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Biomedical subjects

S T Chan

Publications and source records attributed to S T Chan.

At least 109 records · Page 6Linked to original sources
PubMed1986

A new method for the simultaneous determination of androstenedione, testosterone, 11-oxotestosterone and 11 beta-OH-testosterone in fish plasma using combined techniques of Celite chromatography and radioimmunoassay.

A new method for the simultaneous determination of androstenedione, testosterone, 11-oxotestosterone and 11 beta-hydroxy-testosterone in teleost plasma has been developed. Steroids extracted from the plasma were first separated by Celite chromatography using ethanediol as the stationary phase and different concentrations of ethyl acetate in iso-octane as the eluting solvents. Androstenedione, testosterone, 11-oxotestosterone and 11 beta-OH-testosterone were eluted successively with 0, 10, 15 and 40% of ethyl acetate in iso-octane. The eluted steroid fractions were then quantatively determined by radioimmunoassay. Data on the accuracy, precision, and sensitivity were presented showing that this new assay system was precise and reproducible. As an illustration of its application, this method was used in the present study to determine the plasma androgen levels in Monopterus albus and in methyl-testosterone treated Tilapia mossambicus.

Androstenedione↗
PubMed1986

Pituitary extract of the ricefield eel Monopterus albus (Synbranchidae, Teleostei) exhibits gonadotropic activity in the classes Mammalia, Aves, Reptilia and Amphibia.

Pituitary extract of the ricefield eel Monopterus albus demonstrated gonadotropic activity in mammals and non-mammalian vertebrates. Using the rat as the recipient, FSH activity was detected in Monopterus pituitaries in the HCG augmentation test and LH activity in the ovarian ascorbic acid depletion test. Cyclic AMP level in superovulated ovaries, ovarian lactate production and glucose uptake in vitro, plasma testosterone level in males, testicular enzymes, ventral prostate weight and other androgen-dependent parameters were stimulated after treatment with Monopterus pituitary extract. Testicular and ovarian 32P5+ uptake in the chick, testicular weight in the grass turtle Chinemys reevesi, and ovulation in the amphibians Xenopus laevis and Rana tigrina were enhanced. Both the FSH-like and LH-like activities in Monopterus pituitaries were sensitive to proteolytic enzymes and chemicals that attack the disulfide linkage, carbohydrate moiety, tyrosine, tryptophan and histidine residues. This constitutes the first report of dual gonadotropic activities elicited by a teleost pituitary extract in the mammal in vivo.

Animals↗
PubMed1986

Squamous carcinoma of the anus in young homosexual men with T helper cell depletion.

Two cases of squamous carcinoma of the anus in white homosexual men aged 36 and 47 years are reported, each with a short history of rapidly enlarging perianal lesions. Immunological studies showed that both men had pronounced T helper lymphocyte depletion, and antibody to human T cell lymphotropic virus type III (HTLV-III) was detected in both patients. In addition one patient had a long history of wart virus infection of the anal canal. The diminished cellular immunity associated with HTLV-III may have been responsible for the development of the squamous carcinoma, either directly or by its association with human papilloma virus infection.

Adult↗
PubMed1985

Effects of cadmium on preimplantation mouse embryos in vitro with special reference to their implantation capacity and subsequent development.

A short exposure to 5 or 10 micrograms/ml cadmium chloride for 24 hours disturbed the in vitro development of four-cell and morula-stage embryos of F1 (C57 female X A2G male) mice. Morulae appeared to be less sensitive to cadmium than four-cell embryos. However, the in vitro development of four-cell embryos through compaction to morulae was not affected, though most treated embryos degenerated and decompacted later. It was proposed that cadmium toxicity may not be acting through contact effects on the cell surface and cytoskeleton. It probably interferes with the general energy metabolism of the cells. Although 1 microgram/ml cadmium did not disturb the subsequent in vitro development beyond the implantation stage, a reduced capacity of implantation in vivo was observed after surgical transfer to recipients. In spite of the effects of cadmium salts on the maternal side, the present results suggest that a direct embryotoxic and teratogenic activity of cadmium cannot be excluded.

