The effect of thyroid hormones on blood insulin level and metabolic parameters in diabetic rats

The thyroid hormone levels and glucose and lipid metabolism in children with type 1 diabetes: a correlation analysis

BACKGROUND

Type 1 diabetes mellitus (T1DM) is common in clinical setting, the relationship between thyroid hormone levels and glucose and lipid metabolism in patients with T1DM remains unclear. We attempted to analyze the correlation of thyroid hormone levels and blood glucose and lipid metabolism in children with normal thyroid function.

METHODS

Children with T1DM were selected, and 85 healthy children who underwent physical examinations in our hospital as control group. The characteristics and laboratory testing results were compared, the correlation of thyroid hormone levels with blood glucose and blood lipids was analyzed by Pearson correlation analysis.

RESULTS

A total of 167 participants were included. the low-density lipoprotein-cholesterol (LDL-C), triglyceride (TG), fasting blood glucose (FBG), and glycated hemoglobin (HbAlc) in T1DM patients were higher than those in healthy controls, while the high-density lipoprotein-cholesterol (HDL-C), thyroid stimulating hormone (TSH) and free triiodothyronine (FT3) in T1DM patients were lower than that of healthy children (all P<0.05). TSH was positively correlated with LDL-C (r=0.169, P=0.032), TC (r=0.182, P=0.017) and TG (r=0.197, P=0.008), negatively correlated with FBG (r=-0.196, P=0.023) and HbAlc (r=-0.328, P=0.002). FT3 was negatively correlated with TG (r=-0.182, P=0.011), FBG (r=-0.184, P=0.009) and HbAlc (r=-0.223, P=0.005). TG in the high TSH group and the middle TSH group is higher than that of low TSH group. However, FBG and HbAlc were lower than those in the low TSH group (all P<0.05). Compared with the low FT3 group, the TG, FBG and HbAlc decreased in the high and middle FT3 group (all P<0.05).

CONCLUSIONS

The serum TSH are closely associated with FT3 and glycolipid metabolism in children with T1DM, which may be the useful indicators to assess the severity of T1DM in clinical settings to provide insights into the management of T1DM.

Association Between Glycaemic Control and the Intake of Thiazide Diuretics, Beta Blockers and Levothyroxine in People Without Diabetes

OBJECTIVE

The pharmacological additional information for many medications includes warnings stating that the blood sugar control may be worsened by the intake of certain drugs. However a quantification of the effects is missing. This may result in confusion for patients as well as for their physicians. The aim of this study was to assess a potential association between medication (beta blockers, thiazides, levothyroxine) and HbA_1c in people without diabetes.

METHODS

In this cross-sectional study we analysed data from 2 921 people (7 699 visits) without diabetes (age 46.6 y; 69.1% women; BMI 27.6±6.4 kg/m²; HbA_1c 5.2%) who had at least one HbA_1c determination and a complete documentation of their drug intake. An oral glucose tolerance test was not performed. The participants were divided in 8 groups (no regular drug intake, levothyroxine alone, beta blockers alone, thiazides alone, combination 2 of 3, combination of all 3). Patients with known distorting influences of the HbA_1c were excluded.

RESULTS

People with no regular drug intake had an HbA_1c of 5.4% [35.8 mmol/mol]. The HbA_1c of the group that took all 3 drugs in combination was 5.6% [38.2 mmol/mol]. A multiple linear mixed model showed an increase in HbA_1c for thiazides (β=0.0558, p=0.025) and a decrease for combination of levothyroxine and thiazide (β=-0.0765, p=0.010).

CONCLUSION

Thiazides and the combination of levothyroxine and thiazides were associated with slight changes in HbA_1c. In this study there was no association between the intake of beta blockers and HbA_1c. At least for people without diabetes these effects seem to be of minor importance.

The Langerhans islet cells of female rabbits are differentially affected by hypothyroidism depending on the islet size

Effects of hypothyroidism on the glucose and insulin levels are controversial, and its impact on the Langerhans islet morphology of adult subjects has been poorly addressed. In spite of hypothyroidism and diabetes mellitus are more frequent in females than in males, most studies using animal models have been done in males. The effect of hypothyroidism on the immunolabeling of thyroid hormone receptors (TRs) and thyrotropin receptor (TSHR) of islet cells is unknown. The aim of this study was to determine the effect of hypothyroidism on the glucose and insulin concentrations, morphometry of islets, and immunostaining of TRs α1-2 and β1 and TSHR of islet cells in female rabbits. Control and hypothyroid (0.02% of methimazole for 30 days) animals were used to quantify blood levels of glucose and insulin, density of islets, cross-sectional area (CSA) of islets, number of cells per islet, cell proliferation, and the immunolabeling of TRs α1-2, TRβ1, and TSHR. Student's t or Mann-Whitney-U tests, two-way ANOVAs, and Fischer's tests were applied. Concentrations of glucose and insulin, as well as the insulin resistance were similar between groups. Hypothyroidism did not affect the density or the CSA of islets. The analysis of islets by size showed that hypothyroidism reduced the cell number in large and medium islets, but not in small ones. In small islets, cell proliferation was increased. The immunoreactivity of TRα1-2, TRβ1, and TSHR was increased by hypothyroidism in all islet sizes. Our results show that hypothyroidism affects differentially the islet cells depending on the size of islets.

