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Biomedical subjects

M R Davis

Publications and source records attributed to M R Davis.

At least 55 records · Page 3Linked to original sources
PubMed1991

[Prevalence of cardiovascular risk factors in Temuco City].

A random sample of 200 males from 25 to 64 years of age was surveyed for cardiovascular risk factors in Temuco, a city in Southern Chile. Blood pressure was 130 +/- 18/85 +/- 10 mmHg and total cholesterol was 193 +/- 50 mg/dl. 33% were smokers (mean of 8.2 cigarettes per day) and 34% were ex smokers. Prevalence of hypertension was 6.5% from 35 to 44 years of age, 15% from 45 to 54 and 31.9% from 55 to 64 (mean 15%). Cholesterol levels above 240 mg/dl were found in 11.8, 18.3 and 19.1%, respectively (mean 15.5%). Half of the hypertensive subjects were not aware of their high blood pressure and only 16.6% received therapy.

Adult↗
PubMed1990

Social control of neuronal soma size.

Factors responsible for sexual maturation differ significantly among vertebrate species. In many, age is most important, whereas in others seasonal or social cues play a central role. Here we report that maturation in the African cichlid fish Haplochromis burtoni is socially controlled, and that this control includes regulation of soma growth in a population of preoptic neurons immunoreactive to gonadotropin-releasing hormone (irGnRH). Males reared in aquaria among fish of the same age mature sexually in about 3 months, whereas males reared in the presence of older, more aggressive conspecifics remain immature even at 5 months of age. Immature males display hypogonadism and have conspicuously undersized preoptic irGnRH neurons in comparison to those of mature siblings of the same age. This variable maturation rate increases the likelihood that individual males will survive to an age when they can successfully reproduce.

Aggression↗
PubMed1989

Indomethacin augments lymphokine-activated killer cell generation by patients with malignant mesothelioma.

Human malignant mesothelioma (MM) cells are resistant to natural killer (NK) cell lysis but susceptible to lysis by lymphokine-activated killer (LAK) cells from control individuals. The present study was performed to determine the capacity of patients with MM (n = 22) and individuals occupationally exposed to asbestos (the major population at risk of developing this disease, n = 52) to generate LAK cells capable of effectively lysing human mesothelioma cells. Compared to controls (n = 20), both patient groups demonstrated significantly depressed LAK cell activity against mesothelioma tumor cell targets (55 +/- 3% lysis by controls vs 34 +/- 3% lysis by patients with MM, P less than 0.005; and 45 +/- 3% lysis by asbestos-exposed individuals, P less than 0.025). Addition of 10 micrograms/ml indomethacin during LAK cell generation restored normal LAK cell activity for patients with MM (52 +/- 6% lysis of cultured human MM cells, P = NS compared to controls), suggesting that the defective cytolytic cell function observed in some patients with MM is a result of prostaglandin-induced immunosuppression. The ability of indomethacin to restore suppressed LAK cell activity in patients with MM suggests that the concomitant use of this agent in ex vivo LAK cell generation and in patients undergoing interleukin/LAK cell therapy may be beneficial.

Asbestos↗
PubMed1989

Use of aerial color infrared photography as a survey technique for Psorophora columbiae oviposition habitats in Texas ricelands.

This study investigated the possibility of using aerial color infrared (CIR) photography as a survey technique for egg populations of Psorophora columbiae within a riceland agroecosystem. To accomplish this, eight photographic missions were flown over study fields during a variety of seasons and at various altitudes. Assessment of resulting photographic data indicates features reported in the literature as being attractive for oviposition by Ps. columbiae (i.e., rice field levees, tire tracks, ditches and low areas) can be readily detected on aerial CIR photographs. Features associated with Ps. columbiae oviposition sites were easily visible on photographs at scales as small as 1:42,000.

Aircraft↗
PubMed1988

Acute androgen receptor blockade increases luteinizing hormone secretory activity in men.

To investigate the nature of androgen feedback mechanisms in normal men, we studied the hypothalamo-pituitary responses to administration of a potent, highly selective nonsteroidal androgen receptor antagonist, flutamide HCl (1 g/day, orally, for 3 days). The impact of reversible blockade of endogenous androgen action was assessed in 11 normal men by analyzing quantitative alterations in specific pulsatile properties of LH secretion basally (hypothalamic regulation) and after 2 (n = 6) consecutive iv pulses of exogenous GnRH (pituitary responsiveness). Androgen blockade resulted in significant increases in 1) 12-h mean and integrated serum immunoactive LH concentrations (P = 0.01), 2) LH pulse frequency (P = 0.01), and 3) mean interpulse (valley) serum LH concentrations (P = 0.02) and maximal LH peak heights (P = 0.01). Additionally, there were significant decreases in LH interpulse interval (P = 0.02), LH peak duration (P = 0.02), and interpeak valley duration (P = 0.02). The augmented LH pulsatility reflected enhanced hypothalamic activity, since 1) pituitary secretory responses to exogenous GnRH pulses were not altered, and 2) multiple parameter deconvolution disclosed an increased number of computer-resolved LH secretory bursts generated per 12 h, with no changes in the apparent half-duration of LH secretory impulses or the calculated mass of LH released per secretory burst. We conclude that endogenous androgens act selectively to modulate the number of spontaneous LH secretory bursts in man.