Abnormalities, Drug-Induced↗
PubMed1985

The ultrastructural and biosynthetic characteristics of steroidogenic cells in the gonad of Monopterus albus (Teleostei) during natural sex reversal.

The ultrastructural and biosynthetic characteristics of the steroid cells in the gonad of Monopterus albus have been studied. Ultrastructural features related to steroidogenesis have been identified in the interstitial Leydig cells, Sertoli cells, granulosa cells and thecal cells, and are especially abundant in the Leydig cells during the mid-intersexual phase. Steroidogenic ultrastructures in the Sertoli cells develop only during the maturation of the spermatogenic cysts, whereas in the granulosa and thecal cells, these features become obvious only during the maturation of the large oocytes. EM evidence also suggests a nutritive function for the Sertoli cells and the granulosa cells. Results of in vitro steroidogenic studies, using either testosterone or progesterone as a precursor, show a predominant conversion to androstenedione and 5 alpha-reduced compounds, and suggest a change in biosynthesis from 5 alpha-reduced products to androstenedione during sex reversal. 11-Ketotestosterone (11KT) has been identified, but not 11 beta-hydroxytestosterone. Production of 11KT is high in the late intersexual and the male phases, but a lack of a marked variation in 11KT production between the early and the mid-intersexual phase suggests that this steroid is not a trigger for natural sex reversal in Monopterus.

Androgens↗
PubMed1985

The in vitro metabolism of radioactive progesterone and testosterone by the gonads of the protandrous Rhabdosargus sarba at various sexual phases.

The in vitro steroidogenic capacity of the gonadal tissue in the protandrous Rhabdosargus sarba was studied. Testicular and ovarian tissues from various sexual phases were used either separately or combined. With progesterone as precursor, high yield of 5 beta-reduced metabolites, and no 11-ketotestosterone or 11 beta-hydroxytestosterone were found. The production of 5 beta-pregnan-3 alpha-ol-20-one and 5 beta-pregnane-3,20-dione was very high in incubations with testicular tissue from intersexes or males and was low in those with ovarian tissue only. The production of 17 alpha-hydroxyprogesterone was high in the female but was low in other sexual phases. With testosterone as precursor, 11-ketotestoterone and 11 beta-hydroxytestosterone were identified. The latter was the most abundant and prominent polar steroid in all incubations. 5 beta-Reductase activity was high in the male and relatively low in the female. 5 alpha-Reduced products, however, were absent. There was an increase in the production of androstenedione as the animal underwent sex reversal. The significance of this change in steroidogenesis in this protandrous fish is at present under investigation. Experimental results also indicated that in the intersexual gonad there may be interaction between the testicular component and the ovarian component in steroidgenesis.

Animals↗
PubMed1983

Extracellular fluid volume expansion and third space sequestration at the site of small bowel anastomoses.

Intestinal surgery is usually associated with the parenteral administration of sodium and water, sometimes in amounts considerably in excess of excretory capacity. We have studied the effect of this situation on the water content of the gut at and 5 cm from a single-layer end-to-end anastomosis in the rabbit. Water content was measured by desiccation. One group of animals (group 1) did not receive intravenous therapy. The second group (group 2) received 5 ml kg-1 h-1 of Hartmann's solution during the operative period and thereafter to a total volume of 200 ml by 48 h. In group 1 there was a 5-10 per cent increase in tissue weight both at the anastomotic site and at 5 cm (P less than 0.01, Mann-Whitney U test) on the first 3 days. Thereafter, water content at the anastomosis persisted, but resolved in normal gut. In group 2 a further 5 per cent increase in weight over group 1 occurred (P less than 0.01), persistent at the anastomotic site over 5 days, though resolving elsewhere after 2 days. Extracellular fluid volume expansion exaggerates an anatomical third space present in the region of an anastomosis. At the suture line, oedema so induced is persistent and could be deleterious.

