PubMed Health⌕ Search

Biomedical subjects

R Lam

Publications and source records attributed to R Lam.

At least 19 recordsLinked to original sources
PubMed1992

Ovine maternal and fetal renal vasopressin receptor response to maternal dehydration.

OBJECTIVE: Arginine vasopressin secretion increases in response to increased plasma osmolality or hypovolemia. Dehydration-induced increases in plasma arginine vasopressin levels have been shown to down-regulate arginine vasopressin V2 receptors in adult rat kidneys. Our study determined ovine maternal and fetal renal arginine vasopressin receptor characteristics and receptor response to maternal dehydration. STUDY DESIGN: Eight pregnant ewes (113 +/- 1 days) were dehydrated for 72 hours; eight animals served as controls. Renal medullary tissue was isolated from maternal and fetal kidneys, and arginine vasopressin receptor characteristics determined with saturation and competition assays using tritiated arginine vasopressin, arginine vasopressin, and arginine vasopressin analogs. RESULTS: Euhydrated maternal and fetal renal medullary arginine vasopressin receptor dissociation constant (3.0 +/- 0.3 and 1.9 +/- 0.3 nmol/L) and maximal binding capacity (149 +/- 15 and 111 +/- 33 fmol/mg protein) values were similar. Pharmacologic profiles with selective agonists indicated a predominance of V2 receptors. Dehydration significantly increased maternal and fetal plasma osmolalities (304 +/- 2 to 320 +/- 2; 296 +/- 1 to 319 +/- 3 mOsm/kg water, respectively) and arginine vasopressin levels (3.8 +/- 1.4 to 29.3 +/- 4.6; 4.4 +/- 1.0 to 16.9 +/- 5.0 pg/ml, respectively) but had no effect on arginine vasopressin receptor binding. CONCLUSION: Specific, saturable, single-site tritiated arginine vasopressin binding is present in ovine maternal and fetal renal medullary membranes. Ovine maternal and fetal renal arginine vasopressin receptors do not down-regulate in response to dehydration-induced elevations in plasma arginine vasopressin levels.

Animals↗
PubMed1992

Epidermal growth factor prohormone is secreted in human urine.

Examination of adult human urine by immunoblot analysis with antiserum specific to human recombinant 6-kDa epidermal growth factor (EGF) reveals the presence of an immunoreactive protein with a molecular mass of 165 kDa. This protein is consistently found in the morning (first) but not in day urine of adult males and females. Day urine contains variable proportions of four other high-molecular-weight EGFs with approximate molecular masses of 97, 66, 50, and 42 kDa. The 165-kDa EGF immunoreactive protein reacts with mouse amino-terminal EGF prohormone (proEGF) antiserum and comigrates with mouse urinary proEGF, suggesting that the protein is the human EGF prohormone. The 165-kDa human proEGF exhibits strong binding affinity to concanavalin A, indicating that it is glycosylated. Immunoblotting of urine in infants and children of various age groups demonstrates the presence of proEGF in all age groups, but its concentration is highest in children 2-4 yr of age. These findings, taken together with secretion of proEGF of similar molecular mass in mouse and rat urine, suggest that renal proEGF secretion is an evolutionarily conserved phenomenon and may have an important function or functions distal to the site of its synthesis.

Adult↗
PubMed1990

Identification of pro-epidermal growth factor and high molecular weight epidermal growth factors in adult mouse urine.

By use of immunoblot analysis, we demonstrate the presence of a pro-Epidermal growth factor (EGF) with an approximate molecular weight of 165 kDa in adult mouse urine. In addition, urine contains four high molecular weight EGFs with approximate molecular weights of 116, 97, 66 and 56 kDa. The 165 kDa pro-EGF as well as the 66 and 56 kDa EGFs also are detectable in mouse kidney extract. Neither urine nor kidney contain the mature EGF of 6 kDa. The 165 kDa pro-EGF is the major product synthesized in renal tissue and secreted in urine. The finding of high molecular weight EGFs in urine suggests that part of pro-EGF secreted into urine undergoes partial proteolysis distal to its site of synthesis.

