Na(+), K(+)-ATPase content in skeletal muscle of dogs with pituitary-dependent hyperadrenocorticism

Several hormones regulate Na⁺, K⁺-ATPase content in the muscle cell membrane, which is essential for maintaining muscle cell excitability. Chronic glucocorticoid excess is associated with muscle weakness and reduced endurance. We hypothesized that chronic glucocorticoid excess affects Na⁺, K⁺-ATPase content in canine skeletal muscle, and contributes to reduced endurance and muscle weakness associated with pituitary-dependent hyperadrenocorticism (PDH) in dogs. Therefore, Na⁺, K⁺-ATPase content in skeletal muscle was evaluated before and after hypophysectomy and hormone replacement (cortisone and l-thyroxin) in dogs with PDH (n = 13), and in healthy controls (n = 6). In addition, baseline and exercise-induced changes in plasma electrolyte concentrations and acid–base balance were evaluated before and after hypophysectomy in dogs with PDH. Na⁺, K⁺-ATPase content of gluteal muscle in dogs with PDH was significantly lower than in control dogs (201 ± 13 pmol/g versus 260 ± 8 pmol/g wet weight; P < 0.01). Similar differences were found in palatine muscle. After hypophysectomy and on hormone replacement, Na⁺, K⁺-ATPase was increased (234 ± 7 pmol/g wet weight). Both plasma pH and base excess in dogs with PDH (7.44 ± 0.01; 1.7 ± 0.6 mmol/l, respectively) were significantly higher (P < 0.05) than after hypophysectomy and hormone replacement (7.41 ± 0.01; −0.2 ± 0.4 mmol/l, respectively). Exercise induced respiratory alkalosis, but did not result in hyperkalemia in dogs with PDH. In conclusion, chronic glucocorticoid excess in dogs with PDH is associated with decreased Na⁺, K⁺-ATPase content in skeletal muscle. This may contribute to reduce endurance in canine PDH, although dogs with PDH did not exhibit exercise-induced hyperkalemia. Na⁺, K⁺-ATPase content normalized to values statistically not different from healthy controls after hypophysectomy and hormone replacement.     

Effects of a selective and a nonselective muscarinic cholinergic antagonist on heart rate and intestinal motility in dogs

The effects of methoctramine, a cardioselective muscarinic cholinergic antagonist, on heart rate and small intestinal motor activity were compared to those of the nonselective competitive muscarinic antagonist, atropine. Methoctramine or atropine, 6, 10, 30, 60 μg/kg, or sterile isotonic saline, was administered intravenously to six conscious dogs in cross-over studies. Methoctramine administration caused dose-dependent tachycardia without affecting intestinal motility, while atropine administration caused dose-dependent tachycardia accompanied by significant reductions in small intestinal motility. Additionally, methoctramine did not inhibit intestinal smooth muscle contractile activity initiated by the muscarinic agonist bethanechol, while atropine inhibited bethanechol-induced contractile activity in a dose-dependent manner. Calculated dosages of methoctramine and atropine required to produce a 50% increase in heart rate over baseline were 35.1 ± 5.3 and 39.5 ± 6.2 μg/kg, respectively. This dosage of atropine caused a 93 ± 13.9% reduction in intestinal motility. These findings suggest that selective muscarinic antagonists may be useful drugs for those veterinary patients in which nonselective muscarinic antagonists have the potential to produce untoward effects on intestinal motility.     

