1670 AJVR, Vol 69, No. 12, December 2008 C affeine is a drug of the group of methylxanthines, substances that stimulate the CNS. 1,2 The Associa- tion of Racing Commissioners International does not approve of the therapeutic use of caffeine in horses, and when it is found in the urine or other biological fluids, it is classified as a class 2 illegal substance, character- ized as doping. 1,3 However, because of the natural pres- ence of caffeine in teas, coffees, chocolates, and rations, professionals who are involved in the day-to-day prac- tice of equestrian sports argue that the detection of low blood and urinary concentrations of caffeine in athletic horses can be associated with environmental contami- nations and have no effect on the results of equestrian competitions. 3 Currently, investigations of caffeine and its interference with athletic performance in aerobic and anaerobic exercises are performed in a systematic Effects of intravenous administration of caffeine on physiologic variables in exercising horses Guilherme C. Ferraz, DVM, PhD; Antônio R. Teixeira-Neto, DVM, PhD; Maria I. Mataqueiro, PhD; José C. Lacerda-Neto, DVM, PhD; Antonio Queiroz-Neto, DVM, PhD Objective—To investigate the effect of acute administration of caffeine on the athletic per- formance of Arabian horses. Animals—12 healthy adult Arabian horses that were trained for exercise on a treadmill. Procedures—By use of a crossover study design, horses received each of the following treatments: IV administration of caffeine (5 mg/kg) and IV administration of approximately the same volume of saline (0.9% NaCl) solution. Order of treatment was randomized, and there was a 10-day interval between treatments. Thirty minutes after treatments, horses underwent an incremental exercise test (IET) on a treadmill. Blood samples were collected 15 seconds before the end of each velocity step of the IET for determination of blood lactate, blood glucose, plasma cortisol, and plasma insulin concentrations. Heart rate and hematologic variables were also analyzed. Results—Velocities achieved when heart rates were 180 and 200 beats/min increased sig- nificantly in caffeine-treated horses, compared with control horses. Velocities correspond- ing to blood lactate concentrations of 4 and 2 mmol/L decreased significantly in caffeine- treated horses, compared with control horses. In comparison between groups, insulinemia was greater in control horses and glycemia was greater in caffeine-treated horses. Plasma cortisol concentration was significantly lowered by treatment with caffeine. Conclusions and Clinical Relevance—IV administration of caffeine at 5 mg/kg improved the performance of Arabian horses during intense exercise of short duration and diminished the oxidative metabolism of glucose. (Am J Vet Res 2008;69:1670–1675) manner in humans 2,4 as well as horses 3,5 ; most of the studies on horses use the Thoroughbred breed in their experiments. 3,5 In humans, the ergogenic effect of caffeine has been described, and there is consensus on its beneficial effects in aerobic and resistance exercises. 2 During intense exer- cise of short duration, however, there is controversy over the improvement of athletic performance after the admin- istration of caffeine. 2 In horses, caffeine was reported to improve the response of cardiovascular function as a re- sult of the stimulation of the CNS. 5 In contrast, authors of another study 3 did not observe effects on cardiorespiratory variables of horses after the administration of caffeine at a dose of 2.5 mg/kg; horses in that study 3 underwent an IET following caffeine administration. The objective of the study reported here was to determine the effects of acute administration of caffeine on physiologic variables of Ara- bian horses during exercise with increasing intensity on a treadmill, by examining metabolic, endocrine, hemato- logic, and cardiovascular variables. Materials and Methods Animals—In this study, 12 trained horses of the Arabian breed were used, which included geldings and Received December 14, 2007. Accepted March 24, 2008. From the Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinary Sciences, São Paulo State University, Jaboticabal Campus, Jaboticabal, São Paulo, Brazil 14884-900. Dr. Teixeira-Neto’s present address is School of Vet- erinary Medicine, Federal University of Goiás, Goiânia, Brazil 74001-970. Supported by Fundacão de Amparo à Pesquisa do Estado de São Paulo. Presented in part at the 10th International Congress of the European Association for Veterinary Pharmacology and Toxicology, Turin, Italy, September 2006. Address correspondence to Dr. Queiroz-Neto. ABBREVIATION IET Incremental exercise test Unauthenticated | Downloaded 08/19/22 09:12 PM UTC