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Biomedical subjects

B T Jackson

Publications and source records attributed to B T Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Adrenal corticosteroid secretion in fetal sheep: pulsatile pattern at rest.

This study was undertaken to define the resting pattern of fetal pituitary-adrenocortical function. Experiments were performed at 127-145 days gestation in fetal sheep with chronic peripheral and adrenal cannulas inserted under halothane anesthesia. With the fetus in a baseline state, over 6 h, at 30-min intervals, maternal and fetal peripheral samples were collected for blood gases and cortisol (F), corticosterone (B), and adrenocorticotropic hormone (ACTH) concentrations, and three successive, 2-min adrenal samples were collected for determination of F and B secretion rates. We observed high-frequency, episodic bursts of F secretion. A lower frequency oscillation of F secretion, with a period of approximately 90 min, was defined by cosinor analysis. The mean amplitude of the oscillation increased from 45 to 507 ng/min with advancing gestation. The pattern of B secretion was similar to that for F but was quantitatively lower. An oscillatory period of approximately 90 min for plasma F was present in a majority of experiments. Pulsatile rhythms for ACTH were defined in 10 of 14 experiments, with periods ranging from 1.64 h in the least mature group to 2.37 h in the oldest fetus. Mean data revealed exponential increases in both F secretion and plasma ACTH from 129 to 145 days gestation.

Activity Cycles↗
PubMed1992

The effect of hyperglycemia on acid-base and sympathoadrenal responses in the hypoxemic fetal monkey.

We investigated the influence of hyperglycemia on the fetal acid-base and sympathoadrenal responses to hypoxemia (maternal FIO2 9%) in rhesus monkey fetuses. In chronic preparations, we determined PO2, O2 content, PCO2, pH, lactate, glucose, insulin, catecholamines, heart rate, and arterial pressure. Combined hyperglycemia and hypoxemia resulted in a decrease in fetal pH and an increase in lactate; however, the magnitude of these changes was only modestly, and not significantly, greater than those observed during euglycemic hypoxemia. These effects were much less striking than expected, based on earlier work in sheep (Shelley, Bassett & Milner, 1975; Robillard, Sessions, Kennedy & Smith, 1978). Although catecholamines increased significantly in response to hypoxemia both in hyperglycemic and euglycemic fetuses, the increase was less in the hyperglycemic group, possibly resulting from a modulating effect of the high glucose concentration on catecholamine release from the adrenal medulla. Finally, a significant fetal insulin response to hyperglycemia was seen which, suggestively, was partially inhibited in the presence of hypoxemia and its associated increase in sympathoadrenal activity.

Acid-Base Equilibrium↗
PubMed1991

Sympathoadrenal responses during hypoglycemia, hyperinsulinemia, and hypoxemia in the ovine fetus.

Interrelations of sympathoadrenal function and changes in glucose and insulin homeostasis were studied in chronically cannulated late gestation fetal sheep. Catecholamine secretory rates (based on direct adrenal sampling) and plasma concentrations were determined in the fetus during 2 h of insulin-induced hypoglycemia, during a period of hypoxemia, and during hyperinsulinemia per se (i.e., without hypoglycemia). Fetal insulin infusion (5-10 mU.kg-1.min-1) resulted in hypoglycemia and a significant rise in secretion of epinephrine but not of norepinephrine. By contrast, fetal hypoxemia caused a prompt and significant increase in adrenal secretion of both norepinephrine and epinephrine. Changes in peripheral plasma catecholamine levels were usually, but not always, qualitatively similar to those in adrenal secretion; the latter was a far more sensitive indicator of adrenal function. Hyperinsulinemia per se caused no change in adrenal secretory rates or plasma concentrations of catecholamines. Nevertheless, insulin infusion caused a fetal tachycardia even in the absence of hypoglycemia and hypoxemia, suggesting either a direct effect on the heart or stimulation of sympathetic nerves.

Adrenal Medulla↗
PubMed1991

Effects of anesthetic agents and abdominal surgery on liver blood flow.

The cause of postoperative liver dysfunction is often unclear, but a decrease in liver blood flow during anesthesia and/or major surgery may be important. Plasma half-life and clearance of indocyanine green were therefore measured in 42 patients before, during and after anesthesia and abdominal surgery. In 13 patients, liver blood flow was also estimated from indocyanine green extraction using hepatic vein catheterization. The major finding was an early decrease in estimated liver blood flow after induction of anesthesia, but not later during or after surgery. Mean indocyanine green half-life increased by 26% (p less than 0.005), mean indocyanine green plasma clearance decreased by 19% (p less than 0.01) and mean estimated hepatic blood flow decreased by 36% (p less than 0.005) during the first 30 min of anesthesia. These changes were greater in males and in patients older than 55 yr, but changes were similar with each of three anesthetic groups. Half-life, but not indocyanine green clearance, was also significantly prolonged by mid-operation in the older (greater than 55 yr) patients and in those undergoing lower abdominal surgery. We suggest that this period of reduced liver blood flow during anesthesia is caused by the effects of neuromuscular blocking agents and may contribute to postoperative liver damage.