Hypothyroidism Affects Vascularization and Promotes Immune Cells Infiltration into Pancreatic Islets of Female Rabbits

Thyroidectomy induces pancreatic edema and immune cells infiltration similarly to that observed in pancreatitis. In spite of the controverted effects of hypothyroidism on serum glucose and insulin concentrations, the number and proliferation of Langerhans islet cells as well as the presence of extracellular matrix are affected depending on the islet size. In this study, we evaluated the effect of methimazole-induced hypothyroidism on the vascularization and immune cells infiltration into islets. A general observation of pancreas was also done. Twelve Chinchilla-breed female adult rabbits were divided into control (n = 6) and hypothyroid groups (n = 6, methimazole, 0.02% in drinking water for 30 days). After the treatment, rabbits were sacrificed and their pancreas was excised, histologically processed, and stained with Periodic Acid-Schiff (PAS) or Masson's Trichrome techniques. Islets were arbitrarily classified into large, medium, and small ones. The external and internal portions of each islet were also identified. Student-t-test and Mann-Whitney-U test or two-way ANOVAs were used to compare variables between groups. In comparison with control rabbits, hypothyroidism induced a strong infiltration of immune cells and a major presence of collagen and proteoglycans in the interlobular septa. Large islets showed a high vascularization and immune cells infiltration. The present results show that hypothyroidism induces pancreatitis and insulitis.

Hyperinsulinemia and insulin resistance is associated with low T₃/T₄ ratio in pre diabetic euthyroid Pakistani subjects

OBJECTIVE

To investigate the relationship of thyroid hormones in glucose homeostasis in impaired glucose-tolerant subjects with normal thyroid functions.

METHODS

Cross-sectional analysis was carried out in (n=260) impaired glucose-tolerant (IGT) and normal glucose-tolerant (NGT) subjects. Thyrotropin (TSH), total triiodothyronine (TT₃), total thyroxin (TT₄) free T₃ (fT₃), free T₄ (fT₄), and insulin were assessed by enzyme-linked immunoassays (ELISA). Fasting plasma glucose (FPG) and HbA1c were measured by glucose oxidase and low-pressure cation exchange chromatography. Homeostasis model of assessment (HOMA-IR) was employed to assess the level of insulin resistance; fT₃/fT₄ ratio was calculated. Anthropometric measurement and habits were recorded.

RESULTS

Marked hyperinsulinemia and insulin resistance were observed in IGT subjects. Serum TT₃ and fT₃ levels were significantly low in the IGT as compared to normal glucose-tolerant (NGT) controls. TT₄ and TSH were higher in IGT subjects as compared to control subjects. There was a significant positive correlation of TSH with BMI only in the control group (r=0.351; P<0.05). Correlation of insulin with TT₃, fT₃,and TSH was significant (P<0.05) in IGT subjects. A significant low fT₃/fT₄ ratio was observed in IGT subjects as compared to NGT subjects (P<0.01). In multiple regression analysis, TSH, TT₄ and fT₃ contributed significantly to the variance of fasting insulin and insulin resistance in IGT subjects.

CONCLUSION

Hyperinsulinemia and insulin resistance are associated with low T₃/T₄ ratio in pre-diabetic euthyroid Pakistani subjects.

Insulin represses transcription of the thyroid stimulating hormone beta-subunit gene through increased recruitment of nuclear factor I

Although the regulation of thyroid stimulating hormone β-subunit gene (TSHβ) has been intensively studied, the functions of transcription factors involved are not fully understood. The authors found that the -615/-516 promoter region of the TSHβ interacts specifically with nuclear proteins derived from pituitary tissue or from cultured thyrotroph cells. The actual binding site at the nucleotide level, as revealed by DNase I protection assay, includes the consensus sequence for nuclear factor I (NFI). RT-PCR analysis indicated that NFI-B expression is restricted to thyrotroph cells in the anterior pituitary. EMSA and ChIP analysis showed that NFI-B binds most efficiently to the -588/-560 region of TSHβ promoter. The forced expressions of NFI-B markedly reduced TSHβ promoter activity and its mRNA expression. Furthermore, it was also shown that the -588/-560 region is involved in the insulin-mediated repression of the TSHβ. It was of particular interest to observe that NFI-B was recruited to the -588/-560 region of the TSHβ promoter in an insulin-dependent manner. Taken together, this study provides new insights of the delicate regulations of energy metabolism and hormonal homeostasis.