The anterior lobe of pituitary gland secretes Thyroid Stimulating Hormone (TSH), which controls the structure, and functioning of thyroid and Adrenocorticotropic Hormone (ACTH) which controls the structure and functioning of the adrenal cortex. Besides, it secretes FSH, LH, ICSH, etc, which affect the structure and functioning of gonads.

So, if the pituitary gland of an adult rat is surgically removed, out of the four options adrenal medulla will be less affected.