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Biomedical subjects

S C Pang

Publications and source records attributed to S C Pang.

108 records · Page 6Linked to original sources
PubMed1984

Effect of native and synthetic atrial natriuretic factor on cyclic GMP.

Mammalian atrial cardiocyte granules contain a potent natriuretic and diuretic peptide. Since cGMP appears to be involved in the modulation of cholinergic and toxin-induced sodium transport, we examined the effect of atrial natriuretic factor (ANF) on this nucleotide. Atrial but not ventricular extracts elicited approximately a 28-fold increase of urinary cGMP excretion parallel to the natriuresis and diuresis. The atrial extracts also elevated cGMP levels in kidney slices and primary cultures of renal tubular cells. The effect of ANF on cGMP appeared to be specific since antibodies which were capable of inhibiting the ANF-induced diuresis also suppressed cGMP excretion. Furthermore, during the course of ANF purification, the ANF-induced increase of cGMP production by kidney cells paralleled the heightened specific natriuretic activity of the atrial factor. A synthetic peptide (8-33)-ANF similarly increased urinary plasma and kidney tubular cGMP levels. The exact mechanism of action of ANF on cGMP remains to be elucidated, but indirect inhibition of cGMP phosphodiesterase appears to participate in its effect.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1983

The correlation between the development of sympathetic innervation and the development of medial hypertrophy in jejunal arteries in normotensive and spontaneously hypertensive rats.

The catecholaminergic innervation of jejunal arteries was examined during development in normotensive and hypertensive rats. It was determined that a hyperinnervation of jejunal vessels in the hypertensive rats is present from 2 weeks of age onwards, before significant elevation of blood pressure and medial hypertrophy of jejunal arteries occurs. It is concluded that this hyperinnervation may be causally related to the medial hypertrophy in arteries of hypertensive animals.

Age Factors↗
PubMed1981

Digital scintigraphy: principles, design, and performance.

In a digital camera the position of a scintillation event is computed following analog-to-digital conversion of photomultiplier pulse charges. Digital position analysis is essentially a mathematical inversion procedure based upon calibrated responses of the photomultipliers to scintillations from a narrow-beamed source that maps a detector's field of view. Operationally, a camera's image characteristics are optimized by means of computer-generated inversion reference tables, individually tailored to the specific response characteristics of each detector. Design considerations indicate that cameras of varied configurations, e.g., linear, disc-shaped, rectangular, or cylindrical, can be analyzed by this method. Also, for any given electro-optical system, energy resolution, spatial characteristics, and event-rate performance can be made superior to analog systems. The measured performances of a one-dimensional test camera, although limited in its optical and electronic design, support this conclusion.

Analog-Digital Conversion↗
PubMed1981

Stereological analysis of the tunica media of the aorta and renal artery during the development of hypertension in the spontaneously hypertensive rat.

The relationship between the arterial blood pressure and the composition of the tunica media in spontaneously hypertensive, Wistar-America and Wistar-Kyoto rats was examined. The systolic blood pressure of the spontaneously hypertensive rat, measured through an intra-arterial cannula, was significantly higher than that of the controls from 5 weeks and became hypertensive by 18 weeks of age. However, the content of the tunica media of the abdominal aortal and renal artery of the spontaneously hypertensive rats, as revealed by EM stereological analysis, and measurements of the thickness of the wall and diameter of the lumen, were not significantly different from the controls, at least up to the age of 18 weeks. The result of the present investigation suggests that the elevation of arterial blood pressure in the spontaneously hypertensive rat during the first 18 weeks of postnatal development is not a result of stereologically detectable changes in the composition of the tunica media of the abdominal aorta and renal artery.

Animals↗
PubMed1978

Epidermal migration during the healing of suction blisters in rat skin: a scanning and transmission electron microscopic study.

