Search PubMed⌕ Search

Biomedical subjects

D L Davis

Publications and source records attributed to D L Davis.

At least 145 records · Page 8Linked to original sources
PubMed1989

Contribution of the photoperiod to circadian variations in serum cortisol and melatonin in boars.

Four pubertal (25 wk) crossbred boars were used to evaluate the role of the photoperiod in the organization of secretion of cortisol and melatonin throughout a 24-hr period. Boars were exposed to a 16-hr photoperiod in an environmentally controlled room and temperature was kept constant at 22 C. For the first 15 d, the onset of the photophase (light phase) and scotophase (dark phase) was 0200 hr and 1800 hr, respectively (ON2). During the final 15 d, the onset of the photophase and scotophase was advanced by 6 hr (0800 hr and 2400 hr, respectively; ON8). Samples of serum were obtained from catheterized boars at hourly intervals for 24 hr between the 14th to 15th d in both ON2 and ON8 photoperiods. Samples of serum were frozen and later assayed for cortisol and melatonin. The data were normalized to the clock time of onset of the photophase, fit to polynomial equations, and the profiles of cortisol and melatonin in ON2 and ON8 were tested for heterogeneity of regression. A circadian rhythm of cortisol was observed in both ON2 and ON8 and the fitted profiles were parallel, suggesting that the rhythm had shifted with the 6-hr shift in lights-on, lights-off. Generally, higher concentrations were observed during the late subjective evening and scotophase, whereas lower concentrations occurred about 6 to 10 hr after onset of the photophase. Although the profiles of melatonin did not differ in ON2 and ON8, there was no evidence of a nocturnal rise in melatonin in either treatment. It is suggested that some characteristic of the photoperiod organizes the circadian rhythm of cortisol in boars, but melatonin is not secreted in a rhythmic fashion in long photoperiods.

Activity Cycles↗
PubMed1989

Natural anticarcinogens, carcinogens, and changing patterns in cancer: some speculation.

Over the past two decades, marked shifts have occurred in cancer mortality in the United States, the United Kingdom, and the Federal Republic of Germany. Stomach cancer mortality has declined sharply, while brain cancer and multiple myeloma increased nearly twofold for persons ages 75 to 84. Total cancer incidence in the United States, excluding lung cancer, has risen 27% since 1950, adjusted to the aging of the population. The origins of these trends are not known. The diet in the developed countries includes a number of naturally occurring, powerful anticarcinogens and carcinogens. To evaluate the role of these substances in the prevention and causation of human cancer, this paper reviews existing toxicologic and epidemiologic data. These data indicate that naturally occurring substances in food influence cancer initiation, promotion, progression, and demotion by a number of mechanisms, including (1) covalent binding to DNA of naturally occurring anticarcinogenic compounds to block the initiation of carcinogenesis; (2) induction of biotransforming enzymes such as cytochrome P450 and mixed-function oxidase (MFO) which can reduce carcinogenicity; (3) inhibition of tumor promotion by compounds such as retinol, tocopherol, and organosulfates found in garlic, onions, fruits, and vegetables; and (4) physical alteration of carcinogens by food constituents or by food preparation and handling so as to alter carcinogenicity. Systems have been proposed for estimating the relative ranking for humans of individually tested, experimental carcinogens, including some constituents of food. While qualitatively useful, such systems as the HERP Index do not take into account important interactions among naturally occurring and synthetic constituents in foods, nor do they permit examination of the possible role of evolved resistance. Common mixtures in food must be tested for carcinogenicity in human tissue cultures and in long-term rodent bioassays. Such studies need to examine whether the action of synthetic organic carcinogens may be inhibited by potent naturally occurring anticarcinogens.

Carcinogens, Environmental↗
PubMed1989

The variable character of nerves in a Newfoundland fishing village.

The popular complaint nerves has complex and variable meanings in the tiny, coastal fishing village of Grey Rock Harbour, Newfoundland. In everyday life, the term is distinct from mental and physical disease and is instead used to communicate a wide-range of minor psychosomatic complaints as well as emotions, moral standards and world view. The term is so frequently used that in some respects it has become a cliché. Analysis of the variable character of nerves focuses on reconciling the contradictory with the more coherent facets of nerves as a folk idiom. Special attention is paid to the affective character of nerves, especially nerves as "anxiety," which has been hypercognized into a culture-specific and highly elaborated concept of worry.

Anxiety↗
PubMed1989

George Beard and Lydia Pinkham: gender, class, and nerves in late 19th century America.

