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Biomedical subjects

M E Davis

Publications and source records attributed to M E Davis.

At least 109 records · Page 6Linked to original sources
PubMed1989

The effects of intravenous nitroglycerin and isosorbide dinitrate on hemodynamics and myocardial metabolism.

Myocardial ischemia before and during coronary artery surgery is significant, because patients who develop perioperative myocardial ischemia have an increased incidence of postoperative myocardial infarctions. Thus, the prevention of ischemic episodes is of great importance. This study was undertaken to (1) compare the effects of intravenous nitroglycerin (NTG) with isosorbide dinitrate (ISDN); (2) investigate if the continuous infusion of nitrates had beneficial effects on cardiac performance and metabolism; and (3) compare the control of blood pressure with the nitrates versus halothane during a standardized anesthetic. Twenty-one patients participated in the study, and all had the following: a radial arterial catheter, peripheral venous catheter, 7F pulmonary artery catheter, and Baim coronary sinus flow catheter. The study was carried out in the prebypass period beginning with awake measurements of baseline parameters, and ending after median sternotomy. The patients were divided into three groups: group 1 received an infusion of NTG; group 2 received an infusion of ISDN; and group 3, the control, received neither nitrate, but halothane was added to control hemodynamics. Measurements were made at the following time intervals: (1) baseline; (2) after 5 minutes of the nitrate infusions while awake (groups 1 and 2); (3) after induction of anesthesia, laryngoscopy, and intubation; and (4) after median sternotomy. In groups 1 and 2, the nitrates were infused at 0.1 mg/kg/h for 5 minutes. Thereafter, blood pressure control and treatment of episodic hypertension were achieved by alteration of the rate of nitrate infusions, or, in group 3, by 0.5% to 2% of inspired halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Regionalized adaptations and muscle fiber proliferation in stretch-induced enlargement.

The relative contribution of increases in fiber area to stretch-induced muscle enlargement was evaluated in the slow tonic fibers of the anterior latissimus dorsi of adult Japanese quails. A weight corresponding to 10% of the bird's body mass was attached to one wing. Thirty days of stretch in 34 birds averaged 171.8 +/- 13.5% increase in muscle mass and 23.5 +/- 0.8% increase in muscle fiber length. The volume density of noncontractile tissue increased in middle and distal regions of stretch-enlarged muscles. Mean fiber cross-sectional area increased 56.7 +/- 12.3% in the midregion of stretched muscles. Further analysis indicated slow beta-fiber hypertrophy occurred in proximal, middle, and distal regions; however, fast alpha-type fiber hypertrophy was limited to middle regions of stretched muscles. Stretched muscles had a significant increase in the frequency of slow beta-fibers that were less than 500 microns 2 in all regions and fast alpha-type fibers in middle and distal regions. Total fiber number was determined after nitric acid digestion of connective tissue in 10 birds. Fiber number increased 51.8 +/- 19.4% in stretched muscle. These results are the first to clearly show that muscle fiber proliferation contributes substantially to adult skeletal muscle stretch-induced enlargement, although we do not know whether the responses of the slow tonic anterior latissimus dorsi might be similar or different from mammalian twitch muscle.

Adaptation, Physiological↗
PubMed1989

The relationship of insulin-like growth factor-I with postweaning performance in Angus beef cattle.

This study was designed to evaluate the ontogeny of serum IGF-I (SI) concentrations and its relationship to animal performance in a 140-d postweaning feeding trial. Ninety-eight progeny representing six sires (three high and three low feed conversion) and two sexes (43 bulls and 55 heifers) with ad libitum access to feed were allocated by sire and sex to monitor individual weights and pen feed consumption. Blood serum samples were obtained at the beginning of test (average age of 230 d) and every 28 d thereafter until each animal reached a fat thickness (estimated by sonoray) of 8.9 mm. Individual serum samples were acid-ethanol extracted and measured for IGF-I peptide by heterologous RIA. Serum IGF-I concentrations differed (P less than .10) between high (H) and low (L) feed conversion progeny groups at the end of the first 28-d period (125.12 vs 89.52 ng/ml) and tended to differ at the conclusion of the second 28-d period (P less than .15). Weight gains of H and L groups tended to differ in the second and third 28-d periods (P = .11 and .10, respectively). Serum IGF-I concentrations differed (P less than .05) between bulls and heifers for the first through fourth 28-d periods (P less than .01, P less than .05, P less than .10 and P less than .01, respectively). Phenotypic correlations indicated that pens with higher mean SI concentrations at the beginning of the test consumed less feed and had lower cumulative feed:gain ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Use of embryo transfer to induce twinning in beef cattle: embryo survival rate, gestation length, birth weight and weaning weight of calves.

