Herb-drug interactions of silybinin and cilofexor in beagle dogs based on pharmacokinetics by UPLC-MS/MS

Objective: A remarkably sensitive, accurate, and efficient ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) approach was developed as a facile and expeditious method for measuring cilofexor concentration in beagle dogs, the herb-drug interactions between silybinin and cilofexor was explored based on pharmacokinetics. Methods: The plasma sample protein of the beagles were rapidly sedimented with acetonitrile, and cilofexor and tropifexor (internal standard, ISTD) were separated by gradient elution using a 0.1% formic acid aqueous solution and acetonitrile as the mobile phase. The concentrations were detected using positive ion multiple reaction monitoring (MRM) mode. Mass transfer pairs were m/z 587.91→267.91 for cilofexor and m/z 604.08→228.03 for ISTD, respectively. A two-period self-controlled experimental design was adopted for the HDIs experiment. In the first period (Group A), six beagle dogs were orally administered cilofexor at a dose of 1 mg/kg. In the second period (Group B), silybinin (3 mg/kg) was orally administered to the six beagle dogs twice a day for seven consecutive days, after which cilofexor was orally administered. The cilofexor concentration in beagle dogs was determined, and HDIs were evaluated based on their pharmacokinetics. Results: The accuracy and precision of cilofexor were both less than 15%, and the recoveries, matrix effects, and stability met the relevant requirements. The Cmax of cilofexor in group B was 49.62% higher than that in group A, whereas the AUC(0-t) and AUC(0-∞) of cilofexor in group B were 47.85% and 48.52% higher, respectively, than those in group A. Meanwhile, the t1/2 extended from 7.84 h to 9.45 h, CL and Vz decreased in Group B. Conclusion: A novel UPLC-MS/MS approach was successfully applied for the measurement of cilofexor in beagle dog plasma. Silybinin can alter the pharmacokinetics of cilofexor in beagle dogs, thereby increasing plasma exposure to cilofexor.

Toxicity and Toxicokinetics of a Four-Week Repeated Gavage of Levamisole in Male Beagle Dogs: A Good Laboratory Practice Study

Levamisole (LVM) is considered an immunomodulatory agent that has the potential to treat various cancer and inflammation diseases. However, there is still much debate surrounding the toxicokinetic and toxicological information of LVM. Therefore, it is crucial to assess its toxicity to provide useful data for future human LVM risk assessments. In this study, a barrier environment was established under the guidance of good laboratory practice (GLP) at the Fujian Center for New Drug Safety Evaluation. Male beagle dogs were orally administered with 5, 15, and 30 mg/kg of LVM daily for four weeks. Toxicity assessment was based on various factors such as mortality, clinical signs, food and water consumption, body weight, body temperature, electrocardiogram, ophthalmological examination, hematology, serum biochemistry, organ/body coefficients, histopathological study, and toxicokinetic analysis. The results of this study showed that LVM did not exhibit any significant toxicological effects on beagle dogs at the exposure levels tested. A no observed adverse effect level (NOAEL) of LVM was set at 30 mg/kg/day for male beagle dogs, which is equivalent to a 12-fold clinical dose in humans. Moreover, the repeated exposure to LVM for four weeks did not lead to any bioaccumulation. These findings provide valuable insights for future human LVM risk assessments.

The Use of Population Pharmacokinetics to Extrapolate Food Effects from Human Adults and Beagle Dogs to the Pediatric Population Illustrated with Paracetamol as a Test Case

To date, food-drug interactions in the pediatric population remain understudied. The current food effect studies are mostly performed in adults and do not mimic the real-life situation in the pediatric population. Since the potential benefits of food effect studies performed in pediatrics should be counterbalanced with the burden that these studies pose to the patients, alternative research strategies should be evaluated. The present study aimed to evaluate whether population pharmacokinetics (popPK) using data in beagle dogs and human adults could reliably assess food effects relevant for the pediatric population. PopPK was utilized to understand the performance of paracetamol under different dosing conditions (when the participants were fasted, with a reference meal, and with infant formula) in human adults (n = 8) and beagle dogs (n = 6) by constructing models to derive the pharmacokinetic parameters and to evaluate the food effects in both species. A two-compartment model with a single input function for the absorption phase best described the profiles of paracetamol in the beagle dogs. In the human adults, a one-compartment model with a dual input function for the absorption phase best described the data. The simulated profiles for the different dosing conditions demonstrated that both the human adults' and beagle dogs' simulations were able to acceptably describe the plasma concentration-time profiles of paracetamol observed in a representative pediatric population, which opens up perspectives on pediatric-relevant food effect predictions. However, the obtained results should be carefully interpreted, since an accurate validation of these findings was not possible due to the scarcity of the literature on observed pediatric data.

28-day repeated dose toxicity and toxicokinetics study on new melatonergic antidepressant GW117 in beagle dogs

GW117 is new melatonergic antidepressant being developed to show better antidepressant action than agomelatine. The purpose of this study was to evaluate the toxicity and to determine potential target organs after oral (gavage) administration of the test article GW117 for 28 days and to assess the reversibility after a 4-week recovery phase in beagle dogs. Toxicokinetics was also evaluated. Four groups were designed in this study, including the vehicle control group and the GW117 50, 150 and 500 mg/kg/day groups, with 5 dogs/sex/group. Body weight, hematology, clinical chemistry, gross necropsy, organ weight, histopathology, and other indicators were examined. Results showed that animals dosed at ≥150 mg/kg/day showed gastrointestinal reactions (watery feces and dark green/red brown feces), with a dose-response relationship in the incidence and severity grade. Female dogs at 500 mg/kg/day had an increase in organ weight and ratios of the liver at the end of the dosing phase. Histopathology examination showed that some animals at 500 mg/kg/day, especially female animals, had minimal centrilobular hepatocyte hypertrophy in the liver, which reversed after 28-day recovery. With the exception of the above, no GW117-related abnormality was noted. Meanwhile, there were no sexual differences in drug exposure and accumulation after the first and last dosing. The no observed adverse effect dose level (NOAEL) was 150 mg/kg/day, under which mean C_max and AUC_0 → t were 583.5 and 2767.0 ng/ml*h for females and 663.2 and 4046.3 ng/ml*h for males on Day 28.