Pharmacokinetics of indomethacin in sheep after intravenous and intramuscular administration

The pharmacokinetics of indomethacin (1mg/kg) was determined in six adult sheep after intravenous (i.v.) and intramuscular (i.m.) injection. Plasma concentrations were maintained within the therapeutic range (0.3–3.0 μg/mL) from 5 to 50 min after i.v. and from 5 to 60–90 min after i.m. administration. After two trials, indomethacin best fitted an open two-compartment model. The mean (±SD) volumes of distribution at steady state ( V d_ss) were 4.10 ± 1.40 and 4.21 ± 1.93 L/kg and the mean clearance values ( C l_B) were 0.17 ± 0.06 and 0.22 ± 0.12 L/h.kg for i.v. and i.m. routes, respectively. The elimination phase half-lives did not show any significant difference between routes of injection ( t _½β = 17.4 ± 4.6 and 21.25 ± 4.44 h, i.v. and i.m. respectively). After i.m. administration, plasma maximum concentration ( C _max =  1.10 ± 0.68 μg/mL) was reached 10 min after dosing; the absorption phase was fast ( K _ab = 26 ± 18 h-1) and short ( t _½ab = 2.33 ± 1.51 min) and the mean bioavailability was 91.0 ± 32.8%, although there was considerable interanimal variation. In some individuals, bioavailability was higher than 100%. This fact combined with the slower elimination phase after i.m. than after i.v. administration, could be related with enterohepatic recycling.     

Ultrastructure of the Spermatozoa of the Yangtze Finless Porpoise (Neophocaena phocaenoides asiaeorientalis)

Semen sample was collected from two captive adult Yangtze finless porpoises ( Neophocaena phocaenoides asiaeorientalis ) during physical examination. One individual was aged about 9 years with body length 143 cm (total length) and body weight 46.1 kg in 2003. The age of the other was unknown and its body length was 147 cm and body weight was 43 kg in 2004. Ultrastructure of their spermatozoa was examined using scanning and transmission electron microscope. The sperm concentration was 4.17 × 10⁹ spermatozoa per ml by the cytometer. The approximate dimensions of the spermatozoa were as follows: head length, 3.366 ± 0.140 μm (mean ± SE, n  = 15); head width, 1.896 ± 0.099 μm ( n  = 15); and neck length, 1.004 ± 0.074 μm ( n  = 10). The tail included midpiece, principal piece and terminal piece. The length of the midpiece was 1.882 ± 0.077 μm ( n  = 9). There is no apparent boundary between the principal piece and the terminal piece, so the length of the principal piece and the terminal piece was 44.612 ± 3.485 μm ( n  = 5). Total length of the spermatozoa was 53.314 ± 4.580 μm ( n  = 10). The acrosome covered approximately 45.8% of the anterior portion of the head.     

Concentration of enrofloxacin and its active metabolite in alveolar macrophages and pulmonary epithelial lining fluid of dogs

The purpose of this study was to determine the concentration of enrofloxacin and its active metabolite, ciprofloxacin, in alveolar macrophages (AM) and epithelial lining fluid (ELF) of the lungs in comparison to plasma concentrations in healthy dogs. Eleven dogs were given a single oral dose (5 mg/kg) of enrofloxacin. Four hours later, plasma and bronchoalveolar lavage (BAL) fluid were collected. Cells were separated from the BAL fluid and lysed for determination of drug concentrations within AM. Supernatant was used to determine concentrations of drugs in ELF. Drug assays were performed by high-performance liquid chromatography.
  The concentration of enrofloxacin (mean ± SD) was 0.33 ± 0.14 μg/mL in plasma, 3.34 ± 2.4 μg/mL in AM and 4.79 ± 5.0 μg/mL in ELF. The concentration of ciprofloxacin was 0.42 ± 0.26 μg/mL in plasma, 1.15 ± 1.03 μg/mL in AM and 0.26 ± 0.26 μg/mL in ELF. Mean concentrations of both drugs in AM were greater than in plasma (AM to plasma ratio, 10.3 for enrofloxacin and 4.7 for ciprofloxacin). Mean concentrations of enrofloxacin, but not ciprofloxacin, in ELF were greater than in plasma (ELF to plasma ratio, 13.5 for enrofloxacin and 0.52 for ciprofloxacin). Enrofloxacin concentrations in AM and ELF largely exceeded the MICs of the major bacterial pathogens and surpassed by about two times the breakpoint MIC of that drug, and ciprofloxacin concentrations in AM surpassed the MIC of many susceptible organisms. These results suggest that sufficient antimicrobial activity is present in AM and ELF of dogs following oral administration of enrofloxacin to be effective in the treatment of lower respiratory tract infections involving susceptible organisms.     

