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Endocrine response to exercise in young and old horses
Author(s) -
McKEEVER K. H.,
MALINOWSKI KARYN
Publication year - 1999
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.1999.tb05284.x
Subject(s) - horse , endocrinology , medicine , vasopressin , radioimmunoassay , plasma renin activity , aldosterone , atrial natriuretic peptide , treadmill , endocrine system , hormone , vo2 max , renin–angiotensin system , heart rate , blood pressure , biology , paleontology
Summary Six young (mean + s.e., 5.3 ± 0.8 years, 445 ± 13 kg bwt) and 6 old (22.0 ± 0.4 years, 473 ± 18 kg bwt) Standardbred and Thoroughbred mares were used to test the hypothesis that age would alter the endocrine response to exercise. All of the mares were unconditioned but accustomed to the laboratory, to standing quietly and running on a treadmill, and to the standardised incremental exercise test (SET) used in the experiment. Two weeks prior to the experiment, each horse underwent a SET to determine maximal oxygen uptake (V̇O 2max ) and the speeds to be used in the actual experiment. A second graded exercise test (GXT) was performed without instrumentation for the measurement of plasma renin activity (PRA) and the plasma concentrations of atrial natriuretic peptide (ANP), arginine vasopressin (AVP), aldosterone (ALDO), and endothelin‐1 (ET‐1). Blood samples (30 ml) were collected at rest and at the end of each one minute step of the exercise test. Plasma concentrations of hormones were measured using radioimmunoassay kits. There were no differences (P>0.05) between old vs. young mares for resting PRA (2.2 ± 0.3 vs. 1.5 ± 0.3 ng/ml/h), or the plasma concentrations of ANP (10.0 ± 0.9 vs. 10.7 ± 0.6 pg/ml); AVP (0.7 + 0.7 vs. 1.4 ± 0.4 pg/ml); ALDO (39.2 ± 10.3 vs. 22.7 ± 4.6 pg/ml); or ET‐1 (0.23 ± 0.04 vs. 0.18 ± 0.03 pg/ml). Exercise significantly increased PRA and the concentrations of ANP, AVP, and ALDO in both groups of horses; however, ET‐1 was not altered (P>0.05) by exercise in either group. There were differences (P<.05) between means obtained from the old and young groups for PRA (5.4 ± 0.6 vs. 3.9 ± 0.8 ng/ml/h and the concentrations of ANP (14.5 ± 2.3 vs. 26.5 ± 9.0 pg/ml), AVP (13.6 ± 0.3 vs. 26.1 ± 13.9 pg/ml, and ALDO (76.8 ± 22.0 vs. 41.5 ± 4.9 pg/ml) measured in samples obtained at the speed eliciting V̇O 2max . These data suggest that older horses have an age‐altered endocrine response to exercise.