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Biomedical subjects

S L Davis

Publications and source records attributed to S L Davis.

At least 55 records · Page 3Linked to original sources
PubMed1992

Arterial blood gases and brain oxygen availability following infusion of intratracheal fluorocarbon neat liquids.

Eight adult New Zealand Swiss rabbits (3-5 kg) having previously implanted chronic bilateral platinum electrodes in the visual cerebral cortex and subcutaneous silver reference electrodes were tranquilized and monitored in multiple 2-3 hour sessions using voltammetric techniques. Six of these were given intratracheal neat liquid fluorocarbons ranging in boiling point from 132 degrees C to 215 degrees C at doses of 2 or 4cc/kg. Each animal received only one fluorocarbon liquid. Two additional rabbits were match-studied as controls. Half of the rabbits have survived more than five months. Both controls and two experimental rabbits were sacrificed after more than seven months due to gastric hairballs. The period of daytime monitoring sessions, when cathodic brain oxygen currents (aO2), arterial blood gases and pH were obtained, was between 34 and 263 days. In some animals the arterial pCO2 was increased during the first week but the pO2 and pH remained nearly normal in all eight animals throughout. The two best fluorocarbons for liquid breathing on the basis of this limited but intensive work are F-methyldecalin and F-5,6H-dec-5-ene (F44E).

Animals↗
PubMed1992

Response of the rabbit lung as a criterion of safety for fluorocarbon breathing and blood substitutes.

From the first liquid breathing experiments until now, the lung, not surprisingly, has played a central role in the evolution of fluorocarbon blood substitutes. The first breathable fluorocarbon, a mixture of F-alkylfurans(FC75), bp 102 degrees C, while a poor solvent for the lung's lining and a good solvent for oxygen and carbon dioxide, proved to cause a characteristic gas/vapor microbubble embolism following intravenous administration as an emulsion. Higher boiling fluorocarbons, e.g. F-tributylamine (FC47), bp 174 degrees C, do not produce such gas-vapor emboli. However, intermediate boiling compounds such as F-decalin (PP5), bp 141 degrees C, produce lungs which, although they certainly appear not to contain microbubble emboli, do not collapse when the thorax is opened. Such hyperinflated non-collapsible lungs (HNCL) occur in the rabbit after the intravenous infusion of F-decalin emulsions as well as after the intratracheal infusion of F-decalin neat liquid. F-decalin induced HNCL retain their appearance and low specific gravity for many weeks, gradually returning toward normal after many months. F-methyl decalin, bp 165 degrees C, does not cause HNCL after intravascular or intratracheal administration. Fluorocarbons having boiling points between 140 degrees C and 165 degrees C are being tested in order to find a perfluorinate with the highest transpiration rate, and hence vapor pressure, compatible with an acceptable body dwell time. We have given fluorocarbons intratracheally to 75, intravenously to 221 and both intratracheally and intravenously to 8 rabbits. Free radical trapping agents, antineutrophil, antiinflammatory and other drugs have been administered without appreciable decrease of HNCL. Fluorocarbon critical solution temperature, lipid solubility, emulsifiability, and other physicochemical properties may mediate the pulmonary effect. One method of preventing and treating low dose F-decalin-induced HNCL in rabbits is described.

Animals↗
PubMed1992

Male breast carcinoma: clinical experience in a suburban community.

Male breast cancer is difficult to study because it occurs infrequently, accounting for 1% of all breast carcinoma. Breast cancer occurs 10 years later in men than in women, and its presentation parallels that in women. The authors retrospectively review 13 cases of male breast cancer occurring over a 20-year period in four community hospitals. Treatment methods paralleled those used for female cancer patients. Surgery, primarily radical mastectomy, was performed in all patients. In the eight patients in whom hormone receptor assays were obtained, all tests were positive for estrogen receptors, progesterone receptors, or both. Metastases were diagnosed in five patients during follow-up. The longest disease-free survival has been 10 years. Similarities and differences regarding male and female breast cancer are discussed as are the diagnosis and management of men with this disease.

