The metabolic rates differed between the normal rat and the surgically altered rats because the surgically altered rats could not produce specific hormones (t4 and TSH) since they no longer have either a thyroid or pituitary gland.
The rate of energy expenditure per unit time by endothermic animals while at rest is known as the basal metabolic rate (BMR), and it is measured in energy units per unit time.
When thyroxine injections were given to hypophysectomized rats, the basal metabolic rate went up (BMR). In contrast to the basal metabolic rate seen in the case of normal rats given thyroxine, the BMR was still on the lower side.
The normal rat has the fastest basal metabolic rate (BMR). The pituitary or thyroid glands are not removed in normal rats, leading to the highest basal metabolic rate. Rats with thyroidectomies have a slower baseline metabolic rate than normal rats. Thyroid hormones support healthy metabolism and body temperature.
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