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J T Potts

Publications and source records attributed to J T Potts.

At least 217 records · Page 12Linked to original sources
PubMed1976

Experimental parturient hypocalcemia in cows following prepartal chemical inhibition of bone resportion.

Cows fed a balanced diet with the required amounts of calcium and phosphorus developed acute hypocalcemia and hypophosphatemia shortly after parturition, even in the presence of the a responsive parathyroid gland, when bone resorption was selectively inhibited by the prepartal administration of disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP). When serum total and ionized calcium levels declined below 6.0 and 1.0 mg/100 ml, respectively, cows developed clinical signs similar to naturally occurring parturient paresis. The plasma immunoreactive parathroid hormone levels were similar prepartum, at parturition, and 1 day postpartum in cows administered EHDP as in control cows. Parathyroid chief cells were predominately in the actively synthesizing phase of the secretory cycle with a prominent Golgi apparatus and lamellar arrays of rough endoplasmic reticulum. Many chief cells were degranulated of mature secretory gransules. Calcitonin activity in thyroid extracts, determined by bioassay, and the numbers of secretory granules in thyroid C-cells were similar in both groups of cows. EDTA infusion after 60 days of the experiment demonstrated that the immediately available calcium reserves were reduced in EHDP-treated cows. The serum calcium remained significantly lower and did not return to preinfusion levels by 24 hours. Serum calcium in control cows returned to within the normal range by 6 hours after EDTA infusion. The urinary excretion of hydroxyproline was consistently reduced prepartum and following EDTA infusion in cows receiving EHDP. The experimental induction of parturient of parturient hypocalcemia by the prepartal administration of EHDP provides a valuable model for studies to investigate the mechanisms in bone responsible for the development of severe hypocalcemia that occurs in response to the increased calcium demand imposed by parturition and the initiation of lactation.

Animals↗
PubMed1975

Prostaglandins as mediators of hypercalcemia associated with certain types of cancer.

We investigated the role of prostaglandins in the hypercalcemia associated with neoplasia. In patients with hypercalcemia and solid tumors the excretion of the major urinary metabolite of the E prostaglandins, 7 alpha-hydroxy-5, 11-diketotetranorprostane-1, 16-dioic acid (PGE-M), was significantly greater than normal, P LESS THAN 0.01 (median of 58.4 and 7.1 ng per milligram of creatinine respectively). Slightly elevated values were seen in normocalcemic patients with solid tumors (14.3 ng per milligram). The levels of the metabolite were normal in hypercalcemic patients with either hematologic neoplasia or primary hyperparathyroidism. Immunoreactive parathyroid hormone was undetectable in the plasma of all hypercalcemic patients with solid tumors. Inhibition of prostaglandin synthesis by aspirin or indomethacin reduced excretion of both the urinary metabolite and serum calcium in six hypercalcemic patients with solid tumors and elevated excretion of the metabolite. These findings support the concept that prostaglandins are mediators of the hypercalcemia caused by certain solid tumors.

Aspirin↗
PubMed1975

A reinvestigation of the amino-terminal sequence of human parathyroid hormone.

The sequence of the amino-terminal portion of human parathyroid hormone, particularly the identity of residues 22, 28, and 30 (the subject of discrepancies in recent published reports), has been reexamined by two basic methods of structural analysis. A fresh lot of human parathyroid hormone isolated from pooled adenoma tissue was analyzed by Edman degradation with identification of critical residues by thin-layer chromatography and gas-liquid chromatography. In the second approach, -14C or tritiated amino acids were incorporated during biosynthesis of the human hormone in slices of parathyroid glands in vitro; the appropriate amino acid residues were then determined as the -14C or tritiated phenythiohydantoin derivatives of the amino acid after Edman degradation, or by peptide isolation after appropriate cleavage with endopeptidase, or both. The results confirm our previous findings that residue 22 is glutamic acid, residue 28 is leucine, and residue 30 is aspartic acid.

Adenoma↗
PubMed1975

Analysis of the requirements for parathyroid hormone action in renal membranes with the use of inhibiting analogues.

Two synthetic analogues of bovine parathyroid hormone (PTH) with NH2-terminal modifications, PTH-(3-34) and [desamino-Ala-1]PTH-(1-34), were found to lack agonist activity but to demonstrate antagonist properties when tested in the rat renal cortical adenylyl cyclase assay in vitro against the native hormone or against PTH-(1-34), the active synthetic NH2-terminal tetratriacontapeptide. The inhibition exhibited by these analogues was proportional in degree to the dose of inhibitor, abolished by oxidation of the analogue, reversible by addition of an excess of active hormone, and specific for parathyroid hormone-stimulated renal adenylyl cyclase. No inhibition of basal or sodium fluoride-stimulated renal adenylyl cyclase could be demonstrated. Two other synthetic bovine analogues, PTH-(13-34) and PTH-(1-26), were devoid of agonist and antagonist properties. The over-all results suggest that the requirements for receptor binding of parathyroid hormone are rather broad. Conformational factors or binding interactions involving specific residues, or both seem to require the entire sequence from residue 3 to residue 27 for receptor binding to occur. A dichotomy between receptor binding and adenylyl cyclase activation was demonstrated only by alterations or deletions involving the first 2 NH2-terminal residues of the hormone and emphasizes the importance of these residues in eliciting the biological activity of parathyroid hormone. The two antagonists, [desamino-Ala-1]PTH-(1-34) and PTH-(3-34), should be useful in further analysis of the initial steps in hormone action.

