Altered endothelin 1 concentration in brain and peripheral regions during thyroid dysfunction.

Earlier studies have shown that plasma concentrations of endothelin 1 (ET-1) and the receptors for ET are altered during hyperthyroidism, while they are not affected during hypothyroidism. The present study was undertaken to determine the changes in concentration of endogenous ET-1 in various tissues of hyper- and hypothyroid rats. Hyperthyroidism was induced by daily administration of thyroxine (T4, 0.1 mg/kg, i.p.) for 8 weeks, while hypothyroidism was induced by daily administration of methimazole (10 mg/kg, i.p.) for 8 weeks. The concentration of endogenous ET-1 was determined in the brain regions (hypothalamus, corpus striatum, pituitary, hippocampus and spinal cord), heart, adrenals, kidneys and thoracic aorta using a radioimmunoassay procedure. Blood pressure and heart rate were significantly increased in hyperthyroid rats, while they were not affected in hypothyroid rats when compared with control (euthyroid) rats. Serum T4 and T3 levels were significantly increased in hyperthyroid rats, while they were significantly decreased in hypothyroid rats when compared with euthyroid rats. The concentrations of ET-1 in the hypothalamus, corpus striatum, hippocampus and spinal cord were not altered in hyper- or hypothyroid rats when compared with euthyroid rats. However, the pituitary showed a significant (p < 0.001) increase (104%) in ET-1 concentration in hyperthyroid rats when compared with euthyroid ones, while hypothyroid rats did not show any significant change in ET-1 concentration in the pituitary. In peripheral tissues ET-1 concentrations were not altered in the heart and adrenals of hyper- and hypothyroid rats when compared with euthyroid rats.(ABSTRACT TRUNCATED AT 250 WORDS)