Running and shipping elevate plasma levels of beta-endorphin-like substance (B-END-LI) in thoroughbred horses

Abstract

A specific RIA for beta-endorphin (B-END) was developed to measure horse plasma levels of B-END-like material (B-END-LI) during exercises and shipping. Three exercise speeds and durations were: trot at 260–300 m/min for 10 min; slow gallop at 390–420 m/min for 5 min and fast gallop at 700–800 m/min for 2 min. Blood samples were taken from 4 horses before, immediately after, 30 and 60 min after exercise. Trotting increased plasma B-END-LI from a basal level of 109 ± 7 pg/ml to 172 ± 22 at the end of exercise and returned to 127 ± 17 and 107 ± 10 pg/ml at 30 and 60 min after exercise. Similar results were obtained in slow gallop (121 ± 6 to 210 ± 17 then 155 ± 8 and 131 ± 11 pg/ml. However, fast gallop caused the greatest increase (352%) in B-END-LI to concentrations of 544 ± 93 pg/ml and 276 ± 74 pg/ml at 5 and 30 min after exercise. Plasma B-END-LI returned to 199 ± 46 pg/ml in 1 hr. Sequential exercises of trot, slow and fast gallop were conducted in 6 horses. Plasma B-END-LI were 116 ± 19 pg/ml (pre-exercise), 198 ± 21 (trot), 361 ± 51 (slow gallop), 500 ± 57 (fast gallop) and 248 ± 29, 171 ± 24, 143 ±20 and 139 ± 21 pg/ml at 0.5, 1, 2 and 3 hr, respectively, following exercises. Transportation in horse trailer also significantly increased plasma levels of B-END-LI from a basal level of 138 ± 12 to 196 ± 24 pg/ml within 30 min and this levels were maintained at 45 min (177 ± 3 pg/ml). Plasma levels of B-END-LI began to decline at 60 min of shipping. These results showed that plasma B-END-LI was increased in all speeds of exercise and by shipping and returned to pre-exercise and pre-shipping level in 30 min except fast gallop which returned to pre-exercise level in 1 hr.