Pharmacodynamic Actions of a Long-Acting PTH Analog (LA-PTH) in Thyroparathyroidectomized (TPTX) Rats and Normal Monkeys.

Hypoparathyroidism is a disease of chronic hypocalcemia and hyperphosphatemia due to a deficiency of parathyroid hormone (PTH). PTH and analogs of the hormone are of interest as potential therapies. Accordingly, we examined the pharmacological properties of a long-acting PTH analog, [Ala(1,3,12,18,22) , Gln(10) ,Arg(11) ,Trp(14) ,Lys(26) ]-PTH(1-14)/PTHrP(15-36) (LA-PTH) in thyroparathyroidectomized (TPTX) rats, a model of HP, as well as in normal monkeys. In TPTX rats, a single intravenous administration of LA-PTH at a dose of 0.9 nmol/kg increased serum calcium (sCa) and decreased serum phosphate (sPi) to near-normal levels for longer than 48 hours, whereas PTH(1-34) and PTH(1-84), each injected at a dose 80-fold higher than that used for LA-PTH, increased sCa and decreased sPi only modestly and transiently (<6 hours). LA-PTH also exhibited enhanced and prolonged efficacy versus PTH(1-34) and PTH(1-84) for elevating sCa when administered subcutaneously (s.c.) into monkeys. Daily s.c. administration of LA-PTH (1.8 nmol/kg) into TPTX rats for 28 days elevated sCa to near normal levels without causing hypercalciuria or increasing bone resorption markers, a desirable goal in the treatment of hypoparathyroidism. The results are supportive of further study of long-acting PTH analogs as potential therapies for patients with hypoparathyroidism.