Development of na HPLC-MS/MS method for the determination of ginsenosides Rg1 and Rb1 from 'Shenmai' Injection in beagle dogs after single and multiple doses and application in pharmacokinetics

Shenmai Injection (SMI), which tonifies Qi and prevents exhaustion, nourishes Yin and generates body fluid, is usually used in the treatment of shock with deficiency of Qi and Yin, coronary artery disease, viral myocarditis, granulocytopenia and chronic pulmonary heart disease clinically. Ginsenosides Rg1 and Rb1 are the main active ingredients of SMI. In this study, high-performance liquid chromatography tandem mass spectrometry methods for quantification of Rb1 and Rg1 in beagle dogs were developed and validated according to international regulatory guidelines. The methods were applied to measure the pharmacokinetics parameters of the two ginsenoside after intravenous administration. The linear ranges of the analytes were 3.9-1,000 ng/ml for Rg1 and Rb1. After injection of single and multiple doses of SMI (1 ml/kg), the plasma concentration-time profiles of Rg1 and Rb1 met the characteristics of one-compartment and typical two-compartment intravenous injection.

Food Interactions Observed in a Pharmacokinetic Investigation Comparing Two Marketed Cold Preparations (BNO1016 and ELOM-080) after Administration to Beagle Dogs - A Pilot Study

Sinupret extract (BNO 1016) and Gelomyrtol forte (ELOM-080) represent the two top-selling cold remedies in Germany nowadays. Whereas BNO 1016 is a typical immediate release coated tablet, ELOM-080 is an enteric-coated soft gelatin capsule. The latter formulation, however, is at risk of pharmacokinetic interactions affecting absorption, especially in cases of concomitant food intake. In the present pilot study, we investigated the risk of a possible food effect in three male beagle dogs. Single doses of BNO 1016 and ELOM-80 were administered under fasting and fed conditions. Blood was sampled up to 30 h post-administration and plasma concentrations of the characteristic ingredients of BNO 1016 as well as ELOM-080 analytes were determined. Pharmacokinetic parameters focusing on the rate and extent of absorption were derived. BNO 1016 analytes demonstrated a similar course in both the fasted and fed states. ELOM-080 analytes also showed a similar picture in the fasted state. However, lag times (time from administration to first quantifiable time point in plasma) of up to 2 h post-administration with corresponding time to reach maximum concentration (obtained directly from the measured concentration) values of 3 to 4 h were observed, reflecting a longer gastric residence time. In the fed state, ELOM-080 showed significant pharmacokinetic characteristics, suggesting a clear food effect. A major observation was a double peak phenomenon that could be observed in two of three dogs. Furthermore, lag times of some analytes, up to 3 - 4 h, and corresponding time to reach maximum concentration values, up to 6 - 8 h, occurred. In contrast to BNO 1016, these findings suggest that, as with other enteric-coated formulations, there may also be a significant risk for food effects with ELOM-080 in humans.

A rapid and sensitive UPLC-MS/MS method for the determination of zanubrutinib in beagle plasma and its application in pharmacokinetics

A reliable and sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the determination of zanubrutinib in the plasma of beagle dogs. The column used was an Acquity BEH C₁₈ column (2.1 mm × 50 mm, 1.7 μm), maintained at 40°C with an injection volume of 2 μl. The gradient elution program was as follows: 0-1 min, 10-10% A; 1-1.1 min, 10-90% A; 1.1-2.1 min, 90-90% A; 2.1-2.2 min, 90-10% A; 2.2-3.0 min, 10-10% A. Mobile phase A was 0.1% formic acid, B was acetonitrile, and the total analysis time was 3 min. The mass spectrometry was performed in positive ion mode, and the scanning mode was multi-reaction monitoring mode with electrospray ionization as the ion source; m/z 472.2 → 455.01 for zanubrutinib and m/z 441.03 → 137.99 for ibrutinib (internal standard). The plasma samples were processed by protein precipitation. The standard curve showed good linearity (r²  = 0.999 8) in the range of 1.0-1,000 ng/ml (zanubrutinib) with a low limit of quantification of 1 ng/ml. Also, the intra-day and inter-day precision (RSD) was <5.88% and the accuracy (RE) ranged from -1.56 to 1.08%; the recoveries of zanubrutinib in beagle plasma ranged from 90.12 to 93.53% (RSD 1.67-6.42%) and the ME values of zanubrutinib were 98.70-101.06% (RSD 5.37-8.49%, n = 6). All values meet US Food and Drug Administration requirements. A rapid, highly selective and sensitive method for the determination of zanubrutinib concentration in plasma by UPLC-MS/MS was successfully developed. This method is suitable for pharmacokinetic studies in beagle dogs by following oral administration of zanubrutinib.

Pharmacokinetic-pharmacodynamic model to predict drug concentrations and intraocular pressure lowering effect for a bimatoprost six-month slow-release system

INTRODUCTION

Ophthalmic drug product development and dosing regimen selection depend on animal eye drug concentration-effect relationships since human eye tissues cannot be sampled for drug quantification. This study hypothesized that a pharmacokinetic-pharmacodynamic (PK-PD) mathematical model developed based on dog studies can be applied to the human eye of different ages, based on physiological parameter adjustment, to predict drug concentrations and effects in response to a new 6-month slow-release, intracameral, intraocular pressure (IOP) lowering, anti-glaucoma bimatoprost implant.

METHODS

Using previously reported dog concentration-effect relationship data at various doses, and the physiological parameters of dog eye, a PK-PD model was designed to predict dog aqueous humor drug concentrations and IOP lowering effects simultaneously for a given dose. After validating the model using the dog IOP data, it was applied to the human eye.

RESULTS

Using a drug release rate constant of 0.0002 h-1, the model predicted the dog IOP lowering effect with an error less than 6% or less at various doses (Observed = 0.91*Predicted + 2.35; R2 = 0.98). Considering literature reported aqueous humor volumes and flow rates in old (over 60 years) and young (20 to 30 years) humans, aqueous humor elimination rate constant was estimated to be 0.9 and 0.68 h-1, respectively. The model when modified using the older human eye parameters, predicted the IOP lowering effects reported in a clinical trial with 63-year-old adults, with an error of 6.2% or less. The model, when used for young adult eye not previously tested in clinical trials, predicted lower drug concentrations and effects, possibly due to 54% higher aqueous humor volume relative to older adults. The model predicted an IOP reduction of 26.3 and 30.6%, at 10 and 15 microgram doses, respectively, in young adults.

