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Biomedical subjects

D L Davis

Publications and source records attributed to D L Davis.

At least 217 records · Page 12Linked to original sources
PubMed1979

Control of estrus in gilts with a progestogen.

Two trials were conducted to evaluate the effectiveness of a synthetic progestogen, allyl trenbolone, for control of estrus and ovulation in gilts. Estrus was effectively synchronized with 33 of 38 gilts exhibiting estrus 2 to 7 days after last progestogen feeding. There was no effect on fertilization rate in gilts free of ovarian abnormalities. Ovulation rate was higher in gilts fed the progestogen in both Trial 1 (P less than .01) and Trial 2 (P less than .10). Progestogen treatment caused an increase (P less than .01) in the incidence of cystic follicles which resulted in a decrease (P less than .01) in conception rate in Trial 1.

Animals↗
PubMed1979

Frequency-dependent control of nutritional and nonnutritional circuits in the dog paw.

The neural control of blood flow and volume distribution between parallel nutritional and nonnutritional circuits has been investigated in 13 vascularly and neurally isolated dog hindpaws. The superficial and deep fibular nerves and the tibial nerve were cut and individually stimulated at frequencies of 0.1, 1, 5, 10 and 15 Hz. Increasing stimulation rates to each nerve progressively increased blood flow resistance. Vascular volume changes were determined by indicator dilution and tissue volume changes by plethysmography. The permeability surface area product of 86Rb (PS) and the capillary filtration coefficient (CFC) were determined. Superficial fibular nerve and deep fibular nerve stimulations caused progressively increased nonnutritional circuit constriction with increasing stimulation frequencies resulting in blood flow redistribution to the nutritional circuit as evidenced by increasing PS and CFC values. Tibial nerve stimulation at 0.1 Hz caused nonnutritional circuit constriction and blood flow redistribution to the nutritional circuit (PS and CFC increased). As the stimulation frequency was increased, there was progressive increase of the nutritional circuit constriction and altered blood flow distribution; i.e., CFC and PS decreased with increasing frequency of stimulation, presumably due to predominantly arterial segment resistance increase.

Animals↗
PubMed1979

Microvascular plasma velocity and indicator dispersion with hemorrhage.

The effects of stepwise hemorrhages on plasma flow velocity and indicator (FITC-Dextran) dispersion in series and parallel coupled microvascular vessels has been studied. The mesentery of cats (0.6 kg) anesthetized with Dial-Urethane was exposed and studied with a microscope equipped for fluorescense microscopy. Indicator was injected as a bolus (0.1 ml in 0.5 seconds) in a small branch of the mesenteric artery. Indicator curves were recorded from a video tape recording of the passage of the indicator by a video sampler with intensity sensitive windows. The mean transit time (t), appearance time (t(a)), peak time (t(p)), curve duration (t(E)), plasma velocity and vessel diameter changes were determined. Arterioles 68 +/- 8 micron and 35 +/- 3 micron and venules 55 +/- 6 micron constricted gradually with hemorrhage. Arterioles 20 +/- 2 micron constricted with mild hemorrhage and remained constricted with further hemorrhage. Arteriolar and venular plasma velocities decreased abruptly with mild hemorrhage and then continued to decrease gradually with further hemorrhage. Capillary flow ceased after moderate hemorrhage and was not reestablished until at least an hour after reinfusion. Arteriole t increased with hemorrhage but t increased much more in capillaries and venules. t(E) changes paralled t changes. The ratio t(a)/t was lower for venules than arterioles and both decreased with hemorrhage but the venular ratio decreased significantly more. Venular t(p)-t(a) and t(E)-t(p) increased more than arteriolar values. Hemorrhage increased indicator dispersion with the greatest effect occurring between the arteriolar and venular vessels.

Animals↗
PubMed1978

Neural control of nutritional and nonnutritional circuits in the dog hindpaw.

The neural control of blood flow and volume distribution between parallel nutritional and nonnutritional circuits has been investigated in the vascularly and neurally isolated dog hindpaw. Twelve paws were perfused by controlled pressure and ten paws were perfused by controlled flow via the cranial tibial artery. Venous outflow was measured and collected from the lateral saphenous vein. The superficial and deep fibular nerves and the tibial nerve were cut and individually stimulated, resulting in rates which at least doubled the blood flow resistance. Vascular volume changes were measured by injections of 51Cr-labeled red cells and 131I-labeled albumin. Tissue volume changes were measured by plethysmography. Capillary diffusion capacity was calculated from 86Rb extractions, and capillary filtration coefficients were determined. Superficial fibular nerve and deep fibular nerve stimulations apparently resulted in nonnutritional circuit constriction with resulting blood flow redistribution to nutritional circuits, possibly located in tissues other than the skin, e.g., adipose tissue. Tibial nerve stimulation caused no redistribution of blood flow between the two circuits presumably due to a uniform constriction of arteries and small vessel segments.

