APStracts 2:0335A, 1995.

Selective brain cooling in the horse during exercise and environmental heat stress. McConaghy, F. F., J. R. S. Hales, R. J. Rose, and D. R. Hodgson. Departments of Animal Health and Veterinary Clinical Sciences, University of Sydney, PMB 4, Werombi Rd. Camden, NSW 2570; and School of Physiology and Pharmacology, University of New South Wales, Sydney, NSW 2052, Australia.

APStracts 2:0335A, 1995.

Five horses were exercised on a treadmill (to Tcore nearly equal to 42.5 degrees C). Three of those horses were heated at rest in a climate room (53 degrees C/90% humidity) (to Tcore nearly equal to 41.5 degrees C). Temperatures were measured in the rectum (Tre), hypothalamus (Thyp), cerebrum (Tce), central blood (Tcore), cavernous sinus (Tsinus), and on the skin of the head (Thsk) and midside (Tmsk). When Tcore increased above 38.5 degrees C, Thyp remained 0.6 +/- 0.1 degrees C (mean +/- S.E.) lower during heat exposure and 1 +/- 0.2 degrees C lower during exercise. During heat exposure Tsinus was 2.2 +/- 0.4 degrees C below Tcore and during exercise Tsinus was 5 +/- 0.9 degrees C below Tcore. Upper respiratory tract bypass during exercise in one horse resulted in substantial reductions in Tcore - Thyp to 0.4 +/- 0.3 degrees C and Tcore - Tsinus to 0.9 +/- 0.2 degrees C. Thus, the horse, a species without a carotid rete, can selectively cool the brain during exercise or heat exposure: this occurs, at least in part, via cool blood within the cavernous sinus, presumably resulting principally from cooling of venous blood within the upper respiratory tract.

Received 22 February 1995; accepted in final form 30 June 1995.
APS Manuscript Number A207-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.