Fluid-filled blisters, created on the skin of the inner surface of the pinna of heparinized rats by the application of suction, showed an intact basal lamina through which protruded hairs and remnants of hair follicles. The origin of epithelial cells and their spreading over the basal lamina were studied at intervals over 36 hours using scanning and transmission electron microscopy. The majority of epidermal cells arose from the outer root sheath of hair follicles and began to spread radially before 12 hours. By 36 hours the cells were confluent over most of the blister base. Inflammatory cells were few in number and rested mainly on the bare basal lamina rather than on the resurfacing cells. Some elongated epidermal cells showing tapering foot processes appeared to be migrating in from the epidermis at the edge of the blisters. The cells spreading from hair follicles were flat and polygonal. On these sheets of cells a few small folds and many filopodia were present at intercellular junctions and at the free margin of the leading cells. Large numbers of short microvilli covered the surface of some of the epidermal cells, especially at 24 and 36 hours; other epidermal cells were relatively smooth.

Animals↗
PubMedDate not supplied

Acute ethanol ingestion modifies the circulating plasma levels of atrial natriuretic peptide.

Since ethanol ingestion is associated with a disruption of water and electrolyte balance in a variety of species, we sought to evaluate the regulatory control of atrial natriuretic peptide (ANP) in response to acute doses of ethanol. Male Sprague-Dawley rats were administered a 5-g/kg dose of ethanol (40% w/v) via a gastric tube, while control animals received an equivalent volume of water. Expressed as a percentage of control, plasma ANP levels were 39.0%, 28.5%, and 23.6% in the ethanol-treated animals at 30, 60, and 120 min postintubation, respectively. Ethanol-treated animals displayed blood alcohol concentrations of 89.0, 137.6, and 214.1 mg/dl at the same time periods. After 120 min, plasma renin activity was elevated from 8.7 to 20.3 ng/ml/h in conjunction with an increase in the levels of circulating aldosterone from 16.3 to 42.5 ng/dl and an increase in plasma vasopressin from 2.2 to 3.6 pg/ml. Levels of atrial ANP mRNA remained consistent over the time course of the experiment, and no changes in the amount of ventricular ANP transcript were observed. Tissue ANP levels were similar between ethanol-treated and water-loaded control animals. In vitro experiments using cultured cardiac myocytes suggest that ethanol exposure may not directly affect ANP secretion. We propose that acute ethanol treatment may inhibit atrial distension and subsequently modify the control of ANP release under volume loading conditions.

Aldosterone↗
PubMedDate not supplied

A survey of ventilatory capacity in Chinese subjects in Hong Kong.

A survey of three indices of ventilatory capacity (forced expiratory volume in one second, FEV1; forced vital capacity, FVC; and peak expiratory flow rate, PEFR) was carried out on 3490 Chinese inhabitants of Hong Kong aged between 5 and 97 years. The results are compared with those of previous surveys of ventilatory capacity in a variety of ethnic groups. Our results confirm previous findings that the indices FEV1 and FVC are proportional to the square of the height of the subject, but we have found that PEFR is proportional to height itself. Using the indices FEV1/height2, and PEFR/height we have derived regression equations which may be used to predict normal values of the ventilatory indices for both adults and children. An interesting observation in this cross-sectional survey was that although all ventilatory indices were adversely affected by smoking, the rates of decline of these indices with age were not accelerated in smokers compared with non-smokers, in contrast to the findings of previous surveys on European populations.

Adolescent↗
PubMedDate not supplied

Forskolin and isoproterenol effect discrete responses on epidermal growth factor induced DNA synthesis in aortic smooth muscle cells.

Defining the mechanisms regulating the proliferation of vascular smooth muscle is necessary to better understand the pathogenesis of atherosclerosis and hypertension. In the present investigation, we examined the effects of incubation with forskolin or isoproterenol on the proliferation of cultured rat aortic smooth muscle cells. Forskolin, a direct activator of adenylate cyclase, and isoproterenol, a beta-adrenergic agonist, increased intracellular cyclic AMP levels in a concentration-dependent manner, subsequent to a 5-min exposure. Isobutylmethylxanthine at 100 microM attenuated epidermal growth factor stimulated DNA synthesis by 35% without affecting intracellular cyclic AMP levels. Forskolin dose-dependently augmented this inhibition. In contrast, a 24-h exposure of cells to isoproterenol resulted in a biphasic effect on growth factor stimulated thymidine incorporation. Both forskolin and isoproterenol attenuated thymidine incorporation to the same degree up to 12 h poststimulation, the onset of S phase. By 16 h poststimulation, [3H]thymidine incorporation in smooth muscle cells treated with isoproterenol was significantly enhanced by 50%, whereas forskolin treatment continued to attenuate DNA synthesis by 40%. Somewhat surprisingly, this disparity in effect on DNA synthesis was evident in spite of heterologous desensitization to rechallenge by either forskolin or isoproterenol subsequent to a 24-h incubation with either drug. These results suggest that the isoproterenol enhancement of epidermal growth factor stimulated DNA synthesis in rat aortic smooth muscle cells may be cyclic AMP independent.

