COLD EXPOSURE ATTENUATES PLASMA AVP AND PERCEPTION OF THIRST AT REST AND DURING MODERATE EXERCISE

Abstract

Previous research has observed diminished thirst sensations in subjects exposed to a cold environment [4°C], however the mechanism underlying this response has not been identified. PURPOSE This investigation examined the impact of hypohydration [HYPO] on perception of thirst and plasma arginine vasopressin [AVP] responses at rest and during moderate exercise in the cold. It was hypothesized that cold induced peripheral vasoconstriction would increase central blood volume and attenuate the response of plasma AVP and perception of thirst. METHODS On four occasions, 9 males [21.3 ±1yr, 177.5 ±2.3 cm, 75.8 ± 4.3 kg, 55.5 ±2.9 ml·kg −1·min-1, 9.9 ±1.8% fat] underwent a dehydration [Dh] protocol [treadmill exercise at 50% VO2max; 37°C] to induce a 3–4% reduction in body weight. During two Dh sessions subjects remained euhydrated [EU] by replacing the fluid lost; on the other two occasions subjects remained HYPO. The morning following Dh, subjects in either EU or HYPO states randomly performed one of four experimental protocols: 30 min standing equilibration at 25°C, followed by 30 min standing rest and 30 min of treadmill exercise at 50% of V02max in either a 25°C [Amb], or 4°C [Cold] environment. Measures of plasma AVP, perception of thirst, plasma osmolality, heart rate [HR], and mean weighted skin temperature [Tsk] were measured post- equilibration, post-standing rest and post-exercise. RESULTS Tsk was lower [p < 0.05] post-rest and post- exercise in the EU and HYPO-Cold trials. HR tended to be lower in these trials, suggesting an increase in stroke volume. Perception of thirst and plasma AVP similarly decreased [p < 0.05] at rest and during exercise in the HYPO-Cold trial. In the HYPO-Amb, EU-Amb and EU-Cold trials plasma AVP increased post-equilibration to post- exercise, while perception of thirst increased or remained unchanged. CONCLUSION These findings suggest that cold induced vaso-constriction may have increased central blood flow and attenuated plasma AVP responses, subsequently resulting in a decrease in perception of thirst.