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Biomedical subjects

S A Stalcup

Publications and source records attributed to S A Stalcup.

10 recordsLinked to original sources
PubMed1979

Inhibition of converting enzyme activity by acute hypoxia in dogs.

We studied the effect of a change in oxygen tension on converting enzyme activity in anesthetized, paralyzed, catheterized dogs ventilated with room air, 100% O2, and hypoxic gas mixtures. Bradykinin was continuously infused into the femoral vein and simultaneous samples drawn from the pulmonary artery and left atrium; bradykinin was extracted into ethanol and measured by radioimmunoassay. Clearance of bradykinin by lung converting enzyme decreased from 96% at PaO2 levels above 95 Torr to 0% below 26 Torr. Inhibition of enzyme activity was rapid in onset (less than 2 min), closely correlated with PaO2 (r = 0.92, P less than 0.001), and reversible within 2 min after return to room air breathing. Converting enzyme activity of the systemic vascular bed was also inhibited by hypoxia; kininase I activity was unaffected by oxygen tension. Although arterial bradykinin concentrations in the range of 0.5 ng/ml produced hypotension in normoxic animals, elevations to 30 ng/ml had no hypotensive effect in hypoxic dogs. During acute hypoxia, venous bradykinin will pass through the lung unmetabolized, and local levels of angiotensin II and bradykinin will vary in vascular beds with different oxygen tensions, providing a finely-graded mechanism for blood flow regulation.

Animals↗
PubMed1979

Increased circulating bradykinin during hypothermia and cardiopulmonary bypass in children.

To determine whether cold could activate the kallikrein-kinin system in vivo as it does in vitro, the circulating systemic concentrations of bradykinin were serially measured in 10 cyildren with congenital diseases of the heart undergoing corrective cardiac surgery. Bradykinin was measured by radioimmunoassay in blood samples obtained before, during and after profound hypothermia (to 18 degrees C) and cardiopulmonary bypass. The circulating concentrations of bradykinin increased significantly as body temperature decreased during surface cooling. The increase in circulating bradykinin was associated with a decrease in the circulating level of bradykininogen, the precursor of bradykinin. With the onset of cardiopulmonary bypass and hence, removal of the lung and pulmonary converting enzyme from the circulation, there was a further rise in the already elevated concentrations of bradykinin. This is the first in vivo demonstration that hypothermia leads to an increase in the circulating concentrations of bradykinin.

Blood Pressure↗
PubMed1979

Inhibition of angiotensin converting enzyme activity in cultured endothelial cells by hypoxia.

Endothelial cells in tissue culture degrade bradykinin and convert angiotensin I to angiotensin II. These are both functions of a single dipeptidyl hydrolase, angiotensin converting enzyme. Monolayer cultures were prepared from human, rabbit, pig, and calf vessels. Angiotensin converting enzyme activity was assessed by adding either bradykinin or angiotensin I to the cells in culture flasks, and measuring residual peptide over time by radioimmunoassay. Peptide degradation was inhibited by the specific converting enzyme inhibitor, SQ 20881. The flasks were equilibrated with varying hypoxic gas mixtures: hypoxia rapidly (less than 2 min) decreased enzyme activity and room air restored it as rapidly. The extent to which activity was reduced was a direct function of PO2 (r = 0.93, P less than 0.001), and there was no enzyme activity below a PO2 of 30 mm Hg. Four preparations were studied with respect to decrease in enzyme activity by hypoxia: (a) intact cells in monolayer, (b) sonicated cells, (c) sonicated cells from which converting enzyme was partially dissolved by a detergent, and (d) purified converting enzyme. Hypoxia had progressively less of an inhibiting effect on the enzyme activity of the preparations as the degree of cell integrity decreased. Hypoxia inhibits angiotensin converting enzyme activity in cultured endothelial cells, but the effect of hypoxia is not on the enzyme per se, but appears to be a unique characteristic of the endothelial cell.

Animals↗
PubMed1978

Effect of hyperinflation and atelectasis on fluid accumulation in the puppy lung.

The effects of hyperinflation and of atelectasis on accumulation of fluid in the lung was studied in 12 anesthetized spontaneously breathing puppies. Vascular pressures were raised and the plasma colloid osmotic pressure was reduced by the infusion of 0.9% saline thus promoting the formation of pulmonary edema. A tracheostomy was performed and the left lower lobe catheterized in all puppies. In five puppies hyperinflation of the left lower lobe was achieved by applying a continuous positive airway pressure (CPAP) of 10 Torr. In seven other puppies the left lobe was made atelectatic by occluding its bronchus after ventilating the lungs with 100% oxygen. The right lung was ventilated to ambient pressure in all puppies. The extravascular lung water content was determined by the difference in wet and dry lung weights corrected for residual blood. We found that hyperinflation produced by CPAP enhanced and atelectasis opposed fluid accumulation in the puppy lung.

Animals↗
PubMed1978

Gestational changes in pulmonary converting enzyme activity in the fetal rabbit.

