Final answer:
The BMR of a hypophysectomized rat after PTU treatment would be lower due to a deficiency in thyroid hormones, as PTU inhibits the production of thyroid hormones and the lack of the pituitary gland results in decreased TSH and thyroid hormones.
Step-by-step explanation:
The BMR of a hypophysectomized rat after PTU injections would be lower when compared to a normal rat's BMR. This effect is observed due to a deficiency in thyroid hormones.
When a rat undergoes hypophysectomy, it means its pituitary gland has been removed, leading to a lack of thyroid-stimulating hormone (TSH). This reduces the production of thyroid hormones. PTU (propylthiouracil) is a medication that inhibits the synthesis of thyroid hormones within the thyroid gland. A lack of thyroid hormones in the bloodstream signals hypothyroidism, which corresponds to a decreased basal metabolic rate.
Hypothyroidism is characterized by a low metabolic rate, sensitivity to cold, and reduced mental activity, among other symptoms. Without the normal stimulatory effects of thyroid hormones, mainly thyroxine, which increases metabolic activity, the BMR in the hypophysectomized and PTU-treated rat drops significantly. This situation is akin to medical conditions such as myxedema, where BMR can fall to 30-40 percent of the normal rate due to reduced levels of thyroid hormones.