Plasma endothelin levels are unaltered by thyroid hormone status in humans

Endothelin is a novel potent vasoconstrictor peptide produced by a wide variety of cell types and which has diverse biological activities. Previously we have reported that thyroid hormone status alters tissue levels of immunoreactive endothelin (irET) in rats. In order to study whether plasma irET levels in humans are affected by thyroid hormone status, we measured irET concentrations by means of radioimmunoassay in plasma samples from euthyroid controls as well as from patients with either hypothyroidism or hyperthyroidism. Plasma samples from the above-mentioned three groups of subjects were collected. After extraction with Sep-Pak C18 cartridges, plasma irET levels were measured by radioimmunoassay. The plasma irET levels in the three groups of subjects did not show any significant difference. Also, no correlations were found between plasma irET levels, thyroid hormones and the thyroid-stimulating hormone thyrotropin (TSH) in euthyroid, hypothyroid and hyperthyroid subjects. These results suggest that thyroid function per se is not a major determinant of plasma irET levels in humans.