Applying the indicator amino acid oxidation technique in the domestic cat: results of a pilot study and development of a non-steady state prediction model.

The aim of this study was to evaluate whether the indicator amino acid oxidation (IAAO) method could be applied in the domestic cat. Six adult male cats were used in a replicated 3 × 3 Latin square design. Three semi-synthetic diets were developed: a methionine (Met) and total sulfur AA (TSAA) deficient diet (T-BASAL; 0.24% Met+Cys - DM basis) and two Met and TSAA-sufficient diets in which either dl-Met (T-DLM) or 2-hydroxy-4-(methylthio)-butanoic acid (T-MHA) were supplemented, respectively, on an equimolar basis to meet the TSAA requirement (0.34%). After a 2-d diet adaptation, IAAO studies were performed. Cats were offered 13 small meals. The sixth meal contained a priming dose (4.8 mg/kg-BW) of l-[1-13C]-Phe and the remaining meals a constant dose (1.04 mg/kg-BW). Breath samples were collected every 25 min to measure 13CO2 enrichment. The following morning, fasted blood samples were collected. Cats returned to the T-BASAL top dressed with a dl-Met solution for 4 d prior to being fed a new dietary treatment. Isotopic steady state was evaluated through visual inspection. Data were analyzed using PROC GLIMMIX procedure in SAS 9.4. While 13CO2 enrichment was successfully captured in breath samples, cats failed to reach 13CO2 steady state. Thus, a non-steady state isotope model was developed and coded in ACSLX (V3.1.4.2) individually for each cat on each study day to predict 13CO2 enrichment, and then, calculate oxidation of l-[1-13C]-Phe (F13CO2). A higher predicted F13CO2 was observed for cats fed T-BASAL compared to the others (P < 0.05), while no differences were observed between T-DLM and T-MHA (P > 0.05). Cats fed T-DLM tended to have higher plasma Met concentrations compared to those fed T-BASAL with cats fed T-MHA intermediate (P = 0.0867). Plasma homocysteine concentrations were higher in cats fed T-BASAL compared to the others (P < 0.05), while threonine concentrations tended to be higher in cats fed T-BASAL compared to those fed T-MHA (P = 0.0750). In conclusion, short-term provision of a semi-synthetic diet deficient in Met may elicit a metabolic response aiming to conserve Met. The successful quantification of 13CO2 enrichment in breath and the higher predicted F13CO2 in cats fed a Met deficient diet suggest that the IAAO technique may be used in cats. Adaptations in the isotope protocol should be made to achieve 13CO2 steady state in breath and avoid mathematical modeling to predict F13CO2.

It is necessary to apply more sensitive techniques to improve our limited understanding of amino acid (AA) requirements of adult cats. The non-invasive indicator amino acid oxidation (IAAO) technique is highly sensitive in mature animals. However, while it has been widely applied in different species, this technique has yet to be used in cats. We used six healthy adult cats to evaluate whether the IAAO method could be successfully applied in this species. A similar continuous small meals regimen as reported in IAAO studies in dogs was used. An oral primed-constant isotope infusion protocol was applied where l-13C-Phenylalanine (l-[1-13C]-Phe) was used as the tracer and the oxidation of l-[1-13C]-Phe as the response of interest. Breath samples were collected to determine enrichment of 13CO2 in breath and calculate oxidation of l-[1-13C]-Phe. While we were able to collect breath samples using calorimetry chambers and capture enrichment of 13CO2 in breath, cats did not achieve steady state, which is necessary to calculate oxidation of l-[1-13C]-Phe. Modifications in the isotope protocol should be made to achieve steady state of 13CO2 in breath, and thus, to successfully apply the IAAO technique to determine requirement of AA in adult cats.

Enteric function in cats after subtotal colectomy for treatment of megacolon.

The enteric function of four cats that had undergone subtotal colectomy for megacolon was compared with that of four normal cats. All cats were fed the same diet before and during the study. History, physical condition, body weight, blood chemistry panel, fasting and postprandial serum bile acids, serum cobalamin concentration, serum folate concentration, fecal weight, fecal water content, fecal fat content, fecal osmolality and electrolyte concentration, quantitative anaerobic fecal bacterial culture, partial thromboplastin time, prothrombin time, breath hydrogen concentration, urinary calcium, phosphorus and electrolyte concentrations, and abdominal radiographic examination with air contrast studies (pneumocolon) were examined. The four cats treated surgically were healthy and thriving and, in general, enteric function was similar to the controls. Bowel movements occurred only slightly more frequently with no significant differences in fecal volume or water content. Serum cobalamin concentrations were significantly higher in cats treated surgically. Fecal sodium concentrations were high and fecal potassium concentrations were low. Results of this study did not show any significant subclinical evidence of abnormal bowel function in cats after subtotal colectomy.