Kinetics and residues after intraperitoneal procaine penicillin G administration in lactating dairy cows

This paper describes the pharmacokinetic profile of procaine penicillin G after intraperitoneal (IP) administration in eight lactating dairy cows. Procaine pencillin G (PPG, 21 000 IU/kg) was deposited into the abdominal cavity of each cow following an incision in the right paralumbar fossa. Blood and milk samples were taken over the following 10 days, at which point the cows were euthanized. Plasma, milk, muscle, liver, and kidney penicillin concentrations were determined by HPLC, with a limit of quantification of 5 ng/mL for plasma and milk and 40 ng/g for tissue samples. A noncompartmental method was used to analyze plasma kinetics. The mean pharmacokinetic parameters (±SD) were: C _max, 5.5 ± 2.6 μg/mL; T _max, 0.75 ± 0.27 h; AUC _0-∞, 10.8 ± 4.9 μg·h/mL; MRT , 2.2 ± 0.9 h. All milk from treated cows contained detectable penicillin residues for a minimum of three milkings (31 h) and maximum of five milkings (52 h) after administration. Concentrations of penicillin in all muscle, liver, and kidney samples taken 10 days postadministration were below the limit of quantification. Necropsy examinations revealed foci of hemorrhage on the rumenal omentum of most cows but peritonitis was not observed. Systemic inflammation as determined by change in leukogram or plasma fibrinogen was noted in one cow. The results of this study demonstrate that IP PPG is absorbed and eliminated rapidly in lactating dairy cows.     

In vitro kinetics of hepatic albendazole sulfoxidation in channel catfish (Ictalurus punctatus), tilapia (Oreochromis sp.), rainbow trout (Oncorhynchus mykiss) and induction of EROD activity in ABZ-dosed channel catfish

Liver microsomes from market-size ( n  = 6) rainbow trout, channel catfish and tilapia were used to investigate in vitro biotransformation kinetics of albendazole (ABZ). ABZ was transformed to a single metabolite, ABZ sulfoxide (ABZ-SO). Catfish displayed the highest maximal velocity ( V _max = 264.0 ± 58.6 pmols ABZ-SO/min/mg protein) followed by tilapia (112.3 ± 8.2) and rainbow trout (73.3 ± 10.3). V _max in catfish was significantly different ( P  < 0.05) from the other two species. Michaelis–Menten constant ( K _m) values (μ m ) varied significantly among the species: rainbow trout (3.9 ± 0.5), tilapia (9.2 ± 1.7) and catfish (22.0 ± 3.2). However, V _max/ K _m ratios showed no difference among the three species, making them equally efficient performing this phase I biotransformation reaction. In a second series of experiments, channel catfish ( n  = 6 per treatment) were dosed in vivo with gel-food containing ABZ (10 mg/kg, p.o.). Fish were killed at 24, 48, 72 and 120 h after dosage. Control fish were fed ABZ-free feed. Induction of ethoxyresorufin-o-deethylase activity was significant ( P  < 0.05) in all ABZ-dosed treatments as compared with controls.     