CONCLUSIONS

The PK-PD model developed is useful for product design and patient dosing by predicting eye drug concentration and effect time-courses in response to implant administration at various doses, frequencies, and release rates.

Acute toxicity, 28-day repeated-dose toxicity and toxicokinetic study of timosaponin BII in beagle dogs

The safety evaluation of timosaponin BII (TBII) in beagle dogs with toxicokinetic study was performed. For the acute oral toxicity study, the minimum lethal dose (MLD) of TBII was more than 2000 mg/kg and suggested the characteristics of absorption saturation. For the 28-day repeated dose oral toxicity and toxicokinetic studies, there was no significant effect on all test parameters except for prolonged APTT in the 60 and 180 mg/kg groups, which recovered after withdrawal. The increase of drug exposure of 180 mg/kg group was not proportional to the increase of administration dose, showing the characteristics of absorption saturation.

Contraceptive efficacy of recombinant porcine zona proteins and fusion protein encompassing canine ZP3 fragment and GnRH in female beagle dogs

PROBLEM

To manage population of dogs (Canis familiaris), the efficacy of recombinant proteins-based contraceptive vaccines to inhibit fertility has been evaluated in female beagle dogs.

METHOD OF STUDY

Female beagle dogs (n = 4) were immunized with physical mixture of Escherichia coli-expressed recombinant porcine ZP3 with promiscuous T cell epitope of tetanus toxoid (TT-KK-pZP3) and porcine ZP4 with promiscuous T cell epitope of bovine RNase (bRNase-KK-pZP4), or with a fusion protein encompassing dog ZP3 fragment and two copies of GnRH with appropriate promiscuous T cell epitopes (dZP3-GnRH₂ ); control animals received only alum, the adjuvant. The immunized animals were followed-up for antibody titres by ELISA as well as for fertility status subsequent to mating with male dogs.

RESULTS

Active immunization of female dogs following a three injections schedule at 4-week intervals with a physical mixture of TT-KK-pZP3 + bRNase-KK-pZP4 as well as dZP3-GnRH₂ , led to generation of significant antibody titres against respective recombinant proteins. Active immunization with dZP3-GnRH₂ also led to generation of antibodies reactive with both dZP3 and GnRH. A booster dose on day 383 led to an increase in antibody titres and circulating antibodies against respective recombinant proteins could be observed on day 528. Antibodies in immune serum samples from dogs immunized with TT-KK-pZP3 + bRNase-KK-pZP4 or dZP3-GnRH₂ reacted with native canine ZP as assessed by an indirect immunofluorescence assay. Mating studies revealed a reduced number of pregnancies as well as a significant reduction in the number of pups born in the female dogs immunized with dZP3-GnRH₂ as compared to the adjuvanted control. Curtailment of pregnancy in dZP3-GnRH₂ immunized group was associated with antibody titres against dZP3-GnRH₂ . However, immunization with recombinant TT-KK-pZP3 + bRNase-KK-pZP4 did not significantly decrease the number of pups born as compared to the adjuvanted control.

CONCLUSION

These studies revealed the potential of recombinant dZP3-GnRH₂ -based contraceptive vaccine to curtail fertility in female dogs. Large scale studies to establish the efficacy and safety of this recombinant protein for the management of community dog population are thus warranted.

Sensory attributes, dog preference ranking, and oxidation rate evaluation of sorghum-based baked treats supplemented with soluble animal proteins

Treats are offered to dogs to reinforce the animal-owner bond and as rewards. Wheat, which contains gluten (gliadin and glutenin proteins), is often used in treats. The US is a leading producer of sorghum which might be an alternative; however, it does not have functional properties to form viscoelastic doughs, because is mainly composed of kafirin protein. Therefore, the objectives of this study were to determine the effects of supplementing soluble animal proteins in whole sorghum rotary molded baked dog treats on dog preference, sensory attributes, and oxidation rate. The treats were produced in triplicate in a 2x4 + 1 augmented factorial arrangement of treatments. Two whole sorghum flours (WWS and WRS), four protein sources [none (NC), spray-dried plasma (SDP), egg protein (EP), and gelatin (GL)], and a positive control with wheat (WWF-GTN) were evaluated. A preference ranking test with twelve dogs was performed. Additionally, five trained panelists scored the intensity of appearance, aroma, flavor, texture/mouthfeel, and aftertaste attributes. Finally, the treats were stored at 30°C and 60% RH, and hexanal concentrations were measured on days 0, 28, 56, and 112. The data was analyzed using the statistical software SAS for the animal and oxidation rate evaluations with significance considered at P<0.05. The descriptive sensory evaluation data was analyzed using multivariate analysis (XLSTAT). The dogs did not detect differences among WWF-GTN, WWS, or WRS treats when evaluated together. However, the WWF-GTN, WWS-SDP and WWS-EP treatments were preferred among the white sorghum treatments. The EP treatments led to some consumption difficulties by dogs because of their hard texture. The panelists reported a high degree of variation in the appearance and texture across treatments. The WRS and WWS treats with SDP or EP were darker, while NC treats had more surface cracks. Initial crispness, hardness, and fracturability were higher in EP treatments compared to all other sorghum treatments. The predominant flavor and aftertaste identified were "grainy." The hexanal values for all treats were <1.0 mg/kg except for the EP treatments that had higher values (2.0-19.3 mg/kg) across the shelf-life test. This work indicated that the replacement of WWF-GTN by WWS and WRS, along with soluble animal proteins like SDP or GL would produce comparable preference by dogs, oxidation rates, product aromatics, flavor, aftertaste attributes, and, at a lower degree, product texture.

Study on feasibility of the partial meniscal allograft transplantation

Since the meniscus is an important stabilizing structure of the knee joint and has a significant role in load-bearing and shock absorption, so the complete structural and functional reconstructions of the teared menisci should be done not only after partial meniscectomy but also post total meniscectomy. So far, animal experiments and good clinical practice have showed that TMAT after total meniscectomy has partially solved the problem of structural and functional reconstructions after total meniscectomy. However, partial meniscectomy will also lead to accelerated knee degeneration, and its proportion is much higher than that of patients with total meniscectomy. Herein, the feasibility of PMAT after partial meniscectomy was investigated for the first time by using the 40% posterior horn meniscectomy model of the medial meniscus in Beagle dogs, and also for the first time, TMAT group and the total meniscectomy group were used as control groups. Compared with the TMAT, the transcriptomics evaluation, scanning electron microscope observation, histological regeneration and structure, biomechanical property, inflammation environment, and the knee function post PMAT were more similar to that of normal meniscus was first reported. This study provides a PMAT scheme with clinical translational value for the complete structural and functional reconstruction of the patients with partial meniscectomy and fills the gap in the field of teared meniscus therapy on the basis of quite well clinical applications of the meniscus repair and the TMAT.

