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Biomedical subjects

R D Smith

Publications and source records attributed to R D Smith.

At least 469 records · Page 26Linked to original sources
PubMed1977

The brown dog tick Rhipicephalus sanguineus and the dog as experimental hosts of Ehrlichia canis.

Adult Rhipicephalus sanguineus ticks efficiently transmitted Ehrlichia canis to susceptible dogs for 155 days after detachment as engorged nymphs from a dog in the acute phase of ehrlichiosis. Adult ticks that had similarly engorged on a dog in the chronic phase of ehrlichiosis failed to transmit E canis to susceptible dogs. Infected but unfed adult ticks may be of greater importance than the chronically infected carrier dog as a natural reservoir of E canis.

Animals↗
PubMed1977

Experimental intracranial aneurysms.

Methods and results of creation of an experimental intracranial aneurysm on the canine basilar artery using an autogenous vein graft are presented. Aneurysms were produced either on the wall of the basilar artery or at a lingual-basilar artery anastomosis site. Postoperative angiography revealed no success in the first group and 55% success in the second group, with better results occurring later in the series. Mortality was higher in the first group. Hemodynamic and technical factors are discussed and compared with earlier work on experimental aneurysms in the rat. Construction of an aneurysm at the site of a lingual-basilar artery anastomosis seems to provide a satisfactory model for biophysical and catheter embolization experimentation, although at present it is unsuitable for studies of acute subarachnoid hemorrhage.

Animals↗
PubMed1976

Plasma growth hormone and insulin during early lactation in cows fed silage based diets.

Peripheral plasma insulin, growth hormone, and blood glucose were determined in 24 dairy cows during early lactation. Blood samples were obtained at 4-day intervals during the first 56 days of experimental lactations 1 and 3 of a 3-lactation experiment. The cows were divided equally among three groups and fed one of the following forage rations for three consecutive lactations: corn silage (18.2 kg/day) plus alfalfa-timothy hay ad libitum; corn silage (18.2 kg/day) plus alfalfa-timothy silage ad libitum; or corn silage ad libitum. These diets were continued throughout the intervening dry periods except in the latter group where corn silage intake was limited if individual animals exhibited excessive body weight gain. Four animals in each group received prepartum supplemental concentrates. The remaining four animals received no prepartum concentrate supplementation. Following parturition, concentrates were fed in increasing amounts to a maximum of 14.6 kg/day during the first 56 days of lactation. Plasma insulin, growth hormone, and blood glucose were not affected by forage diet or prepartum supplemental concentrate feeding. Plasma insulin and blood glucose increased and plasma growth hormone decreased with time after parturition. These changes were correlated with nutrient intake which increased during the experiment. Changes in plasma insulin and growth hormone are related to metabolic adjustments during early lactation.

Animal Feed↗
PubMed1976

Prolactin binding to mammary gland, 7,12-dimethylbenz(a)-anthracene-induced mammary tumors, and liver in rats.

Specific binding of radioactively labeled prolactin was determined in membrane preparations from mammary glands and livers of rats during pregnancy and lactation. Prolactin binding to mammary gland increased throughout late pregnancy and early lactation, reached a maximum on Day 11 of lactation, and then declined. Maximum prolactin binding to liver membrane preparations was observed during late pregnancy and declined throughout lactation. Estradiol benzoate (20 mug/day), administered on Days 5 to 10 of lactation, reduced prolactin binding to mammary gland by 55%, increased binding to liver 2-fold, and reduced litter weight gain by 25%. Prolactin binding to 7,12-dimethylbenz(a)anthracene-induced mammary tumors was 3 times higher than that observed in lactating mammary gland. Administration of prolactin enhanced tumor growth but decreased specific prolactin binding to tumors. Lergotrile mesylate inhibited and estradiol benzoate (2 mug/day) enhanced tumor growth, but neither treatment affected prolactin binding to tumor membrane preparations. In contrast, higher doses of estradiol benzoate (20 mug/day) inhibited tumor growth and reduced prolactin binding. Prolactin binding varied widely within all groups of mammary tumors and was not clearly related to growth response or to altered circulating estrogen and/or prolactin levels. Hormone dependence in this animal tumor model is complex and may not be predicted on the basis of prolactin-binding capacity alone.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Development of Ehrlichia canis, causative agent of canine ehrlichiosis, in the tick Rhipicephalus sanguineus and its differentiation from a symbiotic Rickettsia.

