Transient cutaneous vasodilatation and hypotension after drinking in dehydrated and exercising men

Abstract

We examined whether oropharyngeal stimulation by drinking released the dehydration-induced suppression of cutaneous vasodilatation and decreased mean arterial pressure (MAP) in exercising subjects, and assessed the effects of hypovolaemia or hyperosmolality alone on these responses. Seven young males underwent four hydration conditions. These were two normal plasma volume (PV) trials: normal plasma osmolality (P osmol , control trial) and hyperosmolality (∆P osmol = +11 mosmol (kg H 2 O) −1 ); and two low PV trials: isosmolality (∆PV = −310 ml) and hyperosmolality (∆PV = −345 ml; ∆P osmol = +9 mosmol (kg H 2 O) −1 ), attained by combined treatment with furosemide (frusemide), hypertonic saline and/or 24 h water restriction. In each trial, the subjects exercised at 60% peak aerobic power for ∼50 min at 30• C atmospheric temperature and 50% relative humidity. When oesophageal temperature (T oes ) reached a plateau after ∼30 min of exercise, the subjects drank 200 ml water at 37.5• C within a minute. Before drinking, forearm vascular conductance (FVC), calculated as forearm blood flow divided by MAP, was lowered by 20-40% in hypovolaemia, hyperosmolality, or both, compared with that in the control trial, despite increased T oes . After drinking, FVC increased by ∼20% compared with that before drinking (P < 0.05) in both hyperosmotic trials, but it was greater in normovolaemia than in hypovolaemia (P < 0.05). However, no increases occurred in either isosmotic trial. MAP fell by 4-8 mmHg in both hyperosmotic trials (P < 0.05) after drinking, but more rapidly in normovolaemia than in hypovolaemia. PV and P osmol did not change during this period. Thus, oropharyngeal stimulation by drinking released the dehydration-induced suppression of cutaneous vasodilatation and reduced MAP during exercise, and this was accelerated when PV was restored.

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

“…Baboons, which do not possess a carotid rete and are incapable of regulating brain temperature independently of arterial blood temperature (27), also demonstrated a rapid fall in blood temperature (and a fall rather than rise in brain temperature) after drinking body-temperature water after three days of water deprivation (D. Mitchell, unpublished observations). Dehydration-induced suppression of cutaneous vasodilatation was released immediately after drinking in humans, presumably by the stimulation of oropharyngeal reflexes (19).…”

Body Temperature Regulation During Exercise and Hyperthermia in Diabetics

“…Dodt et al [20] also observed decreased skin sympathetic nerve activity following LBNP in passively heated subjects. In contrast, Kamijo et al [21] reported that isotonic hypovolemia induced by diuretic (−10%) before exercise dampened increases in SkBF, similar to the results of Nadel et al [12]. However, it did not dampen the increase in sweat rate during exercise at 60% VO 2max in a warm environment (T a , 30°C; RH, 45%).…”

“…Indeed, it has been reported that, when drinking such a small amount of water so as not to change PV and P osm in dehydrated individuals, thirst sensation and plasma vasopressin secretion induced by increased P osm are released rapidly by a stimulation of oropharyngeal reflexes [25,26]. It also simultaneously releases the dehydration-induced attenuated responses of SkBF [21] and SR [26].…”

Mechanisms and controllers of eccrine sweating in humans

“…In contrast, drinking deionized water in iso-osmotic subjects did not alter sweat rate. In a follow-up study, Kamijo et al (36) confirmed such a release of sweating suppression by drinking occurred during exercise. These investigators concluded that stimulation of an oral-pharyngeal reflex, associated with the act of drinking, releases an otherwise inhibition of sweating by dehydration.…”