Biochem/Physiol Actions | Megestrol Acetate is the acetate salt form of megestrol, a synthetic derivative of the naturally occurring female sex hormone progesterone with potential anti-estrogenic and antineoplastic activity. Mimicking the action of progesterone, megestrol acetate binds to and activates nuclear progesterone receptors in the reproductive system, and causes the ligand-receptor complex to be translocated to the nucleus where it binds to and promotes of target genes. This leads to an alteration in protein synthesis, which modulates cell growth of reproductive tissues. Due to the negative feedback mechanism seen with progesterone, megestrol also blocks luteinizing hormone (LH) release from the pituitary gland, thereby leading to an inhibition of ovulation and an alteration in the cervical mucus and endometrium. Furthermore, without stimulation of LH, estrogen release from the ovaries is stopped, hence impedes the growth of estrogen-sensitive tumor cells. Primarily hepatic. Megestrol metabolites which were identified in urine constituted 5% to 8% of the dose administered. Respiratory excretion as labeled carbon dioxide and fat storage may have accounted for at least part of the radioactivity not found in urine and feces. No active metabolites have been identified. The precise mechanism by which megestrol acetate produces effects in anorexia and cachexia is unknown at the present time, but its progestin antitumour activity may involve suppression of luteinizing hormone by inhibition of pituitary function. Studies also suggest that the megestrol's weight gain effect is related to its appetite-stimulant or metabolic effects rather than its glucocorticoid-like effects or the production of edema. It has also been suggested that megestrol may alter metabolic pathyways via interferences with the production or action of mediators such as cachectin, a hormone that inhibits adipocyte lipogenic enzymes. |
Application | 1. Antineoplastic Agents, Hormonal Antineoplastic agents that are used to treat hormone-sensitive tumors. Hormone-sensitive tumors may be hormone-dependent, hormone-responsive, or both. A hormone-dependent tumor regresses on removal of the hormonal stimulus, by surgery or pharmacological block. Hormone-responsive tumors may regress when pharmacologic amounts of hormones are administered regardless of whether previous signs of hormone sensitivity were observed. The major hormone-responsive cancers include carcinomas of the breast, prostate, and endometrium; lymphomas; and certain leukemias 2. Appetite Stimulants Agents that are used to stimulate appetite. These drugs are frequently used to treat anorexia associated with cancer and AIDS. |
