Final answer:
TRH is produced in response to a decreased metabolic rate as part of a feedback mechanism to stimulate thyroid hormone production and thus increase the metabolic rate.
Step-by-step explanation:
The production of both T4 (thyroxine) and T3 (triiodothyronine) thyroid hormones is critical for regulating the body's basal metabolic rate (BMR). These hormones are produced by the thyroid gland under the control of thyroid stimulating hormone (TSH), which in turn is regulated by TRH from the hypothalamus. In a state of low metabolic activity, there may be less T3 and T4 in the bloodstream, leading to an increase in TRH production as part of a negative feedback mechanism.
This is because TRH stimulates the release of TSH from the anterior pituitary, which subsequently promotes the release of thyroid hormones from the thyroid gland, increasing metabolic rate and heat production in cells throughout the body. If the metabolic rate is already increased, for instance in hyperthyroidism, there would be less need for TRH due to the high levels of thyroid hormones suppressing the secretion of TRH.