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J T Potts

Publications and source records attributed to J T Potts.

At least 145 records · Page 8Linked to original sources
PubMed1981

Nucleotide sequence of cloned cDNAs encoding human preproparathyroid hormone.

We have cloned cDNA copies of human preproparathyroid hormone in Escherichia coli after insertion of double-stranded DNA into the Pst I site of plasmid pBR322 using the poly(dG) . poly(dC) homopolymer extension technique. Recombinant plasmids coding for preproparathyroid hormone were identified by filter hybridization assay using as a probe 32P-labeled bovine preproparathyroid cDNA. Nucleotide sequence analysis of five recombinant plasmids permitted the assignment of 74 nucleotides of the 5' noncoding region, the entire coding region of 345 nucleotides, and the entire 3' noncoding region of 348 nucleotides of the mRNA. The coding sequence predicts the previously unknown "pre" amino acid sequence and clarifies the hormone's amino acid sequence, which has been disrupted. The 5' noncoding region contains an AUG codon followed by a UGA stop codon before the authentic initiator codon. The 3' noncoding region is 120 nucleotides longer than in bovine preproparathyroid mRNA and contains two A-A-U-A-A-A sequences, potential signals for polyadenylation.

Base Sequence↗
PubMed1981

Effects of hepatectomy, nephrectomy, and nephrectomy/uremia on the metabolism of parathyroid hormone in the rat.

Reports from several laboratories, showing extensive hepatic extraction of circulating parathyroid hormone, led us to examine the effect of near-total hepatectomy on the metabolism of the hormone to circulating fragments, and on its clearance from plasma. The rate of disappearance of (125)I-labeled and unlabeled bovine parathyroid hormone from plasma, and the appearance, disappearance, and chemical and immunochemical characteristics of circulating fragments were examined by gel filtration and either sequence-specific radioimmunoassays or sequence analysis using the Edman reaction. Results from awake rats subjected to near-total hepatectomy were compared with those found in sham-treated, nephrectomized, and short-term uremic rats (studied 2 d after nephrectomy). When compared with the sham-treated group, all other groups clear (125)I-labeled hormone more slowly; after hepatectomy, however, the clearance rate is most strikingly decreased. After injection of intact hormone, the concentration of carboxy-terminal fragments in the circulation of hepatectomized rats is greatly reduced at all time intervals when compared with that in sham-treated rats. Sequence analysis of plasma samples, collected from rats into which (125)I-labeled hormone had been injected, shows that carboxy-terminal fragments having positions 34 and 37 of the intact hormone sequence as their amino-terminal amino acids are abundant in sham-treated, nephrectomized, and nephrectomized/uremic rats, but are undetectable in hepatectomized rats. The data suggest that inasmuch as the liver in vivo generates most of the carboxy-terminal fragments resulting from the metabolism of injected hormone, specific cell types within the liver must be the principal locus of the responsible enzyme(s); thus, studies of the enzymic properties of isolated hepatic cells in vitro most likely will yield information of physiologic relevance to the metabolism of the hormone in the intact animal.

Animals↗
PubMed1981

Short-term effects of synthetic human parathyroid hormone-(1--34) administration on bone mineral metabolism in osteoporotic patients.

Since studies in animals and humans have shown that parathyroid hormone can stimulate bone formation and increase trabecular bone, and patients with primary and secondary hyperparathyroidism may exhibit osteosclerosis, we evaluated the effect of short-term administration of human parathyroid hormone, hPTH-(1--34), in patients with osteoporosis. Six patients with osteoporosis underwent detailed studies including blood and urinary measurements of calcium, phosphate, and magnesium; 47Ca kinetic studies; and 18-d balance studies before and during the short-term administration (3--4 wk) of a daily subcutaneous injection of hPTH fragment 1--34 given as 450 or 750 U/dose. The mean fasting plasma calcium values rose slightly after hPTH-(1--34) administration, primarily in the high-dose group. There was no difference in the mean fasting plasma inorganic phosphate levels. The mean daily urinary excretion of calcium and phosphate was significantly increased in patients given the higher dose. In patients given 750 U, net intestinal calcium absorption increased, phosphate absorption increased, calcium balance improved, and phosphate balance improved. In patients given 450 U, calcium balance and phosphate balance worsened. 47Ca kinetic studies showed a minimal increase in bone accretion rate, a decrease in the mean transit time of calcium in the exchangeable pools, and a decrease in the exchangeable-pool size. In all six patients there was an increased renal clearance of 47Ca as a result of hPTH-(1--34) administration. These studies indicate that low doses of parathyroid hormone may promote bone formation, whereas higher doses clearly have an adverse effect on the skeleton.

Aged↗
PubMed1981

Bone collagen synthesis in vitro: structure/activity relations among parathyroid hormone fragments and analogs.

