20 healthy female pigs weighing 29 to 55 kg, after a single intravenous dose of 8.6 mg kg(-1) bodyweight. Following intravenous administration the plasma concentration-time curves were best described by a three-compartment open model. The elimination half-life and the mean residence time were 2.5 and 1.4 hours, respectively. The volume of distribution at steady state was 0.52 litres kg(-1), and the body clearance was 0.40 litres hour(-1) kg(-1). In all structures (except alveolar macrophages) amoxycillin concentration peaked at the first sampling point, one hour after drug administration. The tissue to plasma ratio (based on AUC values) were 0.33 for bronchial secretions, 0.37 for bronchial mucosa, 0.39 for lung tissue and 0.68 for lymph nodes. Traces of amoxycillin were found in alveolar macrophages, but the concentrations were below the limit of quantification. The concentration of amoxycillin in secretions and tissue decreased by a slower rate than the concentration in plasma, resulting in increasing secretion- and tissue-to-plasma concentration ratios.

Penetration of amoxycillin to the respiratory tract tissues and secretions in Actinobacillus pleuropneumoniae infected pigs

The pharmokinetic properties of amoxycillin, and its penetration into respiratory tract tissue, were determined in 18 Actinobacillus pleuropneumoniae infected pigs, after a single i.v. dose of 8.6 mg amoxycillin kg(-1) bodyweight. Pleuropneumoniae was produced experimentally in pigs by an aerosol infection model. The infection created a homogeneous response, characterised by depression of breathing and increased body temperature. The clinical symptoms were accompanied by increased haptoglobin levels and circulating white blood cell counts. At necropsy the findings were characterised by a bilateral fibrinous pleuropneumonia. Twenty hours after infection, the pigs were administered amoxycillin i.v. The plasma concentration-time curve was described by a three compartment open model. The mean residence time and the elimination half-life were 1.5 and 3.4 hours, respectively. The steady-state volume of distribution was 0.67 litres kg(-1), and the clearance was 0.46 litres kg(-1) hour(-1). There were no significant differences between these values and those reported previously for healthy pigs. The concentration of amoxycillin in bronchial secretions, lung tissue and diseased lung tissue peaked two hours after intravenous drug administration, while amoxycillin concentration in pleural fluid, lymph nodes and tonsil tissue peaked at the first sampling point one hour after drug administration. The concentration of amoxycillin in secretions and tissue decreased by a slower rate than amoxycillin concentration in plasma, resulting in an increasing tissue-to-plasma concentration ratio. The distribution ratios (AUCtissue/AUCplasma) was 0.53 for bronchial secretions, 0.44 for pneumonic lung tissue, 0.42 for lung tissue, 1.04 for pleural fluid, 0.58 for lymph nodes and 0.37 for tonsil tissue. The distribution of amoxycillin to secretions was increased compared with that previously reported for healthy pigs, while only minor changes were observed in lung tissue.

Bioavailability of amoxycillin in pigs

Amoxycillin was administered to pigs intravenously (i.v.), intramuscularly (i.m.) and orally (p.o.), in a cross-over design to examine the bioavailability (F) of various drug formulations. These included: a sodium salt for reconstitution in water and administration i.v.; trihydrate salt in an oil base for intramuscular administration producing 'conventional' duration of plasma concentrations; a trihydrate salt in oil base giving prolonged (LA) duration, and a trihydrate powder for oral administration in solution. The concentration of amoxycillin in plasma was measured by high-performance liquid chromatography, and its pharmacokinetic variables were assessed for the individual pigs by use of noncompartmental methods. Following i.v. administration (8.6 mg/kg), amoxycillin was eliminated rapidly with a mean residence time (MRT) of 1.4 h. After i.m. administration of the conventional formulation (14.7 mg/kg), the plasma amoxycillin concentration peaked at 2 h at 5.1 micrograms/mL. The bioavailability was 0.83. Intramuscular administration (14.1 mg/kg) of the long acting formulation (i.m. LA), lead to two peaks in plasma at 1.3 and 6.6 h. The bioavailability was calculated to be 1.11. After p.o. administration to fasted pigs, peak concentration was reached after 1.9 h, and the bioavailability was 0.33. In fed pigs, the corresponding values were 3.6 h and 0.28. Data showed that treatment of respiratory tract diseases in pigs by p.o. dosing alone, may not be optimal, because of the relatively low bioavailability and the fact that infections often result in reduced feed and water consumption. A rational treatment regime for susceptible respiratory pathogens includes an initial i.m. injection, followed by p.o. dosing every 12 h. Alternatively, the long acting formulation may be administered i.m. in a dose of 15 mg/kg, which would lead to active plasma concentrations for approximately 48 h.

