P. P. A. Smyth

A method for the direct estimation of total serum thyroxine.

SummarySerum is deprotenized using 95% ethanol. The T4 thus released from the protein binding is quantitated by its competition with a fixed amount of T4123I for binding sites on a fixed amount of TBG. The mean value for thyroxine iodine in a group of 72 clinically euthyroid subjects is 5.94±1.34 g/100mls. giving a normal range of 3.3–8.6 μg/100mls. Agreement with the elinical status in a group of 130 subjects under assessment is 96.2%.As well as providing a direct measurement of circulating thyroxine the method is not affected by the contaminants which invalidate the P.B.I. estimation.

Irish endocrine society: 23rd annual meeting

C CLARKE, CG BRENNAN, K RODGERS, RM DWYER, PPA SMYTH ENDOCRINE LABORATORY, DEPARTMENT OF MEDICINE AND THERAPEUTICS, UNIVERSITY COLLEGE DUBLIN, IRELAND he demonstration in extrathyroidal human tissues of the sodium iodide symporter (NIS) has raised the possibility that 1311, commonly used as a systemic therapeutic ablative agent in hyperthyroidism and thyroid cancer, might be applied in the treatment of tumours in other NISexpressing tissues such as human breast cancer. Thyroidal transport of 1311 is known to be proportional to circulating stable I and the aim of this study was to determine how stable I (KI) would effect such transport in human breast cancer cell lines MDA-MB-231, MCF-7 and in FRTL-5 thyroid cells. All cells were incubated with KI (01 00mM) for 72 hours after which 1Th I was added . Incubation and uptake of l by cells was counted every four hours. Timed efflux of ^I was measured every five minutes. KI in the incubation medium blocked 1251 uptake in a dose-dependent manner in the E receptor positive MCF7 cell line. The effect was less marked in the E receptor negative MDA-MB-231 with significant uptake being maintained even at an I concentration of 50mM. A similar blockade was seen in the FRTL-5 cells with maximum uptake blockade of 25mM I. The rate of efflux of 15I was similar in both MCF-7 and MDA-MB-231 cell lines with a tin of 35 and 40 minutes respectively. In contrast, efflux from the FRTL-5 cells was faster (tire=15 mins). As the human breast has a much lower avidity for I than the thyroid, control of dietary intake would assume even greater importance in radioactive iodine treatment of breast tumours or their metastases.

The "free thyroxine index".

SummaryThe direct estimation of serum thyroxine iodine (T4I) and the uptake of125I labelled thyroxine from serum by anion exchange resin (R.U.R.) can both be used independently to assess thyroid status. The results from these two tests can be combined to give a free thyroxine index (F.T.I.) which is believed to be proportional to the concentration of free thyroxine in the serum.A comparison has been made between the diagnostic accuracy of the T4I, R.U.R. and F.T.I. as done by the above method, carried out on a series of 137 patients who fall into five diagnostic categories, euthyroid, hypothyroid, hyperthyroid, pregnant and nephrotic. It was found that the amended F.T.I. gives better agreement with clinical status than either the T4I or R.U.R. alone.

Irish Endocrine Society: Proceedings of Annual Meeting held at St Vincents Hospital, Dublin, October 121h/13th, 1984.

LDL oxidation has been implicated as an important atherogenic factor. We have previously shown that the LDL estetified/free cholesterol ratio is different in diabetes. This study examines the effect ofLDL glycosylation on the susceptibility of LDL to in vitro oxidation. In particular it examines whether there is a relationship between LDL cholesterol esterification, LDL glycosylation and the susceptibility to oxidation. LDL was isolated by sequential ultracentrifugation from normoc holesternlaemic (n=l 0, serum cholesterol 5.30-+0.18mmol/ 1 ) and hypercholesterolaemic diabetic patients(n=7 serum cholesterol 7.18_+0.2mmol/1) and normocholesterolaemic control subjects (n=10, serum cholesterol 5.14_+0.28mmo1/1). LDL glycosylation was determined using aminophenylborate gel chromatography and LDL composition was determined. The susceptibility of LDL to oxidation in the presence of CuS04 was assessed by measuring thiobarbituric reactive substances (TBARS) LDL from the hypercholesterolaemic diabetic patients was more rapidly oxidised, TBARS at 1, 2, 3 and 4 hours being 12.6+3.7, 24.5+3.3, 38.4+2.3, and 40.0_+2.1 nmol/mg LDL protein compared with 4.8_+0.6,16.0+2.5, 24.5+9.5, and 32.4+2.1 for LDL from control subjects (p<0.05). Oxidation of LDL from the normocholeslerolaemic diabetic patients of 6.3_+0.7, 18.4=[_,0.3, 34.0+2.4 and 37.2+2.1, nmol/mg LDL protein, was also significantly greater than that from controls (p<0.05). The esterified/free cholesterol ratio correlated positively with the susceptibility of the LDL to oxidation (p<0.05) which was also related positively to the degree of LDL glycosylation (p<0.01). These results suggest a mechanism which would account for the increased accumulation of cholesterol in the atherosclerotic plaque of the normocholesterolaemic diabetic patient.