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Biomedical subjects

M D Bailie

Publications and source records attributed to M D Bailie.

At least 19 recordsLinked to original sources
PubMed1993

Diuretic treatment agents.

Diuretics are important drugs in the treatment of fluid overload and other related conditions in infants and children. Their rational use depends on adequate knowledge of how they work and how they interact with other drugs and the changing physiology caused by normal growth and development and by various disease states. It is in the best interest of the patient for the physician prescribing these drugs to have appropriate knowledge of their mode of action. It is clear that with the exception of a few drugs the amount of appropriate data available on the use of these drugs in children is limited at best. As newer drugs become available, the physician caring for such children must be sure that there is some clear indication for its use in preference to those with which we have more experience.

Diuretics↗
PubMed1992

Development of the endocrine function of the kidney.

The kidney is a complex endocrine organ, and many of the renal hormones have actions that help regulate renal function. Although we have much more to learn about the role of most of these hormones in the regulation of renal function in both the newborn and adult kidney, there are some important aspects to keep in mind as we approach therapeutic interventions in sick newborn and premature infants. Because of the many interactions between hormonal systems, drugs that we may use for specific actions on one system may have effects on others as well (ACE inhibitors, cyclooxygenase inhibitors, dopamine antagonists). In addition, it is clear that the state of the organism may play a role in which of the renal hormones is active. Finally, the nonrenal hormonal systems that affect renal function (aldosterone, atrial natriuretic peptide, vasopressin, etc) may interact to change further expected results of any therapeutic intervention. Therefore, it behooves the clinician to monitor carefully renal function whenever modifications in therapy are made, whether it is a change in mechanical or pharmacologic intervention.

Adult↗
PubMed1984

Role of the renin-angiotensin system in hypertension after coarctation of the aorta.

The effect of inhibition of angiotensin I converting enzyme by captopril was studied in rats with aortic coarctation produced above the renal arteries. When captopril therapy was started before coarctation, blood pressure above the narrowing and the pressure difference across the coarctation were reduced, compared with values in animals with coarctation not given therapy. When captopril therapy was started 10 days after the coarctation, there was no effect on blood pressure. Plasma renin activity increased 24 hours after coarctation and returned to control levels by 5 days. Captopril caused an increase in renin activity and a decrease in plasma aldosterone concentrations. After 5 days, there was no difference in renin activity and plasma aldosterone levels between animals with coarctation given captopril therapy early and late and between appropriate controls. Our data suggest that the renin-angiotensin system is important in the early development but not in the maintenance of coarctation hypertension.

Animals↗
PubMed1983

Intrarenal distribution of renin in the developing rabbit.

The purpose of this study was to evaluate the intrarenal distribution of renin in individual glomeruli during development in the rabbit. Superficial cortical and juxtamedullary glomeruli were obtained from animals at 1, 2, and 4 wk of age and from adults to determine renin concentration. In addition, kidney weight, total renal renin content, plasma renin concentration, and plasma angiotensin I concentration were also measured during this time period. Superficial cortical glomerular renin concentration at 1 wk of age averaged 7.7 +/- 1.6 (S.E.M.) pg/h whereas juxtamedullary glomerular renin concentration was 4.5 +/- 1.8 pg/h. There was no difference in concentration between the superficial and deep glomeruli at this age. At 2 wk of age, however, superficial glomerular content had increased significantly to 143.8 +/- 2.94 pg/h whereas the juxtamedullary concentration remained unchanged (7.9 +/- 1.6 pg/h). The concentration in the superficial nephrons continued to increase with age. At 4 wk, superficial renin content was 224.6 +/- 27.2 whereas the deep nephrons did not change (16.0 +/- 7.5 pg/h). Adult animals demonstrated a further increase to 842.7 +/- 15.1 pg/h in the superficial nephrons whereas the deep nephrons continued to remain low (15.9 +/- 4.7 pg/h). The results of this study demonstrate that after the first week of life there was significantly more renin activity in glomeruli in the outer cortex than in the juxtamedullary cortex. Total renal renin concentration increased with age and showed a significant positive correlation with the concomitant increase in kidney weight. But renal renin content increased more than kidney weight between 1-2 wk of age.

Age Factors↗
PubMed1983

Urinary excretion of renin in the dog: effect of changes in plasma renin.

By using standard clearance and stop flow techniques, studies were carried out in anesthetized dogs to clarify further the mechanism(s) of excretion of renin in urine. The clearance of renin was 0.61 +/- 0.19 ml/min in control experiments and increased significantly to 1.26 +/- 0.38 ml/min after furosemide. The fractional excretion of renin increased from 1.51 +/- 0.45% during control to 3.90 +/- 0.98% after furosemide. The rate of excretion of renin was increased 10-fold during furosemide diuresis associated with a 10-fold increase in plasma renin concentration. Extracellular fluid volume expansion also produced a diuresis but no increase in plasma renin or renin excretion. Hemorrhage produced a 3.5-fold increase in plasma renin concentration and a 200-fold increase in urinary excretion of renin. When renal artery perfusion pressure was reduced to one kidney, the excretion of renin in the urine from that kidney increased, whereas there was no significant change in the excretion from the contralateral kidney. Reduction in renal artery perfusion pressure was associated with a 3-fold increase in the concentration of renin in the renal vein from the experimental kidney but an insignificant 2-fold increase in the arterial plasma renin concentration. Stop-flow studies demonstrated that renin enters the urine with the glomerular filtrate. The decreased concentration of renin in samples from the proximal tubule suggests that renin is being metabolized and/or reabsorbed in this nephron segment. In the distal nephron, there appears to be a site in which renin may be added to the tubular fluid. The results of these studies suggest that renin excretion in the urine is a complicated process. Excretion of renin in the urine is related in part to plasma renin activity but probably more importantly to the rate of production of renin in the kidney.

