OBJECTIVE To investigate the in vitro stability of atrial natriuretic peptide (ANP) in plasma samples under various storage conditions and the influence of anesthesia on plasma ANP concentration in cats. ANIMALS 1 cat with congestive heart failure and 5 healthy adult mixed-breed cats. PROCEDURES A plasma sample from the cat with heart failure was serially diluted, and dilutional parallelism of ANP concentration was evaluated. Plasma samples containing aprotinin or serum samples from the 5 healthy cats were kept at room temperature (27°C) for ≤ 12 hours. Plasma samples from the same healthy cats were stored at −70°, −20°, or 4°C for ≤ 14 days. Plasma samples were obtained from the healthy cats before and during isoflurane anesthesia. Plasma ANP concentrations were measured at a commercial laboratory by use of a human ANP chemiluminescence assay. RESULTS Intra- and interassay coefficients of variation were 1.5% and 2.5%, respectively, and dilutional parallelism was established. Although ANP concentration decreased by 82.4 ± 13.6% (mean ± SD) after sample storage for 12 hours at room temperature, this decrease was prevented by aprotinin. Plasma ANP concentrations were stable for 7 days at −20°C and for 14 days at −70°C. However, concentrations decreased markedly to 57.6 ± 6.9% at −20°C and to 18.0 ± 3.0% at 4°C after 14 days. Plasma ANP concentration decreased significantly in cats during anesthesia and was correlated with blood pressure. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that aprotinin should be added routinely in preparation of plasma samples from cats for measurement of ANP concentration, and those samples, if stored, should be frozen immediately at ≤ −20°C. General anesthesia or systemic blood pressure may affect plasma ANP concentration in cats.

OBJECTIVE To compare tear cortisol concentrations between horses and ponies with pituitary pars intermedia dysfunction (PPID) and healthy nonaged (≤ 15 years old) and aged (≥ 20 years old) horses and to determine whether serum and tear cortisol concentrations were correlated. ANIMALS 11 horses and ponies with PPID and 20 healthy control horses and ponies (11 nonaged and 9 aged). PROCEDURES Paired tear and serum samples were obtained from PPID and control animals. All animals were free of active ocular disease. Tear and serum cortisol concentrations were measured with an ELISA and chemiluminescent assay, respectively. Groups were compared with Kruskal-Wallis and Mann-Whitney U tests, and Spearman correlation analysis was used to examine relationships between tear and serum cortisol concentrations within groups. RESULTS Median tear cortisol concentration was significantly higher in PPID animals than in aged control animals, despite comparable serum cortisol concentrations in PPID and aged control animals. Median tear-to-serum cortisol concentration ratios were also significantly higher in PPID animals than in aged control animals. Serum and tear cortisol concentrations were not significantly correlated in PPID or control animals. CONCLUSIONS AND CLINICAL RELEVANCE Some horses and ponies with PPID had increased tear cortisol concentrations, compared with concentrations in healthy aged animals. Localized cortisol production in the tear film or altered cortisol binding dynamics could have contributed to this increase. Further studies are warranted to evaluate these mechanisms and to determine whether increased tear cortisol concentrations are associated with delays in corneal wound healing in horses and ponies with and without PPID.