Animals↗
PubMed1990

The nature of cytoplasmic vacuoles in chordoma cells. A correlative enzyme and electron microscopic histochemical study.

Enzyme histochemical study revealed that a sacrococcygeal chordoma not only was rich in oxidoreductive enzymes but also in the enzymes (phosphorylase, hexokinase, phosphoglucomutase, glucose phosphate isomerase and UDP-glucose dehydrogenase) leading to the synthesis of stromal glycosaminoglycans from glycogen. UDP-glucose dehydrogenase is particularly important in oxidizing UDP-glucose to UDP-glucuronic acid, the building block of hyaluronic acid and chondroitin sulfates. These enzymatic activities were consistent with the ultrastructural findings of abundant membrane-bound glycogen as well as large intracytoplasmic vacuoles with occasional residual glycogen particles. Furthermore, ultrastructural histochemical study using high iron diamine (HID) specifically localized the sulfated glycosaminoglycans (SG) extracellularly as well as intracellularly in distended Golgi saccules and 187-320 nm mature secretory vesicles. No HID staining was noted in the large intracytoplasmic vacuoles or rough endoplasmic reticulum. This study not only supports the hypothesis that the vacuoles of physaliphorous cells are the result of breakdown and utilization of membrane bound glycogen in the biosynthesis of SG, but also demonstrates that intracellular synthesis and storage of SG in chordoma are not in large vacuoles as previous investigators have believed.

Aged↗
PubMed1990

Transforming growth factor alpha in developing rats.

Transforming growth factor-alpha (TGF-alpha) concentrations were measured in lung, brain, liver, and kidney of rats at three different ages (20 days gestation and 9 and 50 days postnatal). TGF-alpha concentrations were maximal in the lung and brain by 20 days of gestation and showed minimal changes during nursing (day 9) and young adulthood (day 50). The liver, which also showed maximal TGF-alpha concentration by 20 days of gestation, demonstrated a progressive reduction with age to nadir values in the young adult. In contrast to the pattern in other tissues, kidney had the lowest concentration of TGF-alpha in late gestation and showed an increase by 50 days of age. As TGF-alpha acts via the epidermal growth factor (EGF) receptor, its function in development may be analogous to that of EGF. Thus TGF-alpha may have a role in lung maturation and postinjury repair, liver repair and regeneration, and neuronal cell growth.

Aging↗
PubMed1989

Effects of adrenergic agonists and adenosine on cholinergic neurotransmission in human tracheal smooth muscle.

There is only limited information available on the prejunctional regulation of acetylcholine (ACh) release from cholinergic nerves in human airway smooth muscle. Stimulation of cholinergic nerves in fresh postmortem tracheal muscle strips with electrical field stimulation (EFS) causes reproducible contractions. We have studied the effect on contractile responses of: 1) The alpha 2-adrenoceptor agonist effect of noradrenaline (NA, 0.1-30 microM) and clonidine (10 nM-30 microM), in the presence of 1 microM propranolol and prazosin +/- idazoxan (0.1 microM); 2) The beta-adrenoceptor agonist effect of fenoterol (FEN) and isoprenaline (ISO, 1 nM-30 microM) +/- ICI 118,551 (10 nM), comparing EFS responses to comparable responses to exogenous ACh; 3) The A1 and A2 adenosine receptor agonists effects of L-PIA and NECA (1 nM-10 microM). NA caused a concentration-dependent depression of the cholinergic frequency-response curve. However responses at 5 Hz were not modified by the addition of idazoxan. Similarly clonidine did not reduce contractile responses. The concentrations of isoprenaline (56 nM) and fenoterol (165 nM) required to inhibit EFS (5 Hz) by 50% (IC50) were significantly less than those required to inhibit closely matched ACh responses to a comparable degree (ISO = 117 and FEN = 304 nM), and the maximum inhibition of EFS was greater. Following isoprenaline and the beta 2-antagonist ICI 118,551 the IC50's for EFS and ACh were not different. NECA and PIA had no effect on cholinergic EFS. We conclude that a prejunctional beta 2 receptor may be present on cholinergic nerves in post-mortem tracheal smooth muscle but no evidence for alpha 2-adrenoceptor or adenosine-receptor regulation was obtained.

