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Biomedical subjects

B T Jackson

Publications and source records attributed to B T Jackson.

At least 55 records · Page 3Linked to original sources
PubMed1983

Placental transfer of phenylalanine in Macaca mulatta and Macaca fascicularis.

We investigated placental transport mechanisms of phenylalanine in Macaca mulatta and Macaca fascicularis. In the beginning of the third trimester we administered i.v. phenylalanine and p-chlorophenylalanine to pregnant animals. Initial higher phenylalanine concentrations were observed followed by a rapid decrease in both rhesus mothers and fetuses when compared with phenylalanine levels in fascicularis mothers and fetuses. In general, however, placental transfer mechanisms of phenylalanine did not differ significantly between the two species.

Animals↗
PubMed1982

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia.

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia was studied in six lamb fetuses with gestational ages of 119 to 140 days. In chronic preparations, we determined fetal heart rate, umbilical blood flow (by electromagnetic flowmeter), PO2, PCO2, and pH and calculated fetal cardiac output and organ blood flows (using 15 mu nuclide-labeled microspheres). Observations were made during control periods and periods of hypoxemia, beta-adrenergic blockade by propranolol, and hypoxemia superimposed upon the beta-adrenergic blockade. Beta blockade effected a decrease in fetal heart rate both at rest and with hypoxemic stress. Propranolol produced a fall in cardiac output with hypoxemia, but the meaning of this in regard to beta-adrenergic effects is unclear. Beta blockade did not alter fetal arterial pressure or general blood flow distribution. However, we observed a decrease in umbilical blood flow in response to propranolol under both normoxic and hypoxemic conditions.

Animals↗
PubMed1982

Plasma catecholamines during hypoxemia in fetal lamb.

Changes in peripheral plasma catecholamines were studied during varying degrees of hypoxemia in fetal lambs of 95-140 days gestation. Epinephrine and norepinephrine concentrations were measured by radioenzymatic assay in plasma obtained simultaneously from the distal aorta and inferior vena cava in 15 chronically catheterized fetuses with the mother breathing 20, 10, or 8% oxygen mixtures. Levels of both epinephrine and norepinephrine increased significantly after 5 min of hypoxemia and showed a strong inverse exponential correlation with PO2 (P less than 0.001). Plasma norepinephrine always exceeded epinephrine concentrations (P less than 0.01). Resting arterial and venous catecholamine levels were not different, but during hypoxemia arterial levels of both epinephrine and norepinephrine exceeded venous levels significantly, suggesting the adrenal medulla as a major source of these substances. Hypoxemia led to fetal bradycardia, the degree of which moderated somewhat with extremely low oxygen tensions and associated very high catecholamine levels. Fetal blood pressure increased initially in proportion to norepinephrine levels but reached a plateau at concentrations higher than 10 ng/ml. Although concentrations of catecholamines were lower in the earlier gestation fetuses studied, similar qualitative relations between catecholamines and PO2 were evident at all gestational ages.

Animals↗
PubMed1982

A study of placental transfer mechanisms in nonhuman primates using [14C]phenylalanine.

Placental transfer mechanisms were investigated in pregnant Macaca Fascicularis and Macaca mulatta during the gestational age of 120 to 130 days. These primates underwent an operative procedure that allowed continuous fetal blood sampling. The administration of [14C]phenylalanine into the maternal circulation revealed a significant increase of radioactive material in the fetal circulation, indicating an active placental transport mechanism unidirectional to the fetus. When [14C]phenylalanine was injected into the fetus, radioactive aromatic amino acids in the maternal circulation increased only slightly over time, resembling a simple diffusion process.

Animals↗
PubMed1981

Control of the simian fetal hemoglobin switch at the progenitor cell level.

