The present study investigated the effects of caffeine on performance, cardiorespiratory function and plasma hormonal responses of exercising Thoroughbreds on a treadmill. Five Thoroughbreds completed an incremental graded exercise (IG) test and two endurance exercise tests at 80% and 105% of the maximal O2 uptake (VO2max), starting 1 hr after the intramuscular administration of either physiological saline or 2.5 mg/kg caffeine and continuing until exhaustion. The mean exercise time was not significantly affected by caffeine, but there were caffeine-induced inconsistent effects on the individual exercise times in the three exercise tests, which were related to its stimulant effects through the central nervous system (CNS). Caffeine tended to increase blood lactate (LA) and plasma catecholamines (CA) of adrenaline and noradrenaline as well as the cardiorespiratory variables such as O2 uptake, heart rate and packed cell volume during exercise. Caffeine significantly increased VO2max and the maximal levels in LA in the IG test. The maximal levels in plasma CA during the IG test were doubled by caffeine. Caffeine-mediated increases in the plasma CA significantly correlated with those in LA. Plasma ACTH levels reflected less exercise stress under caffeine during the endurance exercise test at 105%VO2max, in which caffeine increased the exercise times of three Thoroughbreds. Caffeine had no effect on the plasma cortisol responses to exercise. The present study suggests that caffeine improves exercise performance through actions on the CNS with the increase in cardiorespiratory function which is probably related to plasma CA responses during exercise.
Complementary DNA (cDNA) clones encoding equine testicular steroidogenic enzyme 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) have been isolated from equine testicular cDNA library. Polymerase chain reaction (PCR) with 3β-HSD specific primers was performed with equine testicular cDNA, and PCR fragment was used as a probe for screening of equine testicular λ ZAP II phage cDNA library. Positive clones were excised into plasmid vector pBluescript and determined their nucleotide sequences. Total 1651 bp of the cDNA sequence was consisted with 112 bp of 5' flanking untranslated sequence, 1122 bp open reading frame encodes 373 amino acids, and putative poly-adenylation signal “AATAAA” at 385 bp downstream of the stop codon. The nucleotide and the deduced amino acid sequence of equine 3β-HSD were very similar to the known mammalian 3β-HSD sequences. From the deduced amino acid sequence, equine testicular 3β-HSD may be concluded to catalyze 3β-dehydrogenation and Δ-isomerization, but 3-ketoreduction as well as murine isoforms. As the clone was used in Northern blot analysis of equine tissues, the expression of equine 3β-HSD mRNA was prominent in the classical steroidogenic tissues including placenta.
A total of 2, 415 blood samples from 8 populations of Japanese native horses, 18 populations of Asian native horses and 8 breeds of European horses (race-horses, draft-horses and ponies) collected since 1971 were electrophoretically examined at 33 biochemical genetic loci. Gene diversity within populations or breeds measured by the proportion of polymorphic loci (Ppoly) and the expected average heterozygosity per individual (H) was observed to be higher in the Mongolian native horses than in other populations or breeds, and in the Tokara horse of Japan was on the lowest level. Gene diversity between populations or breeds was evaluated by the principal component analysis (PC). It was also measured by computing the Nei's standard genetic distances from the allele frequency data, and the dendrograms were drawn from the genetic distance matrix by the unweighted-pair-group (UWPG) method and the neighbor-joining (NJ) method for estimating the phylogenetic relationships among the horse populations or breeds. The results revealed that the horse populations or breeds were roughly classified into four clusters, that is, Asian native horses, European race-horse breeds, European draft-horse breeds and European pony breeds. The cluster of Asian native horses included some subclusters of Mongolian native horses, south and southeast Asian native horses, Indonesian native horses, and Japanese native horses, although the Batak horse of Indonesia was observed to diverge from the subcluster of Indonesian native horses and the Tokara and Noma horses of Japan diverged remarkably from the subcluster of Japanese native horses in gene constitution. Such diversifications are postulated to be on account of the effect of random genetic drift and/or a bottle-neck effect resulting from their geographic isolation and small reproductive population size. The Mori-Hayashida's two-wave immigration hypothesis for formation of eight local populations of the Japanese native horses can not be supported from our genetic data.
Plate fixation was conducted in a 3 year old male Thoroughbred racehorse (480 kg) for a spiral undisplaced fracture of the tibia. The fracture line spirally occupied approximately two-thirds of the bone. The horse was anesthetized with sevoflurane and oxygen and placed in dorsal recumbency. Two dynamic compression plates (DCP) were applied on the cranio-lateral and cranio-medial sides. Histopathological examination revealed active callus formation and remodeling on the fracture line 180 days after the surgery. Based on these findings, it was concluded that good synostosis was achieved. Therefore, it was suggested that DCP fixation based on the present technique can be applied to adult horses with undisplaced or minimally displaced fractured tibia to prevent their developing a completely displaced fracture.