Final answer:
The administration of TSH did not affect the metabolic rate of the thyroidectomized rat because the rat lacked a thyroid gland (option C ) and could not produce thyroid hormones to regulate metabolism.
Step-by-step explanation:
The administration of Thyroid Stimulating Hormone (TSH) did not affect the metabolic rate of the thyroidectomized rat because of option C. The rat lacked a thyroid gland. TSH is secreted by the anterior pituitary and stimulates the thyroid gland to produce thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), which regulate the body's metabolic rate. In the absence of the thyroid gland, there is no tissue available to respond to TSH and produce these metabolic-regulating hormones. Therefore, no amount of TSH can influence the metabolic rate in a thyroidectomized rat.
When it comes to the metabolism and thyroid hormones, the general rule is that more thyroid hormones increase metabolism and less thyroid hormones decrease metabolism. Issues like an underactive thyroid (hypothyroidism) lead to a lower metabolic rate, whereas an overactive thyroid (hyperthyroidism) leads to a higher metabolic rate.