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SUMMARY
In rats to which 125I was administered for 28 days, the level of protein-bound 125I (PB125I) (estimated by trichloroacetic acid precipitation or filtration on a Sephadex G-25 column) was measured. In intact animals, after a single dose of 16 mg thiocyanate ion, a significant decrease of PB125I was found, which was inversely related to the level of thiocyanate in plasma. The decrease was much faster than that in rats after thyroidectomy. From these findings an extrathyroidal effect of thiocyanate was postulated and tested in rats fed 125I− for 28 days and then thyroidectomized immediately before the administration of a single dose of 16 mg thiocyanate ion or 15 mg propylthiouracil. The level of PB125I in most of the latter animals 4, 8, 18 and 24 h after the administration of the drugs was significantly lower than that in thyroidectomized controls.
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ABSTRACT
Polyethylene tubes were inserted into the bile duct and femoral vein of rats under pentobarbital anaesthesia and bile was collected for three 2-h periods. After the first (control) period the animals were infused intravenously at a rate of 1·2 ml/h with the following compounds: (1) 0·9% (w/v) NaCl (control group), (2) glucagon (1200 ng/h), (3) vasopressin (1200 ng/h) or (4) angiotensin II (600 ng/h). The concentrations of thyroxine (T4), tri-iodothyronine (T3) and reverse tri-iodothyronine (rT3) in the bile were estimated by radioimmunoassay. No significant differences between groups were found in the biliary excretion of T4 and T3, while the excretion of rT3 after the infusion of all the hormones used was significantly (P < 0·001 at 2 to 4 h of the infusion) increased, no such increase being found in the controls. It may be concluded therefore that the administration of the above hormones resulted in some changes in iodothyronine metabolism in the liver. These may be explained by an inhibition of iodothyronine 5′-monodeiodination related to the glycogenolytic and gluconeogenetic effects of these hormones.
Journal of Endocrinology (1989) 121, 299–302
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ABSTRACT
5-Methoxytryptamine is a potent agonist of presynaptic 5-hydroxytryptamine autoreceptors modulating serotonin release in the central nervous system. This methoxyindole can be synthesized in the pineal gland, but its presence in vivo is still controversial, probably because of rapid catabolism by monoamine oxidase. An improved high-pressure liquid chromatography method, with coulometric detection, has been developed for the simultaneous measurement of melatonin, 5-methoxytryptamine, 5-methoxytryptophol and 5-methoxyindolacetic acid. We have demonstrated a day–night rhythmicity in the amount of 5-methoxytryptamine in the pineal gland of golden hamsters (Mesocricetus auratus) maintained under a long photoperiod (14 h light: 10 h darkness) and pretreated with the monoamine oxidase inhibitor pargyline. Levels of 5-methoxytryptamine were highest at 16.30 h and lowest at 00.30 h. The rhythm for 5-methoxytryptamine appears to be the same as for serotonin (opposite in phase to that of melatonin). The identification of 5-methoxytryptamine has been confirmed by analysis with gas chromatography–mass spectrometry.
J. Endocr. (1988) 118, 389–397