Animals↗
PubMed1983

The hourly pattern of urine solute and electrolyte excretion following standard surgical trauma.

Although urine volume (and, less frequently, concentration) is often measured in the perioperative period, little attempt has been made to separate temporal phases of the intra- and postoperative response to surgery. In 7 patients undergoing standard severe single trauma and managed by a conventional regimen which included intraoperative Hartmann's solution, we have investigated the hourly pattern of urine solute and electrolyte excretion over the first 48 h. Contrary to expectation, in the first 5 h Na+ excretion increases in association with overall solute excretion, and thereafter progressively diminishes. K+ excretion increases 4 h postoperatively and remains elevated for 24 h, after which it returns to normal, even though Na+ excretion remains low. Free water excretion is negative for the first 24 h, though urine osmolality does not suggest a maximal antidiuretic response by the kidney--the highest concentration achieved being just below 800 mosmol/kg. In order to distinguish between the physiological adaptive changes due to starvation and those due to injury, the hourly pattern of urine solute and electrolyte excretion was further investigated in 12 healthy volunteers mimicking postoperative conditions. Apart from the early postoperative period, the hourly pattern of Na+, K+ and osmolar excretion shows no discernible difference from the operated group. These results show that, particularly in relation to Na+, the changes seen in the post-injury patient, even after major uncomplicated surgery, are largely adaptive, and this is especially striking at 24 h after surgery.

Esophagus↗
PubMed1982

Early weight gain and glycogen-obligated water during nutritional rehabilitation.

Early weight gain by starving patients managed with total parenteral nutrition has been regarded as spurious - that is, merely an increase in body water. We designed an experiment to mimic the starved state in which glycogen stores are depleted and sodium intake is very low. The subjects were then repleted with a sodium-free, high carbohydrate intake. All subjects who received potassium gained weight and switched to a respiratory exchange ratio which suggested mainly carbohydrate oxidation. From changes in weight and total body water the weight gain was calculated to be the consequence of glycogen storage with 1 g of glycogen obligating 3.21 +/- 0.57 g water. Two patients with total dysphagia showed a similar pattern. Two subjects who did not receive potassium showed a rise in respiratory exchange ratio but failed to store glycogen. Early weight gain in patients who received high-carbohydrate feeding after starvation is a normal phenomenon and represents a return to a more hydrated state consequent upon glycogen repletion.

Body Water↗
PubMed1978

Evidence of active sodium transport in the visceral yolk sac of the rat in vitro.

1. Na transport has been studied in the isolated rat visceral yolk sac from day 17.5 of gestation to term. 2. The transepithelial potential difference (p.d.) and the short circuit current (s.c.c.) in the isolated yolk sac were found to vary with gestational age, with peak values at day 19.5. The maximal p.d. and s.c.c. were 3.85 +/- 0.32 mV (the fetal side positive) and 19.5 +/- 5.3 microamperemeter cm-2 respectively. 3. Simultaneous determination of the two-way Na+ flux and the s.c.c. revealed a preferential active movement of Na in the maternal to fetal direction. The net flux was found to be 50% higher than the s.c.c. 4. Both the p.d. and the s.c.c. were found to be reduced by cooling and by the uncoupling agent 2,4-dinitrophenol. 5. The s.c.c. altered in a curvilinear fashion with the Na+ concentration in the bathing solution, with an apparent Km of about 20 mM-Na+. Removing Cl ions from the bathing solutions had no effect on the p.d. and s.c.c. 6. Addition of amiloride (10(-4) M) to either side of the visceral yolk sac had no effect on the s.c.c. but application of ouabain (10(-5) M) to the fetal side caused a profound fall in the s.c.c. 7. The possible physiological role of this active Na transport by the visceral yolk sac in the formation of amniotic fluid is discussed.