Animals↗
PubMed1977

Dogmatism as a mediating influence on the perception of risk in consumer choice decisions.

The risk perceived by individual consumers when faced with an unfamiliar purchase situation was examined across three groups of females for three product categories. Group membership was determined on the basis of high, medium, and low scores on the Trodahl-Powell dogmatism instrument. Ss were 155 housewives of a medium size midwestern city in the United States surveyed as part of a two-tiered sampling process. The results of a multivariate analysis of variance procedure supported the hypothesis that consumers of a less dogmatic nature perceive lower levels of risk inherent within unfamiliar purchase situations than more dogmatic individuals. The implication for management is that the likelihood of obtaining successful new product introductions may be substantially enhanced through the process of risk reduction across dogmatic consumer segments by use of direct testimonial promotional themes stressing product acceptance in support of more traditional and informative advertising messages. The feasibility of this approach is based upon the premise that the behavior of dogmatic individuals is more frequently affected by pressures from peers and significant others than the behavior of individuals low in dogmatism which is generally based on more factual and relevant information.

Anxiety↗
PubMed1976

Digital artery blood flow and digital pad opacity during vasoconstriction.

Digital artery blood flows were compared with digital pad opacity pulse amplitudes in dogs during vasoconstrictor responses. A high correlation between digital artery flow and opacity pulse amplitudes occurred during infusions of epinephrine and sciatic and tibial nerve stimulations, but not during superficial fibular nerve stimulation. The results confirmed earlier findings that tibial nerve stimulation produced predominantly precapillary constriction, and that superficial fibular nerve stimulation produced predominantly postcapillary constriction. Events in precapillary vessels appeared to be responsible for the opacity pulse. This fact probably forms the basis for the close relationship between opacity pulse amplitude and blood flow.

Animals↗
PubMed1976

Longitudinal tension of anterior tibial artery segments during constrictor responses.

Longitudinal tensions were recorded from in situ isolated segments of dog anterior tibial arteries during vasoconstrictor responses. Two factors appeared to be responsible for longitudinal tensions occurring during vasoconstrictor responses. One was due to changes in intraluminal pressure and appeared to be the dominant factor. Increases in intraluminal pressures produced decreases in longitudinal tensions, indicating that the vessel segments were elongated. Thus, increases in intraluminal pressure passively stretched the blood vessel walls so that increases in both the circumferential and longitudinal axes of the vessel segment occurred. These findings agree with similar findings reported earlier (4, 7, 8). The other factor was apparently due to changes in longitudinal tension produced by vascular smooth muscle contraction. In some cases longitudinal tension changes were positive, in others they were negative. Increases in longitudinal tension were probably the result of contractions of helical smooth muscle elements. Decreases in tension may have been due to displacement of tissue parallel to the long axis of the vessel as smooth muscle elements contracted.

Animals↗
PubMed1976

Spastic eversion of the upper eyelids.

A 2-year-old black Nigerian infant presented with eversion of the upper eyelids which followed an episode of presumed measles conjunctivitis. Eversion recurred despite patching and taping, but was terminated by facial akinesia and placement of lid sutures. Orbicularis spasm undoubtedly plays a role in the pathophysiology of this disorder, acting together with other etiologic factors.

Blepharospasm↗
PubMed1975

The history and sociology of the scientific study of acupuncture.

Although known to the medical community in some form since the 19th century, acupuncture is only recently receiving concerted research attention from the conventional medical and scientific community. The overall amount of scientific acupuncture research has doubled since the mid 1960's. Employing the approaches of the science, history, sociology and social relations of science, this article explores factors which explain why the present time is conducive to acupuncture research by the scientific and medical community. Perhaps this study of scientific acupuncture research will provide the basis for a later theory of scientific development.

Acupuncture Therapy↗
PubMed1974

Sterol Accumulation and Composition in Developing Zea mays L. Kernels.

Kernels were collected from three maize (Zea mays L.) inbreds from 10 days after pollination until kernel maturity. Sitosterol, campesterol, and stigmasterol were the major sterols at all stages of kernel development. Cholesterol was less than 1% of the dry weight. The three major sterols accumulated during kernel development, but at a rate slower than dry weight. The ratio of the sterols did not vary greatly among the inbreds. At maturity, the three inbreds, Wf9, Oh43, and Ky226, had sterol levels of 325, 228, and 173 micrograms per kernel, respectively. Sitosterol accounted for 75 to 85% of the sterol. The relative amount of stigmasterol decreased during the linear phase of development, while sitosterol increased in the free fraction and campesterol increased in the steryl ester fraction.Free sterols and steryl esters were the major sterol fractions and steryl glycosides and acylated steryl glycosides were only minor components during kernel development. Free sterol content decreased rapidly in two maize inbreds between 10 and 26 days after pollination, but partially recovered in one of the inbreds during final stages of development. In the same two inbreds the steryl ester content reached a maximum during the late stages of linear kernel growth.

Journal Article↗