Disposition and metabolism of the novel macrolide antibiotic CP-163505 in cattle

The plasma pharmacokinetics, lung tissue to plasma concentration ratios, and depletion profiles in edible tissue (liver, muscle, kidney, fat and injection site) for a single subcutaneous dose of a novel macrolide antibiotic, CP-163505 (20-[3-dimethylaminopropyl(L-alanyl)amino]-20-deoxo-repromicin), were investigated in crossbred beef cattle. Mean peak plasma concentration of 2.5 ± 0.4 μg/mL, occurring at 0.5 h, was found for CP-163505 following a 5 mg/kg dose ( n  = 5). The pharmacokinetic profile consisted of a distribution phase, followed by an extended terminal elimination phase (t_1/2 of 19 h). The disposition of CP-163505 was characterized by distribution from the plasma into the tissue resulting in lung to plasma ratios of 103 and 87 at 72 h following a single 5 or 10 mg/kg dose, respectively. The depletion of CP-163505 from edible tissues was determined following administration of tritiated CP-163505 at a dose of 10 mg/kg. On day 42, the liver contained the highest mean concentration of total tritium residues, 5.9 ± 3.4 μg/g. CP-163505 was determined to be a significant component of the total residues in liver with 72% on day 3 and 50% on day 42. Three metabolites of CP-163505 were identified by liquid chromatography with mass spectrometry (LC/MS/MS) in liver samples: loss of alanine, formation of an hydroxyl derivative, and sulfate addition to the lactone ring.     

Consumption of resistant starch decreases lipogenesis in adipose tissues but not in muscular tissues of growing pigs

The aim of the present study was to evaluate the effect of two different sources of starch on plasma glucose, acetate and insulin responses and peripheral lipogenesis in adipose and skeletal muscle tissues. Eighteen male growing pigs were fed a diet containing 250 g native corn starch/kg (CS; 26% amylose, 74% amylopectin) or 250 g raw potato starch/kg (RPS; 20% amylose, 80% amylopectin) as examples of digestible and resistant starch (type II), respectively. After 38 days on the experimental diets, twelve pigs (6 per treatment, Experiment 1) were killed and samples of adipose and muscular tissues were analysed for intramuscular lipid content and lipogenic enzyme activity. Lipogenic enzyme activities were significantly higher for CS than RPS in adipose tissues but not in muscular tissues. No differences were detected on the lipid content of the muscles tested. The six remaining pigs (3 per treatment, Experiment 2) were fitted with catheters in the saphenous vein and femoral artery after 28 days on the experimental diets. After feeding restoration to a level of 1.1 kg/day, they received a primed constant infusion of 1-¹³C acetate for a period of 90 min, starting 5 h after feeding the meal ingestion, and a primed constant infusion of 6,6-D₂ glucose for 7 h, starting 1 h before the following meal ingestion. No differences were observed between diets on peripheral acetate entry rate. Glucose concentration, the rate of peripheral glucose appearance and insulin concentration were quantitatively higher after the meal for CS than for RPS diet. This shows the importance of type of dietary starch on lipogenesis as a result of changes in glycemia and insulinemia in adipose but not in muscular tissues of growing pigs.     

Pharmacokinetics of ketamine and its metabolite norketamine administered at a sub-anesthetic dose together with xylazine to calves prior to castration

The objective of this study was to evaluate the plasma pharmacokinetics of ketamine and its active metabolite norketamine administered intravenously at a dose of 0.1 mg/kg together with xylazine (0.05 mg/kg) to control the pain associated with castration in calves. A two-compartment model with an additional metabolite compartment linked to the central compartment was used to simultaneously describe the time-concentration profiles of both ketamine and its major metabolite norketamine. Parameter values estimated from the time-concentration profiles observed in this study were volume of the central compartment (V_c = 132.82 ± 68.23 mL/kg), distribution clearance (CL_D = 15.49 ± 2.56 mL/min/kg), volume of the peripheral compartment (V_T = 257.05 ± 41.65 mL/kg), ketamine clearance by the formation of the norketamine metabolite (CL_2M = 8.56 ± 7.37 mL/kg/min) and ketamine clearance by other routes (CL_o = 16.41 ± 3.42 mL/kg/min). Previously published data from rats suggest that the metabolite norketamine contributes to the analgesic effect of ketamine, with a potency that is one-third of the parent drug. An understanding of the time-concentration relationships and the disposition of the parent drug and its metabolite is therefore important for a better understanding of the analgesic potential of ketamine in cattle.     

