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Biomedical subjects

C A Thompson

Publications and source records attributed to C A Thompson.

101 records · Page 6Linked to original sources
PubMed1990

Baroreflex responses to acute changes in blood volume in humans.

To test the hypothesis that acute changes in plasma volume affect the stimulus-response relations of high- and low-pressure baroreflexes, eight men (27-44 yr old) underwent measurements for carotid-cardiac and cardiopulmonary baroreflex responses under the following three volemic conditions: hypovolemic, normovolemic, and hypervolemic. The stimulus-response relation of the carotid-cardiac response curve was generated using a neck cuff device, which delivered pressure changes between +40 and -65 mmHg in continuous steps of 15 mmHg. The stimulus-response relationships of the cardiopulmonary baroreflex were studied by measurements of forearm vascular resistance (FVR) and peripheral venous pressure (PVP) during low levels of lower body negative pressure (0 to -20 mmHg). Altered vascular volume had no effect on response relations of the carotid-cardiac baroreflex but did alter the gain of the cardiopulmonary baroreflex (-7.93 +/- 1.73, -4.36 +/- 1.38, and -2.56 +/- 1.59 peripheral resistance units/mmHg for hypovolemic, normovolemic, and hypervolemic, respectively) independent of shifts in baseline FVR and PVP. These results indicate greater demand for vasoconstriction for equal reductions in venous pressure during progressive hypovolemia; this condition may compromise the capacity to provide adequate peripheral resistance during severe orthostatic stress. Fluid loading before reentry after spaceflight may act to restore vasoconstrictive capacity of the cardiopulmonary baroreflex but may not be an effective countermeasure against potential post-flight impairment of the carotid-cardiac baroreflex.

Adult↗
PubMed1986

Exaggerated response to gentamicin-induced nephrotoxicity in Sprague-Dawley rats: identification of a highly sensitive outlier population.

A number of factors have been shown to predispose patients treated with aminoglycosides to nephrotoxicity. In a previous study in our laboratory investigating the interaction of prior renal dysfunction with gentamicin toxicokinetics, 9.4% of rats in all treatment groups were relatively more sensitive to gentamicin-induced nephrotoxicity. To determine if these outliers had an underlying disease or physiological abnormality, serum was collected from 99 Sprague-Dawley rats prior to daily treatment with 75 mg/kg gentamicin for seven days. Urea nitrogen, creatinine, Na, K, Ca, Mg, P, total protein, albumin, aspartate transaminase, serum osmolality, total white and red blood cell count, hematocrit, hemoglobin, blood gases, and thyroxine were measured. Blood was collected one and four hours after the first dose of gentamicin for pharmacokinetic analysis. Elevations in post-treatment creatinine and nitrogen were significantly greater in the outliers (4.10 +/- 0.24 mg/dl (n = 12) vs 1.92 +/- 0.06 mg/dl (n = 87) and 146.4 +/- 7.2 mg/dl (n = 12) vs 71.5 +/- 2.0 mg/dl (n = 87); both p = 0.0001) and served as criteria for identifying this subgroup. Post-treatment creatinine and urea nitrogen were not normally distributed in the entire study population. However, when the population was divided into normal and sensitive subgroups, both subgroup values were normally distributed. The gentamicin pharmacokinetic profiles were similar in both groups. Postmortem histopathology showed significant increases in tubular casts and tubular necrosis (p = 0.01) in the sensitive rats, compared to the normally responding subgroup.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

The toxicity and neuropathology of 2,4,5-tribromoimidazole and its derivatives in rats.

