Objective-To determine the pharmacokinetics, pharmacodynamics, and safety of zoledronic acid in horses. Animals-8 healthy horses. Procedures-A single dose of zoledronic acid (0.057 mg/kg, IV) was administered during a 30-minute period. Venous blood was collected at several time points. Zoledronic acid concentration in plasma was measured by liquid chromatography-tandem mass spectrometry, and pertinent pharmacokinetic parameters were determined. Plasma was analyzed for total calcium, BUN, and creatinine concentrations and a marker for bone resorption (C-terminal telopeptides of type I collagen). Results-Zoledronic acid was safely administered IV during a 30-minute period, and no adverse effects were observed. Plasma concentrations of zoledronic acid were consistent with a 2-compartment mammillary model. Plasma concentrations of zoledronic acid were detected for up to 8 hours after administration. Mean total calcium concentrations in plasma were less than the reference range 7 days after zoledronic acid administration. A marker for bone remodeling decreased in concentration after zoledronic acid administration and remained low for the 1-year duration of the study. No changes in BUN and creatinine concentrations were observed after zoledronic acid administration. Conclusions and Clinical Relevance-Zoledronic acid was safely administered in healthy horses. Zoledronic acid is reported as the strongest bisphosphonate presently available, and studies evaluating potential benefits of zoledronic acid in horses with orthopedic conditions are warranted.

Objective-To evaluate the platelet activation response before and after treatment with clopidogrel in horses. Animals-12 healthy adult mares. Procedures-In a masked study, horses (6/group) were randomly allocated to alternately receive placebo or clopidogrel via nasogastric tube at a loading dose of 4 mg/kg followed by 2 mg/kg every 24 hours. Blood samples were collected before and 72 hours after initiation of treatment for ADP- and collagen-induced light transmission aggregometry; determination of closure time in collagen-ADP cartridges; modified thrombelastography for comparison of maximal amplitudes generated by kaolin, reptilase, and reptilase plus ADP activation; and flow cytometric tests to detect platelet fibrinogen binding, P-selectin expression, and phosphatidylserine externalization before and after ex vivo stimulation with thrombin, convulxin, thrombin with convulxin, and calcium ionophore. Results-Clopidogrel administration induced a significant decrease in mean aggregation response to 5μM and 10μM ADP stimulation; however, 2 horses had resistance to clopidogrel's inhibitory action. Significant differences after clopidogrel treatment were not found in any other tests of platelet function. Conclusions and Clinical Relevance-Assays using commercially available reagents were configured to measure different variables of the platelet activation response; however, clopidogrel's platelet inhibitory action was only detected by ADP-induced light transmission aggregometry. Results also suggested that horses, like humans, have interindividual variability in response to clopidogrel that may influence the drug's clinical efficacy as an antiplatelet agent.

Objective—To evaluate the influence of acidifying or alkalinizing diets on bone mineral density and urine relative supersaturation (URSS) with calcium oxalate and struvite in healthy cats. Animals—6 castrated male and 6 spayed female cats. Procedures—3 groups of 4 cats each were fed diets for 12 months that differed only in acidifying or alkalinizing properties (alkalinizing, neutral, and acidifying). Body composition was estimated by use of dual energy x-ray absorptiometry, and 48-hour urine samples were collected for URSS determination. Results—Urine pH differed significantly among diet groups, with the lowest urine pH values in the acidifying diet group and the highest values in the alkalinizing diet group. Differences were not observed in other variables except urinary ammonia excretion, which was significantly higher in the neutral diet group. Calcium oxalate URSS was highest in the acidifying diet group and lowest in the alkalinizing diet group; struvite URSS was not different among groups. Diet was not significantly associated with bone mineral content or density. Conclusions and Clinical Relevance—Urinary undersaturation with calcium oxalate was achieved by inducing alkaluria. Feeding an alkalinizing diet was not associated with URSS with struvite. Bone mineral density and calcium content were not adversely affected by diet; therefore, release of calcium from bone caused by feeding an acidifying diet may not occur in healthy cats.

