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  • Title: Effects of synthetic bovine parathyroid hormone (1-34) and its analogues on 45Ca uptake and adenylate cyclase activation in bone and plasma calcium levels in the chick.
    Author: Dacke CG, Shaw AJ.
    Journal: Q J Exp Physiol; 1988 Jul; 73(4):573-84. PubMed ID: 3174916.
    Abstract:
    We have previously demonstrated that intravenous injection of synthetic bovine parathyroid hormone (1-34) (bPTH(1-34)), but not necessarily bPTH(1-84), into chicks rapidly (3 min) inhibits skeletal uptake of an acute 45Ca label. In the present study hydrogen peroxide oxidation of bPTH(1-34) abolished this response and reduced its ability to activate adenylate cyclase in bone and kidney. Oxidised bPTH(1-34) did, however, exhibit the full hypercalcaemic activity of untreated hormone. In contrast, the analogue [Nle8, Nle18, Tyr34]-bPTH(1-34)amide reduced chick bone 45Ca uptake but failed to raise plasma Ca levels. Cyclic AMP formation in response to this analogue was also slight. Another analogue, [Nle8, Nle18, Tyr34]-bPTH(3-34)amide, failed to inhibit 45Ca uptake or stimulate cyclic AMP formation in chick bone. It was also without hypercalcaemic activity. These data suggest that the hypercalcaemic response to bPTH(1-34) in chicks is not merely a reflection of its inhibitory effect on bone 45Ca uptake. They also question the relevance of cyclic AMP in the former action. A model is proposed by which PTH could rapidly inhibit bone net 45Ca uptake by stimulating release and turnover of intracellular calcium stores in bone lining cells, thereby creating a gradient for Ca out of bone.
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