Water Extract: General Toxicity Studies in Sprague-Dawley Rats and Beagle Dogs With Re-evaluation of Genotoxic Potentials

Acer tegmentosum Maxim., commonly known as Manchurian stripe maple, is a deciduous tree belonging to the family of Aceraceae and has been traditionally used in folk medicine for its remedial effects in liver diseases and traumatic bleedings. With a growing body of experimental evidence for its pharmacological efficacies, such as neuroprotective, hepatoprotective, antioxidant, and anti-inflammatory activities, A. tegmentosum has gradually gained popularity as a health supplement and functional food. However, the large part of essential toxicity information still remained lacking despite the possibility of mutagenic potentials as previously suggested, posing safety concerns for human consumption. In this study, we evaluated 90-day repeated oral toxicity of A. tegmentosum Maxim. water extract (ATWE) in SD rats with acute toxicity assessment in beagle dogs, and reevaluated genotoxicity using a combination of in vitro and in vivo assays. During the oral study period, ATWE did not cause toxicity-related clinical signs and mortality in rodents without adverse effects observed in the analysis of hematology, serum biochemistry, and histopathology, establishing >5,000 mg/kg BW as the NOAEL. In addition, doses up to 5,000 mg/kg BW did not cause acute toxicity in beagle dogs. When assessed for genotoxicity using bacterial reverse mutation, chromosome aberration, and micronucleus formation, ATWE showed lack of mutagenicity and clastogenicity. These results demonstrated that AWTE was safe in the present preclinical study for systemic toxicity and genotoxicity at the tested doses, providing a guideline for safe use in humans.

Effect of Antibacterial Root Canal Sealer on Persistent Apical Periodontitis

The infection of Enterococcus faecalis and its interacting microorganisms in the root canal could cause persistent apical periodontitis (AP). Antibacterial root canal sealer has favorable prospects to inhibit biofilms. The purpose of this study was to investigated the antibacterial effect of root canal sealer containing dimethylaminododecyl methacrylate (DMADDM) on persistent AP in beagle dogs for the first time. Persistent AP was established by a two-step infection with Enterococcus faecalis and multi-bacteria (Enterococcus faecalis, Lactobacillus acidophilus, Actinomycesnaeslundii, Streptococcus gordonii). Root canal sealer containing DMADDM (0%, 1.25%, 2.5%) was used to complete root canal filling. The volume of lesions and inflammatory grade in the apical area were evaluated by cone beam computer tomography (CBCT) and hematoxylin-eosin staining. Both Enterococcus-faecalis- and multi-bacteria-induced persistent AP caused severe apical destruction, and there were no significant differences in pathogenicity between them. DMADDM-modified sealer significantly reduced the volume of periapical lesion and inflammatory grade compared with the control group, among them, the therapeutic effect of the 2.5% group was better than the 1.25% group. In addition, E.faecalis-induced reinfection was more sensitive to the 2.5% group than multi-bacteria reinfection. This study shows that root canal sealer containing DMADDM had a remarkable therapeutic effect on persistent AP, especially on E. faecalis-induced reinfection.

Subacute Toxicity Study of Nicotinamide Mononucleotide via Oral Administration

Nicotinamide mononucleotide (NMN), a key precursory metabolite of NAD⁺, has been shown to elevate the cellular level of NAD⁺ and ameliorate various age-related diseases. Despite these progresses, systemic evaluation pertaining to the subacute toxicity of NMN remains to be determined. Here, we examine the subacute toxicity of NMN in mice and beagle dogs. Mice were gavaged with a saturated concentration of NMN solution at the maximum intragastric dose once or twice per day for 7 days. Dogs were gavaged twice per day for 14 days. In mice, NMN administrated once per day for 7 days is well tolerated with minimal deleterious effects. Upon higher dosage, we observe slightly increased level of alamine aminotransferase, while other biomarkers remain unchanged. Consistently, administration of NMN in beagle dogs only results in mild increases in creatinine and uric acid. Together, our study highlights the safety of NMN, providing a possible safe dose range for oral administration of NMN.

Toxocara canis Differentially Affects Hepatic MicroRNA Expression in Beagle Dogs at Different Stages of Infection

Toxocara canis is a neglected zoonotic parasite, which threatens the health of dogs and humans worldwide. The molecular mechanisms that underlie the progression of T. canis infection remain mostly unknown. MicroRNAs (miRNAs) are small non-coding RNAs that have been identified in T. canis; however, the regulation and role of miRNAs in the host during infection remain incompletely understood. In this study, we determined hepatic miRNA expression at different stages of T. canis infection in beagle dogs. Individual dogs were infected by 300 embryonated T. canis eggs, and their livers were collected at 12 hpi (hours post-infection), 24 hpi, and 36 dpi (days post-infection). The expression profiles of liver miRNAs were determined using RNA-sequencing. Compared to the control groups, 9, 16, and 34 differentially expressed miRNAs (DEmiRNAs) were detected in the livers of infected dogs at the three infection stages, respectively. Among those DEmiRNAs, the novel-294 and cfa-miR-885 were predicted to regulate inflammation-related genes at the initial stage of infection (12 hpi). The cfa-miR-1839 was predicted to regulate the target gene TRIM71, which may influence the development of T. canis larvae at 24 hpi. Moreover, cfa-miR-370 and cfa-miR-133c were associated with immune response at the final stage of infection (36 dpi). Some immunity-related Gene Ontology terms were enriched particularly at 24 hpi. Likewise, Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that many significantly enriched pathways were involved in inflammation and immune responses. The expression level of nine DEmiRNAs was validated using quantitative real-time PCR (qRT-PCR). These results show that miRNAs play critical roles in the pathogenesis of T. canis during the hepatic phase of parasite development. Our data provide fundamental information for further investigation of the roles of miRNAs in the innate/adaptive immune response of dogs infected by T. canis.