Experiments were conducted in 1985 and 1986 at the Eastern Ohio Resource Development Center, Belle Valley, to examine the feasibility of using embryo transfer to induce twinning and to examine the influence of twinning on traits of the cow and calf. Embryos were collected from a total of 14 superovulated Angus donors on two dates each in 1985 and 1986 and were transferred to Angus recipients. A total of 124 embryos were transferred to 79 recipients, with 43 (34.7%) calves born alive. Seven of 45 (15.6%) recipients implanted with two embryos produced twins. In no case did both halves of the 15 embryos that were split to produce identical twins and implanted in the same recipient survive to birth. Proportion of calves born alive did not differ among transfer codes 3 (nonsplit embryos from two different donors implanted in separate uterine horns of the same recipient), 6 (nonsplit embryos from one embryo flush implanted in separate uterine horns of the same recipient) and 7 (nonsplit embryos from two different donors implanted in the same uterine horn of one recipient). Surgical transfers tended to result in a higher proportion of embryos surviving to birth (.43 vs .21; P = .16) and a higher twinning rate (.29 vs .04; P = .36) than did nonsurgical transfers. Age of recipient did not influence embryo survival (P = .98) or twinning rate (P = .99). Gestation length was 5 d shorter (P less than .01) for twin calves than for singles. Singles were 9 kg heavier (P less than .01) at birth and 32 kg heavier (P less than .01) at weaning than twins. However, cows raising twins produced 108 kg (51%) more total weaning weight than did cows raising singles.

Animals↗
PubMed1989

Que Pasa?

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Emigration and Immigration↗
PubMed1988

Intravenous nifedipine for control of hypertension in patients after coronary artery bypass graft surgery.

A study was undertaken to assess the use of intravenous nifedipine in controlling hypertension in patients following coronary artery surgery. A combined hemodynamic and metabolic assessment was carried out in 15 patients on data recorded at six sequential time intervals: (1) baseline, (2) control of blood pressure, (3) 30 minutes after control of blood pressure, (4) 1.5 hours after control of blood pressure, (5) 3.5 hours after control of blood pressure, and (6) 30 minutes after discontinuing nifedipine. Coronary sinus and great cardiac vein blood flows were measured by the continuous thermodilution technique using the Baim coronary sinus flow catheter. Intravenous nifedipine was run initially at an average rate of 1.82 microg/kg/min. It took an average time of 12 minutes to lower the blood pressure to less than 130 mmHg systolic. There were highly significant decreases in systolic, mean, and diastolic blood pressures (P < .001), associated with significant decreases in systemic vascular resistance (P < .001) and left ventricular stroke work index (P < .05). There was an increase in cardiac output at 30 and 90 minutes of infusion (P < .05), and the stroke volume was increased 90 minutes after starting nifedipine (P < .05). The increase in heart rate was not significant. There was no significant effect on conduction times as measured by PR and QRS intervals on the ECG. However, the QTc interval was decreased after 3.5 hours (P < .05). There was an increase in right atrial pressure at 90 minutes and again 30 minutes after stopping nifedipine. (P < .05). The pulmonary artery pressure also was increased after stopping the infusion (P < .05). The pulmonary capillary wedge pressure, pulmonary vascular resistance, and right ventricular stroke work index remained unchanged. Coronary sinus and great cardiac vein flows were maintained despite a decrease in perfusion pressure, suggesting that nifedipine is a potent coronary vasodilator. Indeed, coronary vascular resistance was significantly decreased (P < .05). Myocardial oxygen consumption remained unchanged. The lactate extraction indicated that myocardial metabolism remained aerobic regionally and globally. Thus, the results suggest that blood pressure was easy to control and that there were no adverse effects on atrioventricular conduction, cardiac performance, regional and global myocardial oxygen utilization, or lactate extraction.

Adult↗
PubMed1988

Effects of AT-125 on the nephrotoxicity of hexachloro-1,3-butadiene in rats.

