Analysis of Parathyroid Hormone and Its Fragments in Rat Tissues

Abstract

A B S T R A C T After intravenous injection of [125LI]iodo-parathyroid hormone in the rat, uptake of the hormone was greatest in the liver and kidneys. Uptake was rapid, reaching a maximal concentration by 4 and 8 min, respectively. Extracts, prepared from both these organs at intervals soon after the injection of intact hormone, showed three main radioactive peaks when samples were subjected to gel filtration under proteindenaturing conditions. The first peak coeluted with intact hormone.The second eluted at a position corresponding to the carboxy-terminal fragments previously described in plasma, and the last eluted at the salt volume of the column. Microsequence analysis of the radioiodinated fragments, a method that has proved valuable for chemically defining the circulating fragments resulting from metabolism of injected hormone, showed that extracts of liver and kidney, prepared at 4 and 8 min after injection of the intact hormone, contained different fragments. The radioiodinated fragments in liver extracts were identical to those previously reported in the plasma of rats and dogs, fragments resulting principally from proteolysis between positions 33 and 34, and 36 and 37 of the intact hormone. Although the same fragments were also present in the kidneys, they constituted less than 15% of the amount present in the liver. More than 50% of the

A theoretical study of the structure of parathyroid hormone.

“…Additionally, since in native PTH position 34 is followed by several hydrophobic residues, which probably draw this region of the molecule more tightly into the hydrophobic core of the NH2-terminal domain, the possible existence of natural forms of PTH even more active than the 1-34 peptide should be considered. Such fragments may in fact be generated in vivo by the reported cleavages at positions 37 and 39 (25), and it may be that this region (residues 34-39) is of major significance in producing the most active conformation of PTH and its natural fragments. Both theoretical calculations in this paper predict a particularly exposed portion of the chain at positions 37-40, and this may provide a rationale for the known in vivo cleavage of PTH in this region.…”

Peripheral Metabolism of Intact Parathyroid Hormone

“…The plasma samples taken at various times following single injections of both b-PTH 1-84 and oxidized b-PTH 1-84 into dogs, were subjected to gel permeation chromatography using Bio-gel P-100 (Bio-Rad Laboratories, Richmond, Calif.). The (3,17). In fact, Neuman et al (3), using radiolabeled intact PTH by a technique reported to preserve biological activity, demonstrated increasing hepatic PTH uptake associated with increasing biological activity of the hormone.…”

“…The metabolism of the hormone is thought to be rapid, judging from the rapid initial rates of disappearance of PTH following its addition to the circulation (1,3,15,16 (3,17). The liver has been identified as having the greatest uptake rate for intact hormone (3,9,17). Studies by D'Amour et al (17) suggest that most of hepatic PTH uptake is localized to Kupffer cells, and that hepatic cleavage of intact PTH and production of C-terminal fragments can be attributed to this cell type.…”

“…The liver has been identified as having the greatest uptake rate for intact hormone (3,9,17). Studies by D'Amour et al (17) suggest that most of hepatic PTH uptake is localized to Kupffer cells, and that hepatic cleavage of intact PTH and production of C-terminal fragments can be attributed to this cell type. However, data from our laboratory (18) and others (19,20) (5).…”

Stimulation of creatine kinase activity in rat skeletal tissue in vivo and in vitro by protease-resistant variants of parathyroid hormone fragments

“…One reason for the reduced activity of hPTH-(28-48) could be less resistance to circulating and/or cellular proteases. The main PTHmetabolizing activity has been ascribed to the Kupffer cells (macrophages) of the liver, where a cathepsin D-like activity appears to be responsible for the degradation of the hormone [36,37]. Metabolism of PTH has also been shown to occur by cathepsin D action within the endosomes of alveolar macrophages [38].…”