Adult↗
PubMed1987

Screening for postmenopausal osteoporosis.

Postmenopausal osteoporosis is an area of increasing concern to the gynecologist. Fractures will develop in approximately 15% to 25% of women in their later years and preventive therapy is best aimed specifically at this group. Predicting who will be the ones to sustain fracture is a difficult and imprecise clinical task. The clinical, laboratory, and radiologic methods available for this purpose are reviewed. A rational approach to this problem in today's setting is outlined.

Absorptiometry, Photon↗
PubMed1987

Sustained inhibitory actions of a potent antagonist of gonadotropin-releasing hormone in postmenopausal women.

The inhibitory time course and dose-related characteristics of a new potent GnRH antagonist peptide, [N-acetyl-D-pCl-Phe1,2-D-Trp3-D-Lys6-D-Ala10]GnRH, on gonadotropin secretion were studied in nine postmenopausal women. Effective suppression of gonadotropin secretion was correlated with increased circulating concentrations of immunoassayable GnRH antagonist. Inhibition of gonadotropin secretion was achieved by a parenteral dose of 300 micrograms/kg GnRH antagonist. This dose reduced plasma bioactive LH concentrations by 49-59%, immunoactive LH by 41-46%, and immunoactive FSH by 25-40%. Blockade of gonadotropin secretion was sustained for 10-28 h after a single injection of the synthetic decapeptide. This prolonged action was associated with significant plasma protein binding of the GnRH antagonist and mean plasma half-times of disappearance of 1.5 and 21 h for the fast and slow components, respectively. In summary, we have described the biological actions of a potent GnRH antagonist that binds avidly to serum proteins, has a prolonged plasma residence time, and exerts sustained inhibitory effects on bio- and immunoactive LH release in man. The extended duration of action of this compound may reflect in part its significant binding to circulating plasma proteins.

Aged↗
PubMed1986

Peripartum cardiomyopathy: two case reports and a review.

Peripartum cardiomyopathy is a myocardial disease of a dilatative (congestive) nature which typically presents in the last month of pregnancy or within the first 5 postpartum months. In the first case described, heart failure was noted prior to delivery, and complete recovery was achieved with early and aggressive management. Cardiomyopathy developed postpartum in the second case, with a fatal outcome. Early diagnosis and prompt treatment are of paramount importance. Mortality is still high. Recent pathologic findings, methods of diagnosis and theories on etiology are discussed.

Adult↗
PubMed1986

Recurrent ectopic pregnancy after tubal sterilization.

Tubal sterilization is a known etiologic factor for ectopic pregnancy. A case is presented in which a patient had two subsequent ectopic pregnancies after sterilization. Such an occurrence has important clinical implications.

Adult↗
PubMed1984

Pneumomediastinum in pregnancy: two case reports and a review of the literature, pathophysiology, and management.

Pneumomediastinum, free air trapped in the mediastinal connective tissue, is a rare complication of pregnancy, occurring most frequently in the second stage of labor. Symptoms are often not noted until after delivery. Occurrence before and in the first stage of labor, as seen in the two cases reported here, is more uncommon. One case history is the first report of the coexistence of pneumomediastinum and pneumothorax in pregnancy. The prognosis for spontaneous pneumomediastinum in pregnancy is favorable. Pathophysiologic mechanisms, diagnosis, and management are discussed, and a review of the literature is presented.

Adult↗
PubMed1983

Hyperplasia in the spinal sensory system of the frog. I. Plasticity in the most caudal dorsal root ganglion.

Increases in the amount of periphery available for innervation have been achieved by the unilateral removal of hindlimb dorsal root ganglion (DRGs) in Rana pipiens, a procedure which generally results in a compensatory cell number increase (hyperplasia) in the DRGs which remain. We have found that the hyperplastic response is extremely variable, and we have investigated various factors which might control its production. Our findings indicate, however, that the pattern of DRGs removed, the animal's age at the time of removal, and the survival period are not strictly related to the production of hyperplasia in hindlimb DRGs. Special emphasis has been placed on DRG 10, the caudalmost DRG which normally innervates the cloaca and sends a small projection to the hindlimb. This DRG displayed dramatic cell number increases of up to 564%. In addition, several unique features of the hyperplastic response have been observed in DRG 10. This DRG showed increases in cell number on both the operated and the unoperated sides. It showed hyperplasias in animals subjected to ganglionectomy past metamorphosis as well as during larval development. Finally the production of DRG 10 hyperplasias exclusively occurred in male pre- and postmetamorphic animals. To account for these distinctive features of DRG 10 hyperplasia, baseline studies of the normal course of proliferation and cell death in DRG 10 were undertaken. They reveal no fundamental developmental differences between DRG 10 and other hindlimb DRGs. Other mechanisms responsible for these unusual features of developmental plasticity in DRG 10 are discussed.