Animals↗
PubMed1978

Steroidogenesis in preovulatory follicles of patients given human menopausal and chorionic gonadotrophins as judged by the radioimmunoassay of steroids in follicular fluid.

The administration of human menopausal gonadotrophin (HMG) followed by human chorionic gonadotrophin (HCG) stimulated the development of various numbers of follicles in patients treated for infertility. Graafian follicles from these patients were aspirated 32-33 h after the injection of HCG and the levels of steroids in the follicular fluid and matching serum samples were measured by radioimmunoassay. The follicles could not be grouped into two distinct clusters as found in patients given HCG during the menstrual cycle but a broad classification of follicles into four groups was indicated from the dendrogram. Two of the groups were similar to the ovulatory and non-ovulatory groups found previously, whereas the other two groups of follicles were more intermediate in nature. The use of a discriminant analysis showed that these two groups had clearly been stimulated by the HMG and HCG, although they were not yet fully ovulatory. Our data indicate that the number of developing follicles is considerably increased by treatment with HMG and HCG but there is asynchrony in follicular development because the pattern of steroid synthesis differs in many follicles. The effects of this asynchronous development on oocyte maturation and disorders of the luteal phase are discussed.

Androgens↗
PubMed1977

Changes in the composition of maternal plasma, fetal plasma and fetal extraembryonic fluid during gestation in the rat.

The changes in the biochemical composition of maternal plasma, fetal plasma and fetal extraembryonic fluid were studied in Wistar rats from Days 13 1/2 to 21 1/2 of gestation. During this period, there was an increase in maternal plasma volume and total blood volume. The total protein concentration decreased, but little change was observed in the protein pattern, total alpha-amino nitrogen, urea nitrogen and sodium concentration. In fetal plasma, total protein concentration increased progressively with a prominent increase in albumin near term. The albumin:globulin ratio was lower than that in maternal plasma because of the presence of two alpha-fetoproteins and four transferrins. The concentration of alpha-amino nitrogen was higher than that in maternal plasma but the urea nitrogen level did not change significantly. The fetal extraembryonic fluid reflected the changes in composition of fetal plasma, especially in the protein pattern, and concentrations of alpha-amino nitrogen and sodium. Total protein and urea nitrogen increased markedly in concentration near term but there was reduction in the fluid volume at this time.

Albumins↗
PubMed1977

Steroidogenesis in human follicles approaching ovulation as judged from assays of follicular fluid.

Human chorionic gonadotrophin (HCG) was given to patients at mid-cycle before the endogenous LH surge. Graafian follicles were aspirated 32-33 h later, before ovulation was expected, and the levels of several steroids in follicular fluid and in matching serum samples were measured by radioimmunoassay. Two types of Graafian follicle were identified at laparoscopy , based on the nature of the oocyte, granulosa cells and follicular fluid withdrawn from the follicles. Some were large, preovulatory and presumably becoming luteinized while others were generally smaller, non-ovulatory and still growing. The concentrations of dehydroepiandrosterone (DHEA) and 17alpha-hydroxypregnenolone (delta5 intermediates), androstenedione and testosterone were higher in non-ovulatory follicles, whereas large follicles usually contained high levels of progesterone, 17alpha-hydroxyprogesterone, pregnenolone and oestradiol-17beta. A cluster analysis of these data grouped follicles into two distinct clusters, which accorded with their identification as ovulatory or non-ovulatory at laparoscopy. Levels of progesterone, 17alpha-hydroxyprogesterone and oestradiol-17beta in follicular fluid were high in preovulatory follicles in comparison with plasma. Results in two patients indicated that plasma levels of these steroids were determined by the preovulatory follicle. Levels of plasma delta5 steroids were closer to follicular fluid concentrations, whereas DHEA was higher in plasma. The role of the theca and granulosa is discussed in relation to the synthesis of progesterone and oestradiol-17beta in follicles as ovulation approaches.

Chorionic Gonadotropin↗