The effect of propranolol on plasma triiodothyronine (T3), thyroxine (T4) and triiodothyronine uptake by Sephadex G-25 (RT3U%) was studied in fourteen thyrotoxic patients and eight normal volunteers. 40 mg of propranolol as a single oral dose caused significant reduction in total serum T3 which began 60 min after administration. No significant changes were observed in T4 and RT3U% values. Plasma T3 levels remained suppressed during a 5 day course of treatment with propranolol. These results suggest that propranolol has a direct effect on peripheral metabolism of T3 rather than on thyroid hormone secretion.

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A single dose of pyridoxine (300 mg iv) produced significant rises in peak levels of immunoreactive growth hormone GH and significant decrease of plasma prolactin PRL in 8 hospitalized healthy subjects. Serum glucose, luteinizing hormone LH, follicle stimulating hormone FSH and thyrotropin TSH were not altered significantly. In addition, in 5 acromegalic patients who were studied with both L-dopa and pyridoxine, inhibition of GH secretion followed either agent in a similar pattern. These data suggest a hypothalamic dopaminergic effect of pyridoxine.

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