Impact of insulin sensitivity in relationship with prolactin and thyroid stimulating hormone

It is well recognized that there is a close relationship between TSH and PRL levels. The aim of this study was to evaluate the impact of insulin sensitivity on the association between TSH and PRL in euthyroid obese subjects.

Retrospective cross-sectional analysis was carried out on 165 euthyroid obese or overweight female patients. Prolactin, TSH, free thyroxine (FT4), free triiodothyronine (FT3), fasting plasma levels of insulin and glucose, postprandial levels of glucose, homeostasis model assessment (HOMA) for insulin resistance (HOMA-IR) and insulin secretion (HOMA-beta cell), body weight, height, body mass index (BMI) and waist circumference were assessed. Statistical tests used were unpaired Student's t-test adjusted by Bonferroni's method and Pearson correlations with Bonferroni corrections.

There was no significant difference in prolactin levels between insulin sensitive and resistant subjects. Compared to insulin sensitive subjects, TSH levels were higher in insulin resistant subjects but it was not statistically significant. We observed significant positive correlation between prolactin and TSH in insulin sensitive and normoglycemic subjects (r=0.273, p=0.039 and r=0.253, p=0.023, respectively) but this correlation was lost in insulin resistant subjects and subjects who had fasting glucose levels >or=100 mg/dl (r=0.057, p=0.609 and r=0.090, p=0.404, respectively).

The findings of this study provide some clues about the relationship between PRL and TSH in insulin sensitive obese subjects. The insulin sensitivity and carbohydrate homeostasis seem to be involved in relationship with PRL and TSH by the brain via serotoninergic and dopaminergic system.