In a randomized, double-blind, crossover study in 10 healthy volunteers the hemodynamic effects, drug plasma concentrations, and thyroid hormone profiles were compared after oral administration for 1 week of 40 mg t.i.d. racemic (R,S)-propranolol versus 20 mg t.i.d. optically pure (S)-propranolol. During exercise, both substances decreased heart rate (-14%, p less than 0.01), as well as the overall rate pressure product (-19%, p less than 0.01) to the same extent, indicating similar beta-blocking effects. After oral application of (R,S)-propranolol the maximal plasma concentration (Cmax) and the area under the plasma concentration-time curve (AUC) of (S)-propranolol were higher than those of (R)-propranolol (eudismic ratios (S)- over (R)-propranolol Cmax, 1.36 [p less than 0.01] and AUC, 1.42 [p less than 0.01]) despite dose-equivalence of both enantiomers in the administered racemic (R,S)-propranolol preparation indicating different pharmacokinetic properties. Mean values of Cmax and the AUC of (S)-propranolol did not differ significantly after 1 week of oral administration of 40 mg (R,S)-propranolol and 20 mg (S)-propranolol t.i.d., respectively. The ratio of triiodothyronine to thyroxine was decreased by (R,S)-propranolol (-25%, p less than 0.01) but not by (S)-propranolol, suggesting that only the (R)-enantiomer inhibits the conversion of thyroxine to triiodothyronine. Thus, half-dosed optically pure (S)-propranolol is an equally effective beta-adrenergic receptor antagonist compared with currently used racemic (R,S)-propranolol. By contrast, the conversion of thyroxine to triiodothyronine is inhibited by (R)-propranolol only.(ABSTRACT TRUNCATED AT 250 WORDS)
Levothyroxine as well as iodine was effective in reducing thyroid size as well as thyroid growth stimulating immunoglobulins levels in endemic goitre patients. Since in both groups TSH levels were not related to thyroid size reduction, other factors than TSH suppression must be responsible for the observed thyroid size reduction. Iodine itself by virtue of its antiproliferative action on thyrocytes may have had a direct action on the goitre reduction during iodine treatment; however, the levothyroxine dose, containing less iodine, had a similar effect. A complicated picture hence emerges with regard to factors involved in the shrinkage of iodine deficiency goitre during thyroxine or iodine therapy. These findings indicate that TSH and thyroid growth promoting immunoglobulins are not the only influences on the size of endemic goitres, although it cannot be excluded that these two factors contribute to influence the pathogenetic process.
A new and simple scintigraphic method for the measurement of gastric emptying was developed and validated. The test meal consists of 200 g potato mash mixed with 0.5 g Dowex 2X8 particles (mesh 20-50) labelled with 37 MBq (1 mCi) technetium-99m. After ingestion of the meal, sequential dynamic 15-s anteroposterior exposures in the supine position are obtained for 90 min. A second recording sequence of 20 min is added after a 30-min interval. The results can be displayed as immediate cine-replay, as time-activity diagrams and/or as activity retention values. Complicated mathematical fittings are not necessary. The method lends itself equally to the testing of in- and outpatients.
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