Biomedical subjects

Calvert T Larsen

Publications and source records attributed to Calvert T Larsen.

5 recordsLinked to original sources

PubMed2005

Food avoidance behavior to dietary octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) exposure in the northern bobwhite (Colinusvirginianus).

High-melting explosive (HMX; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) is a widely utilized explosive component of munitions used by the military. Consequently, production and use through testing and training at military installations has resulted in deposition of HMX in soil. Since these areas are often used by birds, the oral toxicity of HMX exposure to northern bobwhite (Colinus virginianus) was evaluated. Attempts to determine the acute lethal dose were unsuccessful. Initially, 8 birds (1 male/1 female per dose group) were orally dosed at levels ranging from 125 to 2125 mg HMX/kg body weight. A single death at the midrange resulted in subsequent trials of oral doses up to 10,760 mg/kg body weight. Only a single death occurred at 7173 mg/kg. A subsequent 28-d feeding study was then conducted to evaluate the potential for toxicity resulting from repetitive oral exposures. Northern bobwhite were exposed to concentrations of HMX in feed of either 10000, 1000, 100, or 0 mg/kg. These exposures resulted in a clear concentration-related reduction in feed consumption and body mass. Reductions in egg production in females were correlated with changes in body mass and feed consumption. Other physiological indicators were consistent with a considerable reduction in feed intake. These results suggest that HMX concentration is responsible for intense feed aversion behavior and thus not likely a factor that would appreciably contribute to risk for wild birds at military ranges.

Administration, Oral↗

PubMed2004

Does thyroid function in developing birds adapt to sustained ammonium perchlorate exposure?

The effects of a wide range of ammonium perchlorate (AP) concentrations in drinking water on thyroid function in bobwhite quail chicks was investigated at 2, 4, and 8 weeks of exposure. We measured plasma thyroid hormones (THs) to evaluate organismal thyroid status, thyroid weights to evaluate hypothalamic-pituitary-thyroid (HPT) axis activation, and thyroidal TH content to assess TH stores. At the highest AP exposures plasma THs were decreased, thyroid glands were hypertrophied, and thyroidal TH content was decreased. As in our previous studies, thyroidal thyroxine (T(4)) content was the most sensitive indicator of decreased thyroid function; plasma T(4) and thyroid weight were much less sensitive. The lack of sensitivity of these variables appears to result from cyclic patterns of thyroid responses involving the HPT axis and intermittent release of stored THs from the thyroid gland. With sustained AP exposure (8 weeks), at the lowest range of AP concentrations used, chicks showed adaptation in thyroid function that fully compensated for the initial (2 week) effects of AP. At the intermediate AP concentrations there was partial compensation for the initial AP effects. At the highest AP exposures used, thyroid function was very low throughout the study, with no indication of compensatory responses. The capability of chicks to increase some aspects of their thyroid function adaptively in response to some levels of sustained AP exposure is contrary to the common generalization that developing animals are most vulnerable to environmental contaminants.

Adaptation, Physiological↗

PubMed2004

Ammonium perchlorate effects on thyroid function and growth in bobwhite quail chicks.

Bobwhite quail chicks were used to investigate ammonium perchlorate (AP; NH4ClO4) effects on thyroid function and growth. Beginning at 3 to 4 d posthatch, we evaluated organismal thyroid status (circulating hormones), activation of the hypothalamic-pituitary-thyroid axis (thyroid wt) and thyroidal hormone content over a wide range of AP concentrations (50 microg/L - 4,000 mg/L) in drinking water, for relatively short (2-week) and longer (8-week) exposures. Thyroidal thyroxine (T4) content, the most sensitive index of decreased thyroid function, decreased markedly in response to increasing perchlorate exposure. Thyroid weight and plasma T4 were less sensitive indicators and similar in their ability to detect thyroid changes. Growth measurements (body wt and skeletal growth) were very insensitive indices. Because thyroids contain large hormone stores, with low exposures or short time periods, these stores can be used to maintain circulating hormones, at least temporarily. Most depletion of thyroidal T4 occurred during the first two weeks of AP exposure. Subsequent decreases were at a slower rate presumably because thyrotropin stimulation of the thyroids at least partially compensated for some of the perchlorate effect. Additional studies of the interactions between AP concentration and exposure time are needed for understanding the complex nature of thyroid responses to perchlorate.

Animals↗

PubMed2003

Dietary oral exposure to l,3,5-trinitro-1,3,5-triazine in the northern bobwhite (Colinus virginianus).

The potential risk to wildlife from exposure to explosives, including 1,3,5-trinitro-1,3,5-triazine (RDX), has been an issue at numerous U.S. military installations where these substances are found in soil and water. Presently, no data describing the effects of RDX exposure in avian species exist. Therefore, an acute lethal dose (ALD) and 14- and 90-d subchronic dietary exposures to RDX were evaluated in a species potentially present at many contaminated sites, i.e., the northern bobwhite (Colinus virginianus). The ALDs for females and males were 187 and 280 mg/kg, respectively. Data from the 14-d dietary trial suggested that RDX exposure inhibited food consumption, weight gain, and egg production. Dietary RDX exposure for 90-d produced a dose-dependant decreasing trend in total feed consumption, total egg production, and hen-housed production parameters. These collective data suggest that quail may respond differently to oral RDX exposure compared with mammals.

Administration, Oral↗

PubMed2002

Influence of dietary 2,4,6-trinitrotoluene exposure in the northern bobwhite (Colinus virginianus).

The risk to wildlife from exposure to the explosive, 2,4,6-trinitrotoluene (TNT) has been a concern at numerous military installations where it has been found in the soil. To date, no published data are available describing effects of TNT exposure in an avian species. Subchronic dietary exposure to TNT was therefore evaluated in a species of management concern at military installations, the northern bobwhite (Colinus virginianus). Adult male and female quail (n = 5/sex/dose) were given commercial feed containing 3,000, 1,500, 750, and 100 mg/kg TNT for 90 d following the determination of an acute lethal dose and a 14-d range finding study. Dietary TNT intake caused a dose-dependent decrease in total red blood cell counts, packed cell volume, total plasma protein, blood prolymphocytes, and blood lymphocytes. An increased trend in late apoptotic/necrotic blood leukocytic cells was also observed in TNT-exposed birds, as was hemosiderosis in the liver. With the exception of hemosiderosis, these trends were statistically significant yet of questionable biological significance. Since treatment-related responses in this preliminary study were variable, a conservative interpretation is suggested. However, since these treatments had concentrations that were a log-fold or more than doses in similar studies using mammals, these data suggest that northern bobwhite are less sensitive to oral exposures of TNT than mammals.

Animal Feed↗