Assessing the Safety, Tolerability, Pharmacokinetics, and Biodistribution of Novel Oral Formulations of Amphotericin B following Single- and Multiple-Dose Administration to Beagle Dogs

The purpose of this study was to assess the safety, tolerability, pharmacokinetics (PK), and biodistribution of novel oral amphotericin B (AmpB) formulations following single- and multiple-oral-dose administration to healthy beagle dogs. The liquid formulation of AmpB was administered to three male dogs, and the capsule formulations of AmpB were administered to each of two groups of six male dogs. Blood was collected for pharmacokinetic evaluation on days 1, 2, and 3 (up to 72 h postdosing). Dogs receiving the capsule formulations further received a single oral dose of 100 mg once daily for three more days, and on the 4th day, blood samples were taken at 24 h postdosing and the dogs were humanely sacrificed with the removal of organs, from which tissue samples were taken for analysis of the AmpB content. Multiple-dose studies were completed for 7 or 14 days with daily doses of up to 1,000 mg/day with the capsule formulations. All oral formulations of AmpB following both single- and multiple-dose administration were well tolerated in the dogs, and there were no relevant adverse signs observed, such as changes in hematologic, coagulation, or biochemistry parameters; loss of weight; changes in food or water intake; or signs of gastrointestinal distress. The oral absorption of AmpB from the liquid formulation and the capsule formulations were similar, with no significant differences. The tissue distributions of AmpB were similar following repeated doses of the two capsule formulations to dogs. Following 14 days of treatment with the iCo-010 liquid formulation and the iCo-019 and iCo-022 capsule formulations, the range of values of the maximum observed plasma concentration (C _max) was 53.2 to 62.3, 24.9 to 66.4, and 36.7 to 85.2 ng/ml, respectively; the range of values of the time to C _max was 4 to 12, 4 to 24, and 2 to 24 h, respectively; and the range of values of the area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration was 2,635 to 3,071, 1,053 to 2,517, and 1,443 to 3,713 ng · h/ml, respectively. We have developed a safe novel oral AmpB formulation suitable for future efficacy studies.

Simultaneous UPLC-MS/MS Determination of 6-mercaptopurine, 6-methylmercaptopurine and 6-thioguanine in Plasma: Application to the Pharmacokinetic Evaluation of Novel Dosage forms in Beagle Dogs

BACKGROUND

6-Mercaptopurine (6-MP) is widely used to treat pediatric acute lymphoblastic leukemia (ALL). Mini-tablets of 5 mg per tablet were developed for precision individual therapy for children and individuals with poor thiopurine S-methyltransferase (TPMT) or nucleoside diphophate-linked moiety X-type motif 15 (NUDT15) metabolism. This study investigated the pharmacokinetic profiles of mini-tablets and conventional tablets with an improved ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method.

METHODS

After giving 8 healthy beagle dogs 50 mg 6-MP in different dosage forms, plasma samples collected at different time points were analyzed for pharmacokinetic evaluation. The samples were precipitated by methanol with 0.05% formic acid and separated on a Waters Atlantis T3 column (2.1 × 150 mm, 3 μm particles) using 0.1% formic acid in water and methanol at a flow rate of 0.4 mL/min in 4 min.

RESULTS

This method showed good linearity, accuracy, precision and stability with a detection range of 5.0-500.0 ng/mL for 6-MP, 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TG). The main parameters, half-life of apparent terminal disposition, maximum observed plasma concentration, total AUC extrapolated to infinity, AUC since initiation of the experiment, mean residence time, distribution volume and clearance were 1.62 ± 0.87 hours, 90.58 ± 60.43 ng/mL, 151.20 ± 94.18 ng·h/mL, 292.06 ± 184.02 ng·h2/mL, 1.90 ± 0.92 hours, 864.08 ± 538.52 L, and 432.75 ± 360.64 L/h for conventional tablets and 1.70 ± 1.10 hours, 84.15 ± 39.50 ng/mL, 147.70 ± 51.80 ng·h/mL, 300.92 ± 124.48 ng·h2/mL, 2.07 ± 0.50 hours, 756.90 ± 324.00 L, and 340.75 ± 125.81 L/h for minitablets, respectively. Paired t-tests showed no significant difference in any of the evaluated pharmacokinetic parameters between the two types tablets (P > 0.05).

CONCLUSION

Two dosage forms showed the same pharmacokinetic characteristics. This developing, novel formulation will help to provide a more accurate and optimal dosing regimen of 6-MP for humans in the future.

The Use of Capsule Endoscopy to Determine Tablet Disintegration In Vivo

The preferred delivery route for drugs targeted for systemic effect is by oral administration. Following oral administration, a solid dosage form must disintegrate and the drug dissolve, thereafter permeating the intestinal mucosa. Several different in vitro methods are used to investigate these processes, i.e., disintegration tests, dissolution tests, and permeability models. However, the actual behavior of oral dosage forms in the environment of the gastro-intestinal tract is not very well elucidated using these conventional methods. In this study, the use of capsule endoscopy to determine tablet disintegration in vivo was assessed. Panadol and Panadol Rapid (acetaminophen/paracetamol) were used as the test material. The in vivo tablet disintegration behavior in beagle dogs was assessed by the use of capsule endoscopy. The in vitro tablet disintegration behavior was assessed using the European Pharmacopeia (Ph. Eur.) disintegration test. The study showed that the in vivo disintegration times of Panadol and Panadol Rapid were 24.7 and 16.5 min, respectively, when determined by capsule endoscopy, which corresponded to the pharmacokinetic data. By contrast, the in vitro disintegration times of the same formulations were 5.5 and 4.0 min, respectively, when determined by the Ph. Eur. disintegration test. In conclusion, capsule endoscopy can be used to determine the in vivo tablet disintegration behavior. By contrast, the in vitro methods appear to not be predictive of the disintegration behavior in vivo but may be used to rank the order the formulations with respect to disintegration time.