The structural requirements for the inhibition of net bone collagen synthesis by parathyroid hormone (PTH) in vitro have been examined by study of the effects of selected fragments and analogs of bovine PTH (bPTH) upon the incorporation of [3H]proline into collagenase-digestible and -nondigestible proteins by neonatal mouse calvarial bone in organ culture. At concentrations of 10(-10)-10(-7) M, the amino-terminal fragment bPTH-(1-34) was found to be as potent as intact bPTH in the specific suppression of net bone collagen synthesis after 24 h in culture. The synthetic fragments bPTH-(1-30), bPTH-(1-28), and bPTH-(3-34) were approximately 3%, 1%, and 0.2% as active, respectively, as bPTH-(1-34), in good agreement with previous estimates of the relative potencies of these hormonal fragments on bone resorption in vitro and in vivo and on adenylate cyclase activation in and receptor binding to isolated renal membranes. The amino-terminal analog [Ser1]bPTH-(1-34) displayed no reduction in biological activity compared with bPTH-(1-34), as previously found for bone resorption in vivo. The overall results with this assay system indicate a minimum sequence for biological activity that extends from residues 3-28 of intact bPTH, which is consistent with similar estimates in other test systems and emphasizes the importance of the aminoterminus of the hormone in the expression of its biological effects on bone formation as well as resorption. Moreover, these findings support the potential usefulness of the mouse calvarial culture system in predicting the skeletal activity in vivo of new synthetic analogs of PTH.

Animals↗
PubMed1980

Photosynthesis of previtamin D3 in human skin and the physiologic consequences.

Photosynthesis of previtamin D3 can occur throughout the epidermis in the dermis when hypopigmented Caucasian skin is exposed to solar ultraviolet radiation. Once previtamin D3 is formed in the skin, it undergoes a temperature-dependent thermal isomerization that takes at least 3 days to complete. The vitamin D-binding protein preferentially translocates the thermal product, vitamin D3, into the circulation. These processes suggest a unique mechanism for the synthesis, storage, and slow, steady release of vitamin D3 from the skin into the circulation.

Animals↗
PubMed1980

The photoproduction of 1 alpha,25-dihydroxyvitamin D3 in skin: an approach to the therapy of vitamin-D-resistant syndromes.

Cutaneous 7-dehydrocholesterol, exposed to ultraviolet radiation, converts to previtamin D3, which in turn converts in skin to vitamin D3 and is carried into the circulation. We investigated the feasibility of the photochemical conversion in skin of hydroxylated derivatives of 7-dehydrocholesterol - such as 1 alpha, 25-dihydroxy-7-dehydrocholesterol (1 alpha, 25-(OH)2-7-DHC) - to the corresponding hydroxylated previtamin as an alternative method of delivery of 1 alpha, 25-dihydroxyvitamin D3 (1 alpha, 25-(OH)2-D3) to subjects who are deficient in the endogenous metabolite. In human volunteers and in vitamin-D-deficient rats [24-3H] 1 alpha, 25-(OH)2-D3 appeared in blood after [24-3H] 1 alpha, 25-(OH)2-7-DHC was applied to the skin and exposed to ultraviolet radiation. In anephric rats, intestinal calcium absorption and serum calcium levels were elevated after a topical dose of 1 alpha, 25-(OH)2-7-DHC combined with ultraviolet phototherapy. Delivery of equivalent doses of 1 alpha, 25-(OH)2-D3 through the skin and orally showed that there was more prolonged stimulation in intestinal calcium absorption and serum calcium elevation after cutaneous administration. The photochemical conversion of precursors may be useful in the treatment of patients with impaired vitamin-D metabolism.

Administration, Topical↗
PubMed1980

Anabolic effect of human parathyroid hormone fragment on trabecular bone in involutional osteoporosis: a multicentre trial.

After baseline studies, 21 patients with osteoporosis were treated with human parathyroid hormone fragment (PTH 1-34) given as once-daily subcutaneous injections for 6-24 months. The dose used did not cause hypercalcaemia even in the first few hours after injection. Calcium and phosphate balances improved in some patients, but there was no significant improvement in the group values. There were, however, substantial increases in iliac trabecular bone volume: the mean increase, confirmed by repeat blind measurements, was 70% above mean baseline volume. The new bone was histologically normal. Those patients who had the largest increases in 47Ca-kinetic and histomorphometric indices of new bone formation showed the greatest increases in trabecular bone volume, suggesting that treatment with human parathyroid hormone fragment caused a dissociation between formation and resorption rates that was confined to trabecular bone. Since vertebrae are four-fifths composed of trabecular bone, this hormone fragment may prove useful in treating patients with the crush fracture syndrome.

Aged↗
PubMed1980

Early events in the cellular formation of proparathyroid hormone.