A historical comparison of the careers of George Beard, medical doctor, and Lydia Pinkham, feminist and patent medicine maker, demonstrates the complex social nature of the experience of nerves among late 19th century women. Special attention is paid to the roles played by changing gender and class ideologies in Pinkham's and Beard's theories of nerves during the period from the 1870s to World War I. A comparison of contemporary anthropological and historical studies of gender and nerves leads to the conclusion that nerves, as a female complaint, takes hold of the popular and medical imagination during periods of dramatic social change which threaten women's traditional family roles and challenge their sense of self-identity.

Attitude to Health↗
PubMed1989

Postponing pregnancy after perinatal death: perspectives on doctor advice.

The Perinatal Loss Interview was administered to 24 mothers who had experienced perinatal loss and were raising a child born subsequent to the loss; mothers were asked about postponing subsequent pregnancy, including what their doctors advised. Mothers were dissatisfied with doctor advice, reporting that the timing of a subsequent pregnancy was a personal decision and many factors influenced their decision. Furthermore, regardless of timing, most mothers reported overprotective and replacement feelings toward the subsequent child. These results imply that physicians may be most effective by educating mothers about advantages and disadvantages of postponing pregnancy so that an informed decision can be made.

Adaptation, Psychological↗
PubMed1989

Utero-placental transfer of octanoic, palmitic and linoleic acids during late gestation in gilts.

The transfer across the swine uterus and placenta of [1-14C]octanoic acid, [9,10(n)-3H]palmitic acid and [1-14C]linoleic acid was studied in five gilts and their fetuses during late gestation following a single bolus injection. Only trace amounts of labeled fatty acids were found in fetal plasma lipid. The highest fetal plasma lipid values were less than 1.2% of the peak maternal values. The concentration of plasma free fatty acids (FFA) and fatty acid profiles in the umbilical artery (FA) and vein (FV) and uterine artery (UA) and vein (UV) were compared. There were no measurable umbilical arterio-venous differences. Concentrations of FFA in FA and FV were about 40% of the UA and UV values (187, 194, 73, 82 microEq/liter for UA, UV, FA and FV, respectively). Fetal plasma contained larger amounts of 14:0, 16:1, 18:1 and 20:4, whereas maternal plasma contained larger amounts of 18:0 and 18:2. There was difference between fetal and maternal plasma for 16:0 and 18:3; the latter was present only in minute amounts. In conclusion, only trace amounts of FFA cross the swine placental tissues during late gestation; therefore, their contribution to fetal energy supply or lipid storage appears limited.

Animals↗
PubMed1989

Pattern and tissue distribution of catechol estrogen forming activity by pig conceptuses during the peri-implantation period.

The profile of catechol estrogen formation by pig conceptuses from d 14 to 20 of pregnancy (d 0 = 1st d of estrus) was studied using a direct product isolation assay for estrogen-2/4-hydroxylase (E-2/4-H). High performance liquid chromatography was coupled to detection of radioactive products in a flowing system to separate the 2- and 4-hydroxyestradiol (2- and 4-OH-E2) formed from estradiol. The major product was 2-OH-E2; its formation increased with increasing amounts of nicotinamide cofactors and exhibited a preference for NADPH. Maximum velocities were 909 and 154 pmol.mg protein-1.30 min-1, and apparent Michaelis constants were 7.14 and 5.12 microns, for 2- and 4-OH-E2 formation, respectively. Homogenates of d-13 conceptuses produced 1,151 +/- 142 pmol.mg protein-1.30 min-1 of 2-OH-E2. Estradiol-2-hydroxylase was affected (P less than .01) by day of pregnancy, and day effects from d 14 to 20 were described by a fourth-order equation (P less than .001). Conceptuses collected on d 14 produced 119 +/- 15.4 pmol of 2-OH-E2.mg protein-1.30 min-1. By d 15, E-2-activity had declined to 15.7 +/- 1.8 pmol.mg protein-1.30 min-1. Formation of 2-OH-E2 increased to 64.2 +/- 15.4 pmol.mg protein-1.30 min-1 on d 17, remained stable through d 19, and was 39.4 +/- 13.8 pmol.mg protein-1. 30 min-1 on d 20. Therefore, E-2/4-H activity appears to be regulated from d 14 to 20 of pregnancy in pigs; it may participate in the establishment of pregnancy.

Animals↗
PubMed1989

Pig blastocyst development in vitro is affected by amino acids.

