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Biomedical subjects

V Chan

Publications and source records attributed to V Chan.

At least 199 records · Page 11Linked to original sources
PubMed1978

The relationship between circadian variations in circulating thyrotrophin, thyroid hormones and prolactin.

Half-hourly blood samples were taken from six clinically euthyroid men over a continuous period of 24 h. Their concentrations of total thyroxine (T4), total triiodothyronine (T3), thyrotrophin (TSH) and prolactin (PRL) were assessed together with the degree of unsaturation of thyroid hormone binding proteins as determined by the thyroid hormone uptake test (THUT). Both T3 and T4 were also measured in urine samples collected serially during the same 24 h period. Significant circadian changes in serum TSH, THUT, serum and urine T4 and serum PRL were demonstrated in all subjects. TSH showed a reciprocal pattern to serum T4, with higher levels during the evening and at night than the daytime. This TSH pattern did not coincide with PRL secretion. Further studies on the same subjects did not show any significant effect of posture, corticosteroid or T4 administration upon circadian changes in TSH. There appeared to be no consistent circadian changes in serum or urinary T3. It seems likely that the TSH circadian rhythm is centrally determined and that free T3 levels are maintained more or less constant by variation in peripheral conversion from T4.

Adult↗
PubMed1978

The effect of heroin addiction on pituitary-testicular function.

The effect of heroin addiction on pituitary-testicular function was studied in 54 active and 19 abstinent addicts and their results were compared with those of 43 age-matched controls. Abnormal sexual function was frequently found in heroin addicts and this persisted after drug withdrawal. The mean total (mean +/- SE, 18.1 +/- 1.0 nmol/1) and free (0.17 +/- 0.03 nmol/1) testosterone (T) levels in heroin addicts were significantly lower than those in healthy controls (total T 22.8 +/- 1.1 nmol/1), P less than 0.005; free T 0.30 +/- 0.03 nmol/1, P less than 0.005). The mean sex hormone binding globulin binding capacity was higher in heroin addicts (60.1 +/- 5.2 mM) than in healthy controls (35.5 +/- 2.1 mM). These hormonal changes returned promptly to normal after withdrawal. The basal LH and FSH and the responses to LHRH were comparable in the three groups studied. The finding of significantly lower total and free T together with higher SHBG indicates an abnormal testicular function in heroin addiction. Normal basal and LHRH-stimulated LH and FSH levels suggest that chronic heroin abuse depressed testicular function via the hypothalamus or higher centres.

Adult↗
PubMed1978

Transfer of digoxin across the placenta and into breast milk.

Eleven mothers given digoxin throughout pregnancy because of rheumatic heart disease were studied. Digoxin was identified in the placenta and, for the first time, in milk. Paired cord and maternal blood samples obtained at parturition showed lower digoxin levels in cord blood than in maternal blood. The total tissue-bound digoxin level in the placenta correlated closely with maternal digoxin levels. These findings suggest strongly the presence of a placental barrier for digoxin. Similar digoxin concentrations (0.825 +/- 0.015 nmol/l) were found in milk samples obtained daily between the third and seventh days post partum. The half-life of digoxin in the newborn was 36.2 +/- 5.43 hours (Mean +/- SEM); thus all the digoxin present at birth would be excreted within 10 to 11 days.

Adolescent↗
PubMed1978

Pituitary-thyroid responses to surgical stress.

The effect of surgery on pituitary-thyroid function was studied in 12 euthyroid patients. There was a sharp early increase in total thyroxine level, causing displacement of triiodothyronine from thyroid hormone binding proteins resulting in the elevation of the biologically more potent free triiodothyronine fraction. The serum triiodothyronine concentration fell rapidly during and after the operation, with a concomitant rise in reverse triiodothyronine level. Increased prolactin levels were found during and after surgery. With no post-operative complication, recovery of normal pituitary-thyroid function occurred after 4 to 7 days of convalescence.

Humans↗
PubMed1977

Thyrotoxicosis: relations between clinical state and biochemical changes during carbimazole treatment.