Aged↗
PubMed1990

A nationwide evaluation of the academic performance of male and female optometry students.

The number of women entering optometry has risen steadily over the last two decades. The present study is a nationwide evaluation of the academic performance of male and female optometry students graduating in 1986. The data presented was obtained through the cooperation of 12 of the 15 U.S. schools and colleges of optometry. Factors which were investigated include preoptometry grade point average (GPA), GPA at the end of the first two years of optometry school, GPA for the second two years of optometry (calculated independently from the first two years GPA), Optometry College Admission Test (OCAT) scores, class rank at graduation and awards received at graduation. This analysis revealed very little difference in overall academic performance between male and female optometry students.

Achievement↗
PubMed1987

Developmental outcome following posthemorrhagic hydrocephalus in preterm infants. Comparison of twins discordant for hydrocephalus.

The mental development and neurologic outcome of four sets of preterm twins, in whom one infant within each pair developed posthemorrhagic hydrocephalus during the neonatal period, were assessed. Each hydrocephalic infant presented with signs of increased intracranial pressure and required placement of a ventriculoperitoneal shunt. Three of the four hydrocephalic infants required revision or replacement of the shunt during the first year. The four nonhydrocephalic infants had normal neurologic outcomes. All four hydrocephalic infants had some neurologic abnormalities on follow-up examination. Neurologic abnormalities were transient in one infant and persistent in three others, each of whom showed evidence of mild right hemiparesis. Within each twin pair, developmental rates and mental test scores were strikingly similar throughout infancy and early childhood. Two of the twin pairs have undergone psychological assessments at 8 and 11 years of age. Relatively lower IQ scores were obtained for the hydrocephalic child in each twin pair at these ages.

Cerebral Hemorrhage↗
PubMed1987

Relationship of growth hormone, prolactin and thyrotropin secretion to individual and progeny performance of Hereford bulls.

Six Hereford bulls from a line selected with an index of body weight and muscling score were compared with six bulls from a control line to determine if increased growth in the selected line was associated with changes in plasma levels of growth hormone (GH), prolactin (PRL) and (or) thyrotropin (TSH). The predictive value of sire hormone data for growth rate of progeny was also evaluated. Bulls of the index line were heavier at birth (P less than .02) and had higher postweaning daily gains (P less than .01) than bulls of the control line. Blood samples were collected from bulls (ages 2 and 3 yr) at 15-min intervals for 8 h. Overall plasma GH concentrations were higher (P less than .03) in the index bulls than those in the control line. All characteristics of PRL secretion examined tended to be higher in the index bulls, but only mean overall and baseline differences approached significance (P less than .10). There were no significant differences in measures of TSH secretion between lines. Sire differences in hormone characteristics accounted for significant amounts of variation in birth weight and postweaning gain of progeny, but not in gain to weaning. Also, when considered jointly, hormone characteristics generally added significantly to predictions that used sire growth rate alone. The results suggest that serum hormone characteristics in parents may provide additional predictors of growth rates of progeny.

Animals↗
PubMed1986

Changes in the auditory brainstem response associated with intravenous infusion of unconjugated bilirubin into infant rhesus monkeys.

The auditory brainstem response (ABR) was monitored in nine infant rhesus monkeys during the intravenous infusion of 50-168 mg/kg of unconjugated bilirubin. Sulfisoxazole (200 mg/kg) was sometimes given near the end of or just before the bilirubin infusion if no obvious ABR change had yet occurred. Five of the animals were term gestation, four were preterm, and they ranged from 1 to 40 days of age at the time of study. The three oldest term animals, studied at 20, 35 and 40 days of age, respectively, showed variable changes in the ABR waves during bilirubin infusion and these changes were not altered further by sulfisoxazole administration. The other two term infants, studied at 1 and 6 days of age, respectively, showed sulfisoxazole enhanced ABR wave latency increase and amplitude reduction followed by loss of the ABR. Both of these animals became apneic following ABR loss and eventually died. The ABR reappeared in one animal prior to death. Minimal gross and microscopic changes were present in the brain of the 6-day-old animal at autopsy. The four preterm animals all had a progressive wave amplitude decrease followed by loss of the ABR with bilirubin alone. These preterm animals were sacrificed shortly after the ABR loss with only one showing yellow staining of the basal ganglia at autopsy. The infant rhesus monkey may be a useful paradigm for bilirubin-induced ototoxicity as manifested by potentially reversible ABR changes. The changes are dependent on gestational and chronological age of the animal and appear to occur in the peripheral eighth nerve or cochlea as well as in brainstem pathways.