Pig embryos were removed 5 d after onset of estrus and cultured in modified Krebs-Ringer bicarbonate (mKRB) medium containing bovine serum albumin (BSA; 1 mg/ml). Media in Exp. 1 and 2, but not in Exp. 3, contained 10% heat-inactivated lamb serum (LS). In Exp. 1, embryos were cultured in 1) mKRB + LS or mKRB + LS supplemented with 2) glutamine (2 mM); 3) phenylalanine (.1 mM), methionine (.05 mM) and isoleucine (.2 mM); or 4) phenylalanine, methionine, isoleucine and glutamine. Embryos cultured in media with supplemental phenylalanine, methionine and isoleucine attained larger (P less than .05) volumes during culture and initiated hatching at an increased (P less than .05) frequency compared with embryos cultured without additional amino acids. In contrast, adding glutamine depressed (P less than .05) the maximum volumes observed during culture. In Exp. 2 mKRB + LS was compared with mKRB + LS plus phenylalanine (.1 mM), methionine (.05 mM) and isoleucine (.2 mM); methionine and isoleucine; phenylalanine and isoleucine, or phenylalanine and methionine. Embryos cultured in media supplemented with phenylalanine and methionine attained larger (P less than .05) volumes than embryos cultured in either media without added methionine. Fewer (P less than .05) embryos cultured without methionine initiated hatching (56%) compared with embryos provided methionine (89%). In Exp. 3, we evaluated the addition of glutamine (1 mM) with or without phenylalanine (.1 mM), methionine (.05 mM) and isoleucine (.2 mM) to serum-free mKRB. Adding glutamine alone, but not in combination, increased (P less than .05) blastocyst volumes on d 3 and maximum volume attained during culture compared with embryos cultured in mKRB alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1989

Blood flow distribution with adrenergic and histaminergic antagonists.

Superficial fibular nerve stimulation (SFNS) causes increased pre- and post-capillary resistances as well as increased capillary permeability in the dog hind paw. These responses indicate possible adrenergic and histaminergic interactions. The distribution of blood flow between capillaries and arteriovenous anastomoses (AVA) may depend on the relative effects of these neural inputs. Right hind paws of anesthetized heparinized dogs were vascularly and neurally isolated and perfused with controlled pressure. Blood flow distribution was calculated from the venous recovery of 85Sr-labeled microspheres (15 microns). The mean transit times of 131I-albumin and 85Sr-labeled microspheres were calculated. The effects of adrenergic and histaminergic antagonists with and without SFNS were determined. Phentolamine blocked the entire response to SFNS. Prazosin attenuated increases in total and AVA resistance. Yohimbine prevented increased total resistance, attenuated the AVA resistance increase, and revealed a decrease in capillary circuit resistance. Pyrilamine attenuated total resistance increase while SFNS increased capillary and AVA resistances. Metiamide had no effect on blood flow distribution with SFNS. The increase in AVA resistance with SFNS apparently resulted from a combination of alpha 1 and alpha 2 receptor stimulation but not histaminergic effects.

Animals↗
PubMed1988

Trends in cancer mortality: US white males and females, 1968-83.

From 1968 to 1983, age-specific cancer mortality for all cancers fell by 2.1% annually for men and women aged 35-44 and rose by 1.1% annually for men and 0.3% for women aged 75-84. In the 75-84 age group brain cancer mortality rose by 8% annually and multiple myeloma by 2.75%. Lung cancer mortality rose in men and women aged 45-84 (by 8.2% annually in 65-74 year-old women) but fell by over 3% annually in men aged 35-44. Stomach cancer declined by 4% annually in 75-84 year-olds and about 3% annually in 55-74 year-olds. These trends do not support the hypothesis that recent increases in specific cancers in the elderly chiefly reflect improved diagnosis of cases that would formerly have been misrepresented or miscoded.

Adult↗
PubMed1988

Characteristics of estrogen-2/4-hydroxylase in pig blastocysts: inhibition by steroidal and nonsteroidal agents.

The inhibitory potencies of steroidal and non-steroidal estrogens, catechol-estrogens, methoxyestrogen, haloestrogens, cholesterol and its side-chain-cleaved products, and inhibitors of steroid aromatase against the activity of estradiol-2/4-hydroxylase (E-2/4-H) in pig blastocysts were studied. All tested compounds, except cholesterol and 4-hydroxyandrostenedione, inhibited E-2/4-H in vitro. The fluctuation of E-2/4-H activity in pig blastocysts on different days of pregnancy may be due to the modulation of enzyme activity by steroids in the uterine lumen. Although alpha-naphthoflavone and aminoglutethimide did not affect E-2/4-H activity in vitro, inhibition by CO (95% CO + 5% O2), SKF-525A, piperonyl butoxide, and antibody to cytochrome P-450 reductase provides evidence for the involvement of cytochrome P-450 in E-2/4-H activity in pig blastocysts.