Animals↗
PubMed1983

Hyperplasia in the spinal sensory system of the frog. II. Central and peripheral connectivity patterns.

Central and peripheral connectivity patterns of hyperplastic dorsal root ganglia (DRGs) in Rana pipiens are examined in order to determine the relative roles of peripheral and central contacts in the production of DRG hyperplasias. The hyperplasias are produced in the intact hindlimb DRGs after the removal in tadpoles and young postmetamorphic frogs of neighboring DRGs (Davis and Constantine-Paton, '83). The peripheral target zones of the hyperplastic DRGs, determined by physiological recordings of sensory receptive fields, are found to undergo a significant degree of expansion relative to controls. Peripheral expansion is most pronounced in caudalmost DRG 10, and this effect occurs in experimental animals operated during larval and postmetamorphic stages. Further, anatomical labelling of peripheral sensory fibers coursing to the hindlimb reveals that the hyperplastic DRG 10 actually contains additional fibers projecting to the denervated regions. The central projection of the hyperplastic DRG 10 does not show corresponding increases in longitudinal arborization after the application of horseradish peroxidase to the appropriate dorsal roots. These observations are made on some of the same experimental animals in which peripheral fields are shown to have vastly expanded. We conclude that the peripheral processes of the hyperplastic DRGs are less rigidly specified than the central terminations, and that it is the periphery which plays the primary role in controlling the cell numbers increases. A second aim of this investigation is to identify whether sexually dimorphic connectivity patterns in normal frogs explain the production of DRG 10 hyperplasias exclusively in male experimental animals (Davis and Constantine-Paton, '83). We apply the same techniques used in our connectivity studies of hyperplastic DRGs to the investigation of connectivity patterns of DRG 10s in normal males and females. No sex-dependent differences in peripheral and central connectivity are found. Thus, since normal male and female frogs possess an equivalent amount of target space for DRG 10, the unique production of hyperplasias in male experimental animals cannot be explained solely on the basis of connectivity. We speculate on what other factors may be involved.

Animals↗
PubMed1983

A three step method of the determination of fixation status and retinal correspondence.

In examination and treatment of patients with strabismus one often encounters abnormal sensory adaptations such as eccentric fixation and anomalous retinal correspondence. Prognosis and treatment of strabismus are dependent on the presence or absence of these conditions. When eccentric fixation is present it becomes difficult to interpret the results of many tests used to determine retinal correspondence. This determination is further complicated when the patient is unable to give accurate responses. A technique utilizing visuoscopy and an afterimage has been performed on somewhat less cooperative patients. The results compare favorably to amblyoscopic measurements of the angle of anomaly.

Afterimage↗
PubMed1982

Anchorage-independent growth-conferring factor production by rat mammary tumor cells.

Conditioned medium from cultures of 7,12-dimethylbenz(a)anthracene-induced rat mammary tumor cells contain factors that resemble sarcoma growth factor and other transforming growth factors in biological activity but differ in their physical properties. The mammary tumor factors (MTF) are acid stable and heat and protease sensitive. They inhibit the binding of epidermal growth factor, but not insulin, to mouse embryonal carcinoma cells. MTF confers upon normal rat kidney and BALB/c-3T3 cells the ability to grow in soft agar. This effect is enhanced synergistically by high concentrations of fetal calf serum but not by epidermal growth factor. Anchorage-independent growth promotion, however, is not seen with normal mammary epithelial cells, although MTF is mitogenic for these cells as well as normal rat kidney cells, BALB/c-3T3 cells, and chick embryo fibroblasts in monolayer culture, MTF is not mitogenic for primary cultures of the tumor cells from which the factors are derived. Two major molecular weight species of MTF, eluting at Mr 6,000 and 65,000 to 70,000 on Bio-Gel P-100 columns, are present in acid-ethanol extracts of 7,12-dimethylbenz(a)anthracene- and nitrosomethylurea-induced rat mammary tumors. Transplantable tumors derived from primary 7,12-dimethylbenz(a)anthracene- or nitrosomethylurea-induced tumors have little or no MTF activity. These results demonstrate that different chemically induced rat mammary tumors contain transforming growth factor-like activities. Furthermore, it is possible that MTF is unnecessary for the maintenance of tumorigenicity, since some tumors contain no detectable MTF.

Animals↗