The C bicarbonate dilution technique to determine energy expenditure in young bulls validated by indirect calorimetry

We explored the applicability of the ¹³C bicarbonate dilution technique for determination of energy expenditure (EE) in young bulls in comparison to whole body indirect calorimetry (IC). Twelve bulls of a F2 German Holstein x Charolais cross (4.5 months, 332 ± 16 kg BM) received a diet providing 1000 kJ ME d^− 1 kg BM^− 0.75 and 4.3 g crude protein d^− 1 kg BM^− 0.75. Bulls were housed in respiration chambers and received an intravenous bolus of NaH¹³CO₃ (A: 3 μmol kg BM^− 1 (n = 2), B: 7 μmol kg BM^− 1 (n = 4), C: 17.5 μmol kg BM^− 1 (n = 6), 99 at.% ¹³C) into the jugular vein to measure EE. Simultaneously, EE was determined by IC. After the ¹³C administration blood samples and breath gas were collected from the animals in the respiration chamber during a 24-h period (7.00–7.00 h). The recovery of ¹³C in breath CO₂ (% of ¹³C dose) was irrespective of NaH¹³CO₃ dose (A: 69.7 ± 2.7%, B: 70.5 ± 4.5%, C: 75.0 ± 4.9%; P > 0.05). Only small amounts of ¹³C were excreted in urine (3.4 ± 2.6%) and feces (2.0 ± 1.3%). The EE determined by the ¹³C bicarbonate method using breath and blood ¹³C recovery rates as correction factors was not different from that measured by IC (816 ± 81 [blood] or 827 ± 101 [breath] vs. 820 ± 90 kJ d^− 1 kg BM^− 0.75). Bland–Altman analysis showed a 95% confidence interval for EE of ± 99 and ± 109 kJ d^− 1 kg BM^− 0.75 based on blood and breath ¹³C recovery, respectively. In conclusion, the ¹³C bicarbonate dilution method is appropriate to obtain reliable estimates of EE in young bulls using blood CO₂ or breath CO₂ under standardized experimental conditions, i.e. in the fasting state.     

Effect of Anti-Basic Fibroblast Growth Factor (Anti-bFGF) on In Vitro Embryonic Development in Rat

In this study, we aimed at the in vitro effects of anti-fibroblast growth factor-2 (anti-FGF-2 or anti-bFGF) on embryo culture in rats. In vitro effects of anti-bFGF on total embryonic development were investigated in 40 rat embryos (which were divided into four groups) (obtained from five pregnant females) at 9.5 days of gestation that were cultured in whole rat serum (WRS), and in WRS+ 2.5, 5, and 10 μg/ml anti-bFGF. After 48 h of culturing, the embryos from each group were harvested to be analysed morphologically according to a morphological scoring system and biochemically to obtain the embryo protein content. The morphological score, embryo protein content, somite number and crown-rump length of embryos indicated that embryos cultured in WRS+ anti-bFGF had significant embryonic retardation. Mean morphological scores for the embryos grown in WRS, in the presence of 2.5, 5 and 10 μg anti-FGF-2 were 61.4 ± 1.64, 46.3 ± 8.42, 27 ± 2.58 and13.6 ± 0.96 respectively. These results suggest that bFGF is very important for normal embryonic development and rat anti-bFGF neutralizes bFGF effect.     

Oxidative capacity of skeletal muscle fibres in racehorses: histochemical versus biochemical analysis

