Influence of discontinuance of methimazole and propylthiouracil on 24 h radioactive iodine uptake in normal rats

Abstract

Objective To investigate the influence of discontinuance of methimazole (MMI) and propylthiouracil (PTU) on 24 h radioactive iodine uptake( RAIU) in normal rats. Methods A total of 66 female SD rats were randomly divided into 3 groups by simple random sampling method. MMI group (30 rats) received MMI with a dose of 0.6 mg·ml-1·d-1 orally for 2 weeks, PTU group (30 rats) received PTU with a dose of 6 mg·ml-1·d-1 orally for 2 weeks. At 1, 3, 5, 7 and 9 d after MMI or PTU was discontinued, 6 rats were sacrificed to measure 24 h RAIU respectively. The control group (6 rats) received normal saline with a dose of 1 ml/d orally for 2 weeks, and then they were sacrificed to measure 24 h RAIU too. Data were analyzed with two-sample t test or t′ test. Results Thyroid 24 h RAIU in normal rats was (14.6±4.3)%. The 24 h RAIU on 1, 3, 5, 7 and 9 d was (4.6±0.7)%, (24.2±7.2)%, (13.1±2.9)%, (14.1±2.6)%, (16.1±3.7)% respectively after MMI withdrawal. The 24 h RAIU was significantly lower than that in control group at day 1 (t′=5.55, P 0.05). The 24 h RAIU on 1, 3, 5, 7 and 9 d was (1.9±0.8)%, (3.3±1.2)%, (7.7±2.4)%, (29.0±4.0)%, (17.1±4.8)% respectively after PTU withdrawal. It was lower than that in control group (t=7.01, 6.10, 3.40, all P 0.05). Conclusions MMI and PTU can inhibit the iodine uptake of thyroid, the 24 h RAIU returns to normal level at day 5 after withdrawal of MMI and at day 9 after withdrawal of PTU in euthyroid rats. Key words: Thyroid gland; Iodine uptake; Iodine radioisotopes; Methimazole; Propylthiouracil; Rats