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Summary

Six nontrained mares were subjected to steady-state, submaximal treadmill exercise to examine the effect of exercise on the plasma concentration of atrial natriuretic peptide (anp) in arterial, compared with mixed venous, blood. Horses ran on a treadmill up a 6° grade for 20 minutes at a speed calculated to require a power equivalent to 80% of maximal oxygen uptake (Vo 2MAX). Arterial and mixed venous blood samples were collected simultaneously from the carotid and pulmonary arteries of horses at rest and at 10 and 20 minutes of exercise. Plasma was stored at − 80 C and was later thawed; anp was extracted, and its concentration was determined by radioimmunoassay. Exercise caused significant (P < 0.05) increases in arterial and venous plasma anp concentrations. Mean ± sem arterial anp concentration increased from 25.2 ± 4.4 pg/ml at rest to 52.7 ± 5.2 pg/ml at 10 minutes of exercise and 62.5 ± 5.2 pg/ml at 20 minutes of exercise. Mean venous anp concentration increased from 24.8 ± 4.3 pg/ml at rest to 67.2 ± 14.5 pg/ml at 10 minutes of exercise and 65.3 ± 13.5 pg/ml at 20 minutes of exercise. Significant differences were not evident between arterial or mixed venous anp concentration at rest or during exercise, indicating that anp either is not metabolized in the lungs or is released from the left atrium at a rate matching that of pulmonary metabolism.

Free access
in American Journal of Veterinary Research

Summary

Six untrained mares were subjected to incremental treadmill exercise to examine exercise-induced changes in plasma renin activity (pra) and plasma aldosterone (aldo) and plasma arginine vasopressin (avp) concentrations. Plasma renin activity, aldo and avp concentrations, and heart rate (hr) were measured at each step of an incremental maximal exercise test. Mares ran up a 6° slope on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s each minute until hr reached a plateau. Plasma obtained was stored at − 80 C and later was thawed, extracted, and assayed for pra and aldo and avp values by use of radioimmunoassay. Exercise caused significant increase in hr from 40 ± 2 beats/min (mean ± sem) at rest to 206 ± 4 beats/min (hr max) at speed of 9 m/s. Plasma renin activity increased from 1.9 ± 1.0 ng/ml/h at rest to a peak of 5.2 ± 1.0 ng/ml/h at 9 m/s, paralleling changes in hr. Up to treadmill speed of 9 m/s, strong linear correlations were obtained between exercise intensity (and duration) and hr (r = 0.87, P < 0.05) and pra (r = 0.93, P < 0.05). Heart rate and pra reached a plateau and did not increase when speed was increased from 9 to 10 m/s. Plasma aldo concentration increased from 48 ± 16 pg/ml at rest to 191 ± 72 pg/ml at speed of 10 m/s. Linear relation was found between exercise intensity (and duration) and aldo concentration (r = 0.97, P < 0.05). Plasma avp concentration increased from 4.0 ± 3.0 pg/ml at rest to 95 ± 5.0 pg/ml at speed of 10 m/s. The relation between avp concentration and exercise intensity (and duration) appeared to be curvilinear, and was described by an exponential function (r = 0.92, P < 0.05). These data indicate that pra and aldo and avp concentrations increase in horses during progressive treadmill exercise.

Free access
in American Journal of Veterinary Research

Abstract

OBJECTIVE

To evaluate surfactant protein D (SP-D) concentrations in serum and bronchoalveolar lavage fluid (BALF) from young healthy horses on pasture or housed in a typical barn.

ANIMALS

20 young healthy horses.

PROCEDURES

Horses were randomly assigned to 1 of 2 groups (pasture, n = 10; barn, 10), and serum and BALF samples were collected for SP-D determination at baseline (all horses on pasture) and 2 weeks and 4 weeks after the barn group of horses was relocated from the pasture to the barn. Other evaluations included physical and tracheoscopic examinations. Findings were compared within and between groups.

RESULTS

Physical and tracheoscopic examinations, CBC, and serum biochemical analysis did not reveal evidence of respiratory disease, and no significant differences were present within and between groups. Serum SP-D concentrations did not significantly differ within and between groups, but BALF SP-D concentrations were significantly lower for the barn group at 2 weeks but not at 4 weeks, compared with baseline. The BALF SP-D concentration-to-BALF total protein concentration ratio was < 1.5 and did not significantly differ within and between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

A mild decrease was evident in the concentration of SP-D in the BALF collected from young healthy horses after 2 weeks of exposure to a barn environment. The clinical importance of this finding remains to be determined.

Full access
in American Journal of Veterinary Research