The oxidative capacity of skeletal muscle fibre types was evaluated histochemically using the nicotinamide dinucleotide diaphorase (NADH-D) staining, and biochemically by measuring the activity of citrate synthase (CS) in both whole muscle samples and in pools of fibres of identified type. Duplicate determinations of the NADH-D staining pattern resulted in standard deviations (sd) between duplicates of 6 and 11 per cent for two observers. The NADH-D pattern was found to differ between observers. Duplicate determinations of CS activity in the same fibre pools resulted in an sd value of 2.9 mumol/g/min. Measurements of whole muscle CS activity did not provide information about the distribution of oxidative capacity among fibre types. The NADH-D stain and CS activity in fibre pools both showed that, in general, type I and IIA fibres had a higher oxidative capacity than type IIB fibres. Biochemical techniques also showed, however, that the CS activity in type I and IIA fibres of different horses could vary as much as twofold, whereas the NADH-D rating showed a high intensity staining for most type I and IIA fibres in all horses. Furthermore, type IIB fibres received a lower NADH-D rating than the other fibre types even when the CS activities were quite similar. For purposes of research, biochemical measurement of oxidative capacity in individual muscle fibre types provides valuable quantitative and comparative information. The ease of histochemical NADH-D staining in comparison to fibre dissections makes this technique more practical for routine estimates of the distribution of oxidative capacity among muscle fibres.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of pradofloxacin and doxycycline in serum, saliva, and tear fluid of cats after oral administration

The pharmacokinetic properties of pradofloxacin and doxycycline were investigated in serum, saliva, and tear fluid of cats. In a crossover study design, six cats were treated orally with a single dose of pradofloxacin (Veraflox^® Oral Suspension 2.5%) and doxycycline (Ronaxan^® 100 mg) at 5 mg/kg body weight. Following administration, samples of serum, saliva, and tear fluid were taken in regular intervals over a period of 24 h and analysed by turbulent flow chromatography/tandem mass spectrometry. All values are given as mean ± SD. Pradofloxacin reached a mean maximum serum concentration ( C _max) of 1.1 ± 0.5 μg/mL after 1.8 ± 1.3 h ( t _max). In saliva and tear fluid, mean C _max was 6.3 ± 7.0 and 13.4 ± 20.9 μg/mL, respectively, and mean t _max was 0.5 ± 0 and 0.8 ± 0.3 h, respectively. Doxycycline reached a mean C _max in serum of 4.0 ± 0.8 μg/mL after 4.3 ± 3.2 h. Whilst only at two time-points doxycycline concentrations close to the limit of quantification were determined in tear fluid, no detectable levels were found in saliva. The high concentrations of pradofloxacin in saliva and tear fluid are promising to apply pradofloxacin for the treatment of conjunctivitis and upper respiratory tract infections in cats. As doxycycline is barely secreted into these fluids after oral application the mechanisms of its clinical efficacy remain unclear.     

Thyroid testing in Sloughis

Background: Thyroid hormone concentrations were found to be different in Greyhounds and Whippets compared with nonsight hound dogs.
Hypothesis: In Sloughis, thyroid hormone concentration is lower than in nonsight hounds and comparable to Greyhounds.
Animals: Fifty-one Sloughis with no evidence of disease and a mean age of 4 years (range, 1–12 years).
Methods: Thyroid profiles consisting of total thyroxine (tT4), free thyroxine (fT4), free thyroxine after equilibrium dialysis (fT4 after ED), canine thyroid stimulation hormone (cTSH), and thyroglobulin antibodies as well as CBC and serum biochemistry results of Sloughis were compared with those of normal dogs. In 8 Sloughis, TSH stimulation tests were performed.
Results: In Sloughis, tT4 concentrations and fT4 concentrations measured by chemiluminescence were lower than those of controls (1.13 ± 0.65 μg/dL compared with 2.9 ± 0.8 μg/dL, P < .0001 and 11 ± 4.3 pmol/L compared with 16.7 ± 5.2 pmol/L, P < .0001, respectively). Concentrations of fT4 after ED and TSH were increased in Sloughis, when compared with controls (41.3 ± 26.9 pmol/L compared with 20.98 ± 10.29 pmol/L, P < .0001 and 0.22 ± 0.15 pmol/L compared with 0.15 ± 0.13 pmol/L, P = .0138, respectively). T4 concentration after TSH stimulation increased from 1.5 μg/dL (range, 0.2–2.7 μg/dL) to 2.7 μg/dL (range, 1.2–4.7 μg/dL); the recommended post-TSH T4 concentration was achieved by only 3 of 8 Sloughis. Hemoconcentration was found in 84.3% and hypoglobulinemia in 80.3%.
Conclusions and Clinical Importance: When evaluating Sloughis for hypothyroidism, veterinarians should be aware that these dogs have different thyroid hormone concentrations than nonsight hound dogs.     