The role of gamma-glutamyl transpeptidase (gamma-GTP) in the nephrotoxicity of hexachloro-1,3-butadiene (HCBD) was studied using male Sprague-Dawley rats pretreated with AT-125 (Acivicin; L-(alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid). Inhibition of gamma-GTP by more than 95% did not affect urine output, glomerular filtration rate, or tubular reabsorption of filtrate, sodium, or glucose. Nephrotoxicity observed during the first 24 hr after HCBD was not decreased by inhibition of gamma-GTP and beyond 24 hr nephrotoxicity was increased, rather than decreased, in the AT-125-pretreated group. HCBD impairs glucose reabsorption and this was greatly increased in the AT-125-pretreated group, indicating that function of the initial segment of the nephron is impaired by HCBD. Since inhibition of gamma-GTP did not protect against HCBD nephrotoxicity, it is concluded that gamma-GTP inhibition does not limit the formation of metabolites(s) which cause HCBD nephrotoxicity. Therefore, distribution of gamma-glutamyltranspeptidase does not account for the selective nephrotoxicity of hexachloro-1,3-butadiene.

Animals↗
PubMed1988

WR-2721 entry into the brain across a modified blood-brain barrier.

Radioprotection of the CNS by WR-2721 has not been possible because of its inability to cross the blood-brain barrier (BBB) and so gain access to the neural tissue. Modification of the BBB using hypertonic arabinose (1.8 m), injected via the internal carotid artery (ica), permitted entry of ip-injected [14C]WR-2721 into the ipsilateral cerebral hemisphere. The BBB-modified hemisphere had a 5.34-fold increased uptake compared to nonmodified controls. Delivery as a bolus via the ica further enhanced uptake after BBB opening; WR-2721 was 3.73 times greater than by ip injection. A 20-fold increase of WR-2721 brain uptake has been calculated for ica administration with the BBB opened as compared to the ip route without BBB modification. Toxicity of ip-administered WR-2721 with the BBB open was only 1.4 times greater than non-modified controls and 1.96 times more toxic when delivered via the ica. These data demonstrate significant uptake of WR-2721 into the CNS, a previously unprotected organ, and provide a model for future radioprotective studies.

Amifostine↗
PubMed1987

Synchronization of estrus in beef cows and heifers with prostaglandin F(2alpha) and estradiol benzoate.

An experiment was conducted to study an estrous synchronization regimen that involved the use of prostaglandin F(2alpha) (PGF(2alpha)) alone or in combination with estradiol benzoate (EB) and appointment breeding. Fifty-three registered Angus yearling heifers and 167 registered Angus cows (3 to 9 yr of age) were given two injections of PGF(2alpha) 11 d apart. Forty-eight hours after the second injection of PGF(2alpha') a random sample consisting of 117 cows and heifers was injected with EB in sesame seed oil. All females in the herd were artificially inseminated 80 h after the second injection of PGF(2alpha). Nearly equal percentages (25.1 vs 25.6%; P = 0.93) of treated (EB) and control (no EB) females conceived at the appointment breeding. Use of EB tended to reduce (P = 0.06) natural service conception rate (83.4 vs 93.1% for EB and control groups, respectively). Estrous synchronization treatment did not affect interval from Day 1 of the breeding season to calving.

Journal Article↗
PubMed1987

Synchronization of estrus in beef cows and heifers with fenprostalene, cloprostenol sodium, and prostaglandin F2 alpha.

The effects of fenprostalene, cloprostenol sodium and prostaglandin F2 alpha (PGF2alpha) on estrus, conception rate, pregnancy rate, and the interval from Day 1 of the breeding season to calving were studied on 135 purebred Angus cows and heifers. The cows and heifers were randomly allotted within age to the three estrus synchronization treatments and a control group. The calving percentages (for cows and heifers combined) that resulted from artificial insemination (AI) were 32.3, 31.4, 43.6, and 51.1% for the control, fenprostalene, cloprostenol sodium, and PGF2alpha groups, respectively. The calving percentage during the AI period by ages of dam at breeding were 54.2% for yearling heifers, 30.5% for two-year-olds, 47.6% for three-year-olds, and 26.1% for four-year-old or older cows. The percentage of cows and heifers detected in estrus and the percentage that conceived after the first injection for control, fenprostalene, cloprostenol sodium, and PGF2alpha groups were 51.6 and 22.3%, 59.3 and 32.1%, 76.8 and 44.1%, and 66.6 and 50.2%, respectively. The intervals from Day 1 of the breeding season to calving and from Day 1 of the calving season within each treatment to the birth of each calf were control, 285.9 and 23.8 d; fenprostalene, 283.6 and 13.4 d; cloprostenol sodium, 285.5 and 6.5 d; and PGF2alpha, 284.0 and 11.1 d.

