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

Abstract

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.

Authors+Show Affiliations

School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa. fullera@physiology.wits.ac.zaNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17363686

Citation

Fuller, Andrea, et al. "Dehydration Increases the Magnitude of Selective Brain Cooling Independently of Core Temperature in Sheep." American Journal of Physiology. Regulatory, Integrative and Comparative Physiology, vol. 293, no. 1, 2007, pp. R438-46.
Fuller A, Meyer LC, Mitchell D, et al. Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep. Am J Physiol Regul Integr Comp Physiol. 2007;293(1):R438-46.
Fuller, A., Meyer, L. C., Mitchell, D., & Maloney, S. K. (2007). Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology, 293(1), pp. R438-46.
Fuller A, et al. Dehydration Increases the Magnitude of Selective Brain Cooling Independently of Core Temperature in Sheep. Am J Physiol Regul Integr Comp Physiol. 2007;293(1):R438-46. PubMed PMID: 17363686.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep. AU - Fuller,Andrea, AU - Meyer,Leith C R, AU - Mitchell,Duncan, AU - Maloney,Shane K, Y1 - 2007/03/15/ PY - 2007/3/17/pubmed PY - 2007/8/31/medline PY - 2007/3/17/entrez SP - R438 EP - 46 JF - American journal of physiology. Regulatory, integrative and comparative physiology JO - Am. J. Physiol. Regul. Integr. Comp. Physiol. VL - 293 IS - 1 N2 - By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated. SN - 0363-6119 UR - https://www.unboundmedicine.com/medline/citation/17363686/Dehydration_increases_the_magnitude_of_selective_brain_cooling_independently_of_core_temperature_in_sheep_ L2 - http://www.physiology.org/doi/full/10.1152/ajpregu.00074.2007?url_ver=Z39.88-2003&amp;rfr_id=ori:rid:crossref.org&amp;rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -