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Biomedical subjects

S C Pang

Publications and source records attributed to S C Pang.

At least 19 recordsLinked to original sources
PubMed1992

Expression of natriuretic peptide genes in cardiac tissues of hypertensive rats.

A quantitative assay using a reverse transcriptase-linked polymerase chain reaction has been developed for measuring the levels of rANP and iso-rANP mRNA. A linear correlation between total RNA template and amplified cDNA was obtained for the amplification of cDNA from both iso-rANP and rANP mRNAs even when both cDNAs were amplified in the same assay. Application of the assay showed that in contrast to rANP levels of iso-rANP transcript in hypertensive rats remained approximately the same in atrium but were increased 10-fold in ventricle compared to normal rats. Given the relative size of the ventricle the increase of iso-rANP in this tissue in SHR may be a major response to the hypertensive state.

Animals↗
PubMed1992

Mycobacterial lymphadenitis in Western Australia.

The records of 172 patients with culture-positive mycobacterial lymphadenitis in Western Australia between January 1972 and December 1989 inclusive have been reviewed. Of the 118 children under 7 years of age, the disease was caused by M. tuberculosis in 4%, the M. avium complex in 74% and M. scrofulaceum in 20%, whereas in the 54 adults aged 15 years and over, the same organisms were responsible for 89%, 2% and 4% respectively of their diseases. Tuberculous (TBC) lymphadenitis affected mainly adult Asian migrants (71%), while non-tuberculous mycobacterial (NTM) lymphadenitis predominantly affected non-Aboriginal Australian children (92%). The two conditions differed significantly in their distribution of disease in the lymph nodes (P < 0.001). Patients with the TBC disease had a longer (P < 0.001) duration of symptoms before diagnosis but less common (P < 0.02) local complications at presentation than those with the NTM disease. The response of TBC lymphadenitis to medical treatment was excellent with no failure or relapse in the 43 patients followed up to 12 months. Total excision was curative for NTM lymphadenitis although in 10% a second excision was needed because of relapse or residual disease. In a selected group of children, the double Mantoux test was shown to have a 79% sensitivity and a 69% specificity in the diagnosis of the NTM disease. Over the last decade, the prevalence of NTM lymphadenitis in Western Australia decreased while that of TBC lymphadenitis remained steady.

Adolescent↗
PubMed1992

Ovulation induction in women age 40 and older: the importance of basal follicle-stimulating hormone level and chronological age.

OBJECTIVES: To determine pregnancy and livebirth rates for women age 40 and older undergoing ovulation induction and to assess the impact of basal follicle-stimulating hormone (FSH) on outcome in these patients. DESIGN: Prospective, observational. SETTING: Fertility service of university medical center. PATIENTS: Infertile couples in whom the female partner was age 40 or older referred for ovulation induction therapy. INTERVENTION: Assessment of basal hormonal status; ovulation induction. MAIN OUTCOME MEASURES: Clinical pregnancy rate (PR), livebirth rate. RESULTS: Analysis of 402 cycles in 85 women age 40 and older demonstrated a clinical PR of 3.5% per cycle (95% confidence interval [CI] 1.7% to 5.3%). The livebirth rate was 1.2% per cycle (95% CI 0.1% to 2.3%). Women with a basal FSH < 25 IU/L and age < 44 years had a clinical PR of 5.2% per cycle (95% CI 2.5% to 7.9%) compared with 0.0% per cycle (95% CI 0.0% to 2.1%) in cases in which either basal FSH was > or = 25 IU/L or age was > or = 44 (P < 0.005). The prognostic importance of basal FSH and chronological age was confirmed by multivariate logistic regression analysis. The predictive value of the resulting regression equation was high (R2 = 0.94; P < 0.01). CONCLUSIONS: Pregnancy and livebirth rates are generally low during ovulation induction in women age 40 and older. In combination, basal FSH and chronological age are accurate predictors of PR, in these couples and can define a subset of patients with a more favorable prognosis. The spontaneous abortion rate in women who do conceive is high, substantially lowering the livebirth rate.

Adult↗
PubMed1992

Assessment of sperm for cryopreservation using the hypoosmotic viability test.

In summary, the hypoosmotic viability parameter was significantly correlated with the outcome of the thawed sperm motility. The prefreeze supravital staining for sperm viability and the hypoosmotic sperm swelling test were not predictive of the thawed sperm total motility. The hypoosmotic viability parameter was not correlated to the postwarmed sperm motility after refrigeration. The results indicated that the integrity of the sperm membranes at the head were more important than the tail membrane.