Pig hepatocytes as an in vitro model to study the regulation of human CYP3A4: prediction of drug-drug interactions with 17 alpha-ethynylestradiol

The objective of this study was to provide evidence of the validity of pig hepatocytes as a model to study the regulation of human CYP3A4 with special emphasis on drug-drug interactions. Thirteen different drugs were incubated with primary monolayer cultures of pig hepatocytes (n = 4). The study included both drugs reported to cause drug interactions in the clinic with 17 alpha-ethynylestradiol (EE2), other drugs metabolized by CYP3A4, and drugs not reported to cause any problems. Effect of the drug exposure to pig hepatocytes was determined by immunodetection using a monoclonal human CYP3A4 antibody and measurement of 6 beta-hydroxylation of testosterone and 2-hydroxylation of 17 alpha-ethynylestradiol (EE2), both reactions known to be catalyzed by CYP3A4 in humans. Data were compared to data from human hepatocytes and to reported observations of drug-drug interactions in the clinic. The drugs known to be inducers of CYP3A4 in humans significantly increased a CYP isoform in pigs catalyzing 6 beta-hydroxylation of testosterone and 2-hydroxylation of EE2, whereas drugs not reported to have clinical interactions with EE2 had no or only marginal effect. Induction by the drugs known to be inducers of CYP3A4 increased with drug exposure time and the CYP3A4 activity, represented by testosterone 6 beta-hydroxylation, was highest at 72 h for the investigated induction periods (24, 48 and 72 h), except for dexamethasone where the effect peaked after 24 h. Induction of the 2-hydroxylation of EE2 correlated well with the increase in 6 beta-hydroxylation of testosterone (except for sulphinpyranzone) and the increase in the protein level of CYP3A detected by a monoclonal human CYP3A4 antibody, thus confirming the 2-hydroxylation of EE2 in pigs as being biotransformed by a CYP isoform presumably belonging to the CYP3A subfamily as in humans. In conclusion, these results indicate that pig hepatocytes may be a valuable model to mimic the regulation of human CYP3A4.

A new in vitro assay of benzimidazole activity against adult Oesophagostomum dentatum

A new in vitro assay of benzimidazole activity against adult Oesophagostomum dentatum is described. The method is based on the ability of O. dentatum to migrate through polyamide nets after exposure to various concentrations of benzimidazole. To determine an appropriate mesh size, control worms and worms exposed to 10 microM oxfendazole for 24 h were allowed to migrate through nets with various mesh sizes (300-500 microns) for up to 1 h. A mesh size of 350 microns and migration periods of 10, 20 and 30 min were selected. Exposure to oxfendazole at 10 microM for 24, 48 and 72 h inhibited the migration in a time-dependent manner. After 72 h of exposure and with a 20-min migration period, the EC50 of oxfendazole for O. dentatum was 0.564 microM. In further studies the activities of albendazole sulphoxide, albendazole, cambendazole, fenbendazole, flubendazole, luxabendazole, mebendazole, oxfendazole, oxibendazole, parbendazole and thiabendazole were compared. The worms were exposed to each drug at two concentrations (0.1 and 3.16 microM) for 72 h. At 3.16 microM there were no significant differences in the activity of the drugs. At 0.1 microM significant differences in activity were found. Albendazole sulphoxide and oxfendazole were poor inhibitors of migration compared with their parent compounds, albendazole and fenbendazole.

