difference. Studies now show that the female sex hormone, estrogen, stimulates leptin production, while the male sex hormone, testosterone, suppresses leptin. Researchers know that girls go into puberty when they reach a certain weight. Puberty begins when a hormone from the hypothalamus, a part of the brain, begins to be released. This hormone is called gonadotrophin-releasing hormone (GnRH). The question arose, what was the signal to release GnRH? The presence of leptin proved to be the answer to that question, because it clearly indicates when the fat mass is sufficient for puberty to begin.
Interacting with thyroid hormone Researchers have now shown that leptin interacts with several other hormones in the body, especially insulin, which appears to have an important place in regulating leptin secretion. Leptin interacts with the adrenal gland and growth hormone as well. Because thyroid hormone increases the metabolic rate, which increases the body temperature, researchers thought that leptin (which also regulates metabolism and body temperature) may interact with thyroid hormone. Researchers have now shown that leptin helps to regulate the part of the brain that releases thyrotrophin-releasing hormone (TRH), and it also regulates the release of thyroid-stimulating hormone. When a person fasts, both the thyroid hormone and leptin concentrations fall. If leptin is given to the fasting individual, the TSH and the T4 hormone return to normal. On the other hand, researchers have found that thyroid hormone controls leptin production to some extent. In animals without thyroids, leptin is increased, but when thyroid hormone is replaced, leptin is suppressed. So far in humans, researchers havenâ€™t shown that thyroid hormone causes either a rise or a fall in leptin concentration. The understanding of the role of leptin is at an early stage. Much more will be learned in the next few years. Doctors and scientists are just starting to clarify leptinâ€™s place in thyroid disease; stay tuned.