Effects Of Intranasal Cocaine On Thermoregulatory Responses During Exercise In The Heat

The lethal effects of cocaine are unique because of its propensity to cause hyperthermia. A previous study, using passive heating of humans, showed impaired thermoregulation with accompanying impairments of the perception of the heat stress when receiving cocaine. Yet, it is unknown whether cocaine has the same effect during conditions of high metabolic heat generation associated with exercise in a heated environment. Purpose: Therefore, the purpose of this study was to test the effects of cocaine on thermoregulatory responses to heat stress and exercise in humans. Methods: In randomized order, 7 healthy participants (4 males/3 females (age: 31 ± 5 years) participated in a crossover, double-blinded, placebo (lidocaine) controlled trial. Following intranasal administration (3 mg/kg) of cocaine (cocaine hydrochloride 4% nasal solution) or lidocaine (lidocaine hydrochloride 4% nasal solution), participants exercised on a semi-recumbent cycle ergometer for 60 minutes at a metabolic heat production of 5.14 ± 0.62 Watts/kg in an environmental chamber set to 38 °C and 40% relative humidity. We compared data between cocaine and lidocaine trials using one-tailed paired t-tests. Results: When compared to lidocaine, ending mean skin temperature was greater in the cocaine trial (cocaine: 35.94 ± 0.43 °C vs. lidocaine: 35.45 ± 0.58 °C, p = 0.037). Yet, there were no differences in the increase in core temperature (cocaine: 1.27 ± 0.26 °C vs. lidocaine: 1.16 ± 0.30 °C, p = 0.149) or whole body sweat loss (cocaine: 979 ± 271 g/hr vs. lidocaine: 960 ± 302 g/hr, p = 0.374) between trials. Moreover, neither ending heart rate (cocaine: 155 ± 25 bpm vs. lidocaine: 148 ± 17 bpm, p = .085) nor an index of thermal sensation (cocaine: 30 ± 12 vs. lidocaine: 34 ± 9, p = 0.145) were different between trials. Conclusion: These preliminary data show that intranasal cocaine has limited effects on the thermoregulatory responses to exercise in the heat.