Influence of estrous stages on electrocardiography, clinical pathology and ovarian weight of experimental beagle dogs: a retrospective analysis

Estrous cycle is a repetitive phenomenon occurring during the reproductive life of a female dog. The duration of the canine estrous cycle is considerably longer than one in the most of the other animals and is broadly grouped into follicular phase (proestrus and estrus), luteal phase (diestrus) and non-seasonal anestrus. Dogs in the same stage of cycle can be inadvertently assigned to same group during routine safety and metabolic studies leading to possible erroneous interpretation of test-item related effects. This retrospective analysis was conducted by analyzing data of 86 female beagle dogs from control/placebo treated groups to correlate any possible effect of estrous stages with electrocardiography, clinical pathology and ovarian weight. Different estrous cycle stages of beagles were confirmed histologically by evaluating ovary, uterus, vagina and mammary glands. The incidence of beagles in diestrus was the highest, followed by anestrus, proestrus and estrus. No significant effect was noticed on heart rate, P–A, P–D, RR, QRS and QT intervals across different stages of estrous cycle. However, significantly higher PQ (PR) interval in dogs in proestrus stage was observed compared to dogs in anestrus and estrus. Marginally higher WBCs, neutrophils, lymphocytes, RBCs, hemoglobin, AST and lower hematocrit, lipid profile (total cholesterol, HDL, LDL, triglycerides), ALP level was evident in estrous period. Relative ovary weight was significantly higher in dogs in diestrus stage. Considering these results, one may need to exercise caution while interpreting experimental data from female beagle dogs.

Electroacupuncture-induced cannabinoid receptor expression in repair of abducens nerve

Objective: Through the development of beagle abducens nerve injury model, taking electroacupuncture as the core and microglia as the starting point, the author investigated whether electroacupuncture can promote the repair of injured abducens nerve by cannabinoid receptor-mediated regulation of microglia activation. Methods: Healthy beagle dogs were randomly divided into five groups: sham operation group (A), injury group (B), electroacupuncture pretreatment group (C), antagonist group (D) and solvent group (E). After stimulation with electroacupuncture, the expression of cannabinoid 1 receptor (CB1R) and cannabinoid 2 receptor (CB2R) in A, B and C microglia cells was detected by Western Bolt analysis, and further the expression of CB2R in five groups was further analyzed by immunofluorescence, thereby statistical differences were analyzed. Results: Among group A, group B and group C, Western Blot analysis showed that there were no significant changes in the expression of CB1R protein after electroacupuncture [F (2, 12)=1.75, p = 0.215]. After electroacupuncture preconditioning for 15 min for 2 weeks, group C was compared with group A and group B, which showed CB2 was affected. The expression of CB2R protein was significantly increased among groups A, B and C [F (2, 12)=5189.57, p < 0.001], but there was no significant difference in the expression of CB2R protein between group A and group B (p > 0.05). The results of immunofluorescence showed that Arginse/CD11b was significantly increased in group C comparing to group A (*p < 0.001), while there was a significant increase in group E comparing to group A about Arginse/CD11b [F (4, 20)=4345.44, p < 0.001]. Conclusions: The CB2R in the cannabinoid receptor is mainly involved in the electro-acupuncture-induced neuroprotection. Electroacupuncture can promote the repair of injured abducens nerve by CB2R-mediated activation of microglia.

Protective Effect of UP446 on Ligature-Induced Periodontitis in Beagle Dogs

Periodontal disease is an inflammatory disease of the gum caused by a formation of a plaque that triggers immune responses and inflammation leading to the destruction of tissues surrounding and supporting the teeth. Chronic usage of synthetic chemicals and antibiotics is limited by undesired adverse events to the host. A botanical composition (UP446), which consists primarily of bioflavonoids such as baicalin from roots of Scutellaria baicalensis and catechins from heartwoods of Acacia catechu, was evaluated for its effect on ligature-induced periodontal disease in beagle dogs. Disease model was induced in 20 male and female dogs. After a 12-week induction of periodontitis, animals were assigned to a placebo, positive control (doxycycline), and two treatment groups consisting of five animals each. The placebo group was only administrated to normal dog chow (25 g/kg/day). In the doxycycline treatment group, animals were fed a normal diet (25 g/kg/day) and doxycycline (5 mg/kg) was orally administrated every day. Treatment of UP446 was done by feeding the regular diet formulated with 0.1% and 0.2% of UP446 by weight. Clinical indices such as plaque index (PI), gingival index (GI), clinical attachment level (CAL), probing pocket depth (PPD), and bleeding on probing (BoP) were measured every two weeks for 12 weeks. UP446 administered to beagle dogs for 12 weeks at 0.1% and 0.2% resulted in statistically significant reductions in gingivitis, pocket depth, loss of attachment, and gum bleeding. UP446 could potentially be used alone or as an adjunct with other oral hygiene preparations for periodontal disease in both human and companion animals.

Cardiovascular and respiratory safety evaluation of Musca Domestica larvae low molecular weight peptide in beagle dogs

Background: Many studies have demonstrated that the water extracts and low-molecular-weight peptide (LMWP) of the Musca domestica larvae contain significant biological activity. However, the cardiovascular and respiratory safety evaluations of LMWP are yet to be sufficiently investigated. Aim: This study focused on the cardiovascular and respiratory safety evaluations of the M. domestica larvae LMWP in beagle dogs. Methods: Direct cardiovascular and respiratory effects of three different doses of the M. domestica larvae LMWP were investigated following only once oral administration in conscious telemetered dogs, whereby ECG, arterial pressure, and respiratory data were collected using the Data Science International telemetric system. Results: The PR, QT, and QTcf intervals were significantly shortened in the medium-dose LMWP treatment group at 3 h after drug administration. Furthermore, no significant differences were observed in any of the corresponding indexes of other treatment groups at different time points compared to those of the control group. P wave, ST segment, R wave, systolic pressure, diastolic pressure, and mean pressure were significantly different, although these differences had no significant dose-effect relationship. Respiratory frequency significantly increased in the medium-dose LMWP treatment group at 8 h after drug administration compared to that of the control group. Respiratory rate and tidal volume showed no significant differences at varying time points among all LMWP treatment groups. Conclusions: No toxicological effects related to cardiovascular and respiratory safety in beagle dogs were observed at any dose level of the M. domestica larvae LMWP.

