Hyperthyroidism and estradiol increased the prolactin level. After adjusting for age and estradiol, hyperthyroidism increased the serum prolactin level (P<. 001). Conclusion: The results of this study revealed that hyperprolactinemia is more frequent in hyperthyroid females.

In patients with primary hypothyroidism, increased levels of TRH can cause to rise prolactin levels and these patients may have galactorrhea (3). Different increased level of serum prolactin has been reported in 30% of patients with primary hypothyroidism (4).

These results led to the conclusion that more severe hypothyroidism, as displayed by higher TSH levels, leads to a greater thyrotropin-releasing hormone–mediated prolactin release. Investigators concluded that raised prolactin levels were found in 18% of patients with subclinical hypothyroidism.

TRH stimulates prolactin synthesis through the activation of ERK, whereas prolactin release occurs via elevation of intracellular Ca(2+).

The main stimulus for prolactin secretion is suckling, the effect of which is neuronally mediated. A key regulator of prolactin production is estrogens that enhance growth of prolactin-producing cells and stimulate prolactin production directly, as well as suppressing dopamine.

Thyroid-releasing hormone (TRH) from the hypothalamus stimulates TSH from the pituitary, which stimulates thyroid hormone release. As blood concentrations of thyroid hormones increase, they inhibit both TSH and TRH, leading to “shutdown” of thyroid epithelial cells.

When low thyroid hormone levels trace back to a failure of the hypothalamus to secrete Thyroid Releasing Hormone (TRH), which in turn stimulates the anterior pituitary to produce TSH, the resulting hypothyroidism is hypothalamic hypothyroidism, also known as tertiary hypothyroidism.

When the hypothalamus and pituitary are working normally, they sense when: Thyroid hormone levels are low, so they secrete more TRH and TSH, which stimulates the thyroid to make more hormones. Thyroid hormone levels are too high, so they secrete less TRH and TSH, which reduces hormone production by the thyroid.

Primary hypothyroidism causes an elevation of TRH, which can cause an elevation of prolactin along with TSH. Prolactin levels in patients with hypothyroidism tend to be lower than those usually seen with prolactinomas (the latter are usually 150-200 ng/mL or higher).

Normal and Abnormal TSH Ranges TSH > 4.0/mU/L with a low T4 level indicates hypothyroidism. If your TSH is > 4.0 mU/L and your T4 level is normal, this may prompt your physician to test your serum anti-thyroid peroxidase (anti-TPO) antibodies.

Prolactin is a hormone known for its role in milk production in female mammals. Apart from this, it also has a role in metabolism, the regulation of the immune system, and the development of the pancreas. It is secreted by the pituitary gland.

TRH = thyrotropin-releasing hormone; TSH = thyroid-stimulating hormone. Binding of TSH to receptors on the thyroid gland leads to the release of thyroid hormones—primarily T4 and to a lesser extent T3.

Experts don’t agree on which TSH levels should be considered too high. Some suggest that TSH levels of over 2.5 milliunits per liter (mU/L) are abnormal, while others consider levels of TSH to be too high only after they have reached 4 to 5 mU/L.

Treatment

1. Radioactive iodine to slow down your thyroid.
2. Anti-thyroid medications to prevent it from overproducing hormones.
3. Beta blockers to reduce a rapid heart rate caused by high thyroid levels.
4. Surgery to remove the thyroid (this is less common)

Subclinical hypothyroidism is defined as a thyroid stimulating hormone (TSH) level of 4.6 to 10 mIU/L. A normal TSH level is 0.4 to 4.0 and full-blown hypothyroidism is 10 or higher.