The influence of free fatty acids on the free fraction of thyroid hormones in serum as estimated by ultrafiltration

Abstract

Thyroid hormones are displaced from their binding proteins in serum during nonthyroidal somatic illness, and FFA have been claimed to contribute. It seems mandatory to evaluate this effect using techniques for the measurements of serum free thyroid hormones in which serum remains undiluted. We measured the effect of 7 common human FFA on the free fraction of T4, T3 and rT3 in serum from healthy subjects using an ultrafiltration technique by which serum is diluted only minimally. In addition we measured the effect of oleic acid on the free fractions of the iodothyronines in pooled serum from healthy subjects and in pooled serum from patients with nonthyroidal illness. All FFA tested were able to displace both T4, T3 and rT3, but to a varying degree, arachidonic and linoleic acid being the most potent ones. A 20% increase in the free fractions of T4, T3 and rT3, respectively, was obtained by adding between 1.7\p=n-\3.3mmol/l, 1.3\p=n-\4.6 mmol/l and 1.0\p=n-\2.4mmol/l of the different FFA. A serum pool obtained from patients with nonthyroidal somatic illness was more sensitive to oleic acid than a serum pool obtained from healthy subjects, since 2\p=n-\3 times less oleic acid was necessary to induce a 20% increase in the free fractions of thyroid hormones. It is concluded that FFA are able to displace both T4, T3 and rT3 from their serum binding proteins in healthy subjects as well as in patients with nonthyroidal illness. However, serum from patients with nonthyroidal illness was more sensitive to the displacing activity of oleic acid than serum from healthy subjects. This was possibly due to reduced affinity of the serum binding proteins to thyroid hormones, and it could be argued that a factor different from FFA seemed responsible.It is well known that patients suffering from nonthyroidal somatic illness (NTI) often have reduced serum total T4 and T3 concentrations, whereas the serum free non-protein bound frac¬ tions of the iodothyronines T4, T3 and rT3 are increased. This seems not totally explained by the concomitant reduction in the concentrations of the thyroid hormone binding proteins in serum (thyroxine binding globulin (TBG), thyroxine binding prealbumin (TBPA) and albumin), since the reduction in the concentration of the binding proteins is less pronounced than the increase in the free fractions of thyroid hormones (FFT)

Thyroid Functions Before and After Maintenance Hemodialysis in Patients with Chronic Renal Failure.

“…The presence of a factor which differed from NEFA and posessed THBI in the patients with NTI was also suggested by Bregengard et al(1987).…”

“…Non-esterified fatty acid (NEFA), especially oleic acid (OA) (Chopra et al, 1986), was regarded as the main substance which caused THBI activity (Chopra el al., 1985), although there have been some data which denied the contribution of NEFA to low thyroid hormone concentrations (Bregengard et al, 1987;Mendel et al, 1986). The presence of abnormalities in lipid metabolism in patients with CRF is well known and may have an influence on thyroid hormone metabolism in CRF (Schatz et al, 1969).…”

Übersichten

“…Die Schilddrüsenhormonkonzentrationen im Blut hängen keineswegs nur von der Sekretion durch die Schilddrüse selbst ab. Die prinzipiellen Beeinflussungsmöglichkeiten der Schilddrüsenhormonkonzentrationen sind folgende: 1 …”