Application of a sensitive and specific LC-ESI-MS/MS method for the simultaneous quantification of twelve bioactive components in dog plasma for an intravenous pharmacokinetic study of Yiqifumai Injection in beagle dogs

Yiqifumai Injection is a lyophilized powder preparation widely used to treat coronary heart disease. However, its in vivo bioactive components and pharmacokinetic behavior remain unknown. Therefore a sensitive and specific LC-MS/MS was developed and validated for the simultaneous quantification of eight saponins and four lignans in beagle dog plasma. The plasma samples were pretreated by protein precipitation with methanol-acetonitrile (1:1, v/v). Chromatographic separation of all the 12 analytes and estazolam (internal standard, IS) was successfully accomplished on an Ultimate® XB-C₈ column (100 × 2.1 mm, 3 μm) with a gradient elution system. The total running time was 8 min with a flow rate of 0.40 mL/min. Acquisition of mass spectrometric data was performed via positive electrospray ionization in multiple reaction monitoring mode. The assay was fully validated in terms of selectivity, linear range, lower limit of quantitation, precision, accuracy, matrix effect, recovery and stability. This validated method was successfully applied to the pharmacokinetics of 12 bioactive components after intravenous administration of Yiqifumai Injection to beagle dogs at a dose of 0.541 g/kg.

Comparison of naturally aging and D-galactose induced aging model in beagle dogs

Animal models have been used to study aging for decades. In numerous aging studies, beagles are the most commonly used breed of dog. However, few studies have compared between naturally aging models and experimentally induced aging models in beagle dogs. In the present study, a D-galactose induced aging model was compared with a naturally aging model, and young adult dogs were considered as the young control group. The level of malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in serum, and brain tissue were measured. Histopathological comparisons of the liver, kidneys, heart, lungs and spleen were evaluated using hematoxylin and eosin (H&E) staining, in addition, the brain was evaluated by H&E staining, and Nissl staining. The expression levels of aging-associated factors in the hippocampus, including proliferating cell nuclear antigen (PCNA), P16 and P21 were also determined through reverse transcription quantitative-polymerase chain reaction, and western blot analysis. The results indicated that D-galactose induced aging significantly increased the MDA level, while the levels of SOD and GSH-Px were diminished when compared with the young control group, which was similar to the naturally aging group. Parallel histopathological features were observed in the D-galactose induced aging and naturally aging groups compared with the young control group. However, a reduced expression level of PCNA, and increased expression levels of P16 and P21 were observed in the naturally ageing and induced aging groups compared with the young control group. The results of the current study demonstrated that the beagle dogs in D-galactose induced aging model exhibited significant similarities with the naturally aging model, providing evidence to support that the D-galactose induced aging model may be applied to aging studies.

Pharmacokinetics of tildipirosin in beagle dogs

The objective of this study was to investigate the pharmacokinetic profile of tildipirosin (TD) in 24 beagle dogs following intravenous (i.v.) and intramuscular (i.m.) administration, respectively, at 2, 4, and 6 mg/kg. Plasma samples at certain time points (0-14 days) were collected, and the concentrations of drug were quantified by UPLC-MS/MS. Plasma concentration-time data and relevant parameters were described by noncompartmental through WinNonlin 6.4 software. After single i.m. injection at 2, 4, and 6 mg/kg body weight, mean maximum concentration (C_max ) was 412.73 ± 76.01, 1,051 ± 323, and 1,061 ± 352 ng/ml, respectively. Mean time to reach C_max was 0.36 ± 0.2, 0.08 ± 0.00, and 0.13 ± 0.07 hr after i.m. injection at 2, 4, and 6 mg/kg, respectively. The mean value of T_1/2λz for i.m. administration at doses of 2, 4, and 6 mg/kg was 71.39 ± 28.42, 91 .33 ± 50.02, and 96.43 ± 45.02 hr, respectively. The mean residence times were 63.81 ± 10.96, 35.83 ± 15.13, and 38.18 ± 16.77 hr for doses of 2, 4, and 6 mg/kg, respectively. These pharmacokinetic characteristics after i.m. administration indicated that TD could be rapidly distributed into tissues on account of the high lipid solubility and then released into plasma. In addition, the absolute bioavailability of 2 mg/kg after i.m. injection was 112%. No adverse effects were observed after i.v. and i.m. administration.

Evidence That Lifelong Low Dose Rates of Ionizing Radiation Increase Lifespan in Long- and Short-Lived Dogs

After the 1956 radiation scare to stop weapons testing, studies focused on cancer induction by low-level radiation. Concern has shifted to protecting "radiation-sensitive individuals." Since longevity is a measure of health impact, this analysis reexamined data to compare the effect of dose rate on the lifespans of short-lived (5% and 10% mortality) dogs and on the lifespans of dogs at 50% mortality. The data came from 2 large-scale studies. One exposed 10 groups to different γ dose rates; the other exposed 8 groups to different lung burdens of plutonium. Reexamination indicated that normalized lifespans increased more for short-lived dogs than for average dogs, when radiation was moderately above background. This was apparent by interpolating between the lifespans of nonirradiated dogs and exposed dogs. The optimum lifespan increase appeared at 50 mGy/y. The threshold for harm (decreased lifespan) was 700 mGy/y for 50% mortality dogs and 1100 mGy/y for short-lived dogs. For inhaled α-emitting particulates, longevity was remarkably increased for short-lived dogs below the threshold for harm. Short-lived dogs seem more radiosensitive than average dogs and they benefit more from low radiation. If dogs model humans, this evidence would support a change to radiation protection policy. Maintaining exposures "as low as reasonably achievable" (ALARA) appears questionable.

Pharmacokinetics and Metabolism of Cyadox and Its Main Metabolites in Beagle Dogs Following Oral, Intramuscular, and Intravenous Administration

Cyadox (Cyx) is an antibacterial drug of the quinoxaline group that exerts markedly lower toxicity in animals, compared to its congeners. Here, the pharmacokinetics and metabolism of Cyx after oral (PO), intramuscular (IM), and intravenous (IV) routes of administration were studied to establish safety criteria for the clinical use of Cyx in animals. Six beagle dogs (3 males, 3 females) were administered Cyx through PO (40 mg kg⁻¹ b.w.), IM (10 mg kg⁻¹ b.w.), and IV (10 mg kg⁻¹ b.w.) routes with a washout period of 2 weeks in a crossover design. Highly sensitive high-performance liquid chromatography with ultraviolet detection (HPLC-UV) was employed for determination of Cyx and its main metabolites, 1, 4-bisdesoxycyadox (Cy1), cyadox-1-monoxide (Cy2), N-(quinoxaline-2-methyl)-cyanide acetyl hydrazine (Cy4), and quinoxaline-2-carboxylic acid (Cy6) in plasma, urine and feces of dogs. The oral bioavailability of Cyx was 4.75%, suggesting first-pass effect in dogs. The concentration vs. time profile in plasma after PO administration indicates that Cyx is rapidly dissociated into its metabolites and eliminated from plasma earlier, compared to its metabolites. The areas under the curve (AUC) of Cyx after PO, IM and IV administration were 1.22 h × μg mL⁻¹, 6.3 h × μg mL⁻¹, and 6.66 h × μg mL⁻¹, while mean resident times (MRT) were 7.32, 3.58 and 0.556 h, respectively. Total recovery of Cyx and its metabolites was >60% with each administration route. In feces, 48.83% drug was recovered after PO administration, while 18.15% and 17.11% after IM and IV injections, respectively, suggesting renal clearance as the major route of excretion with IM and IV administration and feces as the major route with PO delivery. Our comprehensive evaluation of Cyx has uncovered detailed information that should facilitate its judicious use in animals by improving understanding of its pharmacology.