The cytotoxic effect of paraquat to isolated renal proximal tubular segments from rabbits

Paraquat (PQ) induces lung, liver and kidney damage. Since PQ mainly is eliminated by the kidney, the kidney damage is of particular importance to the outcome of PQ poisoning. The exact toxic mechanism of PQ is still unclear but it is assumed to involve redox cycling and formation of reactive oxygen species. In this study, further investigations on the toxic mechanism and metabolic effects of PQ were performed using isolated renal proximal tubules from rabbits. Proximal tubules were isolated using a combined iron perfusion and collagenase method. Suspended tubules were incubated for varying periods and concentrations of PQ at 25 or 37 degrees C in Krebs-Ringer phosphate buffer or HCO3-/CO2 buffer. The cytotoxic effect of PQ was evaluated by (1) markers of oxidative stress: status of glutathione (GSH/GSSG) and formation of malondialdehyde (MDA); and (2) markers of tubular metabolism: oxygen consumption (QO2), transport of 14C-p-aminohippuric acid (PAH) and 14C-tetraethylammonium (TEA). Using 0.5 and 5 mM PQ, the GSH/GSSG ratio decreased whereas formation of MDA increased indicating oxidative stress. PQ reduced the accumulation of PAH and TEA, the basal QO2 and the ouabain sensitive QO2 indicating inhibition of the Na/K-ATPase. Nystatin-stimulated QO2 was reduced by PQ, excluding inhibition of Na+ entry as a possible cytotoxic mechanism and suggesting mitochondrial injury. This was confirmed by measuring FCCP-uncoupled QO2. Thus high concentrations of PQ appear to disrupt mitochondrial electron chain transfer resulting in reduction of metabolic functions.

Characterization of the P450 system in Göttingen minipigs

It is essential to establish the activity and regulation of the cytochrome P450 system of species selected for toxicological and pharmacological studies. The minipig has become a popular substitute for the traditional non-rodent species although little information is available on its P450 system. The total P450 and the enzyme activity of the most important drug-metabolizing isoenzymes: CYP1A2, CYP2C19, CYP2D6, CYP2E1 and CYP3A4 were measured in liver microsomes from 4 minipigs and 8 conventional pigs of both sexes. Immunochemical levels were determined for 4 of teh isoenzymes. The total P450 activity was slightly higher in minipigs compared to conventional pigs but no sex difference was detected. CYP1A2 activity (7-ethoxyresorufin) was 4 times higher in female minipigs than in male minipigs. The activity in male minipigs was almost identical to the activity in conventional pigs. The activity of CYP2E1 (chlorzoxazone) was 4 times higher in female than in male minipigs and 2 times higher in female than in male conventional pigs. No activity of CYP2D6 (debrisoquine) and CYP2C19 (mephenytoin) could be detected. The CYP3A4 activity (testosterone) detected in minipigs was higher than the activity in conventional pigs. A weak sex difference was seen in both strains. Western blotting using anti-human CYP2E1 and CYP3A4 confirmed the results obtained in the enzyme activity assays, while only CYP1A2 correlated with the activity in the conventional strain. The total P450 enzyme activity was close to the levels reported for human beings, as were the activities of CYP2E1 and CYP3A4.

The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs

The pharmacokinetic disposition of pyrantel after intravenous (i.v.) and oral (p.o.) administration as the citrate and p.o. administration as the pamoate salt was determined in pigs. Following i.v. administration pyrantel was quickly cleared from the bloodstream, exhibiting a terminal half-life of 1.75 +/- 0.19 h and a residence time (MRT) of 2.54 +/- 0.27 h. After p.o. administration as the citrate salt, the absorption time (MAT) of pyrantel was 2.38 +/- 0.25 h and although significant quantities of pyrantel were absorbed (mean bioavailability of 41%) the rapid clearance resulted in a MRT of only 4.92 +/- 0.36 h. By comparison, the significantly extended MAT of the less soluble pamoate salt resulted in reduced circulating concentrations and a significantly lower mean bioavailability of 16%. The poor efficacy of pyrantel citrate against nematodes inhabiting the large intestine of pigs is therefore suggested to result from insufficient quantities of drug passaging to the site of infection. When tested against pyrantel-resistant adult Oesophagostomum dentatum the mean efficacy of pyrantel citrate was only 23%, whereas the efficacy of the lesser absorbed pyrantel pamoate was 75%. These results indicate that for maximum activity pyrantel should be administered to pigs as the pamoate salt.