Estimation of the selenium requirement of growing guinea pigs (Cavia porcellus)

The aim of the study was to determine the selenium (Se) requirement of guinea pigs as a species unable to synthesize ascorbic acid. Forty-nine male guinea pigs (average weight 208 ± 3.5 g) were divided into an initial status group and six experimental groups. The animals received a Se deficient Torula yeast based basal diet (<0.02 mg Se and 26 mg α-tocopherol/kg) or a Se addition of 0.05, 0.10, 0.15, 0.20 and 0.25 mg/kg diet as sodium selenate for 10 weeks. There was no significant difference in weight gain (final weight 643 ± 21 g) between the groups and no clinical symptoms of Se deficiency occurred. With the exception of the testes, there was an increasing Se concentration in liver, plasma and haemolysate dependent on supplementation level. Glutathione peroxidase was determined in the plasma and Se dependent glutathione peroxidase (GPx1) in haemolysate, liver, kidney, heart and lung. Thioredoxin reductase (TR) activity was measured in liver, kidney and heart and deiodinase activity in the liver. A phospholipid hydroperoxide reducing activity with Se influence was determined in liver, kidney, heart, testes and brain. With the exception of GPx1 activity in heart and haemolysate and TR activity in the kidney, all enzymes already reached their maximal activity at 0.05 mg Se/kg diet. The activities of GPx1 and TR were used as parameters for broken line analysis and a Se requirement of 0.080 mg Se/kg diet was derived as sufficient for growing guinea pigs adequately supplied with vitamin E.     

Pharmacokinetics of valacyclovir in the adult horse

Recent outbreaks of equine herpes virus type-1 infections have stimulated renewed interest in the use of effective antiherpetic drugs in horses. The purpose of this study was to investigate the pharmacokinetics of valacyclovir (VCV), the prodrug of acyclovir (ACV), in horses. Six adult horses were used in a randomized cross-over design. Treatments consisted of 10 mg/kg ACV infused intravenously, 5 g (7.7–11.7 mg/kg) VCV delivered intragastrically (IG) and 15 g (22.7–34.1 mg/kg) VCV administered IG. Serum samples were obtained at predetermined times for acyclovir assay using high-performance liquid chromatography. Following the administration of 5 g VCV, the mean observed maximum serum ACV concentration ( C _max) was 1.45 ± 0.38 (SD) μg/mL, at 0.74 ± 0.43 h. At a dose of 15 g VCV, the mean C _max was 5.26 ± 2.82 μg/mL, at 1 ± 0.27 h. The mean bioavailability of ACV from oral VCV was 60 ± 12% after 5 g of VCV and 48 ± 12% after 15 g VCV, and did not differ significantly between dose rates ( P  > 0.05). Superposition suggested that a loading dose of 27 mg/kg VCV every 8 h for 2 days, followed by a maintenance dose of 18 mg/kg every 12 h, will maintain effective serum ACV concentrations.     