Certain aspects of the development of Ehrlichia canis, causative agent of canine ehrlichiosis (tropical canine pancytopenia) in Rhipicephalus sanguineus ticks were studied. It was found that partial feeding of nymphs infected as larvae with E canis was a desirable, if not necessary, preliminary treatment for successful infection of dogs with ground-up ticks. It remains unclear whether feeding increased the number or altered the virulence of ehrlichiae within tick tissues. Ehrlichia canis organisms were detected by immunofluorescent microscopy in the midgut and hemocytes and by electron microscopy in the midgut and salivary glands of partially engorged adult ticks which had been infected as larvae and nymphs. Organisms were not observed in the ovary. Intracytoplasmic inclusions contained 1 to 80 elementary bodies, each provided with 2 distinct membranes. Infection of the midgut and salivary gland was confirmed by injecting homogenates of these tissues into susceptible dogs. Staining of gut smears of partially engorged adult ticks by fluorescein-conjugated anti-E canis antibody was found to be a reliable indicator of the infection.

Animals↗
PubMed1975

Isolation in Illinois of a foreign strain of Ehrlichia canis, the causative agent of canine ehrlichiosis (tropical canine pancytopenia).

Ehrlichiosis (tropical canine pancytopenia) was diagnosed in Illinois in a 4 1/2-year-old mixed breed dog that had spent the previous 2 years in India. The dog had periodic epistaxis, anemia, leukopenia, hypoalbuminemia, and hypergammaglobulinemia. A titer of 1:160 for Ehrlichia canis was detected by the indirect fluorescent antibody test (IFAT). Subinoculation of blood into a clinically normal dgo resulted in typical signs of canine ehrlichiosis, and E canis was identified in circulating mononuclear cells. The recipient died 23 days after inoculation, and typical gross and microscopic lesions of ehrlichiosis were found at necropsy. Ecchymoses and petechiae were found on the gallbladder, kidneys, small intestinal mucosa, cerebrum, and cerebellum. Plasmacytosis and perivascular cuffing was evident in various organs, especially the cerebrum, cerebellum, and meninges.

Animals↗
PubMed1975

Central monaminergic neuronal effects on minimum alveolar concentrations (MAC) of halothane and cyclopropane in rats.

The effect of interference with central catecholamine- or serotonin-containing neurons on the response of rats to inhalation anesthetics were explored. Interference with catecholaminergic function by inhibition of amine synthesis with alpha-methyltyrosine alone or combined with destruction of these neurons by 6-hydroxydopamine reduced brain concentrations of norepinephrine and dopamine without altering serotonin concentrations. These alterations decreased the minimum alveolar concentration (MAC) of halothane when tail-clamping was used as the test stimulus. Similar small reductions of halothane MAC were produced in rats given 5,6-dihydroxytryptamine and p-chlorophenylalanine, which decreased brain serotonin without altering noreopinephrine or doapamine concentrations. When catecholaminergic or serotoninergic neuronal function was similarly disrupted in rats later exposed to cyclopropane, no alternation in MAC was observed. It is suggested that disruption of central amine-containing neurons may lower the MAC's of depressant anesthetics only, and not excitatory anesthetics.

Amines↗
PubMed1975

Platelet kinetics in canine ehrlichiosis: evidence for increased platelet destruction as the cause of thrombocytopenia.

A significant (P < 0.025) increase in the mean platelet diameter occurred in five Ehrlichia canis-infected dogs when platelet numbers decreased to 100,000/mul or less. Maximal incorporation of [(75)Se]selenomethionine into platelets of six uninfected dogs was 0.080 +/- 0.019% (mean +/- standard error) and occurred 5 to 6 days after dosage, whereas maximal incorporation was 0.036 +/- 0.004% within 2 to 3 days after dosage in seven chronically infected dogs that had thrombocytopenia. Analysis of the [(75)Se]selenomethionine curves yielded a platelet lifespan of 9 days in uninfected dogs versus 4 days in chronically infected dogs. Thus, megakaryocyte maturation and/or platelet release occurred at an accelerated rate in infected dogs, whereas increased destruction of newly produced labeled platelets diminished their number of peripheral blood. [(51)Cr]sodium chromate-labeled platelet survival was exponential, with a half-life of approximately 1 day in two dogs at 2 to 4 days postinfection and three chronically infected dogs. Platelet survival time was 8 days and rectilinear in four uninfected dogs. Platelet recovery was 39.43 +/- 2.86% in infected dogs as compared with 68.2 +/- 10.72% in uninfected dogs. Whole-body scans of one dog prior to and 7 days after infection showed that labeled platelets were destroyed primarily in the spleen. It is concluded that the thrombocytopenia in E. canis-infected dogs is the result of increased platelet destruction which begins within a few days after infection.