Cell Survival↗
PubMed1992

Culture-positive tuberculosis in Western Australia.

Notifications of 485 patients with culture-positive tuberculosis (TB) in Western Australia from 1980 to 1989 inclusive have been analysed. In 478 (98.6%) the disease was caused by Mycobacterium tuberculosis hominis and in seven (1.4%) M. bovis. Most (78.5%) of the disease was pulmonary with 4.3% pleural and 17.2% extrapulmonary. The annual incidence decreased from 4.6 per 100,000 in 1980 to 2.5 in 1985 steadying thereafter around 3.3. The Aborigines had over four times the average incidence of the non-Aboriginal Australians but less than a quarter that of the Asians. In a total 297 migrants, 51% of 253 with data available had been in Australia for over five years. Initial drug resistance was found in 48 patients giving an overall rate of 9.9%. In 32 (66.7%), resistance was against a single drug, mainly isoniazid and in 11 (22.9%) against two drugs, predominantly isoniazid and streptomycin. The most disturbing finding was the occurrence of multiple-drug resistance including both isoniazid and rifampicin in five immigrants (10.4%). This study has provided useful baseline TB data, raised important issues such as chemoprophylaxis and drug resistance, and clearly indicates that the campaign against TB is far from over. Continual surveillance, monitoring and regular evaluation of existing policies should be maintained.

Adolescent↗
PubMed1992

Cultured smooth muscle approach in the study of hypertension.

The systemic vasculature is known to undergo marked change in both human and experimental hypertension. The in vitro study of individual cellular components from the blood vessel wall and the regulation of their intracellular biochemical processes will aid in developing an understanding of the pathogenesis of hypertension. Vascular smooth muscle cells derived from the aorta and mesenteric arteries of normotensive and hypertensive rats can be successfully maintained in culture, providing a system free of confounding variables such as blood pressure. To assist in fully understanding the pathophysiology of hypertension, this cell culture model can be used to examine interactions between receptor and ligand, the transduction of an associated signal, characterization of subsequent intracellular responses and ultimately, quantification of a physiological and functional consequence of these events, for example, proliferation. The application of in vitro techniques to hypertension research will continue to contribute new knowledge to increase our understanding of the mechanisms behind the hypertensive disease process.

Animals↗
PubMed1992

Biological effects of rat iso-atrial natriuretic peptide and brain natriuretic peptide are indistinguishable from each other.

Rat brain natriuretic peptide (rBNP) and iso-atrial natriuretic peptide (iso-rANP) were discovered independently by two research laboratories. They are considered to be members of the B-type natriuretic peptides. Except for the Gln/Leu substitution at position 44, the amino acid sequence of iso-rANP is identical with that of the C-terminal 45 amino acids of rat pro-BNP and with the 5-kDa cardiac peptide from rat atria. To determine whether this amino acid substitution can modify the known biological effects of rBNP and iso-rANP, the present investigation examined the cardiovascular and renal responses, vasorelaxant effect, receptor binding characteristics, and cyclic GMP production by the two peptides in relation to that of rat atrial natriuretic peptide (rANP). Results indicate that rBNP and iso-rANP are indistinguishable from each other in terms of these known biological activities of atrial natriuretic peptide. We therefore conclude that rBNP and iso-rANP are identical peptides and that the amino acid substitution at position 44 represents a polymorphic form of the rat B-type natriuretic peptide.

Amino Acids↗
PubMed1992

Differential proliferation of rat aortic and mesenteric smooth muscle cells in culture.

Smooth muscle cells (SMC) from various arterial origins have been successfully maintained in culture. The present study evaluates the proliferative activity of aortic and mesenteric SMC in culture. Aortic and mesenteric SMC were obtained from male Wistar rats by explant and enzyme digestion techniques, respectively. Vascular SMC obtained by either method exhibited a characteristic hill-and-valley growth pattern in culture after confluence and were positively labelled with either anti-smooth muscle actin or myosin by an indirect immunofluorescent method. The rate of incorporation of thymidine into DNA and cell number counting were used as indices of proliferation in vitro. Vascular SMC from passages 4-33 were first synchronized with either Dullbecco's Modified Eagle's Medium (DME) or Ham's F-12 medium, supplemented with insulin-transferring-selenium (ITS), for 72 hours. SMC were then stimulated with 10% bovine serum for either 24 or 72 hours with the former processed for scintillation counting, the latter for cell number determination. The incorporation of tritiated thymidine into DNA following a 2 hour incubation was determined by scintillation counting after perchloric acid extraction. In terms of cell numbers, proliferative responses to bovine serum were determined by Coulter counting. Autoradiography was also carried out in some cultures to determine both thymidine and mitotic labelling indices. The rate of thymidine incorporation in aortic cells was 2-3 fold higher than in mesenteric cells. Aortic and mesenteric SMC lines exhibited similar cell cycle intervals in terms of total duration and individuals cycle parameters. However, the total thymidine index was higher in the aortic than mesenteric SMC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Plasma clearance and tissue binding of rANP[99-126] and iso-rANP[1-45] in the rat.