Expression and Activity of Steroid Sulphatase in the Boar Testis

Oestrogens are essential for male fertility targeting the testicular-epididymal compartment. However, the underlying mechanisms are only vaguely known and species specificities must be considered. The boar has a remarkably high testicular-oestrogen output, with the biologically inactive oestrone-sulphate being the major oestrogen occurring in the testicular vein. In the boar testis and epididymis, activity of steroid sulphatase (StS) and oestrogen sulphotransferase has been demonstrated. Thus apart from their synthesis in Leydig cells, provision of biologically active free oestrone seems also to depend on the activity and localization of these enzymes. Our aim was to establish expression patterns and activity of StS in boar testis. Testes were randomly collected from healthy boars and allotted to five age groups, five animals in each, aged 50, 100, 150, 200 and 250 days. Three extra boars aged over 250 days were castrated to obtain fresh tissue for enzyme activity tests. Immunohistochemistry detected StS only in the cytoplasm of Leydig cells and – except for day-50 group in which 65.1 ± 4.9% (X ± SD) of the cells were positive – expression was constant with virtually all the cells staining positive. RT-PCR and in situ hybridization confirmed expression and localization of StS mRNA. The V _max and K _m value (X ± SD) for StS was 24.05 ± 0.3 fmol/s/μg protein and 2.15 ± 0.12 μ m . These data suggest that StS within the Leydig cells of the boar is involved in modulation of testicular oestrogen bioavailability and that the site of sulpho-conjugation is not the testis but a different compartment of the testes–epididymidis complex.     

Ca2+ ATPase in Dutch warmblood foals compared with Na+, K+ ATPase: intermuscular differences and the effect of exercise

We studied the effects of exercise without or with a subsequent period on pasture on Ca2+ ATPase concentration in foal skeletal muscle, and compared the results with those previously reported on Na+, K+ ATPase. Ca2+ ATPase was measured in homogenates as Ca2+-dependent steady-state phosphorylation from [gamma-32P]ATP. From day 7 after birth, 24 foals were divided into three groups: (i) staying in a box stall (Box); (ii) staying in a box stall with an exercise programme of an increasing number of sprints per day (Exercise); and (iii) staying on pasture (Pasture). Half of the foals (12 with four in each treatment group) were killed after 5 months. The remaining foals stayed on pasture until 11 months. In the 5-month Pasture group, Ca2+ ATPase concentration was 29.4 +/- 4.3 nmol/g wet weight (wt) (n = 4) in gluteus medius muscle, 25.2 +/- 3.3 nmol/g wet wt (n = 4) in semitendinosus muscle (both mixed fibre type), and 4.1 +/- 1.7 nmol/g wet wt (n = 3) in the slow masseter muscle. These values were not altered by exercise or by box rest. This was in contrast to the Na+, K+ ATPase concentration which was not different between the three muscles, but showed a 20% rise in gluteus medius and semitendinosus muscle after exercise. In the period from 5 to 11 months on pasture, there was no change in Ca2+ ATPase in any group. In conclusion, the Ca2+ ATPase concentration in foal muscle is around 6-fold higher in mixed fibres than in slow fibres. Furthermore, the enzyme is not up- or down-regulated by sprint exercise or subsequent rest.     

Enzymes of glucose and fatty acid metabolism of liver, kidney, skeletal muscle, adipose tissue and mammary gland of lactating and non-lactating sheep

The effect of peak lactation on the activities of a number of enzymes of glucose and lipid metabolism of perirenal and subcutaneous adipose tissue, skeletal muscle, liver, kidney cortex and mammary parenchyma of sheep are described. Enzymes studied included hexokinase (glucose utilization), pyruvate carboxylase (gluconeogenesis), pyruvate dehydrogenase (glucose oxidation and production of acetyl CoA for fatty acid synthesis), acetyl CoA carboxylase (fatty acid synthesis) and glycerol-3-phosphate acyltransferase (fatty acid esterification). Major changes that were found include a decrease in activities of enzymes of fatty acid synthesis and esterification in adipose tissues, decreased activity of pyruvate dehydrogenase in muscle and adipose tissues and increased pyruvate carboxylase; there was no change in activities of enzyme of fatty acid esterification in liver. Activities of hexokinase, acetyl CoA carboxylase and glycerol-3-phosphate acyltransferase have been estimated per tissue; this shows the quantitative importance of limiting glucose utilization by muscle and of suppression of fatty acid synthesis in adipose tissue for efficient partitioning of nutrients for milk production.