Parathyroid hormone antagonists

Indications Paget s disease of bone Category Parathyroid hormone antagonist Half-life 70-90 minutes... 

The answer is c. (Hardman, p 15230 Administration of intravenous CaG would immediately correct the tetany that might occur in a patient in whom a thyroidectomy was recently performed. Parathyroid hormone would act more slowly but could be given for its future stabilizing effect. Long-term control of a patient after a thyroidectomy can be obtained with vitamin D and dietary therapy Calcitonin is a hypocalcemic antagonist of parathyroid hormone. Plicamycin (mithramycin) is used to treat Paget s disease and hypercalcemia. The dose employed is about one-tenth the amount used for plicamycin s cytotoxic action. 

Calcitriol and parathyroid hormone, on the one hand, and calcitonin on the other, ensure a more or less constant level of Ca "" in the blood plasma and in the extracellular space (80-110 mg 2.0-2.6 mM). The peptide parathyroid hormone (PTH 84 AA) and the steroid calcitriol (see p. 374) promote direct or indirect processes that raise the Ca "" level in blood. Calcitriol increases Ca "" resorption in the intestines and kidneys by inducing transporters. Parathyroid hormone supports these processes by stimulating calcitriol biosynthesis in the kidneys (see p. 330). In addition, it directly promotes resorption of Ca "" in the kidneys (see p. 328) and Ca "" release from bone (see B). The PTH antagonist calcitonin (32 AA) counteracts these processes. 

Nemeth, E and Scarpa, A, 1987, Rapid mobilization of cellular Ca2+ in bovine parathyroid cells by external divalent cations, J Biol Chem 202 5188-5196 Nemeth, EF, Fox, J, Delmar, EG, Steffey, ME, Lambert, LD, Conklin, RL, Bhatnagar, PK and Gowen, M, 1998a, Stimulation of parathyroid hormone secretion by a small molecule antagonist of the calcium receptor., J Bone Miner Res 23 S156 (absract 1030)... 

E. Peggion, A. Bisello, M. Rosenblatt, M. Chorev, D. F. Mierke, Mono- and bicyclic analogs of parathyroid hormone-related protein. 2. Conformational analysis of antagonists by CD, NMR, and distance geometry calculations, Biochemistry 1997, 36, 3300-3307. 

A number of drugs inhibit the antidiuretic actions of vasopressin. Lithium is of particular importance because of its use in the treatment of manic-depressive disorders. Lithium-induced polyuria is usually reversible. Acutely, lithium appears to reduce V -receptor-mediated stimulation of adeny-lyl cyclase. Also, hthium increases plasma levels of parathyroid hormone, a partial antagonist to vasopressin. In most patients, the antibiotic demeclocycline attenuates the antidiuretic effects of vasopressin, probably owing to decreased accumulation and action of cyclic AMP. 

Calcilytics, Ca + receptor antagonists increasing the secretion of parathyroid hormone (PTH). The first calcQytic compound was NPS 2143, an orally active compound that elicits 3- to 4-fold increases in circulating levels of PTH. Although this... 

FIGURE 6.20.9 The blood calcium control system. Calcitonin and parathyroid hormones act antagonistically to regulate blood calcium level precisely. (From Campbell, N. A. et ah, Biology, 5th edn., Addison Wesley Longman, Menlo Park, CA, 1999. With permission.)... 

Osteoporosis Antiresorptive medications bisphosphonates, calcitonin, estrogen and estrogen agonists/ antagonists anabolic (bone forming) medications parathyroid hormone surgery or bone replacement [5]... 

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