原発性甲状腺機能低下症におけるTolbutamideの下垂体機能抑制作用
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概要
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Since tolbutamide is one of drugs in lowering the blood sugar level by the increase of endogenous insulin secretion, it has been thought that the drug will be able to use clinically the same diagnostic process of the dysfunctions in the human pituitary gland as the insulin-induced hypoglycemia. However, recently Hoshino reported that the tolbutamide inhibited the secretion of cortisol from the adrenal cortex within 30 min after the administration of the drug and in addition, he found also that the PRL levels in the serum were not increased by the tolbutamide-induced hypoglycemia in normal subjects, in whom the PRL levels in the serum were clearly increased by the insulin-induced hypoglycemia. The present study was thus designed to clarify as to whether or not the inhibitory effect of the tolbutamide on several trophic hormones in the pituitary gland such as GH, ACTH, PRL and TSH would be observed in primary hypothyroidism, in which it has been known that at least the production and the release of both TSH and PRL in the pituitary gland are surely increased.<BR>Both of the hypoglycemia induced by insulin or tolbutamide were applied to 6 out of 24 healthy normal subjects (ages; 30-62 yrs, male; 11, female; 13) and 3 primary hypothyroidism (ages; 28, 25, 56 yrs in each, female in all) in the present study. Although the other normal subjects were used to search only the change of the serum GH level in the tolbutamide hypoglycemia, the values of GH, PRL, TSH, ACTH and cortisol in the serum were measured by the method of radioimmunoassay up to 120 min after the injection of tolbutamide or insulin. Five more patients with primary hypothyroidism were employed to study the effect of the tolbutamide on the PRL secretion from the pituitary gland.<BR>Although the tolbutamide stimulated the secretions of GH and ACTH in the pituitary glands of both normal subjects and primary hypothyroidism, the peak values of both trophic hormones in the serum in the tolbutamide group were only 1/3rd times as high as those obtained in the insulin group. These facts were much more strikingly observed in primary hypothyroidism. Such a possible inhibitory effect of the tolbutamide on the pituitary was clearly appeared in the PRL secretion, in which no increase of PRL in the serum was observed in all of normal subjects used herein and a clear decrease of the serum level of PRL was observed in 6 out of 8 primary hypothyroidism. In contrast, the hypoglycemic episodes produced by either tolbutamide or insulin did not affect the secretion of TSH even in primary hypothyroidism.<BR>The facts suggested strongly that an inhibitory effect of the tolbutamide would be appeared the most strongly in PRL, being a questionable extents in GH or ACTH and that no effect of the drug on the TSH secretion was observed.
- 日本内分泌学会の論文