THE EFFECT OF HYPOTHYROIDISM ON INSULIN SECRETION IN RATS

Department of Physiology, Faculty of Medicine and Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Aliashraf Godini

The aim of this study was to assess the effect of hypothyroidism on insulin secretion

in rats

Adult Wistar male rats weighing 250-300 gr were divided into 4 groups

Control

PTU Induced Hypothyroid (0.02% propylthiouracyl in drinking water)

Sham operated thyroidectomized

Surgically thyroidectomized (1% CaCl in drinking water)

After 35±5 days: Intravenous Glucose Tolerance Test (IVGTT)

3 weeks later: Pancreatic Islets Isolation

T3,T4, GLucose and Insulin in Plasma

GSIS and Insulin Content in Pancratic Islets

Intravenous Glucose Tolerance Test (IVGTT) animals were fasted overnight (12-14 h),anesthetized pentobarbital sodium (60 mg / K g) The femoral vein was cannulated .After obtaining the first blood sample from the tail cut at time zero,50% glucose solution (0.1ml/100gr) was administered as a bolus injection at a dose of 0.5 g/kg, and blood samples (0.3ml each) were taken from the tail at 5, 10, 15, 20, 30, and 60 minutes for glucose and insulin assessments. The exposed region was then sutured and animals were allowed to recover.

Islet isolationFollowing 3 weeks recovery from IVGTT, the animals were anesthetized by i. p. injection of

pentobarbital sodium (60 mg/Kg) and the abdomen was exposed. 10 ml ice-cold Hanks’ balanced salt solution (HBSS) containing 0.5 mg/ml of collagenase P was injected into the pancreatic duct, and the expanded pancreas was removed. After digestion and 3 washes with cold HBSS, islets were hand-picked under a stereomicroscope.

GSIS Assay

For evaluation of insulin secretion in vitro, batches of 8 islets (four replicats for each

condition from 5 -6 animals) were transferred into 1.5 mL plastic cups, and 1 ml of

Krebs – Ringer solution with different glucose concentrations (5.6, 8.3, 16.7 mM) were

added into the cups, incubated for 60 min in 37°C water bath and gassed with 95 % O2 /

5 % CO2 for 5 min at the beginning. Aliquots of supernatant were collected and stored at

-20°C for insulin determination.

Statistics All the data are expressed as mean ± SE, and analyzed with GraphPad Prism

software (Version 5). Two-way analysis of variance (ANOVA) followed by a bonferroni post-hoc test or independent Student’s t tests were used to compare the findings. P < 0.05 was considered statistically significant.

Conclusion:

In conclusion hypothyroidism attenuates insulin secretion capacity of the pancreatic islets and can predispose the individual to diabetes. This effect might be reversible if Thyroid hormones return back toward normal values. Since the insulin content is not changed significantly in this experiment, it is suggested that insulin secretion pathways and mechanisms to be studied.

Acknowledgment This work was supported by a grant funding from the Research Institute for Endocrine Sciences of Shahid Beheshti University of Medical Sciences.

Thanks to Dr Asghar Ghasemi and Narges Karbalaei

Supervisor: Professor Saleh Zahediasl

Thanks for your attention