Studies on the renal kinetics of growth hormone (GH) and on the GH receptor and related effects in animals

Growth hormone (GH) is filtered through the kidney, and may exert effects on renal function when presented via the circulation. Investigations on kidney-related aspects of GH are increasing in number. Using in vitro and in vivo approaches, the present study attempted to provide answers to a number of unresolved or debated issues. In vitro, we detected both GH and type 1 IGF receptors (R) in a porcine renal epithelial cell line. The saturation and down regulation kinetics of the GH-R indicate that it has the properties of a classical GH-R. Furthermore, the simultaneous presence of GH-R and IGF-R on a phenotypically homogeneous cell line suggests the presence of GH-induced auto-/paracrine IGF-1 bioactivity in the kidney. Experiments with isolated proximal rabbit tubules incubated with physiological concentrations of 125I-GH demonstrated a time-and dose-dependent increase in unlabelled GH-displaceable cell-associated radioactivity, lending support to the concept of GH mediating its renal effects via proximal tubular GH-R. Short term administration of GH to rats and humans elicited electrolyte and water retention that may cause edema in adults. In the present study, long term administration of GH to rats caused only a minor increase in serum phosphate levels, with no changes observed in the renal electrolyte clearance. During the first 4 days of GH treatment in rats, no change in plasma renin activity was detected and we were thus unable to confirm the hypothesis that the renin-angiotensin system is responsible for the early phase of GH-associated fluid retention. Pharmacokinetically, when GH was administered to rats with functional disconnection of the kidneys as a model of renal insufficiency, the whole body clearance of GH decreased by ca. two thirds, and was reflected by an increase in the mean residence time and AUCplasma for GH. The plasma half-life, however, was not significantly affected, suggesting that the volume of distribution (Vd) had decreased for the GH administered to the renally compromised animals. A renal contribution to the Vd was visualized as intense radioactive staining in the kidney region on whole body autoradiographs (WBA) of rats dosed with 125I-labelled hGH. The liver region was also intensely stained. Kidney-associated radioactivity was found to be related not only to glomerular filtration, but also to peritubular uptake, since the renal clearance of free GH was found to exceed the GFR.(ABSTRACT TRUNCATED AT 400 WORDS)

Penetration of danofloxacin into the respiratory tract tissues and secretions in calves

Pharmacokinetic determinants of danofloxacin (1.25 mg/kg of body weight, IV) and its penetration into the respiratory tract tissues were studied in sixteen 4- to 6-week-old calves. The disposition curve was best described by an open 3-compartment model. Mean elimination half-life was 7.4 hours and the steady-state volume of distribution was 4.3 L/kg. The large volume of distribution was confirmed by a rapid and high penetration of the drug into respiratory tract tissues and secretions. In all structures (lung tissue, bronchial mucosa, bronchial secretions, and nasal secretions), danofloxacin concentration peaked 1 hour after drug administration. The area under the curve ratio for concentrations in tissue or secretions to concentrations in plasma was approximately 5 for lung tissue, 3 for bronchial mucosa, 0.85 for bronchial secretions, and 0.42 for nasal secretions. Protein binding of danofloxacin was 49% in plasma, 31% in bronchial secretions, and 14% in nasal secretions, resulting in consistently higher free danoflaxacin concentrations in bronchial secretions than in plasma. Accumulation of danofloxacin within bronchial mucosa and the high concentration of free drug in bronchial secretions suggested that an active process may be involved in the transport of danofloxacin across the airway epithelium. The dose of danofloxacin administered provided drug concentrations above the minimal inhibitory concentration of common respiratory pathogens for up to 12 hours in bronchial mucosa, up to 8 hours in bronchial secretions, and up to 4 hours in nasal secretions.

