Plasma hyperosmolality elevates the internal temperature threshold for active thermoregulatory vasodilation during heat stress in humans.
Plasma hyperosmolality delays the response in skin blood flow to heat stress by elevating the internal temperature threshold for cutaneous vasodilation. This elevation could be because of a delayed onset of cutaneous active vasodilation and/or to persistent cutaneous active vasoconstriction. Seven healthy men were infused with either hypertonic (3% NaCl) or isotonic (0.9% NaCl) saline and passively heated by immersing their lower legs in 42 degrees C water for 60 min (room temperature, 28 degrees C; relative humidity, 40%). Skin blood flow was monitored via laser-Doppler flowmetry at sites pretreated with bretylium tosylate (BT) to block sympathetic vasoconstriction selectively and at adjacent control sites. Plasma osmolality was increased by approximately 13 mosmol/kgH(2)O following hypertonic saline infusion and was unchanged following isotonic saline infusion. The esophageal temperature (T(es)) threshold for cutaneous vasodilation at untreated sites was significantly elevated in the hyperosmotic state (37.73 +/- 0.11 degrees C) relative to the isosmotic state (36.63 +/- 0.12 degrees C, P < 0.001). A similar elevation of the T(es) threshold for cutaneous vasodilation was observed between osmotic conditions at the BT-treated sites (37.74 +/- 0.18 vs. 36.67 +/- 0.07 degrees C, P < 0.001) as well as sweating. These results suggest that the hyperosmotically induced elevation of the internal temperature threshold for cutaneous vasodilation is due primarily to an elevation in the internal temperature threshold for the onset of active vasodilation, and not to an enhancement of vasoconstrictor activity.
Shibasaki
Manabu
M
Department of Environmental Health, Nara Women's University, Kita-Uoya Nishi-Machi, Nara, Japan 630-8506. shiba@cc.nara-wu.ac.jp
Aoki
Ken
K
Morimoto
Keiko
K
Johnson
John M
JM
Takamata
Akira
A
D000279:Administration, Cutaneous; D018674:Adrenergic Antagonists / Q000008:administration & dosage; D001783:Blood Flow Velocity; D001833:Body Temperature Regulation / Q000187:drug effects; D001950:Bretylium Tosylate / Q000008:administration & dosage; D006339:Heart Rate; D018882:Heat Stress Disorders / Q000097:blood* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D007101:Immersion; D007262:Infusions, Intravenous; D007478:Iontophoresis; D007552:Isotonic Solutions / Q000008:administration & dosage; D017078:Laser-Doppler Flowmetry; D008297:Male; D009994:Osmolar Concentration; D012039:Regional Blood Flow; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage; D012684:Sensory Thresholds / Q000187:drug effects; D012867:Skin / Q000098:blood supply*; D012965:Sodium Chloride / Q000008:administration & dosage; D013997:Time Factors; D014463:Ultrasonography; D014664:Vasodilation / Q000187:drug effects; D055815:Young Adult
D018674:Adrenergic Antagonists; D007552:Isotonic Solutions; D012462:Saline Solution, Hypertonic; D012965:Sodium Chloride; D001950:Bretylium Tosylate