Journal Article↗
PubMed1987

Transplacental uptake of WR 2721 by the rat embryo.

On day 14 post-conception, near the end of the period of major organogenesis, pregnant rats were injected intravenously or intraperitoneally with WR 2721 spiked with 14C-WR 2721. The radioprotectant was shown to cross the placenta rapidly when administered by either route, and the concentration of WR 2721 in the embryos, placentae, and maternal blood plasma was determined during the period 5 to 90 minutes following administration. The concentration of WR 2721 increased continuously in the embryos during this period and did so against a decreasing concentration in the maternal blood. Injection of WR 2721 at 100 mg/kg of maternal body weight resulted in the presence of 8-9-mg/kg embryo weight; this embryo level is about 1/2 the injected dose of WR 2721 currently being used in human radiotherapy trials, that is, 20 mg/kg (740 mg/m2) body weight. Previous toxicity studies of 9, 11, and 14 day rat embryos have shown that this 100 mg/kg dose is much below the level which produces embryotoxic effects.

Amifostine↗
PubMed1987

Divergent selection for postweaning feed conversion in beef cattle: predicted response based on an index of feed intake and gain vs fee: gain ratio.

As part of a divergent selection experiment (high vs low feed conversion) designed to obtain realized genetic parameter estimates for postweaning feed conversion, 35 Angus bull calves were selected each year from 1979 through 1983 to be fed in a 140-d postweaning performance test. From these 35 individually-fed bulls, the three most efficient and three least efficient (in terms of kilograms of total digestible nutrients required per kilogram of gain) were selected each year to each be mated to approximately 20 purebred Angus cows in a test herd. In the last 2 yr of the experiment, feed:gain ratios were adjusted for differences in maintenance requirements before selection. An alternative to selection based on feed/gain or adjusted feed/gain would have been to select on an index of feed intake and gain (Index3 = -1.0 feed intake + 3.87 gain) where feed intake was either unadjusted or adjusted (AdjIndex3) for differences in maintenance requirements. Residual correlations (year effects removed) among the four selection critera were large ([r[ greater than or equal to .76; P less than .01) as were correlations among ranks of the bulls based on the four selection criteria ([r[ greater than or equal to .75). Predicted genetic change for fee:gain ratio in both the high and low directions was greatest when selection was based on feed:gain ratio or Index3. Genetic changes expected to result from selection for feed:gain ratio or Index3 were similar, as were genetic changes expected due to selection for adjusted feed:gain ratio or AdjIndex3.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1986

Effects of cysteine and diethylmaleate pretreatments on renal function and response to a nephrotoxicant.

The effects of treatment with either cysteine (2 X 150 mg/kg) or diethylmaleate (0.7 ml/kg) on renal function and response to the nephrotoxicant hexachloro-1,3-butadiene (HCBD) were examined. Cysteine caused oliguria, blocked the polyuric and glucosuric effects of HCBD and attenuated the reduction of urine osmolality. Diethylmaleate (DEM) decreased urine osmolality; further decreases of urine osmolality were not seen after HCBD. DEM pretreatment increased HCBD-induced proteinuria. HCBD-induced elevation of plasma creatinine concentration was not affected by either of the pretreatments whereas the plasma urea nitrogen concentration was greater in the DEM-pretreated group. The latter may represent an effect of DEM on non-filtration handling of urea. The results suggest that cysteine and diethylmaleate each have effects on kidney function which alter the response of the nephron tubule to a subsequently administered toxic agent.

Animals↗
PubMed1986

Theory of the anomalous resonant absorption of DNA at microwave frequencies.

Aqueous solutions of oligopolymer DNA have been observed by Edwards, Davis, Swicord & Saffer to show structured absorption of microwave energy in the region of several gigahertz characteristic of an ordered series of compressional normal mode vibrations propagating on the polymer chain. Hydrodynamic coupling of such vibrations to the surrounding solvent would preclude the existence of sharp resonances. The inclusion of electromagnetic interactions with surrounding counter ions yields a richer space of possibilities for complex behavior of the combined system. A well defined resonant absorption peak appears when the molecular motion and the nearby solvent motion are even slightly decoupled. The microwave electric fields in the vicinity of the molecule provide a mechanism for such a decoupling not present for the case of electrically neutral solvent.

DNA↗