Disposition of 4-methylimidazole in goats and heifers

4-Methylimidazole (MeI) is formed when hay is ammoniated and it has been suspected of being the compound causing the 'crazy cow' syndrome. The aim of the present study was to describe the disposition of MeI in goats and heifers. The mean residence time was about five hours and the volume of distribution 0.9 litre kg-1 bodyweight in both goats and heifers. Goats metabolised MeI to a much higher extent than heifers which excreted the major part as the unchanged compound. MeI and its metabolites were excreted mainly in urine, but also in milk and faeces. In spite of administration of a dose (20 mg kg-1 bodyweight) which is much higher than the one intoxicated animals may have received through contaminated fodder none of the typical signs of intoxication were observed and it is concluded that MeI may not alone be the cause of the 'crazy cow' syndrome.

Purification and characterization of hepatic microsomal cytochrome P-450 in phenobarbital- and beta-naphthoflavone-treated pigs

Different cytochrome P-450 isoenzymes from hepatic microsomes of phenobarbital (PB) and beta-naphthoflavone (beta-NF) treated pigs and rats were isolated, purified, and characterized. The physico-chemical properties of the porcine isoenzymes were similar to properties of forms isolated from other species. The molecular sizes ranged from 52.5 to 59.5 kD and, in the ferrous-carbonyl state, the isoenzymes had absorbance maxima between 447 and 451 nm. Antigenic similarities were found between the isoenzymes present in PB-induced pigs, and between the isoenzymes present in beta-NF-induced pigs. Cross-reactivity was not observed between PB- and beta-NF-inducible isoenzymes, but beta-NF-inducible isoenzymes in pigs and rats possessed antigenic similarities.

Disposition of parathion in neonatal and young pigs

Pharmacokinetics, metabolism (in vivo and in vitro), elimination and tissue distribution of 14C-parathion was studied after intravenous administration of 0.5 mg/kg to newborn, 1 week and 8 weeks old piglets. Body clearance increased from 7 ml/min./kg in newborn to 35 and 121 ml/min./kg in 1 and 8 weeks old piglets, respectively. Urinary excretion during the first 3 hr rose from 18 to 48 and 82% of the dose in newborn, 1 and 8 week old piglets. The main metabolite of parathion was p-nitrophenyl-glucuronide making up 85% of the urinary 14C excretion. About 6% was excreted as p-nitrophenyl-sulfate and only 1% as free (non-conjugated) p-nitrophenol. Unchanged parathion or paraoxon was not detectable in urine from any of the age groups. The in vitro experiments showed that biotransformation of parathion took place only when cofactors for oxidative reactions were present, indicating that oxidation is the first and necessary metabolic step and that hydrolysis does not contribute significantly to the elimination of parathion. The highest concentration of 14C 3 hr after administration was found in kidney and liver. In newborn piglets the 14C-concentration in tissues was higher than or equal to the plasma concentration. The 14C tissue/plasma ratio decreased with age for all tissues except kidney. Parathion was present in high concentrations in plasma, liver and kidney from newborn piglets, whereas the level just exceeded the detection limit in the 8 week old ones. Paraoxon was clearly detectable in plasma and liver from newborn piglets, while only traces were found in the older groups.

Respiratory tract distribution and bioavailability of spiramycin in calves

Pharmacokinetic determinants of spiramycin and its distribution into the respiratory tract were studied in 2 groups of calves, 4 to 10 weeks old. Group-A calves (n = 4) were used to determine pharmacokinetic variables of spiramycin after IV (15 and 30 mg/kg of body weight) and oral administrations of the drug (30 mg/kg) and to measure distribution of spiramycin into nasal and bronchial secretions. Group-B calves (n = 4) were used to determine distribution of spiramycin into lung tissue and bronchial mucosa. Spiramycin disposition was best described by use of an open 3-compartment model. Mean (+/- SD) elimination half-life was 28.7 +/- 12.3 hours, and steady-state volume of distribution was 23.5 +/- 6.0 L/kg. Bio-availability after oral administration was 4 +/- 3%. High and persistent concentrations of spiramycin were achieved in the respiratory tract tissues and fluids. Tissue-to-plasma concentration ratio was 58 for lung tissue and 18 for bronchial mucosa at 3 hours after spiramycin administration and 137 and 49, respectively at 24 hours. Secretion-to-plasma concentration ratio was 4 for nasal secretions and 7 for bronchial secretions, and remained almost constant with time. Thus, spiramycin penetrates well into the respiratory tract, although the value in bronchial secretions is lower than that in lung tissues and bronchial mucosa. Calculations indicate that a loading dose of 45 mg/kg, administered IV, followed by a maintenance dose of 20 mg/kg, IV, once daily is required to maintain active concentrations of spiramycin against bovine pathogens in bronchial secretions.