Adenosine↗
PubMed1985

Idiopathic degeneration of the aortic valve: a common cause of isolated aortic regurgitation.

To establish the etiology of isolated aortic valvular regurgitation, histologic examination was carried out on 27 consecutive surgically removed aortic valves from patients with aortic regurgitation. In 12 patients, the regurgitation was due to rheumatic or syphilitic valvular disease or a congenital bicuspid aortic valve. In the remaining 15, no etiology was apparent. In the latter group, seven aortic valves were identified by the surgeon as redundant and eight as thickened and retracted. Despite these gross differences, the histologic features of the 15 valves were similar and consisted of increased and disorganized elastic and collagen fibers, with variable quantities of acid mucopolysaccharide and calcium. Although small foci of myxomatous stroma were present, they did not differ substantially from those observed in age-matched competent aortic valves removed at necropsy, nor were they as extensive as described in reports of floppy aortic valves. Idiopathic degeneration was the most common cause of aortic regurgitation, occurring in more than half of the surgically treated patients. An underlying defect in the synthesis of collagen or elastic fibers, similar to that described in mitral valve prolapse, may be an important feature in aortic valve degeneration.

Adult↗
PubMed1985

Ovine fetal-maternal water transfer is independent of fetal prolactin levels.

To examine the effect of prolactin (PRL) on transplacental water flow, we infused mannitol (500 ml; 20% solution) over 10 min into five chronically catheterized ewes (121-134 days' gestation), producing a peak maternal plasma osmolality by 10 min and fetal osmolality by 20 min. One day before or after, an identical amount of mannitol was infused into the same ewe during the 2nd h of a 2-h infusion of PRL (40 +/- 2.2 micrograms/h) into a fetal leg vein. Mean (+/- SE) fetal plasma PRL levels were 6.9 +/- 3.2 ng/ml at baseline. Steady state fetal PRL levels were 17.7 +/- 7.4 ng/ml during PRL infusion. Maternal mannitol infused without administration of PRL to the fetus evoked a rise in fetal plasma osmolality similar to that following maternal mannitol during PRL administration to the fetus. Thus, as shown previously, PRL affects water permeability across the membranous chorioamnion, whereas results of the present study indicate that the hormone does not affect water transfer across the ovine chorionic villi (placenta).

Animals↗
PubMed1979

The effect of acute maternal hemorrhage on the release of catecholamines in the pregnant ewe and the fetus.

Five chronically instrumented pregnant ewes and their fetuses were studied to assess the effect of acute maternal hemorrhage. The hemorrhage was produced in two stages; during the first stage 15% of the total maternal blood volume was removed, and then in a second stage an additional 15% was removed. Biophysical and biochemical variables were monitored. Plasma dopamine, norepinephrine, and epinephrine were determined by a sensitive radioenzymatic assay. A significant rise in maternal and fetal catecholamines was observed following an estimated maternal blood volume depletion of 30%. During a 15-minute recovery period, the maternal catecholamine concentrations returned to normal, while the fetal concentrations remained elevated. These changes were accompanied by significant changes in maternal and fetal homeostasis. The significance of these findings is discussed.

Animals↗
PubMed1979

Free metanephrine in human amniotic fluid as an index of fetal sympathetic nervous system maturation.

Free metanephrine, a major metabolite of catecholamines, was measured in the amniotic fluid of 113 pregnant patients at various gestational ages. The results indicate that prior to 30 weeks the levels of free metanephrine are below the level of assay sensitivity. After 30 weeks' gestation there is a positive correlation of free metanephrine concentrations in amniotic fluid with gestational age. In addition there is a further increase in free metanephrine levels in amniotic fluid with labor.

