Search PubMed⌕ Search

Biomedical subjects

D R Clark

Publications and source records attributed to D R Clark.

At least 73 records · Page 4Linked to original sources
PubMed1978

Capillary density and muscle fibre size in the hearts of rats subjected to stimulated high altitude.

Six Wistar rats were subjected to a barometric pressure of 50.7 kPa (380 mmHg) for 34 days. These rats and six controls were killed and their myocardial capillaries perfused with India ink. Hypoxia did not induce any proliferation of capillaries in the left ventricle neither did it lead to a reduction in myofibre size. In the right ventricle the capillary density was reduced largely due to a two-fold increase in myofibre area but there was an increase in the capillary: fibre ratio indicating a modest proliferation of capillaries secondary to right ventricular hypertrophy.

Altitude↗
PubMed1978

Organochlorine residues and reproduction in the little brown bat, Laurel, Maryland--June 1976.

Twelve of 43 pregnant little brown bats (Myotis lucifugus) collected at Montpelier Barn, Laurel, Maryland, gave birth to dead young. Eleven of these 12 dead neonates were abnormally small. Most of the stillbirths were attributable to unknown reproductive difficulties associated with first pregnancies, but four may have been due to high concentrations of polychlorinated biphenyls (PCB) in the newborn. Residues of the PCB, DDE, and oxychlordane crossed the placenta at similar rates.

Age Factors↗
PubMed1977

Experimental feeding of DDE and PCB to female big brown bats (Eptesicus fuscus).

Twenty-two female big brown bats (Eptesicus fuscus) were collected in a house attic in Montgomery County, Maryland. Seventeen were fed mealworms (Tenebrio molitor larvae) that contained 166 ppm DDE; the other five were fed uncontaminated mealworms. After 54 days of feeding, six dosed bats were frozen and the remaining 16 were starved to death. In a second experiment, 21 female big brown bats were collected in a house attic in Prince Georges County, Maryland. Sixteen were fed mealworms that contained 9.4 ppm Aroclor 1254 (PCB). After 37 days, two bats had died, four dosed bats were frozen, ant the remaining 15 were starved to death. Starvation caused mobilization of stored residues. After the feeding periods, average weights of all four groups (DDE-dosed, DDE control, PCB-dosed, PCB control) had increased. However, weights of DDE-dosed bats had increased significantly more than those of their contols, whereas weights of PCB-dosed bats had increased significantly less than those of their controls. During starvation, PCB-dosed bats lost weight significantly more slowly than controls. Because PCB levels in dosed bats resembled levels found in some free-living big brown bats, PCBs may be slowing metabolic rates of some free-living bats. It is not known how various common organochlorine residues may affect metabolism in hibernating bats. DDE and PCB increased in brains of starving bats as carcass fat was metabolized. Because the tremors and/or convulsions characteristic of neurotoxicity were not observed, we think even the maximum brain levels attained (132 ppm DDE, 20 ppm PCB) were sublethal. However, extrapolation of our DDE data predicted lethal brain levels when fat reserves declined sufficiently. PCB-dosed bats were probably in no danger of neurotoxic poisoning. However, PCB can kill by a nonneurotoxic mode, and this could explain the deaths of two bats on PCB dosage.

Animals↗
PubMed1977

Effects of DDE on experimentally poisoned free-tailed bats (Tadarida brasiliensis): lethal brain concentrations.

Adult female free-tailed bats (Tadarida brasiliensis) were collected at Bracken Cave, Texas, and shipped to the Patuxent Wildlife Research Center. Treated mealworms (Tenebrio molitor) containing 107 ppm DDE were fed to 17 bats; five other bats were fed untreated mealworms. After 40 days on dosage, during which one dosed bat was killed accidentally, four dosed bats were frozen and the remaining 17 were starved to death. The objective was to elevate brain levels of DDE to lethality and measure these concentrations. After the feeding period, dosed bats weighed less than controls. After starvation, the body condition of dosed bats was poorer than that of controls even though there was no difference in the amounts of carcass fat. During starvation, dosed bats lost weight faster than controls. Also, four dosed bats exhibited the prolonged tremoring that characterizes DDE poisoning. DDE increased in brains of starving bats as fat was metabolized. The estimated mean brain concentration of DDE diagnostic of death was 519 ppm with a range of 458-564 ppm. These values resemble diagnostic levels known for two species of passerine birds, but they exceed published levels for two free-tailed bats from Carlsbad Caverns, New Mexico.

Adipose Tissue↗
PubMed1976

Enzymatic assay for methotrexate in serum and cerebrospinal fluid.

We describe an assay for methotrexate in biological fluids. The assay is based on inhibition by methotrexate of dihydrofolate reductase from Lactobacillus casei. The lower limit of sensitivity in serum is 2 X 10(-8) mol (about 10 mug) of methotrexate per liter. Within-run precision is +/- 5% (coefficient of variation) and day-to-day variation is 18%. Advantages of the assay are ease of manipulation, high sensitivity, and specificity.

Evaluation Studies as Topic↗
PubMed1976

Organochlorine residues in three bat species from four localities in Maryland and West Virginia, 1973.

In 1973, 119 bats of three species were collected from four localities in Maryland and West Virginia. The collection included 43 big brown bats (Eptesicus fuscus), 43 little brown brown bats (Myotis lucifugus), and 33 eastern pipistrelles (Pipistrellus subflavus). The bats were collected from Round Top Mountain, Washington Co., Md.; Trout Cave, Pendleton Co., W. Va.; Montpelier Barn, Prince Georges Co., Md. Residues of sigmaDDT were highest in carcasses of bats from Round Top Mountain, which is surrounded by apple orchards. Bats from Trout Cave had the lowest residues, a circumstance which probably reflects the absence of agriculture and industry in the area. A polychlorinated biphenyl (PCB) and oxychlordane were highest at Montpelier Barn. Sources of the PCB are unknown, but chlordane is used against termites and in gardening at nearby housing developments. Residues in bats from North East Methodist Church were low except for dieldrin. Among species, little brown bats usually had the highest residue concentrations in their carcasses, whereas big brown bats had the lowest. When DDE in carcass fat of all species was above 60-90 ppm, it became measurable in brain tissue. Above 60-90 ppm, DDE levels in brains rose with increasing levels in carcass lipids. Residues of the PCB tended to respond similarly. Residue levels in brains were greatest in little brown bats; the maximum level of the PCB, 7.9 Ppm, was more than twice that of DDE.

Age Factors↗
PubMed1975

Pattern of physiologic effects of adrenalectomy in the dog.

Adrenalectomized dogs were observed in order to identify the patterns of physiologic changes occurring during development of adrenocortical insufficiency. Daily measurements included plasma concentrations of sodium and potassium, arterial blood pH, packed cell volume, heart rate, and selected components of the electrocardiogram (ECG). The pattern in which these measurements changed indicated that alterations in plasma concentrations of sodium and potassium, T-wave configuration, and QRS interval were more consistent, whereas alterations in P-wave configuration were not evident until approach of terminal stages.

Adrenal Glands↗