Adenylyl Cyclases↗
PubMed1975

Peripheral metabolism of bovine parathyroid hormone in the dog.

Four dogs were infused with highly purified bovine parathyroid hormone until constant levels of immunoreactive hormone were attained in the circulation. Simultaneous samples of plasma were then obtained from the aorta, from hepatic, renal, and femoral veins, and later from a pulmonary artery and the left ventricle. Radioimmunoassay of these samples revealed mean arteriovenous differences of -23% across the liver and -19% across the kidney. No significant differences were found across the lung or lower extremity. After termination of the infusion the disappearance rate of immunoreactive hormone in external jugular-venous blood was multiexponential: the predominant initial T 1/2 was 4, 6, and 8 min, and the terminal component was 60, 54, and 99 min. respectively, in 3 dogs.

Animals↗
PubMed1975

Effects of 1alpha-hydroxy-vitamin D3 and 1,25-dihydroxy-vitamin D3 on calcium and phosphorus metabolism in hypoparathyroidism.

The effects of 1alpha-OH D3 or 1,25-(OH)2D3 on calcium and phosphorus metabolism have been evaluated in five hypoparathyroid patients to establish the direct effects of these compounds in adult humans, uncomplicated by compensatory changes in parathyroid hormone secretion. Doses of 1-2.5 mug/day in four patients (5 mug/day in a fifth patient on diphenylhydantoin and phenobarbital) caused a marked increase in serum calcium concentration and urinary calcium excretion, without significant changes in renal calcium clearance or urinary hydroxyproline excretion. These results suggest that the correction of hypocalcemia involved primarily a stimulation of intestinal calcium absorption rather than a stimulation of skeletal calcium resorption. Simultaneously, there were increases in urinary phosphorus excretion and variable changes in serum inorganic phosphate concentration. These effects were produced by doses of 1alpha-OH D3 and 1,25-(OH)2D3 which approach the dose needed to prevent rickets, in contrast to the very large doses of vitamin D or 25-OH D3 required for comparable effects in hypoparathyroid patients. The increased relative effectiveness of these one-hydroxylated forms of vitamin D reveals a deficiency of vitamin D one-hydroxylation in hypoparathyroidism. The rapidity of action of 1alpha-OH D3 and 1,25-(OH)2D3 was also striking. Apart from its physiologic implications, the potency of the one-hydroxylated forms of vitamin D offers significant therapeutic advantages in some patients whose hypoparathyroidism is difficult to control with vitamin D itself.

Adult↗
PubMed1975

Pre - proparathyroid hormone identified by cell - free translation of messenger RNA from hyperplastic human parathyroid tissue.

An 8-15S fraction of RNA isolated from hyperplastic human parathyroid tissue (primary chief-cell hyperplasia) and translated in a cell-free extract of wheat germ directs the synthesis of a protein that shares antigenic determinants and tryptic peptides with parathyroid hormone and its previously recognized immediated precursor, proparathyroid hormone. In addition, the protein contains tryptic peptides not found in proparathyroid hormone and migrates more slowly than does proparathyroid hormone on both urea-acid and urea-sodium dodecyl sulfate polyacrylamide gels, indicating that it is more acidic and larger than proparathyroid hormone. Sequential Edman degradation of the cell-free protein, radiolabeled with [35S]methionine, for 25 cycles released [35S]methionine at cycles 1, 7, 11, and 14, indicating that the NH2-terminal peptide sequence of the protein differs from that of both proparathyroid hormone and parathyroid hormone. We propose that this protein is an early biosynthetic precursor of human parathyroid hormone, pre-proparathyroid hormone, analogous to that identified recently by in vitro translation of bovine parathyroid mRNA.

Cell-Free System↗
PubMed1975

Microtubules and the intracellular conversion of proparathyroid hormone to parathyroid hormone.

The effects of several compounds which interfere with cellular microfilaments and microtubules on the conversion of proparathyroid hormone (ProPTH) to parathyroid hormone (PTH) were examined in slices of bovine parathyroid slices incubated in vitro with 3H-leucine. Inhibitors of microtubular function, vinblastine and colchicine, increased the ratio of 3H-labeled ProPTH to PTH in the tissue by 2- to 3-fold. Cytochalasin B, an inhibitor of microfilaments, was without effect. Concentrations of colchicine as low as 10-6M maximally increased the ratio of ProPTH to PTH, whereas lumicolchicine, an analogue of colchicine which does not affect the function of microtubules, had no effect at concentrations as high as 10-4M. The increased ratio of ProPTH to PTH was due partly to a stimulation by vinblastine and colchicine of the incorporation of 3H-leucine into ProPTH but not into general protein. However, after short incubations of parathyroid tissue with 3-H-leucine, the amount of 3H-labeled PTH was less in colchine-treated incubations than in control incubations. In the presence of vinblastine, after a 20-min incubation of parathyroid slices with 3H-leucine and vinblastine, ProPTH was not completely converted to PTH by an additional 90-min "chase" incubation with unlabeled leucine while a 20-min "chase" incubations is sufficient to convert essentially all the ProPTH to PTH in control incubations. These data suggest that the increased ratio of ProPTH to PTH is also due to a partial inhibition of the conversion ProPTH to PTH by vinblastine and colchicine. The data are consistent with the hypothesis that microtubules facilitate the transport of newly synthesized ProPTH to its intracellular site of cleavage to PTH.