Plasma clearance and tissue binding of atrial natriuretic peptide (ANP) and iso-ANP were compared in Inactin-anaesthetized rats. It was found that the plasma half-life of iso-ANP was comparable to ANP. Appearance of trichloroacetic acid-soluble radioactivity of iso-ANP in the plasma was considerably slower than that of ANP, suggesting that the metabolic process of these two peptides may be different. Although the binding distribution of these two peptides was similar, the total binding of iso-ANP to organs other than the kidney was much lower. The kidney, lung, heart and adrenal gland appeared to be major target organs for iso-ANP. Autoradiography showed that iso-ANP bound specifically to the renal glomerulus and proximal part of the proximal tubule. This latter binding site in the kidney was not apparent with ANP, suggesting that iso-ANP may exerts its physiological action at different sites in this organ.

Animals↗
PubMed1991

Mycobacterium kansasii infections in Western Australia (1962-1987).

The records of 81 patients with isolations of Mycobacterium kansasii in Western Australia over 26 years have been reviewed. Thirty-nine individuals with 40 episodes of infection were considered to have disease due to M. kansasii: 36 in the lungs (90%), two in the joints (5%), and one each in the skin (2.5%) and the lymph nodes (2.5%). The average incidence rate per 100,000 per year was 0.14 for the state with the highest in the Geraldton Mid-west region (0.57). The male:female ratio was 4:1 and the mean age 50 years (SD 14.5). For pulmonary disease the male:female ratio was 3.5:1, the mean age 53 years (SD 11), 42% being miners or ex-miners and 91% smokers or ex-smokers. Almost 97% of those infected were Caucasian and none were Aboriginal. Drug treatment was highly successful, particularly with the rifampicin/ethambutol combination, where 12 months appeared to be adequate. There are differences in the demography of the patients having pulmonary disease compared to the 42 with insignificant isolations.

Adult↗
PubMed1991

Combined supravital staining and hypoosmotic swelling test.

The parameter of sperm viability in hypoosmotic solution (VHOS) provides information concerning the membrane integrity of the sperm head. The objective of this study was to determine the association between the VHOS parameter and the sperm penetration assay. The VHOS parameter correctly predicted 70.0-71.4% of the failed sperm penetration assay samples in the short duration preincubation groups. A combination of both the VHOS parameter and the hypoosomotic sperm swelling (HOS) test significantly reduced the number of false negative results. In general, a sperm sample with an abnormal VHOS result and an abnormal HOS test result would be associated with a negative sperm penetration assay. Washing by centrifugation appeared to weaken the sperm head membranes while the swim-up method selected for sperm with strong head and tail membranes. After the various processing methods unique changes in the integrity of the sperm head and tail membranes for each sperm sample may help to identify the optimal method of preparation for individual patients undergoing the newer assisted reproductive technologies such as sperm microinjection.

Cell Membrane↗
PubMed1991

Multi-drug resistant tuberculosis in migrants.

Between 1986 and 1989 three Vietnamese migrants presented at the Perth Chest Clinic with multiple-drug resistant tuberculosis of the lungs. This resistance was to both rifampicin and isoniazid in addition to other antituberculous drugs. Although all three had a long history of past intermittent treatment for tuberculosis and extensive active disease, they were not detected in spite of what should have been adequate premigration screening. This report is to alert those medical personnel concerned with the process of migrant health screening and surveillance. The implications of such multi-drug resistant disease on tuberculosis control in Australia is also briefly discussed.

Adult↗
PubMed1990

Decrease of blood pressure in spontaneously hypertensive mice by heat treatment.

