title: Acute intraperitoneal injection of caffeine improves endurance exercise performance in association with increasing brain dopamine release during exercise.
abstract: The purpose of this study was to examine changes of thermoregulation, neurotransmitters in the preoptic area and anterior hypothalamus (PO/AH), which is the thermoregulatory center, and endurance exercise performance after the intraperitoneal injection of caffeine in rats. Core body temperature (Tcore), oxygen consumption (VO₂) and tail skin temperature (Ttail) were measured. A microdialysis probe was inserted in the PO/AH, and samples for the measurements of extracellular dopamine (DA), noradrenaline (NA) and serotonin (5-HT) levels were collected. During the rest experiment, 1 h after baseline collections in the chamber (23 °C), the rats were intraperitoneally injected with saline, or 3 mg kg(-1) or 10 mg kg(-1) caffeine. The duration of the test was 4 h. During the exercise experiment, baseline collections on the treadmill were obtained for 1 h. One hour before the start of exercise, rats were intraperitoneally injected with either 10 mg kg(-1) caffeine (CAF) or saline (SAL). Animals ran until fatigue at a speed of 18 m min(-1), at a 5% grade, on the treadmill in a normal environment (23 °C). At rest, 3 mg kg(-1) caffeine did not influence Tcore, Ttail, VO₂, extracellular DA, NA and 5-HT. 10 mg kg(-1) caffeine caused significant increases in Tcore, VO₂, Ttail and extracellular DA in the PO/AH. In addition, 10 mg kg(-1) caffeine increased the run time to fatigue (SAL: 104.4 ± 30.9 min, CAF: 134.0 ± 31.1 min, p<0.05). The combination of caffeine and exercise increased Tcore, VO₂, Ttail and extracellular DA in the PO/AH. NA increased during exercise, while neither caffeine nor exercise changed 5-HT. These results indicate that caffeine has ergogenic and hyperthermic effects, and these effects may be related to changes of DA release in the brain.
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Japan.
authors.forename: Xinyan
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Takatsu
authors.affiliation: College of Sports Science, Shenyang Sport University, Shenyang, China.
authors.forename: Hongli
authors.initials: H
authors.lastname: Wang
authors.affiliation: Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Japan. Electronic address: hasehiro@hiroshima-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hasegawa
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D002110:Caffeine / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004298:Dopamine / Q000378:metabolism*; D004311:Double-Blind Method; D017079:Exercise Tolerance / Q000187:drug effects* / Q000502:physiology; D007274:Injections, Intraperitoneal; D008297:Male; D010805:Physical Conditioning, Animal / Q000379:methods* / Q000502:physiology; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002110:Caffeine; D004298:Dopamine
keywords: Caffeine; Core temperature; Dopamine; Ergogenic effect; PO/AH