2,4,5-tribromoimidazole and its 1-n-butylcarboxylate and 1-dimethylcarbamoyl derivatives, when administered to rats, induced poisoning typical of uncouplers of oxidative phosphorylation. At 48 h rats surviving a single toxic dose of 20-60 mg/kg developed permanent incoordination of the hindlimbs in the absence of brain oedema. Neuropathologic examination of brain and spinal cord from perfused fixed rats at 24 h revealed neuronal necrosis and chromatolysis in the vestibular nucleus, the outer parietal neocortex and red nucleus. Chromatolysis and necrosis in these areas had increased at 72-96 h and were also observed in the deeper layers of the neocortex, the medial entorhinal cortex, the reticular formation, the grey matter of the spinal cord extending into the ventral horns, the dorsal, and ventral cochlear nuclei and the deep cerebellar nuclei, in decreasing order of severity. Neuronal necrosis was accompanied by an increased glial response, including neuronophagia and at 16 days with astroglial hypertrophy and hyperplasia.

Administration, Oral↗
PubMed1983

Inhibition by retinoid and ovariectomy of additional primary malignancies in rats following surgical removal of the first mammary cancer.

Retinoids are highly effective inhibitors of mammary carcinogenesis in the rat. This study was designed to determine the influence of retinyl acetate and bilateral ovariectomy on the rate of new tumor appearance when treatment is started at the time of removal of an animal's first mammary tumor. Fifty-day-old virgin female Sprague-Dawley rats received a single intravenous injection of 35 mg N-methyl-N-nitrosourea per kg body weight. When an animal's first mammary tumor reached a diameter of 0.5 cm it was excised and the animal was entered into a treatment group: (1) intact, placebo diet; (2) intact, 328 mg retinyl acetate/kg diet; (3) ovariectomy, placebo diet; (4) ovariectomy, 328 mg retinyl acetate/kg diet. New tumor incidence was reduced from 94% in Group 1 to 15% in Group 4. Groups 2 and 3 had an intermediate tumor response. These data indicate that retinyl acetate and ovariectomy are active in cancer prevention when treatment is began after removal of a palpable tumor, a time at which preneoplastic lesions are present in the mammary glands.

Animals↗
PubMed1982

Temporal association between arterial cholesterol deposition, thymidine incorporation into DNA, and atherosclerosis in Japanese quail fed an atherogenic diet.

Male Japanese quail (strain SEA) rapidly develop atherosclerotic lesions in the aorta and brachiocephalic arteries when fed an atherogenic diet containing 1.0% cholesterol and 0.5% cholic acid. The present study was conducted to determine the parameters of the atherosclerotic response. Groups of 20 quail fed the atherogenic diet were killed at 0 days, 1 day, 3 days, or weekly from 1 to 12 weeks. Quail fed the atherogenic diet for 1 day showed a significant increase in serum cholesterol; a plateau was reached by 2 weeks. A significant increase in arterial cholesterol was seen after 2 weeks on the atherogenic diet, and arterial cholesterol showed a linear increase with time from 2 to 12 weeks. Increased incorporation of tritiated thymidine into the DNA of arterial cells was first seen at 2 weeks; thymidine incorporation increased to a maximum value at 9 weeks, then declined to 50-60% of the 9-week value at weeks 11 and 12. Grossly visible atherosclerotic lesions were first seen at 3 weeks, and 90% of birds showed gross atherosclerotic lesions by 8 weeks. Atherosclerosis induced in Japanese quail by feeding cholesterol and cholic acid is characterized initially by lipid deposition in the arterial wall, followed by increased incorporation of tritiated thymidine and the appearance of gross lesions.

Animals↗
PubMed1982

Enhanced inhibition of mammary carcinogenesis by combined treatment with N-(4-hydroxyphenyl)retinamide and ovariectomy.