This investigation was designed to define the cellular level at which the gamma to beta globin switch is established in the developing simian fetus in order to determine whether the switch is controlled by environmental influences within differentiating erythroid precursors or predetermined by the genetic program of erythroid progenitors. Samples of marrow and liver were obtained from rhesus fetuses throughout the switch period, and marrow was obtained from adult rhesus monkeys. Globin chain synthesis was then measured in differentiated erythroblasts and in erythroid progenitor-derived colonies grown in semisolid media. The relative rates of synthesis of gamma and beta chains were determined by the uptake of [(3)H]leucine into the respective chains separated by Triton gel electrophoresis and in some cases by urea carboxymethyl cellulose chromatography. Four periods of the switch were defined during fetal development. In the preswitch period both erythroblasts and progenitor-derived colonies produced <5% beta globin. In the early switch erythroblasts produced 5-15% beta globin, while progenitor-derived colonies produced 10-35% beta globin. In mid-switch erythroblasts synthesized 50% beta globin, whereas progenitor-derived colonies produced only 15-35% beta. At the completion of the switch erythroblasts produced 100% beta globin, while progenitor-derived colonies produced as little as 40% beta chains. We conclude that the program of globin synthesis that characterizes the fetal switch is established at the level of erythroid progenitors. Fetal erythroid burst-forming units (BFU-E) dominate the marrow prior to the switch. The early switch period is heralded by the appearances of adult erythroid burst-forming units programmed to express increasing beta chain synthesis in colonies. By mid-switch a second class of adult erythroid progenitors capable of giving rise to fetal and adult hemoglobin synthesis in in vitro colonies becomes apparent. These shifting populations of erythroid progenitors with unique globin synthesis programs give rise to the erythroblasts that create the sigmoid pattern of the fetal to adult hemoglobin switch in the developing simian fetus.

Age Factors↗
PubMed1980

The effect of fetal heart rate on cardiovascular function during hypoxemia.

The effect of heart rate changes on cardiovascular function during hypoxemia was studied in lamb fetuses. In chronic preparations, we determined fetal heart rate, descending aortic blood flow (by electromagnetic flowmeter), PO2, PCO2, and pH and calculated fetal cardiac output (CO) and organ blood flows (with the use of 15 mu nuclide-labeled microspheres). Observations were made during control and hypoxemic states either alone or in the presence of parasympathetic blockade by atropine. Fetuses exposed to moderate hypoxemia (ewe breathing 10% oxygen) developed a significant bradycardia which was prevented by atropine pretreatment; no significant change in CO occurred in either case. Fetuses exposed to severe hypoxemia (8% oxygen) developed bradycardia and a significant decrease in CO; atropine pretreatment prevented the bradycardia but failed to prevent the decrease in CO. Atropine administered to the already severely hypoxemic fetus increased the heart rate but did not restore the depressed CO. The redistribution of blood flow from low-priority (e.g., viscera) to high-priority (e.g., myocardium) tissues correlated with the degree of hypoxemia. Myocardial blood flow was greater during hypoxemia when bradycardia was prevented by atropine than during hypoxemia alone; otherwise, blood flow distribution in response to hypoxemia was unaffected by atropine blockade.

Acetylcholine↗
PubMed1980

Circadian periodicity of plasma corticosterone levels in rats subjected to hemorrhagic shock and surgical trauma.

The effects of surgical trauma and hemorrhagic shock on the circadian rhythmicity of corticosteroid secretion in the rat were investigated. The estimations were performed at 4-hour intervals for a 24-hour period. Control animals exhibited a characteristic circadian rhythm of plasma corticosterone with peak concentrations occurring at 8 p.m. followed by a gradual fall during the night, reaching a minimum at 8 a.m. Severe stress induced by hemorrhagic shock or surgical trauma caused a dramatic alteration in corticosterone rhythms which persisted up to 72 h following surgery or hemorrhage. It is apparent that the physiological mechanisms which regulate adrenal rhythmicity are disrupted for a prolonged period following major stress or trauma.

Animals↗
PubMed1979

Prophylactic peroperative intravenous metronidazole in elective colorectal surgery.