Repeated noninvasive measurement of gastrointestinal transit in rats.

A technique for repeated and noninvasive measurement of oro-cecal transit time in rats and other small animals is described. It is based on the incomplete digestion of carbohydrates such as lactose fed orally to the animals. Since the activity of the enzyme lactase is low in almost all species, lactose is fermented by colonic bacteria after it arrived in the cecum, thus producing hydrogen. Hydrogen is delivered to the lungs via the circulation and exhaled by the animal. An increase in breath hydrogen measured by means of an electrochemical cell or a gas-chromatograph indicates the arrival of the nutrient bolus in the cecum. The method can be used repeatedly in individual animals under various experimental conditions such as investigations of stress effects on gastrointestinal transit.

Pulmonary excretion of H2 in calves with Cryptosporidium-induced malabsorption.

Pulmonary hydrogen gas (H2) concentrations were used to assess the malabsorption of dietary nutrients in preruminating calves inoculated with Cryptosporidium sp. Normal values were established in five control calves and seven calves (principals) were inoculated with 1.0 x 10(8) Cryptosporidium sp. oocysts. Hydrogen concentrations and wet fecal weights were measured at three stages: before Cryptosporidium sp. inoculation (stage 1), three days after the onset of diarrhea (stage 2), and after the resolution of diarrhea (stage 3). Mean end-breath and total-breath H2 concentrations in the principal calves were higher (P less than 0.025 and P less than 0.05) for stage 2, when compared to control values. Both end-breath and total-breath H2 concentrations were increased (P less than 0.001 and P less than 0.025, respectively) in the principal calves during stage 2 when compared to values obtained for stages 1 and 3. Concurrently, Cryptosporidium sp. infection was associated with increased (P = 0.06) fecal output during stage 2, only. The increased H2 concentrations and cumulative fecal output show that Cryptosporidium sp. caused malabsorption of fermentable nutrients.

A method for direct measurement of systemic uptake and elimination of volatile organics in small animals.

A method was developed which was suitable for toxicokinetic studies requiring direct, repetitive sampling of blood and breath during exposures of small animals to volatile chemicals. Anesthetized male Sprague-Dawley rats were tracheostomized, and a specially fabricated one-way breathing valve was inserted directly into the trachea, in order that the inhaled and exhaled breath streams could be separated and independently sampled. The desired concentration of 1,1,1-trichloroethane was generated in a gas sampling bag, which was connected to the inlet side of the valve for inhalation exposures. Rats dosed with 1,1,1-trichloroethane by gavage inhaled ambient air through the valve. A pneumotachograph was positioned in the influent air stream to measure respiration. Respiratory rate, minute volume, and core temperature were continuously recorded on a physiograph. Samples of inspired and expired air were periodically collected from sampling ports immediately adjacent to the breathing valve and were analyzed for their 1,1,1-trichloroethane content by gas chromatography. Using this system, it was possible to determine percentage systemic uptake at any given time and to monitor cumulative uptake (i.e., total dose received) over the course of inhalation exposures. Alveolar concentrations were calculated by taking into account the respiratory indexes and dead space volume. A femoral vein was cannulated, so that concentrations of the chemical in the blood and breath could be measured concurrently. Data from rats dosed orally and by inhalation with 1,1,1-trichloroethane are presented to illustrate the applicability of the method in kinetics studies of volatile chemicals.

An easily assembled and inexpensive apparatus for continuous monitoring of expired carbon dioxide concentrations in artificially ventilated animals.

An inexpensive and simple apparatus for monitoring expired carbon dioxide concentrations in artificially ventilated animal preparations is described. The system may be rapidly and easily constructed using a standard recording pH electrometer and a commercially available Pco2 electrode. This assembly has been proven to be an effective and sensitive means of monitoring CO2 levels, detecting changes in this gas within one-half percentage.