Thyroid Hormone Action at the Cell Level

IT is possible to divide hormones into two classes1 on the basis of physical-chemical characteristics (Table 1). The protein and peptide hormones are virtually infinitely soluble in aqueous solution, unlike the hydrophobic (small molecule) "target" hormones, which exist in solution by virtue of being bound by albumin and specific transport proteins. The sex-hormone-binding globulin, transcortin or corticosteroid-binding globulin (CBG), and thyroxine-binding α-globulin (TBG) are the carriers of the hydrophobic secretions of the gonads, the adrenal and thyroid glands, the "target" glands of the pituitary tropic hormones. Protein and peptide hormones, such as growth hormone, the pituitary . . .