Animals↗
PubMed1986

Satellite cell proliferation in response to pituitary hormones.

Proliferation of rat skeletal muscle satellite cells was studied in vitro, and their ability to respond to a variety of protein hormones was examined, including: growth hormone, prolactin, luteinizing hormone, thyrotropin and fibroblast growth factor. All experiments were conducted in serum-free medium to avoid complicating interactions with serum constituents such as other hormones or binding proteins. Dose-response curves were constructed for each protein and encompassed the physiological range plus concentrations two to three orders of magnitude greater than the physiological range. Of the proteins examined, the only one shown to have the ability to directly stimulate satellite cell proliferation was fibroblast growth factor. None of the anterior pituitary protein hormones had the ability to interact directly with satellite cells to stimulate proliferation in vitro. Therefore, satellite cells seem to be selective in their response to protein hormones, and the classes identified thus far are hormones in the insulin-like growth factor family and fibroblast growth factor. These two classes of protein hormones are quite different and would not be expected to act through a common pathway. Consequently, we have proposed a dual regulatory system that may allow for local as well as systemic stimulation of satellite cells.

Animals↗
PubMed1986

Adjuvant chemotherapy of axillary node-negative carcinoma of the breast using doxorubicin and cyclophosphamide.

One hundred fifty-six women with axillary node-negative breast cancer and primary tumors less than or equal to 5 cm in diameter (T1N0 or T2N0) were treated with a brief course of postoperative adjuvant chemotherapy consisting of doxorubicin and cyclophosphamide. Treatment was well tolerated and toxicity was minimal. With a median follow-up time of 58 months, there has been 1 relapse among 58 patients with T1 primary lesions and 15 relapses among 98 patients with T2 primary tumors. When compared with a matched historical control group receiving surgery alone, significant improvement was apparent in disease-free survival among the patients who received adjuvant chemotherapy. Prospective controlled trials are needed if we are to confirm this favorable experience with adjuvant chemotherapy in the treatment of women with node-negative breast cancer.

Adult↗
PubMed1985

Brain-stem auditory evoked potentials in children with brain-stem or cerebellar dysfunction.

Brain-stem auditory evoked potentials (BAEPs) were recorded in 23 children who had signs of brain-stem or cerebellar dysfunction. In patients with brain-stem gliomas, BAEPs were abnormal in all except one, in whom involvement of the brain-stem auditory pathway was limited to the midbrain tectum. The BAEPs were normal in neuronal ceroid lipofuscinosis, but abnormal bilaterally in inheritable leukoencephalopathies. All patients with Leigh's encephalopathy had BAEP abnormalities; in two, abnormalities occurred before the appearance of lesions on computed tomographic scan. Patients with Friedreich's ataxia and giant axonal dystrophy had abnormal BAEPs, but the test was normal in a child with similar neurologic findings with vitamin E deficiency. Patients with diffuse metabolic encephalopathies had variable findings. Thus, BAEP abnormalities are nonspecific for various disease processes but are frequently seen in neoplastic and neurodegenerative diseases, with primary white matter or extensive brain-stem involvement.

Adolescent↗
PubMed1985

Increased serum prolactin levels mediate the suppressive effects of ectopic pituitary grafts on copulatory behavior in male rats.