Animals↗
PubMed1975

Plasma adrenocorticoid response to corticotropin in dairy cattle fed high silage diets.

Responses of plasma corticoids to adrenocorticotropic hormone (.32 U/kg body weight) administered during early lactation were measured in dairy cattle consuming large amounts of concentrate feeds and one of the following forage diets: alfalfa-timothy hay plus corn silage, alfalfa-timothy hay crop silage plus corn silage, or corn silage. Concentrations of plasma corticoids increased to maximum in all groups within 60 to 90 min. Concentrations remained at near maximum for 4 to 5 h and then declined to baseline. Maximum corticoid concentrations following adrenocorticotropic hormone injection differed among forage treatment groups. Responses of corn silage and hay crop silage groups (46.7 +/- 1.1 and 50.1 +/- 2.4 ng/ml) did not differ but were less than those in the hay group (65.5 +/- 2.9 ng/ml). Response measured as area under the curve of plasma corticoid response also differed among forage treatments: hay 443 +/- 17 h (ng/ml) is greater than hay crop silage 334 +/- 34 is greater than corn silage 245 +/- 36. Results are discussed in terms of stress susceptibility in dairy cattle consuming diets containing large amounts of silage.

Adrenal Cortex Hormones↗
PubMed1975

Effect of lithium ions on RNA synthesis in mammary gland explants of mice.

LiC1 was found to stimulate RNA synthesis in the mammary gland in a manner similar to that of prolactin. Since LiC1 is known to inhibit adenyl cyclase and thus to reduce levels of cyclic AMP, it is concluded that a reduced level of cyclic AMP may be one step in the mechanism whereby prolactin regulates the metabolism of the mammary gland.

Animals↗
PubMed1975

A rapid method for measuring guanylate cyclase activity in mammary tissue.

A simple and rapid method for measuring guanylate cyclase activity in broken cell preparations of biological tissues is described. This method employs the rate of conversion of [32P]GTP to [32P]cyclic-GMP. The product of this reaction is isolated by ion-exchange chromatography and by a ZnSO4-Ba(OH)2 precipitation at pH 5.7. Using this method, about 30-50 samples can be assayed for guanylate cyclase activity during a 5-6 hr period. The characteristics of this enzyme in the mammary gland were found to be similar to those described for other tissues using different methods for measuring guanylate cyclase activity.

Animals↗
PubMed1975

Guanylate cyclase and cyclic-GMP phosphodiesterase activities in mammary glands of mice during pregnancy and lactation.

Guanylate cyclase and cyclic-GMP phosphodiesterase activities were measured in homogenates of mammary glands from virgin, pregnant, and lactating mice. Guanylate cyclase activities increased 35% in mammary tissues during pregnancy, and a further 40% increase was observed during lactation. Cyclic-GMP phosphodiesterase activity also increased during pregnancy but activities were not different in glands from lactating mice vs glands from pregnant mice. These results are discussed with regard to a possible role of cyclic-GMP in regulating lactational processes.

Animals↗
PubMed1975

Absence of sensitization to epinephrine-induced cardiac arrhythmia and fibrillation in dogs and cats anesthetized with CI 744.

Ci 744 (20 mg/kg, given intramuscularly (IM) produced a reliable level of surgical anesthesia in both dogs and cats. Animals anesthetized in this way did not have an increased sensitivity to cardiac fibrillation after they were given epinephrine. Epinephrine-induced ventricular arrhythmia observed in C1 744-anesthetized animals was eliminated in cats and was markedly reduced in dogs by bilateral vagotomy. Myocardial fibrillation was not produced by epinephrine (0.1 to 100 mug/kg, intravenously (IV) in dogs and cats anesthetized with C1 744 alone. Pentobarbital anesthesia, like C1 744 anesthesia, did not sensitize the heart, whereas a significant number of thiamylal-halothane-anesthetized animals died from cardiac fibrillation after they had been given epinephrine. Additional dogs were anesthetized with C1 744 or pentobarbital and given a series of pressor and depressor agents (isoproterenol, epinephrine, tyramine, 1, 1-dimethyl-4-phenylpiperazium iodide (DMPP) plus bilateral carotid occlusion) before and after vagotomy. The responses with either anesthetic were similar with the exception that the reflex bradycardia to pressor agents was more evident in C1 744- than in pentobarbital-anesthetized dogs.

Anesthesia, General↗