In a prospective double-blind randomised trial 83 patients undergoing elective colorectal surgery were given either preoperative intravenous metronidazole or intravenous normal saline. No other antimicrobials were given. Bowel preparation was the same for both groups. Deep post-operative wound sepsis occurred in 6 of 44 (13-6%) patients on metronidazole but in 20 of 39 (51-2%) control untreated patients. Anaerobes were responsible for all cases of deep sepsis in the metronidazole group (in 5 of the 6 cases aerobes were also isolated), and for 16 of the 20 cases of deep sepsis in the control group (all with aerobes). Superficial infection in the metronidazole group was caused by aerobes. Anastomotic leakage occurred in 5 of the 6 patients who developed deep sepsis on metronidazole and in 10 of 20 patients on placebo. Peroperative intravenous metronidazole dramatically reduced postoperative sepsis but failed to prevent infection in the presence of anastomotic breakdown.

Bacterial Infections↗
PubMed1979

Tuberculous peritonitis and role of diagnostic laparoscopy.

Eleven patients with tuberculous peritonitis were treated in a London hospital between 1971 and 1978. All the patients were immigrants (mean age 30 years). The history of abdominal symptoms was often short and sometimes difficult to distinguish from that of Crohn's disease or neoplasm. The diagnosis was made by laparoscopy and target peritoneal biopsy in eight of these patients. Laparoscopy is a safe and effective method of obtaining an early diagnosis in patients with suspected tuberculous peritonitis.

Adult↗
PubMed1977

Sclerosing peritonitis due to practolol.

Six patients developed intestinal obstruction from sclerosing peritonitis due to practolol. Complete surgical removal of the abnormal membrane appears to be necessary.

Angina Pectoris↗
PubMed1977

Fetal bile salt metabolism. The intestinal absorption of bile salt.

The intestinal absorption of sodium taurocholate was studied in the near-term fetal and neonatal dog. Absorption rates were measured in vivo in isolated loops of fetal jejunum and ileum. Absorption was also measured in vitro in everted sacs and rings of fetal and neonatal jejunum and ileum. The maximal rates of taurocholate absorption observed after instillation of 1 micronmol taurocholate into closed segments of fetal jejunum and ileum with intact blood supply were not significantly different (P less than 0.2), and equalled 0.282+/-0.026 (mean+/-SEM) and 0.347+/-0.051 micronmol/h per 10-cm segment length jejunum and ileum, respectively. Similarly, the rates of absorption from open segments of jejunum and ileum perfused with 0.4 and 1.0 mM taurocholate were nearly identical (0.232+/-0.040 and 0.255+/-0.039, respectively at 0.4 mM, and 0.470+/-0.065 and 0.431+/-0.013, respectively at 1.0 mm) (P greater than 0.2). At perfusate concentrations of 4.0 mM, moreoever, jejunal absorption exceeded ileal absorption (1.490+/-0.140 and 0.922+/-0.200, respectively (P less than 0.05). As expected, concentration of taurocholate by the mucosa was readily demonstrated in adult ileal, but not in adult jejunal everted rings. In contrast, there were no significant differences in mucosal uptake of taurocholate by fetal jejunal and ileal rings. Fetal ileal mucosal concentrations were not significantly above those in the incubation medium after 1-h exposure of the mucosa to 0.003, 0.03, and 0.3 mM taurocholate. Uptake was proportional to incubation medium concentration over the full range of values. This was also true of tissues from 1-wk-old neonates. However, by 2 wk of age, ileal mucosal concentration of taurocholate was evident and adult levels were attained by 5 wk of age. It is concluded that taurocholate is absorbed by the fetal gut and that ileal absorption is no more efficient than jejunal absorption. Although active glucose transport was demonstrable in both jejunum and ileum, it was not possible to demonstrate an ileal mechanism for active transport of taurocholate in the fetus. Active ileal transport was not demonstrable in the newborn until at least 2 wk after birth.

Age Factors↗