Changes in angiotensin-converting enzyme were measured in the lungs of fetal rabbits isolated and perfused in situ at varying ages from 22 days gestation to 7 days of age under controlled conditions of flow, pH, and temperature. Enzyme activity was assessed by infusing bradykinin or angiotensin I in Krebs-Henseleit solution and measuring residual peptide in the effluent by radioimmunoassay. The levels of substrate studied were below those required for enzyme saturation. Lungs of 22 day gestation fetuses removed only one-third of either peptide. The activity at term and in neonatal life resulted in more than 80% peptide removal. The time of the greatest rise in the percent substrate cleared occurs earlier than the time of the greatest increase in lung and body weight. The lower percentage of substrate cleared in early gestation appears to result in part from a limited surface area for enzyme activity in the primitive fetal pulmonary microvascular bed, since morphological studies with fluorescein-tagged anticonverting enzyme antibody demonstrated the presence of enzyme in the lung as early as 17 days of gestation. Electron micrographs of the pulmonary endothelial cell surface reveal that the degree of surface infolding and hence surface area increases with gestation. The higher percentage of substrate cleared in later gestation closely parallels the structural and ultrastructural development of the vascular bed. The presence of converting enzyme in the placenta by the second third of gestation and the large size of the placenta suggest that this organ may be a major locus of converting enzyme activity in the fetus.

Angiotensin I↗
PubMed1978

Distribution and development of angiotensin converting enzyme in the fetal and newborn rabbit. An immunofluorescence study.

The distribution and development of angiotensin converting enzyme (EC 3.4.15.1) were studied in fetal and newborn rabbits, using fixed tissues embedded in paraffin and stained with a fluorescein-conjugated antibody specific for the enzyme. The enzyme was found at the luminal plasma membrane of endothelial cells from the second third of gestation to the neonatal period. In addition, two types of epithelial cells also contained the enzyme, renal tubular and intestinal. The vascular enzyme may play a role in the regulation of its vasoactive peptide substrates, angiotensin and bradykinin, at term.

Animals↗
PubMed1975

Planning for a pediatric disaster -- experience gained from caring for 1600 Vietnamese orphans.

The sudden arrival of 1600 Vietnamese orphans in San Francisco required the rapid development of a co-ordinated disaster plan, including the overnight establishment of a 1000-bed pediatric field hospital. The plan required rapid identification and involvement of lay and governmental resources, acute medical triage and provision of ongoing medical care and basic nurturing services and eventual discharge to adoptive families. Because one third of the orphans were under six months of age, conventional nursery resources were insufficient, and a "warehouse" model was implemented. This process required development of a specialized transportation and communication system, the services of 800 physicians, 1400 nurses, and 3200 volunteers and 162 back-up acute hospital beds. Disaster planning in most sizable American cities has focused on the problems of adults. Because of the unusual problem presented by infants and small children, we recommend that cities carefully evaluate their disaster planning with special reference to the needs of children.

Adoption↗
PubMedDate not supplied

The effects of pathophysiologic state on the metabolism of vasoactive peptides by mammalian lung.

The pulmonary circulation plays a major role in the metabolism of angiotensin I (AI) and bradykinin through the activity of endothelial cell membrane-bound dipeptidylcarboxypeptidase, converting enzyme of kininase II. This report describes studies which investigate the effects of hypoxia on the function of converting enzyme in vivo in dogs and in endothelial cells in culture. Pulmonary converting enzyme function was assessed by both a blood pressure response technique and radioimmunoassay of bradykinin. Conversion of AI in vivo is decreased during acute alveolar hypoxia. At a PaO2 of 30 mmHg, conversion of AI is decreased to one-half control values. This decrease in AI conversion could not be related to hemodynamic factors in the pulmonary vasculature induced by hypoxia. Clearance of bradykinin by lung converting enzyme decreased from 96% at PaO2 levels above 95 torr to 0% below 26 torr. Hypoxic inhibition of enzyme activity was rapid in onset (less than 2 min), was closely correlated with PaO2 (r = 0.92, p less than 0.001) and reversible within 2 min after return to room air breathing. Converting enzyme activity of the systemic vascular bed also is inhibited by hypoxia. Converting enzyme activity also was studied by adding bradykinin or AI to endothelial cells in culture flasks and measuring residual peptide over time by radioimmunoassay. Hypoxia rapidly (less than 2 min) decreased enzyme activity and room air restored it rapidly. There was no enzyme activity below a PO2 of 30 mmHg. Hypoxia does not affect the activity of purified converting enzyme free of the endothelial cell. Metabolic and respiratory acidosis, as well as metabolic and respiratory alkalosis, had no significant effect on converting enzyme function in vivo in intact animals. While converting enzyme is resistant to a number of pathophysiological insults, it is extraordinarily responsive to acute hypoxia which may have important implications for systemic vasomotor control in conditions associated with clinical hypoxia and hypoxemia.

Acid-Base Equilibrium↗