title: Acute hypoosmolality attenuates the suppression of cutaneous vasodilation with increased exercise intensity.
abstract: We examined the hypothesis that elevation of the body core temperature threshold for forearm skin vasodilation (TH(FVC)) with increased exercise intensity is partially caused by concomitantly increased plasma osmolality (P(osmol)). Eight young male subjects, wearing a body suit perfused with warm water to maintain the mean skin temperature at 34 +/- 1 degree C (ranges), performed 20-min cycle-ergometer exercise at 30% peak aerobic power (VO2(peak)) under isoosmotic conditions (C), and at 65% VO2(peak) under isoosmotic (H(EX)I(OS)) and hypoosmotic (H(EX)L(OS)) conditions. In H(EX)L(OS), hypoosmolality was attained by hypotonic saline infusion with DDAVP, a V2 agonist, before exercise. P(osmol) (mosmol/kg H2O) increased after the start of exercise in both H(EX) trials (P < 0.01) but not in C. The average P(osmol) at 5 and 10 min in H(EX)I(OS) was higher than in C (P < 0.01), whereas that in H(EX)L(OS) was lower than in H(EX)I(OS) (P < 0.01). The change in TH(FVC) was proportional to that in P(osmol) in every subject for three trials. The change in TH(FVC) per unit change in P(osmol) (deltaTH(FVC)/deltaP(osmol), degrees C x mosmol(-1) x kg H2O(-1)) was 0.064 +/- 0.012 when exercise intensity increased from C to H(EX)I(OS), similar to 0.086 +/- 0.020 when P(osmol) decreased from H(EX)I(OS) to H(EX)L(OS) (P > 0.1). Moreover, there were no significant differences in plasma volume, heart rate, mean arterial pressure, and plasma lactate concentration around TH(FVC) between H(EX)I(OS) and H(EX)L(OS) (P > 0.1). Thus the increase in TH(FVC) due to increased exercise intensity was at least partially explained by the concomitantly increased P(osmol).
authors.affiliation: Dept. of Sports Medical Sciences, Institute on Aging and Adaptation, Shinshu Univ. Graduate School of Medicine, 3-1-1 Asahi Matsumoto 390-8621, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mitono
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Endoh
authors.forename: Kazunobu
authors.initials: K
authors.lastname: Okazaki
authors.forename: Takashi
authors.initials: T
authors.lastname: Ichinose
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: Akira
authors.initials: A
authors.lastname: Takamata
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nose
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D005542:Forearm / Q000098:blood supply / Q000502:physiology; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012867:Skin / Q000098:blood supply*; D012879:Skin Physiological Phenomena