Development and validation of a simple, sensitive and accurate LC-MS/MS method for the determination of guanfacine, a selective α2A -adrenergicreceptor agonist, in plasma and its application to a pharmacokinetic study

A simple, practical, accurate and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and fully validated for the quantitation of guanfacine in beagle dog plasma. After protein precipitation by acetonitrile, the analytes were separated on a C18 chromatographic column by methanol and water containing 0.1% (v/v) formic acid with a gradient elution. The subsequent detection utilized a mass spectrometry under positive ion mode with multiple reaction monitoring of guanfacine and enalaprilat (internal standard) at m/z 246.2 → 159.0 and m/z 349.2 → 205.9, respectively. Good linearity was obtained over the concentration range of 0.1-20 ng/mL for guanfacine in dog plasma and the lower limit of quantification of this method was 0.1 ng/mL. The intra- and inter-day precisions were <10.8% relative standard deviation with an accuracy of 92.9-108.4%. The matrix effects ranged from 89.4 to 100.7% and extraction recoveries were >90%. Stability studies showed that both analytes were stable during sample preparation and analysis. The established method was successfully applied to an in vivo pharmacokinetic study in beagle dogs after a single oral dose of 4 mg guanfacine extended-release tablets.

Pharmacokinetics and enhanced oral bioavailability in beagle dogs of cyclosporine A encapsulated in glyceryl monooleate/poloxamer 407 cubic nanoparticles

Efforts to improve the oral bioavailability of cyclosporine A (CyA) remains a challenge in the field of drug delivery. In this study, glyceryl monooleate (GMO)/poloxamer 407 cubic nanoparticles were evaluated as potential vehicles to improve the oral bioavailability of CyA. Cubic nanoparticles were prepared via the fragmentation of a bulk GMO/poloxamer 407 cubic phase gel by sonication and homogenization. The cubic inner structure formed was verified using Cryo-TEM. The mean diameters of the nanoparticles were about 180 nm, and the entrapment efficiency of these particles for CyA was over 85%. The in vitro release of CyA from these nanoparticles was less than 5% at 12 h. The results of a pharmacokinetic study in beagle dogs showed improved absorption of CyA from cubic nanoparticles as compared to microemulsion-based Neoral((R)); higher C(max) (1371.18 +/- 37.34 vs 969.68 +/- 176.3 ng mL(-1)), higher AUC(0-t) (7757.21 +/- 1093.64 vs 4739.52 +/- 806.30 ng h mL(-1)) and AUC(0-infinity) (9004.77 +/- 1090.38 vs 5462.31 +/- 930.76 ng h mL(-1)). The relative oral bioavailability of CyA cubic nanoparticles calculated on the basis of AUC(0-infinity) was about 178% as compared to Neoral((R)). The enhanced bioavailability of CyA is likely due to facilitated absorption by cubic nanoparticles rather than improved release.

The cardiovascular and pharmacokinetic profile of dofetilide in conscious telemetered beagle dogs and cynomolgus monkeys

BACKGROUND AND PURPOSE

The effects of dofetilide were studied in monkeys and dogs. Pharmacokinetic data were generated together with the monitoring of cardiovascular changes in order to compare effects relative to human exposure.

EXPERIMENTAL APPROACH

Beagle dogs and cynomolgus monkeys were telemetered to collect arterial blood pressure, heart rate and ECG for 6 h after selected oral doses of dofetilide. Pharmacokinetic parameters were determined for each dose.

KEY RESULTS

Dogs: increases in the QT(c) interval reached 56 ms in dogs dosed with 0.3 mg kg(-1) of dofetilide. Premature ventricular contractions and right bundle branch block were evident at this dose, without changes in cardiovascular parameters. The mean C(max) values were 3.35 and 60.15 ng mL(-1) at doses of 0.03 and 0.3 mg kg(-1), respectively. Monkeys: increases in QT(c) intervals reached 40-50 ms after 0.03 mg kg(-1). T-wave changes were observed after 0.03 mg kg(-1) without changes in cardiovascular parameters. The mean C(max) values following oral doses of 0.01 and 0.03 mg kg(-1) were 0.919 ng mL(-1) and 1.85 ng mL(-1), respectively.

CONCLUSIONS AND IMPLICATIONS

Despite dofetilide exposure comparable to that in humans, QT(c) responses in dogs were greater than those reported in humans. A comparable human dose used in the monkey achieved only half of the exposure but was associated with twofold greater increases in QT(c). Our data support the view that safety risk assessments of new drugs in animal models should ensure that the clinical therapeutic range of exposure is achieved and any untoward effects interpreted accordingly.

Some effects of a low sodium diet high in potassium on the renin-angiotensin system and plasma electrolyte concentrations in normal dogs

Eight normal male Beagle dogs received 0.7 mmol Na+/kg/day for 5 weeks and 4.0 mmol Na+/kg/day in one 3 week control period preceding and another similar period following the low sodium period. The dogs received 6.8 mmol K+/kg/day throughout the study. The median plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were higher in the low sodium period than in the following control period (0.67 versus 0.28 ng/ml/h, p < 0.0001) and (204 versus 31 pg/ml, p < 0.0001). PRA and PAC quickly stabilized on a new steady level in response to altered intake of sodium chloride. The angiotensin-converting enzyme (ACE) activity was not changed by the altered intake of sodium chloride. The plasma concentrations of sodium and chloride were increased during the low sodium period. This could be due to an indirect effect of the high potassium intake of the dogs. Potassium leads to an increased secretion of aldosterone and thereby to an increased retention of sodium and chloride in the kidney. The possible implications of a high potassium content in a low sodium diet are discussed.