Effects of perchlorate exposure on resting metabolism, peak metabolism, and thyroid function in the prairie vole (Microtus ochrogaster)

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Title: Effects of perchlorate exposure on resting metabolism, peak metabolism, and thyroid function in the prairie vole (Microtus ochrogaster)
Author: Isanhart, John P
Abstract: Perchlorate is the oxidizer component in most solid rocket propellant formulations . It is known to reduce the production and output of the thyroid hormones , triiodothyronine (T3 ) and thyroxine (T4 ) . Thyroid hormones regulate metabolism in endothermic organisms and are responsible for maintenance of body temperatures above that of the environment . Little is known about the effects of perchlorate on metabolic capacity . The objectives of this study were to 1 ) determine if subchronic (51 days ; 0 , 1 , and 10 mg /kg /day ) and chronic (180 days ; 0 .75 mg /kg /day ) perchlorate exposure in adult male prairie voles {Microtus ochrogaster ) would alter resting metabolic rates as a result of decreased circulating thyroid hormone concentrations , and 2 ) determine if perchlorate exposure disrupts thermogenesis in mammals challenged with cold -stress . Voles exposed to perchlorate for 51 or 180 days experienced no significant alterations in resting metabolic rates at any point during the exposure period . Additionally , there was no treatment effect on peak metabolic rates or plasma thyroid hormone concentrations . Mean peak metabolic rates were 10 .17 ± 0 .85 , 10 .17 ± 1 .50 , and 9 .37 ± 0 .89 mL oxygen consumed per gram of body mass per hour for 0 , 1 , and 10 mg /kg /day groups , respectively . Mean plasma T4 concentrations were 3 .01 ± 0 .83 , 2 .74 ± 1 .36 , and 1 .70 ± 0 .91 pg /dL , and mean plasma T3 concentrations were 109 .29 ± 15 .05 , 94 .83 ± 13 .36 , and 95 .57 ± 5 .92 ng /dLforO , 1 , and 10 mg /kg /day treatment groups , respectively . However , thyroid gland thyroxine concentrations , 704 .62 ± 372 .62 , 454 .20 ± 290 .52 , and 219 .54 ± 196 .76 ng T4 per thyroid gland for 0 , 1 , and 10 mg /kg /day treatment groups , respectively , were significantly lower in perchlorate -exposed voles than controls indicating that thyroid gland thyroxine content is a more sensitive endpoint for assessing perchlorate exposure in prairie voles . This study indicates that perchlorate -induced alterations in thyroid function do not necessarily translate into alterations in metabolic rate and /or decreases in thermogenic response . Overall , this study did not provide evidence for energetic alterations associated with perchlorate exposure at concentrations that are higher than those typically found in water in the environment . It may require a longer duration of exposure or higher dose to see a significant effect on resting metabolic rate and /or cold -tolerance . This is also the first study to present data on cold -induced PMR in a helox atmosphere in prairie voles and to show that thyroid gland thyroid T4 decreases are the most sensitive measure of thyroid function in mammals in comparison to plasma thyroid hormone concentrations .
URI: http : / /hdl .handle .net /2346 /12022
Date: 2004-08

Citation

Isanhart, John P Effects of perchlorate exposure on resting metabolism, peak metabolism, and thyroid function in the prairie vole (Microtus ochrogaster). Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /12022 .

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