Endocrine response to exercise in young and old horses

Abstract

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 (V̇O2max) 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 V̇O2max. These data suggest that older horses have an age‐altered endocrine response to exercise.

Interday variation and effect of transportation on indirect blood pressure measurements, plasma endothelin-1 and serum cortisol in Standardbred and Icelandic horses

“…The wide range in interday variation is to be expected as similar interday fluctuations have been reported for other hormones and physiological parameters [16,17]. The concentrations of plasma ET-1 measured in the present study was higher for both breeds compared to the concentrations reported previously in healthy Thoroughbred and Standardbred horses [18] but similar to those reported in horses with summer pasture associated recurrent airway obstruction, SPA-RAO [19] and horses with clinical endotoxaemia [20]. The discrepancy in results between studies are likely related to the use of different ELISA assays [19,20], all developed for quantification of human ET-1, as well as genetic differences between breeds.…”

Adrenocortical Insufficiency in Horses and Foals

“…Basal aldosterone concentrations have been described within a range of approximately 14 to 50 pg/ml 18, 19, 47. Androstenedione concentrations in adult horses reportedly fall within a range of <0.050 to 0.986 ng/ml 16, 19.…”

Mating Behavior Increases Workload of the Heart in Thoroughbred Stallions

“…Interestingly, the serum level of alpha-ANP in this study was also increased after mating, as compared with the baseline at rest. Alpha-ANP has been reported to increase in response to exercise [8][9][10]. The difference between the postmating measurement and the baseline of serum ANP was significantly correlated with the HRmax, but not with the change in Hcts before and after mating.…”

“…Regression analysis was used to determine relationships among all sorts of HR and time parameters, and then coefficients of correlation were determined. 10, recorded twice at 192 and 207 sec after ejaculation in the 1st experiment and four times at leaving his stable, 40 sec before entering the covering yard and 10 sec before 1st and 2nd mounting in the 2nd experiment) were identified before and after mating, as presented in Fig. 1.…”

“…The hematological and biochemical markers indicating heart pathology as well as the increased hemodynamic workload should be also investigated in stallions. Previous studies of athletic horses have shown increases in blood levels of atrial natriuretic peptide (ANP) in response to atrial stretch or distention during exercise [8][9][10]. In any case, the effects of mating behavior on the stallion cardiac function have been poorly understood; enhanced heart function and its association with blood analysis in mating have not been investigated.…”