Early events in the cellular synthesis and subsequent transfer into membrane-limited compartments of pre-proparathyroid hormone (pre-proPTH) and proparathyroid hormone (proPTH) were investigated by electrophoretic analyses of newly synthesized proteins in subcellular fractions of parthyroid gland slices pulse-labeled for 0.5-5 min with [(35)S] methionine. During these short times of incubation, both pre-proPTH and proPTH were confined to the microsomal fraction. Labeled pre-proPTH and proPTH were detected in a 30-s interval between 0.5 and 1.0 min of incubation. The radioactivity in proPTH became relatively constant between 3 and 5 min, whereas the radioactivity in ProPTH increased markedly over this period. When corrected for the known content of methionine in the prohormone and the prohormone, we found four times as much radiolabeled prohormone as prehormone between 0.5 and 1.0 min of synthesis. Sequestration of labeled prohomrone into endoplasmic reticulum compartments was shown by treatment of the microsomal fraction with chymotrypsin and trypsin, which resulted in the degradation of the prehormone but not of the prohormones. Approximately 50 percent of pre-prohormone and 25 percent of prohormone were released from the microsomes by their extraction with 1.0 M KCl, whereas 80-90 percent of both was released by treatment with Triton X-100. These results in intact cells support the signal hypothesis proposed by Blobel and his co-workers in studies utilizing cell-free systems, inasmuch as the results indicate transfer of prohormone into the cisternal space of the rough endoplasmic reticulum concomitant with the growth of the nascent polypeptide chain. Appearance of membrane-sequestered proPTH takes place without entry of pre-proPTH into the cisternal space, suggesting that proteolytic removal of the leader peptide occurs during transfer of the polypeptide through the lipid bilayer. Further evidence in support of this process is that pre-proPTH is only partly extracted from the microsomes by treatment with 1.0 M KCl, suggesting that a substantial fraction of the nascent pre-proPTH is integrally inserted into the membranes before it is cleaved to form proPTH.

Animals↗
PubMed1980

Parathyroid hormone and 25-hydroxyvitamin D levels in glucocorticoid-treated patients.

Abnormalities in parathyroid hormone (PTH) secretion or vitamin D action or metabolism have been suggested as pathogenetic factors in the bone disease associated with chronic glucocorticoid therapy. We have found normal plasma PTH values in forty-eight adult asthmatic patients on chronic glucocorticoid therapy, twelve asthmatics treated without glucocorticoids and ten adults on short-term, high-dose glucocorticoid therapy for non-asthmatic illnesses. The mean serum 25-OHD level in the glucocorticoid-treated asthmatics was not significantly different from a disease control group of asthmatic patients not on glucocorticoids, but nine such patients had abnormally low 25-OHD levels. Our results indicate that in asthmatic patients on chronic glucocorticoid therapy: (1) PTH and 25-OHD values are usually normal regardless of dose or duration of therapy and (2) there is a subset of patients with low 25-OHD values which may reflect unusual sensitivity to glucocorticoids.

Adult↗
PubMed1980

Biosynthesis of parathyroid hormone.

Figure 11 summarizes our present concepts of the biosynthetic sequence for parathyroid hormone, deduced largely from observations in vitro. Many aspects of the presumed process whereby preproparathyroid hormone is converted via proparathyroid hormone to the hormone remain unclarified and require much further study, as is true for many other prehormones. These studies, however, coupled with (1) further investigations of intracellular degradation of parathyroid hormone, if this indeed operates in vivo; (2) the proteolytic conversion of secreted hormone in peripheral tissues; and (3) analysis of transcriptional control of biosynthesis of parathyroid hormone, using radioactive cDNA for hybridization studies of mRNA production and turnover, hold great promise for further understanding of critical regulatory factors central to expression of the actions of parathyroid hormone.

Adenylyl Cyclases↗
PubMed1979

Cellular processing of pre-proparathyroid hormone involves rapid hydrolysis of the leader sequence.

The cellular synthesis of parathyroid hormone (PTH) involves two consecutive cleavages of NH2-terminal peptide sequences from a larger precursor, pre-proparathyroid hormone (Pre-ProPTH). The initial cleavage consists of the removal of an NH2-terminal leader sequence either during or shortly after biosynthesis of the polypeptide chain is complete. To determine the fate of the cleaved leader sequence, we prepared, by chemical synthesis, a peptide based on the known structure of the leader sequence of pre-proparathyroid hormone and used this peptide labeled with 125iodine as a marker to monitor the recovery of the putative cellular leader peptide during extraction and electrophoresis of [35S]methionine-labeled proteins from pulse-labeled parathyroid gland slices. Under conditions in which the recovery of the synthetic leader peptide was 50 to 70%, we found no detectable 35S-labeled product in the region of sodium dodecyl sulfate gels where the synthetic peptide migrates. In view of the known methionine content of pre-proparathyroid hormone and proparathyroid hormone (ProPTH), it would have been possible to detect endogenously labeled leader peptide if present in amounts equal to 0.05% of the amount of labeled ProPTH present in the tissues. These observations indicate that the cellular conversion of Pre-ProPTH to ProPTH involves a rapid hydrolysis of the leader peptide either during or immediately after its removal from the precursor.

Animals↗