Abdomen↗
PubMed1990

Primary extranodal non-Hodgkin's lymphoma of the extrahepatic biliary tract.

A case of extranodal non-Hodgkin's diffuse, mixed small and large cell lymphoma of the extrahepatic biliary tract with jaundice as the initial manifestation is reported in this paper. Obstructive jaundice is very rarely an early symptom in lymphoma. The pathogenesis of jaundice in this case was infiltration of the extrahepatic bile duct by lymphoma cells and fibrosis.

Aged↗
PubMed1989

Invasion and metastasis following orthotopic transplantation of human pancreatic cancer in the nude mouse.

A good experimental model for metastasis of human pancreatic cancer would be a valuable tool for the study of this process, which contributes significantly to morbidity and mortality. Models of experimental metastasis using injection of tumor cells into the portal or systemic circulation bypass some important steps of the metastatic process. We describe invasion and metastasis following orthotopic transplantation of human pancreatic carcinoma into nude mice. Tumor pieces were used as xenografts in this study, and metastases were observed in the regional lymph nodes, liver, lungs, and distant lymph nodes of the animals. Peritoneal implants and ascites were not observed in this study. Orthotopic transplantation of human pancreatic cancer in the nude mouse appears to be a promising model of spontaneous metastasis relevant to clinical reality.

Animals↗
PubMed1989

Effects of insulin infusion on plasma catecholamine concentration in fetal sheep.

To evaluate the response of the sympathoadrenal system in fetal sheep receiving exogenous insulin infusion, we measured plasma catecholamine levels in 14 chronically catheterized fetal sheep before and during an infusion of insulin for 2 days. Catecholamine values were measured in fetal arterial plasma by an electrochemical detection method. Fetal plasma norepinephrine and epinephrine concentrations increased significantly during insulin infusion. Significant inverse correlations were observed between the log norepinephrine concentration and fetal arterial oxygen content and glucose values. A significant direct correlation between the log norepinephrine concentration and fetal arterial carbon dioxide concentration was also observed. The log epinephrine concentration correlated inversely with plasma glucose concentration. Increases in fetal heart rate during both the noninfused and insulin-infused states correlated significantly with increases in norepinephrine concentration. We conclude that the sympathoadrenal system is activated during fetal insulin infusion, potentially supporting some of the fetal cardiovascular responses to insulin infusion.

Animals↗
PubMed1989

Adrenal secretion of glucocorticoids during hypoxemia in fetal sheep.

This work was undertaken to investigate the fetal adrenal corticoid secretory response to hypoxic stress in late gestation. Experiments were performed in two groups of fetal sheep of different gestational ages, group I, 129-132 (mean, 130) days and group II, 135-139 (mean, 136) days. Fetuses were prepared with chronic adrenal cannulas as well as peripheral arterial and venous catheters. With the fetus at rest and after 7, 9, 11 and, in some instances, 30 and 60 min of hypoxia (maternal FIO2 10%), precisely timed (2 min) samples of adrenal effluent were collected for determination of cortisol (F) and corticosterone (B) secretion rates. Peripheral samples were obtained intermittently for blood gas and lactate determinations. Resting corticoid secretory rates were highly variable, suggesting an episodic secretory pattern. Corticoid secretory responses to hypoxemia were significantly elevated at 7-11 min, peaked at 30 min, and remained stable at 60 min. Specifically, in group I, F secretion increased from a baseline value of 37 +/- 19 ng/min to a peak hypoxemic response of 376 +/- 80 ng/min; B secretion increased from 6 +/- 4 to 170 +/- 32 ng/min. In group II, F secretion increased from 99 +/- 20 to 653 +/- 107 ng/min; B secretion increased from 12 +/- 5 to 200 +/- 28 ng/min. When related to adrenal gland weight, there was no difference between F secretory responses in groups I and II, whereas relative B secretory responses were lower in group II than in group I at 9 and 11 min of hypoxemia. We conclude that the 129-139 day sheep fetal adrenal cortex is highly sensitive to hypoxic stress with the effect presumably mediated by elevated levels of endogenous ACTH. The B stress response decreases as gestational age advances from the 129-132 day range to 135-139 days.

Adrenal Cortex↗
PubMed1987

Fetal responses to altered maternal oxygenation in rhesus monkey.