To determine if deficits in sexual activity observed in pituitary-grafted male rats are due to elevated serum prolactin (PRL) levels found in these animals, the effects of whole pituitary grafts, pars distalis grafts, and ovine (o) PRL treatment on male copulatory behavior were compared. Adult sexually experienced CDF male rats were given four whole pituitary grafts, four pars distalis grafts, or were sham operated. Both groups of grafted animals exhibited suppressed copulatory behavior patterns when tested 18 days after pituitary transplantation. Animals given whole pituitary grafts had significantly longer latencies to mount (P less than 0.05) and to intromit (P less than 0.01) than did the sham-operated controls, while the animals given anterior pituitary grafts differed from the sham-operated controls in latencies to mount (P less than 0.05) and to intromit (P less than 0.01), as well as in the number of intromissions (P less than 0.05). Prolactin-injected animals had significantly reduced intromission rates (P less than 0.01) and significantly increased latencies to mount (P less than 0.05) and to intromit (P less than 0.01) when compared to vehicle-injected controls. Furthermore, the time course of behavioral suppression was similar in oPRL-treated animals to that observed in pars distalis-grafted males, with both groups showing the onset of deficits in sexual activity within 8 to 9 days from the induction of the hyperprolactinemic state. The similarity in pattern and time to onset of behavioral suppression in pituitary-grafted and oPRL-treated animals suggests that behavioral deficits observed in animals with pituitary grafts result from chronic elevation of serum PRL levels.

Animals↗
PubMed1985

Ontogeny of growth hormone, prolactin, luteinizing hormone, and testosterone secretory patterns in the ram.

The ontogenetic changes that occur in secretory patterns of growth hormone (GH), prolactin (Prl), luteinizing hormone (LH), and testosterone (T) in rams maintained in constant photoperiod were examined. Nine ram lambs were moved to individual pens in a controlled environment (12L: 12D cycle; 18-24 degrees C temperature) at 66 days of age. Blood samples were collected via indwelling cannulae at 15-min intervals for an 8-h period at 80, 136, 192, 248, and 304 days of age. Plasma concentrations of GH, Prl, LH, and T were quantitated and parameters of the secretory patterns determined. Mean concentration of GH tended to decline with age, probably because the amplitude of secretory peaks was significantly reduced with age. There were no age-associated changes in basal concentration of GH or incidence of GH peaks. There was an increase in Prl secretion (as estimated by mean concentration) at 136 and after 248 days of age. Significant age-associated changes occurred in all parameters of LH and T secretion. At the younger ages, testosterone concentrations were low and LH concentrations were elevated. At the older ages the relationship was reversed, with LH low and testosterone high. There were no significant correlations between frequency and magnitude of LH and T peaks. The significant correlations present among parameters of LH and T secretion were between basal concentration of LH and overall mean concentration and basal concentration of T. These results suggest that LH may not be the sole tropic stimulator of acute T secretion.

Age Factors↗
PubMed1985

Partial purification and characterization of somatomedin from sheep serum.

A rapid, high yield preparative technique for the isolation of sheep somatomedin is reported. Purification of biologically active somatomedin from the 60% ammonium sulfate precipitate of sheep serum was accomplished using three gentle fractionation steps. Biological activity during purification was monitored using the rat adipocyte nonsuppressible insulin-like activity (NSILA) assay. A stepwise pH elution (pH 2.85, 3.5, 4.5, and 6.0) from SP-Sephadex resulted in the elimination of more than 99% of the serum proteins and a 500-fold enhancement of biological activity. The active fraction eluted at pH 6.0 and was further fractionated on Sephadex G-50 (fine) chromatography at pH 2.85. This resulted in about a 10,000-fold enhancement of activity over serum activity. The most active fractions from Sephadex chromatography were further separated on reverse phase HPLC in 0.1% trifluoroacetic acid using a linear gradient of 24-60% acetonitrile. The biological activity of the final preparation was enhanced 61,000- to 182,000-fold over that of serum (mean, 93,000-fold) when assayed in the NSILA assay. Protein yield was estimated to be 467 micrograms/liter serum. In addition to the NSILA activity, the final preparation demonstrated dose-dependent sulfation factor activity in the embryonic chick pelvic leaflet bioassay. Sheep somatomedin was active at physiological levels in both bioassays. Analysis of the somatomedin preparation by sodium dodecyl sulfate-electrophoresis at pH 8.8 showed that it was homogeneous by this criterion. The activity eluted from Sephadex G-50 was estimated to have a molecular size of 6900. Two Coomassie blue-stained bands were present in the final sheep somatomedin preparation after polyacrylamide gel electrophoresis at pH 3.2. Our purification process is a rapid, high yield technique which yields a polypeptide fraction enriched in NSILA and somatomedin-like activity. The molecular size and biological activity in the NSILA and sulfation factor assays suggest that our sheep NSILA is analogous to somatomedins purified from other species of animals.