Amniotic Fluid↗
PubMed1978

Small angle x-ray diffraction studies of mucopolysaccharides in collagen.

Small angle X-ray diffraction (SAXD) was used to locate mucopolysaccharides (MPS) at regular intervals along the collagen axis under physiological conditions. Ruthenium red was used to stain the MPS specifically. The difference in electron density between ruthenium red-stained and unstained moist native rat tail tendon should correspond to the position of the MPS. This difference was calculated from the SAXD intensity data by using difference Fourier transform calculations. Phases calculated independently from the amino acid sequence of collagen by two laboratories were used in this calculation, and the results were compared. At least four to seven bands of MPS per 660 A were found at regular intervals along the collagen axis. Some of these bands match in position to the cross-striations observed by freeze-etching. Electron micrographs of ruthenium red-stained native fibrils also showed bands close in position to the ones calculated.

Amino Acid Sequence↗
PubMed1977

Myocardial alterations associated with aortocoronary saphenous vein bypass.

Clinical observations and gross and microscopic morphology of the hearts of 50 patients who dies at various intervals following aortocoronary saphenous vein bypass procedures are presented. Time of total cardiopulmonary bypass varied inversely with survival time among these patients. Myocardial necrosis with contraction bands and/or hemorrhagic myocardial necrosis was observed in the hearts of 44 of the 50 patients. Pathogenesis of the acute myocardial necrosis with contraction bands was multifactorial: anoxic arrest, cardiotonic drugs, electrical defibrillation, electrolyte imbalance, microthrombi, and hypoperfusion are incriminated. Subendocardial hemorrhagic necrosis was present in 17 of 40 patients whose postoperative survivals were four days or less. Its frequency increased with duration of survival. Hypoperfusion of the myocardium is suggested as the major etiologic factor of the subendocardial hemorrhagic necrosis. Myocardial lesions observed among these 50 patients did not differ from those in patients who had open-heart surgery for other reasons.

Arterioles↗
PubMed1977

Aortic dissection complicating aortocoronary saphenous vein bypass.

A high autopsy incidence, 7 of 50 cases (14%), of aortic dissection as the major cause of death in patients who died following aortocoronary saphenous vein bypass is reported. The patients ranged in age from 45 to 61 years, and all had moderately severe aortic atherosclerosis. None was hypertensive, and no significant predisposing aortic medial disease was recognized. Trauma during surgical cannulation with retrograde perfusion through atherosclerotic femoral or iliac arteries was considered the initiating event leading to ileo-aortic dissection in five of the seven patients. Damage secondary to aortic cross-clamping is suggested as the pathogenetic mechanism leading to dissection in the other two patients. In six patients, the dissection was Type I of DeBakey, and in one patient, Type II. Dissection was recognized intra-operatively in five of the seven patients. In older patients, particularly those likely to have atherosclerosis of the aorta and its main branches, vigilance regarding the possibility of aortic dissection developing during the course of cardiopulmonary bypass must be constant.

Animals↗
PubMed1975

Thyroxine in human amniotic fluid.

Total and free T3 and T4 concentrations were measured in human amniotic fluid and in fetal and maternal blood. Before 20 weeks, the mean AF-T4 level was 0.24 mug/dl; there is a progressive increase in concentration with gestational age. At term, the mean AF total T4 level was much less (0.64 mug/dl) than in fetal or maternal serum (9.3 and 11.3 mug/dl, respectively). Most of the T4 (99.4%) in AF is protein bound, presumably to TBG as in serum, but the mean FT4 concentration in AF at term (4.13 ng/dl) was significantly greater than the levels in fetal or maternal serum (2.67 or 2.56 ng/dl, respectively). The mean TBG level in AF at term was 0.26 mg/dl. T3 was not measurable in AF (less than 15 ng/dl). There were no significant correlations between the total or free T4 concentrations in maternal or fetal sera and in amniotic fluid. Thus AF thyroid hormone concentrations in the euthyroid fetus do not reliably reflect fetal serum T4 or T3 concentrations.

Amniocentesis↗