Objective—To characterize the dynamics of calcitonin secretion in response to experimentally induced hypercalcemia in cats. Animals—13 healthy adult European Shorthair cats.Procedures—For each cat, the calcitonin response to hypercalcemia (defined as an increase in ionized calcium concentration > 0.3mM) was investigated by infusing calcium chloride solution and measuring circulating calcitonin concentrations before infusion (baseline) and at various ionized calcium concentrations. Calcitonin expression in the thyroid glands of 10 of the cats was investigated by immunohistochemical analysis. Results—Preinfusion baseline plasma calcitonin concentrations were very low in many cats, sometimes less than the limit of detection of the assay. Cats had a heterogeneous calcitonin response to hypercalcemia. Calcitonin concentrations only increased in response to hypercalcemia in 6 of 13 cats; in those cats, the increase in calcitonin concentration was quite variable. In cats that responded to hypercalcemia, calcitonin concentration increased from 1.3 ± 0.3 pg/mL at baseline ionized calcium concentration to a maximum of 21.2 ± 8.4 pg/mL at an ionized calcium concentration of 1.60mM. Cats that did not respond to hypercalcemia had a flat calcitonin-to-ionized calcium concentration curve that was not modified by changes in ionized calcium concentration. A significant strong correlation (r = 0.813) was found between the number of calcitonin-positive cells in the thyroid gland and plasma calcitonin concentrations during hypercalcemia. Conclusions and Clinical Relevance—Healthy cats had very low baseline plasma calcitonin concentrations. A heterogeneous increase in plasma calcitonin concentration in response to hypercalcemia, which correlated with the expression of calcitonin-producing cells in the thyroid, was identified in cats.

Objective—To investigate the in vitro differentiation of canine bone marrow stromal cells (BMSCs) into functional, mature neurons. Sample—Bone marrow from 6 adult dogs. Procedures—BMSCs were isolated from bone marrow and chemically induced to develop into neurons. The morphology of the BMSCs during neuronal induction was monitored, and immunocytochemical analyses for neuron markers were performed after the induction. Real-time PCR methods were used to evaluate the mRNA expression levels of markers for neural stem or progenitor cells, neurons, and ion channels, and western blotting was used to assess the expression of neuronal proteins before and after neuronal induction. The electrophysiological properties of the neuron-like cells induced from canine BMSCs were evaluated with fluorescent dye to monitor Ca2+ influx. Results—Canine BMSCs developed a neuron-like morphology after neuronal induction. Immunocytochemical analysis revealed that these neuron-like cells were positive for neuron markers. After induction, the cells’ mRNA expression levels of almost all neuron and ion channel markers increased, and the protein expression levels of nestin and neurofilament-L increased significantly. However, the neuron-like cells derived from canine BMSCs did not have the Ca2+ influx characteristic of spiking neurons. Conclusions and Clinical Relevance—Although canine BMSCs had neuron-like morphological and biochemical properties after induction, they did not develop the electrophysiological characteristics of neurons. Thus, these results have suggested that canine BMSCs could have the capacity to differentiate into a neuronal lineage, but the differentiation protocol used may have been insufficient to induce development into functional neurons.

Objective-To assess dual-energy x-ray absorptiometry (DXA) for evaluating effects of diet and environment on bone mineral density in Hermann's tortoises (Testudo hermanni). Animals-26 Hermann's tortoises within 1 month after hatching. Procedures-Group 1 was housed in an artificial setting and fed naturally growing vegetation. Group 2 was housed in an artificial setting and fed vegetables grown for human consumption. Group 3 was maintained in an outside enclosure and fed naturally growing vegetation. After 10 months, pyramidal growth, body weight, and adverse conditions were assessed. Bone mineral density (BMD) of the axial and appendicular skeleton, shell, vertebral column, and pelvis was measured via DXA. Results-Group 2 had the highest mean +/- SD body weight (65.42 +/- 30.85 g), followed by group 1 (51.08 +/- 22.92 g) and group 3 (35.74 +/- 7.13 g). Mean BMD of the shell varied significantly among groups (group 1, 0.05 +/- 0.03 g/cm2•m; group 2, 0.09 +/- 0.15 g/cm2•m; and group 3, undetectable). The BMD of the axial and appendicular skeleton, vertebral column, and pelvis did not differ significantly among groups. Pyramidal growth was highest in group 1 and not evident in group 3. Conclusions and Clinical Relevance-Tortoises raised in artificial conditions did not have deficits in BMD, compared with results for outdoor-housed hibernating tortoises. Supplemental calcium was apparently not necessary when an adequate photothermal habitat and plant-based diet were provided. Higher BMD of captive-raised tortoises was morphologically associated with a higher incidence of pyramidal growth in captive-raised groups.