I am having problems with exercise 4 Endocrine System Physiology

1)    Thyroxine helps control the rate of chemical reactions (metabolism) in the body and helps regulate growth.  O2 consumption, metabolic rate and heat production all increase in the presence of thyroxine. In the two non-normal rats, the thyroxine compensated for the shoratage of TSH production from absent pit gland and missing thyroid, respectively.

2)   There was almost no change in the metabolic rate of the thyroidectomized rat after the administration of TSH.  This rat has had its thyroid gland removed, so there is no production of thyroxine, which would be necessary to increase the metabolic rate in the rat.

3)   Removal of the thyroid and subsequent underproduction of thyroxine leads to hypothyroidism in the absence of supplementary medications.

4)   Administering propylthiouracil to the normal rat decreased metabolic rate as propythiouracil inhibits thyroxine production from the thyroid..

Administering propylthiouracil to the thyrectomized rat resulted in almost no change from baseline in metabolic rate.  Giving propythiouracil would prevent the body from producing thyroxine in the presence of a thyroid gland.  Without a thyroid gland, no change can occur. 

In the Hx rat, there was no change.  Without a pit gland, no TSH is produced.  Thyroxine production is dependent on the presence of TSH, so no thyroxine can be synthesized.

5)    Propylthiouracil would be used to treat hyperthyroidism as prorylthiouracil prevents thyroxine from being produced in the thyroid.  Too much thyroxine increases the metabolic rate, resulting in hyrperthyroidism.