The purpose of this study was to establish (in the primate) maternal-fetal relations for blood gas parameters and certain related aspects of fetal cardiovascular function with the mother at rest and subjected to a range of altered states of oxygenation. In 10 chronically cannulated rhesus monkey fetuses, with the mother lightly sedated with phencyclidine, on each of two days we studied the effects of maternal hypoxia and hyperoxia [(15, 10, and 100% maternal fractional concentration of inspired O2 (FIO2)] on maternal and fetal pH, PCO2, PO2 and O2 concentration (CaO2) and fetal heart rate, blood pressure, and superior vena caval (SVC) flow distribution. We observed a linear correlation between maternal and fetal pH and PCO2. There was evidence of a fetal metabolic acidosis with 10 but not with 15% hypoxia. Maternal-fetal PO2 and CaO2 correlated in curvilinear and linear fashion, respectively. Maternal-fetal CaO2 difference was maintained within a narrow range (2.7-4.8 vol%) for various states of maternal oxygenation, showing a tendency to expand only with severe (10%) hypoxia. Results indicate that quantitative delivery of O2 to the placenta was of paramount importance as a determinant of O2 transfer to the fetus and are compatible with a "concurrent flow" model of transplacental O2 diffusion. Fetal heart rate decreased progressively with 15 and 10% hypoxia. SVC flow to lungs and placenta varied reciprocally with changes in fetal oxygenation. As indicated by distribution to the heart, shunting of SVC flow through the foramen ovale was modest at rest, with no evident change in response to fetal hypoxemia.

Animals↗
PubMed1987

Plasma catecholamines in the hypoxaemic fetal rhesus monkey.

To assess the response of the sympathoadrenal system of the primate fetus to oxygen deprivation, we measured plasma catecholamines in 8 chronically catheterized fetal rhesus monkeys. A range of fetal hypoxaemia was produced by having the mother inspire 15, 10, or 9% oxygen mixtures while tranquilized with ketamine. Catecholamines from fetal carotid and maternal femoral arteries were measured by radioenzymatic assay. Fetal plasma norepinephrine and epinephrine concentrations increased significantly at all levels of hypoxaemia, but dopamine increased only at very low fetal oxygen tensions. Norepinephrine levels exceeded those of epinephrine and dopamine under all conditions. Relatively more severe hypoxaemia was necessary to elevate concentrations of epinephrine above baseline as compared with norepinephrine. A negative exponential correlation (P less than 0.001) was found between both fetal arterial PO2 and oxygen content and plasma norepinephrine and epinephrine, which was qualitatively similar to that observed previously in the sheep fetus. Maternal catecholamines were found to increase during hypoxaemia as well, but to a lesser degree than in the fetus.

Animals↗
PubMed1986

Bile peritonitis after removal of T-tubes from the common bile duct.

Bile peritonitis can occur when a T-tube is electively removed from the common bile duct, but this is regarded as a rare complication. Plastic T-tubes are known to increase the risk and should not be used. Latex rubber T-tubes are preferred but the complication can still occur. We present three patients with this complication despite the use of a latex T-tube. A questionnaire was sent to 107 surgeons in the South East Thames Region. The replies showed that the complication is far more common than generally realized. Based on these replies the risk of bile peritonitis each time a latex T-tube is electively removed from the common bile duct is calculated to be 0.84 per cent or 1 in every 119 explorations.

Aged↗
PubMed1986

Transfemoral placement of intraluminal polyurethane prosthesis for abdominal aortic aneurysm.

Because of the significant mortality associated with the conventional surgical approach to abdominal aortic aneurysms (AAA) in the high risk patients and in those with ruptured aneurysms, we have developed a new approach to this problem, intraluminal aneurysm exclusion. This was achieved by an intraluminal prosthesis which approximated the diameter of the aorta above and below the aneurysm and is inserted through the femoral artery. The prosthesis consisted of biomedical grade elastomeric polyurethane with a NITINOL and/or stainless steel frame and was designed in such a configuration that it could be compressed inside a 15 F catheter and then regain its original shape after being discharged inside the aorta. The polyurethane prosthesis tolerated static pressures in excess of 300 Torr. Aneurysmal aortas were created in three adult sheep using large knitted Dacron pathches (6 X 9 cm) sewn onto a longitudinal aortotomy. After 4-6 weeks, an intraluminal prosthesis was passed transfemorally to the location of the aortic aneurysm. Following satisfactory placement and expansion of the prosthesis, a laceration was produced in the aneurysmal wall. No bleeding developed, which confirmed the integrity of the prosthesis in excluding the aneurysm from the aorta proper. Pulsation in the iliac arteries indicated the presence of aortic blood flow through the prosthesis. Autopsy examination demonstrated directly that the prosthesis was open and that its two ends were fixed in the aorta above and below the aneurysm. The study has demonstrated that intraluminal AAA exclusion could be achieved with an intraluminal polyurethane prosthesis inserted through the femoral artery.

Animals↗