Bilateral ovariectomy and dietary administration of the retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) are both effective inhibitors of chemical carcinogenesis in the rat mammary gland. The present study was designed to determine whether an enhanced inhibitory effect is obtained with combined ovariectomy and 4-HPR administration, compared to either treatment alone. In separate experiments, 50-day-old virgin female Sprague-Dawley rats received either a single i.v. injection of 50 mg N-methyl-N-nitrosourea per kg body weight or a single intragastric dose of 20 mg 7,12-dimethylbenz(a)anthracene. The experimental design was the same in both the N-methyl-N-nitrosourea and 7,12-dimethylbenz(a)anthracene experiments: Group 1, 25 intact rats, placebo diet; Group 2, 25 intact rats, supplement of 782 mg 4-HPR per kg diet; Group 3, 50 ovariectomized rats, placebo diet; Group 4, 50 ovariectomized rats, supplement of 782 mg 4-HPR per kg diet. Feeding of the 4-HPR supplement was begun 7 days after carcinogen administration; ovariectomy was performed 7 days post-7,12-dimethylbenz(a)anthracene or 14 days post-N-methyl-N-nitrosourea. In both experiments, combined ovariectomy plus 4-HPR was significantly more active in suppressing mammary cancer induction than was either manipulation alone. 4-HPR was a more effective inhibitor of carcinogenesis in ovariectomized rats than in intact animals. These data indicate that 4-HPR is highly effective in inhibiting ovarian hormone-independent cancers and suggest that retinoid inhibition of mammary carcinogenesis does not involve an influence on ovarian hormone action.

9,10-Dimethyl-1,2-benzanthracene↗
PubMedDate not supplied

The toxicity and neuropathology of dimethylethyltin and methyldiethyltin in rats.

Triethyltin causes an increase in brain water with vacuolation of myelin sheaths, whereas trimethyltin is selectively damaging to neurons, especially of the hippocampal formations, causing chromatolysis, accumulation of cytoplasmic dense bodies and often cell death. The effects on rats of the analogues, dimethylethyltin and methyldiethyltin (oral LD50 14 mg/kg and 7.5-10.0 mg/kg respectively) are now reported. The dimethylethyl compound produces functional changes resembling those caused by trimethyltin, while the methyldiethyl compound causes responses similar to those produced by triethyltin. Structurally, however, the dimethylethyl compound, while producing marked nerve cell changes of the trimethyltin type also causes moderate vacuolation of myelin sheaths. By contrast, methyldiethyltin causes marked vacuolation of myelin sheaths of the triethyltin type and relatively minor neuronal changes of the trimethyltin type. These findings are discussed in terms of the structure-activity relationships of trialkyltin compounds.

Animals↗
PubMedDate not supplied

Increased efficacy and tolerability with losartan plus hydrochlorothiazide in patients with uncontrolled hypertension and therapy-related symptoms receiving two monotherapies.

The efficacy and tolerability of losartan 100 mg/hydrochlorothiazide (HCTZ) 25 mg and enalapril 10 mg/HCTZ 25 mg were compared in a double-blind, randomized trial in hypertensive patients inadequately controlled and experiencing side effects on prior therapy. Patients with moderate or severe hypertension, currently treated with at least two single-agent drugs (excluding angiotensin-converting enzyme inhibitors), with a sitting diastolic blood pressure (DBP) above 90 mm Hg, and at least one undesirable drug-related symptom were randomized to once-daily treatment with one of the combinations for 12 weeks. Losartan/HCTZ lowered sitting DBP from the prior therapy baseline by 13.7 mm Hg and sitting systolic blood pressure 19.3 mm Hg; similar reductions occurred with enalapril/HCTZ. Trough sitting DBP was reduced to normal levels (< 90 mm Hg) in 63% of patients switched to the losartan combination and in 58% of those treated with the enalapril combination. Each combination was associated with improved tolerability compared with prior therapy, although fewer patients reported each of 24 undesirable symptoms after 12 weeks of losartan/HCTZ. The improvement from prior therapy in the occurrence of cough was significantly greater with losartan/HCTZ (P = .005). Enalapril/HCTZ, but not losartan/HCTZ, increased serum uric acid levels at week 12. In conclusion, the combination of losartan 100 mg/HCTZ 25 mg offers a beneficial therapeutic option for patients with a history of moderate to severe hypertension whose blood pressure is not adequately controlled or who exhibit side effects while on two or more single-agent antihypertensive drugs. In this population, the switch from prior antihypertensive therapies to once daily losartan 100 mg/HCTZ 25 mg improves blood pressure control and reduces side effects.

Analysis of Variance↗