Animals↗
PubMed1985

Clinical correlations of serial somatosensory evoked potentials in multiple sclerosis.

Serial median nerve somatosensory evoked potentials (SEPs) were recorded in 12 patients with definite MS. On the initial tests, there was no clear association between the severity of clinical disease activity and SEP findings. The cervical response was most frequently affected and, when present, was often abnormal in configuration, suggesting absence or delay in the far field P14 component with preservation of cervical N11 and N13 components. Clinical motor and sensory findings in the corresponding limb frequently correlated with abnormalities of the cervical response. When new motor and sensory findings developed in the arms during the study, the SEP deteriorated in some patients but improved in others. Most SEP changes were not accompanied by clinical changes. Overall disability sometimes increased during the study despite improvements in the SEP.

Adult↗
PubMed1985

Temporal patterns of growth hormone in blood and seminal plasma of mature dairy bulls.

This study was conducted to determine if growth hormone (GH) concentration in bovine seminal plasma would be proportional to but less variable than blood plasma GH. The relationship between GH in blood and seminal plasma was also examined critically. Blood samples were collected at 15-min intervals for 5.75 h, while semen was collected at 30-min intervals over the same time period. Average seminal plasma GH concentrations were 3.2 times higher (P less than .05) than blood plasma GH concentrations (40.4 +/- 15.8 ng/ml vs 12.6 +/- 1.2 ng/ml, respectively). The within animal correlation between blood and seminal plasma was consistently low and nonsignificant (P greater than .05). Overall blood plasma GH and seminal plasma GH concentrations were weakly correlated (r = .418; P greater than .05) among bulls. A predictable relationship between blood and seminal plasma GH concentration does not exist under the conditions of this study.

Analysis of Variance↗
PubMed1984

CGS8216 noncompetitively antagonizes the discriminative effects of diazepam in rats.

The benzodiazepine antagonist properties of CGS8216 were evaluated in rats trained to discriminate between saline and 1.0 mg/kg of diazepam in a two-choice, stimulus-shock termination procedure. CGS8216 (0.3 to 100 mg/kg) administered alone, either s.c., p.o. or i.p., occasioned only saline-appropriate responding. When administered concomitantly with a constant 1.0 mg/kg dose of diazepam, CGS8216 produced dose-related decreases in drug-appropriate responding. CGS8216 was most potent by the i.p. route, and approximately tenfold less potent by the oral route. CGS8216 was dermatotoxic after s.c. administration. CGS8216 i.p. had a long duration of action. A dose of 30 mg/kg completely antagonized the discriminative effects of the 1.0 mg/kg training dose of diazepam when the antagonist was administered 8 hr before the start of the test session. In order to determine the type of antagonism by CGS8216, the dose-effect curve for diazepam was redetermined in the presence of varying doses of CGS8216 (0.3 to 3.0 mg/kg, i.p.). CGS8216 produced a dose-related rightward shift in the diazepam dose-effect curve, but also decreased the slope and appeared to decrease the maximal effect. These results are consistent with the interpretation that CGS8216 antagonizes diazepam in a noncompetitive manner. It may do so because either it interacts with a subpopulation of benzodiazepine receptors, it functions as a pseudo-irreversible antagonist due to its high affinity, or because it is an antagonist with agonist properties.

Animals↗