Biosynthesis of hormones

1. Hormones may be synthesized and secreted in the active form directly. Eg, estriol, aldosterone, hydrocortisone and catecholamines.

2. Hormones that are modified in the secreting cells prior to secretion. Eg. Insulin and parathyroid hormone. Both are synthesized as the prepro hormone and during their passage through the organelles in the process of synthesis the prepro segment are removed and the active hormone is secreted. The anterior pituitary produces pro-opiomelanocortin (POMC) which is cleaved to yield 3 basic peptide groups of hormones- ACTH, beta lipocortin and gamma MSH.

3. Hormones that are converted into active form in the peripheral tissues. The peripheral tissue may be:

a) Target tissue; Conversion of T4 to more active form T3 in liver and pituitary. Conversion of testosterone to dihydrotesterone secondary sex tissues. In both cases, T4 and testosterone act as prohormone.

b) Non target tissue
The prohormone dehydroepianderosterone (DHEA) is converted to the active form by sulfation in the liver. By removal of sulfate, reactivate the hormone which is then converted to androstenedione ( 4 androstene- 3, 17- dione) which on reduction from testerone (17 β hydroxy- 4 androsten trione)

c) Combination of target and non target tissues
Conversion of vitamin D3 (formed from UV light radiation on 7- dehydrocholesterol) to 25 hydroxy cholecalceferol in the liver (nontarget tissue) with subsequent conversion to 1,25- dihydroxy cholecalceferol in the kidney (target tissue).