Effects of Epinephrine, Detomidine, and Butorphanol on Assessments of Insulin Sensitivity in Mares.

Sympathoadrenal stimulation may perturb results of endocrine tests performed on fractious horses. Sedation may be beneficial; however, perturbation of results may preclude useful information. Four experiments were designed to 1) determine the effects of epinephrine on insulin response to glucose (IR2G), 2) assess the effects of detomidine (DET), alone or combined with butorphanol (DET/BUT), on IR2G and glucose response to insulin (GR2I), and 3) assess the effects of BUT alone on IR2G. In Experiment 1, mares were administered saline or epinephrine (5 µg/kg BW) immediately before infusion of glucose (100 mg/kg BW). Glucose stimulated (P < .05) insulin release in controls at 5 minutes that persisted through 30 minutes; insulin was suppressed (P < .05) by epinephrine from 5 to 15 minutes, rising gradually through 30 minutes. Experiments 2 (IR2G) and 3 (GR2I) were conducted as triplicated 3 × 3 Latin squares with the following treatments: saline (SAL), DET, and DET/BUT (all administered at .01 mg/kg BW). Glucose stimulated (P < .05) insulin release that persisted through 30 minutes in SAL mares; DET and DET/BUT severely suppressed (P < .0001) the IR2G. Sedation did not affect resting glucose and had inconsistent effects on the GR2I when mares were treated with 50 mIU/kg BW recombinant human insulin. Butorphanol had no effect on IR2G. In conclusion, adrenergic agonists severely suppress the IR2G and cannot be used for sedation for this test. The use of DET did not alter the GR2I, and therefore may be useful for conducting this test in fractious horses.

Effects of clenbuterol administration on serum biochemical, histologic, and echocardiographic measurements of muscle injury in exercising horses.

OBJECTIVE: To determine the effects of clenbuterol, at a dosage of up to 3.2 µg/kg for 14 days, PO, on skeletal and cardiac muscle in healthy horses undergoing treadmill exercise. ANIMALS: 12 healthy horses from 3 to 10 years old. PROCEDURES: Horses were randomly assigned to a control group (n = 6) or clenbuterol group (6) and received either saline (0.9% NaCl) solution or clenbuterol, PO, every 12 hours for 14 days. Horses were subjected to submaximal treadmill exercise daily during treatment. Muscle biopsy specimens were collected before and after treatment for determination of apoptosis. Echocardiographic measurements, serum clenbuterol and cardiac troponin I concentrations, and serum activities of creatine kinase and aspartate aminotransferase were measured before, during, and after treatment. Jugular venous blood samples were collected every 3 days during treatment. Echocardiography was repeated every 7 days after beginning treatment. Response variables were compared between treatment groups and across time periods. RESULTS: No significant effect of clenbuterol or exercise on response variables was found between treatment and control groups at any time point or within groups over time. CONCLUSIONS AND CLINICAL RELEVANCE: Results did not reveal any adverse effects of treatment with an approved dose of clenbuterol on equine cardiac or skeletal muscle in the small number of horses tested.

Acute diarrhea in hospitalized horses.

The development of diarrhea among hospitalized horses is a major concern for equine veterinary hospitals and referral centers. It is a potential complication of hospitalization for surgical or medical procedures and can contribute to the morbidity and mortality of horses with gastrointestinal and non-gastrointestinal diseases. Unfortunately, it can be difficult to pinpoint the exact cause of acute diarrhea or colitis, and in most cases, the specific etiologic agent is presumptive or undetermined. This article discusses the major etiologic agents of diarrhea in hospitalized horses, considers factors that place hospitalized horses at special risk for diarrhea, and examines several infectious colitis outbreaks that have occurred at veterinary referral centers.