Animals↗
PubMed1982

Age-related differences in the stoichiometry of the renin-angiotensinogen reaction in rat plasma.

Generation of immunoreactive angiotensin I (AI) in plasma of either adult or 10-day-old rats proceeded via first-order kinetics. Although the concentration (Vmax) of renin was 5-fold greater in neonatal compared to adult plasma, the specific activity (kapp/Vmax) of the enzyme was 2-fold greater in adults. Both enzymes exhibited a similar affinity (Km) for angiotensinogen; and at both ages, the generation of AI was limited by insufficient endogenous substrate to sustain maximum rates. In conclusion, although the catalytic properties of renin do not change with age, subtle differences in the stoichiometry of the reaction may have profound implications in determining compensatory mechanisms involved in renin-dependent regulation of homeostasis in developing animals.

Aging↗
PubMed1981

Angiotensin II metabolism by tissues from developing rats.

Asp1-125I-Tyr4-angiotensin II (125I-AII) was degraded during incubation with rat plasma or homogenates of liver or kidney. The electrophoretic profile of peptide fragments revealed that the disappearance of 125I-AII was first order and was accompanied by an accumulation of 125I-tyrosine in the incubation medium. The only other metabolites of angiotensin AII detectable by peptide mapping were the amino-terminus tetrapeptide and the carboxy-terminus hexapeptide. The appearance of these fragments was highly variable, suggesting that endopeptidases did not constitute the ultimate cleavage of angiotensin II hydrolysis. The half-life of 125-AII in plasma or liver homogenates did not change with age (approximately 8 to 12 and 6 to 9 min, respectively). In contrast, the rate of disappearance of 125I-AII in homogenates of rat kidney depended upon the age of the rat from which the tissue was obtained. The half-life of 125AII decreased three-fold (from approximately 8.3 to 2.8 min) between 2 wk after birth and adult (approximately 8 wk). This increase in the rate of metabolism of 125I-AII was accompanied by a concomitant two-fold, age-related increase in the rate of appearance of 125I-tyrosine in the reaction mixture containing renal tissue.

Aging↗
PubMed1981

Effect of acetazolamide on renal function of the newborn piglet.

The effects of renal development on the response of newborns to acetazolamide were determined in an animal model, 5- and 20-day-old piglets. Increasing doses of acetazolamide increased both sodium and potassium excretion in 5-day-old piglets. Sodium excretion increased from 1.89 muEq/min during control periods to 15.7 muEq/min during infusion of acetazolamide (75 mg/kg/h). Potassium excretion increased to 20 muEq/min during acetazolamide infusion and urine pH increased from 5.7 to over 8.0. Sodium excretion by 20-day-old piglets given acetazolamide was similar to that of 5-day-old piglets but potassium excretion was twice as great (40 muEq/min). Changes in urine pH of the two groups were identical. It is concluded that the natriuretic response of 5-day-old piglets to acetazolamide is similar to that of older animals. In newborn piglets, moderate increases in sodium excretion by acetazolamide were accompanied by a marked kaliuresis. These data may identify a role for carbonic anhydrase in potassium excretion by newborn similar to that of adults.

Acetazolamide↗
PubMed1980

Species differences in the kinetics of the renin-substrate reaction in plasma.

In view of the substrate-dependence of renin, it was of interest to examine the kinetics of the renin-angiotensinogen reaction in plasma of various species to establish differences in stoichiometry. The results also provide an indication of assay conditions appropriate for accurate measurement of the reaction velocity. Plasma from hogs, dogs, and rats served as the source of renin for incubation with homologous angiotensinogen. The rate of production of radioimmunoassayable angiotensin I increased with increasing concentrations of angiotensinogen. This substrate-dependence of renin conformed to conventional Michaelis-Menten kinetics. The concentration of angiotensinogen was less than that required for half maximum velocity in dog and rat plasma. In contrast, endogenous substrate in hog plasma was sufficient to sustain near maximal rates of generation of angiotensin I. Purification of angiotensinogen altered the catalytic properties of angiotensinogen making it a poor representative substrate for renin. Hog and rat renin were saturable with high concentrations of unextracted plasma angiotensinogen. In contrast, it was not possible to saturate the dog enzyme with unextracted substrate. The interspecies differences in stoichiometry of the reaction indicate that standardization of assay conditions for various species of renin is not justified.

Angiotensin I↗
PubMed1980

Age-related differences in angiotensin I metabolism by isolated perfused rat lungs.

The pulmonary vasculature has been implicated in the clearance of several vasoactive substances from the circulation including angiotensin I (AI). In view of the previously reported age-related differences in angiotensin-converting enzyme (ACE) activity of lung homogenates, it was of interest to examine the ability of intact perfused lungs to metabolize AI. Lungs from newborn and adult rats were perfused with Krebs bicarbonate buffer containing 1.0 ng/ml AI in a single-pass, nonrecirculating system. The rate of perfusion was normalized to lung mass. Removal of AI was determined from the transpulmonary difference in radioimmunoassayable AI. Lungs from 7-day-old rats removed a smaller fraction of AI from the circulation than did adult lungs. The age-related increase in AI clearance was accompanied by an increase in pulmonary ACE content; however, enzyme content alone could not account for the observed differences. The increased metabolism of AI by the pulmonary vasculature during development may contribute to the age-related increase in circulating angiotensin II concentrations.

Aging↗