The relation between clinical and biochemical changes in thyrotoxicosis were studied in 12 patients with Graves's disease who were being treated with carbimazole. Clinical assessment (using the Crooks-Wayne index) was combined with the measurement of free thyroxine and triiodothyronine indices (FT4I and FT3I) and the assessment of two tissue markers of thyroid hormone action--sex-hormone-binding globulin (SHBG) levels and the thyrotrophin responses to TRH. In general the FT4I and FT3I fell rapidly once treatment was started, and returned to normal in one to four weeks, followed shortly by SHBG levels. The thyrotrophin response returned at this time in two patients, who still had borderline high levels of FT3I and SHBG. The clinical score fell more slowly and variably and was less closely related to any of the biochemical indices than these were to each other. During the early phase of treatment with antithyroid drug the clinical evaluation may be an unreliable indicator of persisting thyroid hormone excess, and when the patient seems clinically but not biochemically thyrotoxic the symptoms should be treated on their own merits with beta-blocking drugs and not with increased doses of antithyroid drugs.

Adult↗
PubMed1975

Assessment of thyroid function during pregnancy.

Serum levels of thyroid stimulating hormone and of the two thyroid hormones were compared in pregnant women and in non-pregnant control subjects. Circulating levels of thyroid stimulating hormone did not alter significantly throughout pregnancy. Total thyroxine and triiodothyronine concentrations increased markedly during the first and second trimesters, associated with a progressive increase in the thyroid binding capacity of serum proteins. Urinary triiodothyronine and thyroxine excretion during the third trimester of pregnancy was comparable to that found in non-pregnant euthyroid females and, it is concluded, provides the simplest method of assessing thyroid function during pregnancy.

Animals↗
PubMed1975

Stability of thyroxine and triiodothyronine in biological fluids.

The stability of thyroxine and triiodothyronine in serum has been investigated. Apparent levels of total thryroxine, as determined by two different protein-binding assays employing thyroxine-binding globulin as the binding protein, increased significantly in serum and plasma samples stored at room temperature and were signficantly lower in haemolysed samples. Values did not change significantly in samples stored at 4 degrees C, nor in samples stored at room temperature when determined by radioimmunoassay. Total triiodothyronine levels, as determined by radioimmunoassay, fell slightly on storage. Failure to appreciate the effect of storing samples at room temperature on apparent levels of total thyroxine, as determined by some protein-binding assays, could lead to an incorrect assessment of thyroid status.

Drug Stability↗
PubMed1972

Effects of oestrogen on urinary thyrosine excretion.

The day to day variation and the effects of oestrogen on the urinary excretion of thyroxine (T-4) were studied in euthyroid women and men. Serial urinary T-4 values over a period of 28 consecutive days were found to lie within relatively narrow limits except for a transient increase during menstruation in women. During oestrogen therapy urinary T-4 was unchanged, but an appreciable rise was seen after stopping oral ovulation inhibitors in women. A similar effect was seen in men after three days' treatment with 20 mug/day of ethinyloestradiol. The increased urinary T-4 excretion on oestrogen withdrawal reached a maximum in one to three days. This response contrasted with that produced by phenytoin, a drug known to bind to thyroxine binding globulin, and which resulted in increased urinary T-4 excretion during the period that it was being administered.

Adult↗
PubMed1972

Comparison of two triiodothyronine uptake techniques for the assessment of thyroid function.

The present study was designed to compare the Thyopac and Triosorb triiodothyronine uptake tests. A normal range was established for the two procedures. Neither test was affected by iodine-containing drugs or contrast media but abnormal results were obtained during pregnancy and in subjects receiving oestrogens. Both tests proved satisfactory in the diagnosis of hypo- and hyperthyroidism, giving results consistent with clinical assessment and with serum protein-bound iodine determinations. The Thyopac procedure was preferred for a number of reasons. It requires less plasma; it is slightly simpler and quicker and it is not time dependent.

Estrogens↗