1-Methyl-3-isobutylxanthine↗
PubMedDate not supplied

Abnormalities of platelet function in hypertension and diabetes.

The increased frequency of hypertension in diabetes and of abnormalities of carbohydrate metabolism in hypertension are now well established. It is conceivable that the high coincidence of the two diseases is based on a common metabolic defect. Studies of platelets permit the evaluation of the stimulatory, phosphoinositol-linked and the inhibitory, cyclic adenosine 3',5'-monophosphate-dependent pathways of cell activation. Furthermore, platelets may be relevant for the development of angiopathy through their contents of growth factors. Abnormalities of platelet aggregation have been demonstrated in hypertension and diabetes. They are accompanied by exaggerated stimulation of adenylate cyclase in hypertension and abnormal activity of cyclic guanosine 3',5'-monophosphate phosphodiesterase in diabetes. Defective function of platelets is also observed in patients and animals when the two diseases are present at the same time. Both increased and decreased aggregation have been described in these two diseases in the literature. The apparent discrepancies may be due to different types of platelet preparation, evaluation of aggregation, evolution of defect with age, and form of the disease. Integrated studies of biochemical mechanisms responsible for cell activation are needed to characterize the exact defect present in diabetes and hypertension in platelets.

Adenylyl Cyclases↗
PubMedDate not supplied

A double method sperm wash for artificial insemination.

Recently, there have been concerns regarding the presence of reactive oxygen species (ROS) produced during sperm processing for insemination. However, the sperm wash methods that yielded low ROS levels also had low sperm recovery after processing. The objective of this study was to compare sperm recovery after swim-up from pellet, overlay, and 2-layer Percoll wash methods with the recovery after the double method wash. The latter method consisted of a combination of 2 sperm wash methods, namely, the overlay and the Percoll method. Motile sperm were first collected through the overlay method. The leftover semen was then processed through the 2-layer Percoll method to scavenge motile sperm and the resultant pellet combined with the pellet from the overlay method. In this manner, the level of ROS was kept to a minimal, sperm recovery was improved, and a mixture of sperm with different surface properties was produced as a result of using different processing methods. The results indicated an improvement in sperm recovery and in total sperm motility in noncryopreserved sperm after using the double method wash when compared with the other wash methods. The study suggests that the double method wash is a feasible method for processing sperm for insemination.

Cell Separation↗
PubMedDate not supplied

Clinical pregnancy rate after the double method wash and intrauterine insemination.

The protocol for intrauterine insemination (IUI) involves sperm processing using different methods that have produced varying results. These sperm wash methods do not take into consideration the problems of the exact timing of ovulation and the requirements of sperm cells at different stages of capacitation. The objectives of this study were 1) to use the double method wash previously reported to produce a mixture of different populations of sperm cells and determine the pregnancy outcome after IUI and 2) to compare the sperm kinematic parameters after the double method wash with those after the centrifuge (or whole-population) wash method. Patients were divided into either the double method group (n = 119) or the centrifuge method group (n = 76). The Hamilton-Thorn HTM-C automated sperm motility analyzer (Hamilton-Thorn Research, Danvers, MA) was used to analyze sperm motility parameters. Pregnancy outcomes were evaluated after controlled ovarian stimulation and IUI. An almost 2-fold increase was seen in the pregnancy rate with the double method wash compared with the centrifuge method wash. Sperm motility and velocity were also enhanced in the double method wash groups. The results support the usefulness of the double method wash for the preparation of sperm for IUI.

Female↗