Uptake of ochratoxin A by slices of pig kidney cortex

Ochratoxin A (OCT A) is a nephrotoxin causing selective necrosis of the proximal tubule. Being an organic anion OCT A might be expected to enter the tubule cells by the organic anion transport system. Pig renal cortical slices were used to characterize the OCT A transport. OCT A (5 X 10(-3) mM) was accumulated against a concentration gradient with a slice to medium ratio of 8.9 +/- 2.9 in the presence of oxygen. This accumulation was markedly reduced in a nitrogen atmosphere (S/M ratio = 2.9 +/- 0.5). OCT A accumulation was dependent on medium concentration. With increasing concentration (5 X 10(-4)-5 X 10(-1) mM), slice to medium ratio initially rose from 6.9 +/- 2.0 to 11.7 +/- 1.2 whereupon it declined to 5.4 +/- 1.1. This pattern indicates that both carrier mediated transport and intracellular metabolism may contribute to the net accumulation of the toxin. OCT A (10(-4) to 1 mM) inhibited p-aminohippurate (PAH) and phenolsulphophthalein (PSP) uptake in a dose-dependent manner. Up to 10(-1) mM, OCT A did not inhibit acetylation of PAH suggesting that aerobic metabolism and the energy supply for the transport process were unaffected. Kinetic studies revealed a competitive inhibition of the PSP transport. It is concluded that OCT A enters the proximal tubule cells by the common organic anion transport system.

Metabolism of sulfadiazine in neonatal and young pigs. Comparative in vivo and in vitro studies

Metabolism of sulfadiazine (SDZ) was studied in vivo and in vitro during postnatal development of piglets in order to examine whether in vitro metabolism approaches the in vivo situation. Experiments were performed in 1-day-, 8-day- and 60-day-old piglets. In vivo: 14C-SDZ was injected intravenously and urine and tissue samples collected after 3 hr. Urinary excretion data as well as data from liver and kidney tissue indicated a relatively high capacity for acetylation at birth, while the capacity for oxidation is low during the first week of life. At 60 days of age the acetylation and oxidation of SDZ is equal each accounting for about 20% of the amount excreted in urine. In vitro: Incubation of subcellular fractions of liver and kidney showed that acetylation of SDZ in liver reached maximum within 1 week. Oxidative activity was absent at 1 day, present at a low level at day 8, and at a high level at day 60. Neither acetylation nor oxidation of SDZ took place in kidney. The results show a close correlation between in vivo and in vitro results with respect to the developmental pattern seen in piglets during the postnatal period of life.

Metabolism of trimethoprim in neonatal and young pigs: comparative in vivo and in vitro studies

Metabolism of trimethoprim (TMP) was investigated in in vivo and in vitro experiments on 1 day (group A), 8 days (group B), and 60 days (group C) old piglets. In the in vivo studies piglets received an intravenous injection of 14C-trimethoprim. Urine was then collected for 3 hours after which the animals were killed. During the collection period 13, 24, and 40% of the dose was excreted in the urine in group A, B, and C, respectively. Trimethoprim and the following metabolites: Metabolite 1 and 4, minor metabolites, and conjugates were determined in plasma, liver, kidney, urine, and bile. The results show that newborn piglets have little capacity for oxidation of TMP while the ability to conjugate with glucuronic acid and sulfate seems somewhat higher. During the following 8 weeks a marked increase in the oxidative as well as conjugative potential took place. The microsomal fractions of liver and kidney were used for the in vitro metabolism studies of TMP. No metabolic activity could be demonstrated in the kidney preparations. Oxidative demethylation was just detectable in livers from the newborn piglets but increased considerably with age. Glucuronidation of metabolite 4 took place in the liver preparations from all three groups but at the highest rate in group C. The development in metabolic capacity was found to be qualitatively similar in vivo and in vitro.

