Diabetes Research and Clinical Practice 51 (2001) 163 – 171 The effects of dexamethasone on insulin release and biosynthesis are dependent on the dose and duration of treatment In-Kyung Jeong, Seung-Hoon Oh, Byung-Joon Kim, Jae-Hoon Chung, Yong-Ki Min, Myung-Shik Lee, Moon-Kyu Lee, Kwang-Won Kim * Diision of Endocrinology and Metabolism, Department of Medicine, Samsung Medical Center, Sungkyunkwan Uniersity School of Medicine, 50 Ilwon -dong, Kangnam-ku, Seoul 135 -230, South Korea Received 13 June 2000; received in revised form 6 September 2000; accepted 27 September 2000 Abstract Complex results concerning the effect of glucocorticoids on insulin secretion have been reported. The aim of this study is to clarify the direct effects of glucocorticoids on pancreatic islets and to determine whether the effect of glucocorticoids on insulin biosynthesis or release is dependent on the dose and duration of treatment with glucocorticoid. Studies on insulin secretion and biosynthesis were performed with different concentrations (0, 1, 10, 100 nmol/l) and durations (1 and 6 h) of treatment with dexamethasone (dexa) in rat pancreatic islets. (1) One nmol/l dexa had no inhibitory effect on insulin secretion and biosynthesis. Ten and 100 nmol/l had an inhibitory effect on insulin secretion, which was mainly due to suppression of the first phase of insulin secretion. (2) Insulin content was significantly increased regardless of the concentration in 1-h treated islets. However, insulin content was markedly diminished with 100 nmol/l dexa in 6-h treated islets. (3) The preproinsulin mRNA expression of 6-h treated islets was suppressed in a dose-dependent manner. Our data revealed that, in the condition of short-term and low-dose glucocorticoid exposure, insulin secretion and biosynthesis are not affected. The secretory process of insulin seems to be the initial step of the inhibitory action of glucocorticoid. Both insulin release and biosynthesis are inhibited by chronic exposure to high dose dexamethasone. It can be concluded that glucocorticoid might be involved in the multisteps of insulin release and biosynthesis. © 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Dexamethasone; Insulin release; Insulin biosynthesis www.elsevier.com/locate/diabres 1. Introduction Glucocorticoids have profound effects on glu- cose metabolism under both normal and patho- logic conditions. The adrenalecomized state and adrenocortical insufficiency result in hypo- * Corresponding author. Tel.: +82-2-34103439/1085; fax: +82-2-34100064/0256. E-mail address: kwwkim@smc.samsung.co.kr (K.-W. Kim). 0168-8227/01/$ - see front matter © 2001 Elsevier Science Ireland Ltd. All rights reserved. PII:S0168-8227(00)00229-1