Animals↗
PubMed1975

Calcium-dependent intracellular degradation of parathyroid hormone: a possible mechanism for the regulation of hormone stores.

The dynamics of parathyroid hormone (PTH) biosynthesis, storage, and secretion in bovine parathyroid slices in vitro in response to alterations in the concentrations of extracellular calcium were studied. Hormone biosynthesis was evaluated by using polyacrylamide gel electrophoresis to measure incorporation of [3H]leucine into newly synthesized PTH and proparathyroid hormone (ProPTH) during short (35 min) incubations. Amounts of newly synthesized PTH stored in and secreted from the tissue slices were determined by electrophoretic analysis of [3H]PTH in extracts of tissue and media. Total PTH and ProPTH is slices and media were measured by specific radioimmunoassays. PTH secretion rates changes 5-fold when calcium was lowered from 2mM to 1mM. Secretion of some PTH continued despite high concentrations of calcium (5 mM). Biosynthesis of ProPTH was changed only slightly, and conversion of ProPTH to PTH was independent of the extracellular calcium concentration. Tissue stores of PTH increased during incubation of parathyroid slices in medium containing high amounts of calcium. The increase in stores was much less, however, than predicted by the findings of marked suppression of secretion and little change in rates of PTH biosynthesis. In high concentrations of calcium, a large fraction (up to 50%) of newly synthesized PTH was degraded within the tissue, whereas in low concentrations of calcium, little (less than 10%) of the PTH was degraded. No fragments of PTH or ProPTH were identified in either extracts of tissue or media, suggesting that degradation occurred rapidly by general proteolysis rather than by limited, specific endopeptidase activity. The data suggest that the parathyroid cell contains a calcium-sensitive degradative pathway for PTH and that this pathway may be involved in the regulation of hormone production and secretion.

Animals↗
PubMed1975

Metabolism and biological activity of proparathyroid hormone and synthetic analogues in renal cortical membranes.

The metabolism of natural and synthetic analogues of bovine proparathyroid hormone (Pro-bPTH) and the biological activity of the synthetic fragments were evaluated in an in vitro assay employing renal cortical membranes (adenylyl cyclase bioassay). Apparent biological activity of the prohormone analogue was correlated with the cleavage of prohormone to hormone by the membranes. Analysis by electrophoresis on polyacrylamide gels and by ion-exchange chromatography on carboxymethyl cellulose (CMC) of the synthetic analogue Pro-bPTH-(-6 leads to +34) labelled with 125I, after incubation with renal cortical membranes, revealed conversion of the analogue to a fragment co-migrating or co-eluting with bPTH (1-34). Similar electrophoretic analyses using biosynthetic Pro-bPTH-(-6 leads to +84) internally labelled with [3H] leucine revealed degradation of Pro-bPTH-(-6 leads to +84) to smaller fragments. Proteolysis of both native prohormone and prohormone analogue was markedly reduced in incubations performed in the presence of benzamidine, a competitive inhibitor of trypsin and trypsin-like enzymes. Inclusion of benzamidine in incubations with purified renal cortical membranes from rat or dog in the in vitro renal adenylyl cyclase bioassay resulted in a ten-fold lowering of the potency of the fragment Pro-bPTH-(-6 leads to +34) relative to that of bPTH-(1-34); the potency of Pro-bPTH-(-6 leads to +34) was reduced from 5.4-3.6% to 0.5-0.3%, on a molar basis, of the potency of bPTH-(1-34). There was no effect of benzamidine on the intrinsic activity of bPTH-(1-34). These studies indicate that most if not all of the apparent biological activity of Pro-bPTH-(-6 leads to +34), at least in vitro, is dependent upon prior enzymic conversion to bPTH-(1-34).

Adenylyl Cyclases↗
PubMed1975

Synthetic analogues of residues 1-34 of human parathyroid hormone: influence of residue number 1 on biological potency in vitro.

A biologically active tetratriacontapeptide of human parathyroid hormone, hPTH (1-34), has been synthesized together with a series of structural analogues involving changes at the amino-terminal residue. Acetylation of the terminal amino group results in a marked reduction in the biological potency as measured in the in vitro rat renal adenylyl cyclase assay. Deletion of the terminal amino group results in a loss of biological activity. Substitution of the amino-terminal serine residue with glycine gives a lowered potency whereas substitution with alanine results in a 2-5-fold increase in biological activity in the in vitro assay. The results are compared with the findings previously reported for a series of amino-terminal analogues of the bovine PTH 1-34 peptide.

Adenylyl Cyclases↗