Pharmacokinetics and metabolism of sulphadiazine in neonatal and young pigs

The pharmacokinetics of sulphadiazine was studied in newborn, 1 week, and 8 weeks old piglets after intravenous administration of 60 mg/kg. Kinetic parameters were calculated using a two compartment open model. Steady state volume of distribution averaged 0.62, 0.56, and 0.48 1/kg at birth, 1 week, and 8 weeks, respectively. Elimination half-life decreased from 455 min. at birth to 322 min. at 1 week and 157 min. at 8 weeks leading to a rise in body clearance from 0.99 to 2.20 ml/min./kg during the same age period. Urinary excretion data indicated that the increase in body clearance reflects maturational changes in both renal function and metabolic capacity. Although renal clearance increased several times more than metabolic clearance, metabolism remained the main contributor to elimination of SDZ at all ages. Metabolism of SDZ involves two important pathways - acetylation and aromatic hydroxylation; the former being well developed at birth, while the latter increased markedly during the age period studied.

Postnatal development of renal function in piglets: changes in excretory pattern of sulphachlorpyridazine

The renal excretion of sulphachlorpyridazine (SCP) was measured in 34 unanaesthetized piglets 5-74 days of age. The renal handling of SCP was found to include: glomerular filtration, active tubular secretion and passive reabsorption. During the age period studied the clearance of ultrafiltrable SCP increased several times more than GFR (inulin clearance) indicating that the balance between filtration, secretion and reabsorption is changed during postnatal maturation. The age-related change in clearance ratio possibly reflects both a greater increase in tubular secretory capacity than in glomerular filtration and a relative decrease in the passive reabsorption.

Postnatal development of the pig kidney: ultrastucure of the glomerulus and the proximal tubule

The detailed anatomy of the structures forming the glomerular filtration barrier and the proximal tubule was studied during postnatal development of the pig kidney. Development of the glomerular filtration barrier included three processes: Formation of visceral epithelial foot processes, flattening and fenestration of the endothelium and formation of a common epithelial and endothelial basal lamina. During formation of foot processes the distribution pattern of aggregated filaments in the epithelial cells was changed, suggesting that the filaments participate in the elongation of the foot processes. In the immature glomerulus the endothelial fenestrae were closed by thin diaphragms which disappeared during differentiation of the endothelium. Microvilli were observed in the proximal tubule cells in an early developmental stage, presumably before onset of glomerular filtration. Few cellular organelles were seen in the tubule anlage but the number of mitochondria, apical vacuoles and lysosome-like bodies increased markedly during maturation. Dense bodies identified as peroxisomes first appeared in a late development stage. The formation of nephrons continued up to about 3 weeks of age; after this time the morphological development was a differentiation of nephrons already present. The present observations, together with results of an accompanying functional study, demonstrate that changes in functional parameters reflect the structural development.

Porcine nephropathy induced by long-term ingestion of ochratoxin A

Nine pigs were fed crystalline ochratoxin A in their feed at a concentration of about 1 mg/kg. Three pigs and their controls were killed after 3 months and 6 pigs and controls were killed after 2 years. A decrease of the ratio TmPAH/CIn, increased urinary glucose excretion and decreased ability to concentrate urine, occurred within a few weeks and aggravated slightly during the 2-year period. Changes in renal structure, characterized by degeneration and atrophy of proximal tubules, interstitial fibrosis and hyalinization of glomeruli, were progressive during time of exposure, but terminal renal failure was not reached. The kidney, liver, muscular and adipose tissue contained 3 to 27 microgram ochratoxin A/kg after 3 months of exposure. No further accumulation of ochratoxin A residue was found after 2 years of exposure.