Animals↗
PubMed1988

Medical and popular traditions of nerves.

We question the assumption that the common complaint of nerves in small Newfoundland fishing villages is a legacy of the late 19th century syndrome called weak nerves or neurasthenia, and instead trace the development of a Western medical science of nerves from the early 1700s to the present. Native descriptions of the physical, especially tonic, nature of nerves and of the moral strength needed to fight nerves are correlated with 18th century medical notions. Less resemblance exists between Newfoundland nerves and concepts of neurasthenia in the late 19th century. Moreover, the contemporary descriptions of nerves as a generalized response to stress and anxiety do not account for the culture-specific aspects of nerves which shape Newfoundland regional identity and shed light on their present day sociocultural adaptations.

Anxiety Disorders↗
PubMed1988

Adrenergic and histaminergic neural interactions in dog paws.

The mechanisms underlying the vascular responses of superficial fibular nerve stimulation (SFNS) have not been defined. Right hindpaws of anesthetized heparinized dogs were vascularly and neurally isolated, enclosed in a volume recorder, and perfused with controlled pressure. Vascular volume (VV) (131I-labeled albumin) and rate of tissue volume changes (VT) (plethysmography) were determined. SFNS increased blood flow resistance, reduced capillary filtration coefficient (CFC) and permeability-surface area product (PS) of 86Rb, increased VV, and reduced 131I-albumin recovery. VT increased at the rate of 3.35 +/- 0.45 ml/min. SFNS during terbutaline increased resistance, CFC, PS, and VV were unchanged, 131I-albumin recovery was complete, and VT increased at one-fourth the control rate. Phentolamine and yohimbine blocked all responses to SFNS. Prazosin with SFNS attenuated hemodynamic changes and VT increased to two-thirds of control, decreased VV, albumin, and Rb recovery but not PS and CFC. SFNS during pyrilamine maleate reduced VT increase to two-thirds of control rate and blocked decreases in PS and CFC. Metiamide did not change the SFNS responses, except to reduce vascular volume and VT. The combined histamine H1 and H2 blockers reduced VT increase to one-third of control and attenuated albumin loss, prevented histamine dilation, attenuated vasopressin and norepinephrine but not angiotensin constriction. SFNS stimulation increased precapillary resistance by alpha 1- and alpha 2-receptors and venous resistance by alpha 2-receptors and increased permeability by histamine release from endothelium.

Adrenergic alpha-Antagonists↗
PubMed1988

Multifaceted therapeutic interventions with the violent psychiatric inpatient.

Treatment interventions are increasingly needed for patients with violent behavior, who make up a growing proportion of the population in public mental hospitals. The literature suggests that these patients repeatedly use violent behavior to obtain their goals because it has worked successfully for them in the past. They also tend to have an image of themselves as persons to be feared and to have limited patterns of imagination and fantasy that inhibit alternative responses. The authors describe a treatment approach that combines cognitive, behavioral, and expressive therapy concepts and incorporates creative therapies such as art and music. The goal of therapy is to alter the self-image of violent patients and help them develop alternative response patterns.

Adult↗
PubMed1988

Growth, carcass traits, boar odor and testicular and endocrine functions of male pigs fed a progestogen, altrenogest.

Crossbred (Chester White X Yorkshire X Duroc) boars were used to evaluate the effects of feeding a progestogen (altrenogest) on body growth, endocrine function (determined during feeding and after withdrawal of altrenogest), carcass composition, boar odor and testicular function (determined after a 30-d withdrawal from altrenogest). Boars from 18 litters were assigned at 12 wk of age to three treatments: 1) 18 control boars; 2) 18 boars fed altrenogest (20 mg/day) for 6 wk from 15 to 21 wk of age, followed by 30 d with no treatment; and 3) 18 boars castrated at 2 wk of age (barrows). Daily gains were greater (P less than .05) in boars fed altrenogest than in barrows through 21 wk of age but were lower (P less than .05) than those of control boars and barrows during the 30-d withdrawal period. Boars fed altrenogest weighed less (P less than .05) than control boars and barrows at 25 wk of age (at slaughter). Both groups of boars were similar in percentage of muscle and had less (P less than .05) backfat than barrows, whereas control boars had the largest (P less than .05) loineye areas. Based on evaluations by a trained sensory panel, intensity of boar odor in fat samples was similar for both groups of boars and was greater (P less than .05) than that for barrows. Weights of accessory reproductive glands and weight and sperm content of testes and epididymides were reduced (P less than .05) in boars fed altrenogest.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