Final answer:
PTU injections decrease BMR by inhibiting thyroid hormone production, leading to goiter due to TSH overproduction, not iodine deficiency; thus, answer B is correct.
Step-by-step explanation:
The effect of PTU injections on the normal rat's BMR is a decreased BMR due to thyroid hormone underproduction. The development of a palpable goiter is attributed to the overproduction of TSH in response to low levels of thyroid hormones, not directly due to iodine deficiency. So the correct answer is B. Decreased BMR; thyroid hyperactivity. PTU (propylthiouracil) is a medication that inhibits the synthesis of thyroid hormones (T3 and T4), which are responsible for regulating the body's metabolic rate.
With lower levels of T3 and T4, the BMR decreases. This hormonal imbalance prompts the pituitary gland to release more thyroid-stimulating hormone (TSH), leading to the overstimulation of the thyroid gland and the resultant enlargement, known as a goiter. However, this process is not a result of iodine deficiency but rather a direct effect of drug-induced thyroid underactivity.