Although the increased sensitivity of hypertensive animals to heat stress has been reported, the effect of chronic heat exposure has not been examined. The specific goal of the present investigation was to study the impact of chronic heat treatment on the blood pressure of spontaneously hypertensive mice. Chronic 40 degrees C heat exposure for 5 min daily progressively lowered basal blood pressure in hypertensive mice within 20 days, without any change in normal mice. In fact, after 35 days of chronic heat treatment, the basal blood pressure of hypertensive mice was indistinguishable from that of the normotensives. Repeated immobilization and prewarming as normal procedures for recording blood pressure contributed to the decrease in blood pressure by 10 to 12 mm Hg, but chronic heat by itself was significantly more potent in reducing it by an additional 20 mm Hg. After the discontinuation of chronic heat application, the basal blood pressure of hypertensive mice returned with time to the level registered in sham-handled hypertensive controls. These results demonstrate that, although acute heat is more detrimental to hypertensive mice, brief, chronic exposure to mild heat stress is beneficial in that it normalizes basal blood pressure.

Animals↗
PubMed1989

Atrial natriuretic factor-induced egression of cyclic guanosine 3':5'-monophosphate in cultured vascular smooth muscle and endothelial cells.

The induction of cyclic GMP formation in target tissues, i.e. vascular smooth muscle and endothelial cells, by atrial natriuretic factor is followed by its egression into plasma and urine. Since the extracellular appearance of this cyclic nucleotide is used as a marker of atrial natriuretic factor's biological activity, the present study was designed to investigate the characteristics of its egression to the extracellular fluid. In contrast to cyclic AMP, whose profile of egression in time closely follows its intracellular levels, cyclic GMP egression begins with the intracellular decline but continues for a prolonged period, even accumulating for up to 24 h in the extracellular medium. The relative egression of cyclic GMP decreases slightly in the presence of phosphodiesterase inhibitors. On the other hand, the process is sensitive to temperature, inhibited by such agents as probenecid, and occurs against a gradient of 7 orders of magnitude. Large increases of cyclic AMP, as induced by forskolin, can effectively compete for the cyclic GMP transport system, resulting in a 3-fold rise in intracellular cyclic GMP levels, which corresponds to a 3-fold decline of extracellular accumulation. Although the biological significance of cyclic GMP egression is unknown, the results of this study suggest that the process may be one of the significant contributors to the control of cyclic GMP levels in the cell with potential physiological consequences.

Animals↗
PubMed1989

In vitro proliferation of aortic smooth muscle cells from spontaneously hypertensive and normotensive rats.

The characteristics and proliferation of aortic smooth muscle cells (SMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were studied in culture. Smooth muscle cells were isolated from the tunica media of the thoracic aorta by an explant method. Immunofluorescence microscopy showed that 93-95 per cent of cells were positively labelled with antibodies raised against smooth muscle actin, indicating that these were smooth muscle cells. The proliferative activity was compared between aortic smooth muscle cells from hypertensive and normotensive rats in culture by thymidine incorporation and cell number determinations. The results demonstrate that aortic smooth muscle cells from hypertensive rats grew faster than those from normotensive rats in culture. The increased proliferative activity of cultured aortic smooth muscle cells from hypertensive rats was detectable even when they were cultured in a chemically defined serum-free medium. These data have shown that an increased proliferative activity of aortic smooth muscle cells from hypertensive rats can occur in culture conditions without the influence of arterial pressure or other stimuli as in intact animals. The mechanisms underlying the accelerated proliferative activity of aortic smooth muscle cells from genetically hypertensive rats in vitro remain to be determined.

Animals↗
PubMed1989

Effect of atrial natriuretic factor on blood-brain barrier permeability.

Recent studies have demonstrated receptors for atrial natriuretic factor on endothelium of intracerebral vessels. The physiological role of these receptors is not known. The present study was undertaken to determine whether atrial natriuretic factor has an effect on blood-brain barrier permeability to protein and ions using horseradish peroxidase and lanthanum as markers of permeability alterations. This study does not demonstrate a significant effect of atrial natriuretic factor on blood-brain barrier permeability mechanisms in steady states.

Animals↗
PubMed1989

Ultrastructure of atrial and ventricular myocytes of newborn rats: evidence for the existence of specific atrial granule-like organelles in the ventricle.

The present study examined the ultrastructure of atrial and ventricular myocytes from the heart of newborn rats. It was found that, despite former reports stating that ventricular myocytes in adults do not contain cytoplasmic granules, specific atrial granule-like organelles are present in the ventricles of rats at birth. The presence of these granules together with the relatively underdeveloped contractile apparatus and extensive Golgi complex suggests that the ventricular, like the atrial, myocytes may have an endocrine function before or at birth. Further study is required to determine whether these ventricular cytoplasmic granules contain the same atrial natriuretic peptide species known to be present in the atrial specific granules.

Animals↗