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First published online June 29, 2007
Journal of Experimental Biology 210, 2444-2452 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005587

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Thermoregulation in pronghorn antelope (Antilocapra americana Ord) in the summer

A. Lust¹, A. Fuller², S. K. Maloney³, D. Mitchell² and G. Mitchell^1,*

¹ Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA
² Department of Physiology, University of the Witwatersrand, Johannesburg, South Africa
³ Physiology, School of Biomedical and Chemical Sciences, University of Western Australia, Perth, Australia

View larger version (20K): [in this window] [in a new window]   Fig. 1. Frequency of occurrence of 0.1°C intervals of (A) brain and jugular temperatures and (B) carotid temperature. The brain distribution is narrower and its mode temperature occurs to the right of the carotid and jugular distributions. The frequency of occurrence of jugular temperatures is to the left of the carotid distribution and is characterized by a long tail. Values are means ± s.d. (see text for N).

View larger version (5K): [in this window] [in a new window]   Fig. 2. The weekly mean pronghorn carotid blood temperature plotted against the weekly mean (red) black globe temperature and the weekly range (blue) of black globe temperature. As mean and variability of globe temperature increases and decreases over the summer, mean pronghorn temperature tends to change in the same direction.

View larger version (20K): [in this window] [in a new window]   Fig. 3. (A) Circadian rhythms over 3 days for one animal (22–24 July 2005) shown by cosinor analysis (Nelson et al., 1979), which fits a `best fit' cosine wave to the actual data if such a wave form exists. Raw data are represented by the blue line and the best-fit curve is in pink. (B) Changes in Tglobe over the same 3 days. Note that the time of maximum Tglobe occurs about 7 h before the time of maximum Tcarotid. In both A and B, actual data points (diamonds) and their corresponding calculated points (squares) are shown.

View larger version (17K): [in this window] [in a new window]   Fig. 4. (A) Tsubcut and Tglobe (means ± s.d.) from 2 animals in July over 24 h with means derived from 12 temperatures per hour, showing coincident changes during the day (pink) and the separation of temperatures at night (black). (B) In the mornings and evenings the difference between carotid and subcutaneous temperatures increases suggesting vasoconstriction, but narrows at midday suggesting vasodilation.

View larger version (15K): [in this window] [in a new window]   Fig. 5. (A) Minimum and maximum (blue) and mean (red) Tjugular and (B) minimum and maximum (light blue) and mean (dark blue) Tbrain plotted against Tcarotid. At Tcarotid below 38°C brain temperature stays constant; between 38°C and 39.5°C brain and carotid temperatures approach each other as CBF increases and SBC begins. Above 39.5°C typical SBC is evident. At carotid temperatures below 37°C all three jugular temperatures are above carotid temperature, but at higher carotid temperatures mean and minimum jugular temperatures become cooler reflecting an increase in REHL. Values are means ± s.d. but note that error bars disappear from the mean jugular trace at low Tcarotid because data from only two animals could be matched to corresponding data points for Tcarotid.

View larger version (9K): [in this window] [in a new window]   Fig. 6. Mean jugular (Tjugular; red) and brain temperatures (Tbrain; blue) plotted against carotid temperature Tcarotid, with the three phases of brain temperature demarcated (see text). Tjugular and Tbrain change in parallel as Tcarotid increases, and increase at a slower rate than Tcarotid, showing that Tjugular and Tbrain are linked.

View larger version (8K): [in this window] [in a new window]   Fig. 7. Calculated CBFs for 130 brain minus carotid temperature gradients (Tbrain–Tcarotid). The gradients were calculated by obtaining a mean Tcarotid for 0.1°C intervals of Tcarotid and subtracting that mean value from the corresponding average Tbrain. (A) CBFs above the upper maximum CBF (pink line) cannot be achieved and the gradients associated with these CBFs are produced by SBC. (C) CBFs below the minimum CBF (yellow line) are unable to provide adequate oxygen and glucose to the brain (see text) and the gradients measured cannot be the result of reduced CBF. They must result from a brain warming mechanism. (B) Gradients between A and C can be produced by changes in CBF alone but are likely to be the result of changes in both CBF and SBC.