Final answer:
The BMR of a thyroidectomized rat after PTU injections would be lower than that of a normal rat because the lack of thyroid hormones decreases the metabolic rate to potentially 30-40% of normal.
Step-by-step explanation:
The Basal Metabolic Rate (BMR) of a thyroidectomized rat, which has been injected with propylthiouracil (PTU), would compare to a normal rat's BMR as follows: B. Lower BMR. Thyroidectomy involves the removal of the thyroid gland, which is responsible for producing thyroxine, a hormone that significantly elevates metabolic rate. In the absence of the thyroid gland, and with the administration of PTU, which inhibits the synthesis of thyroid hormones, the metabolic rate of the rat would decrease because it is unable to produce the amount of thyroxine necessary to maintain a normal BMR.
Considering thyroid's role in metabolism, a decreased level of thyroid hormones due to thyroidectomy and PTU injection leads to hypothyroidism. This condition is characterized by a reduced BMR, which can drop to 30-40 percent of the normal rate in severe cases, as indicated by the reduced availability of thyroid hormones disrupting the metabolic equilibrium.