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Biomedical subjects

A F Stewart

Publications and source records attributed to A F Stewart.

At least 109 records · Page 6Linked to original sources
PubMed1993

Expression of parathyroid hormone-related protein in the rat glomerulus and tubule during recovery from renal ischemia.

Parathyroid hormone-related protein (PTHrP) is widely expressed in normal adult and fetal tissues, where it acts in an autocrine/paracrine fashion, stimulates growth and differentiation, and shares early response gene characteristics. Since recovery from renal injury is associated with release of local growth factors, we examined the expression and localization of PTHrP in normal and ischemic adult rat kidney. Male Sprague-Dawley rats underwent complete bilateral renal artery occlusion for 45 min, followed by reperfusion for 15 min, and 2, 6, 24, 48, and 72 h. Renal PTHrP mRNA levels, when compared with sham-operated animals, increased twofold after ischemia, and peaked within 6 h after reperfusion. PTH receptor, beta-actin, and cyclophilin mRNA levels all decreased after ischemia. PTHrP immunohistochemical staining intensity increased in proximal tubular cells after ischemia, changing its location from diffusely cytoplasmic to subapical by 24 h after reperfusion. In addition, PTHrP localized to glomerular epithelial cells (visceral and parietal), but not to mesangial cells. PTHrP and PTH stimulated proliferation two- to threefold in cultured mesangial cells. We conclude that PTHrP mRNA and protein production are upregulated after acute renal ischemic injury, that PTHrP is present in glomerulus and in both proximal and distal tubular cells, and that PTHrP stimulates DNA synthesis in mesangial cells. The precise functions of PTHrP in normal and injured kidney remain to be defined.

Actins↗
PubMed1993

Dose-response study of alendronate sodium for the treatment of cancer-associated hypercalcemia.

PURPOSE: A randomized, double-blind, dose-ranging study of single-dose intravenous (IV) therapy with alendronate sodium (aminohydroxybutylidene bisphosphonate) was performed in patients with cancer-associated hypercalcemia. PATIENTS AND METHODS: Patients with hypercalcemia who had not received antitumor therapy in the preceding 7 days were treated with 48 hours of IV hydration. Patients with persistent hypercalcemia (albumin-corrected serum calcium concentration [CSCC] > or = 11.5 mg/dL) were randomly assigned to receive 2.5, 5, 10, or 15 mg of alendronate infused over 2 hours, or 10 mg of alendronate infused over 24 hours. Fifty-nine patients were treated and 50 patients were assessable for the dose-response relationship. RESULTS: Normalization of CSCC (< or = 10.5 mg/dL) was achieved in 22%, 82%, 75%, and 90% of assessable patients in the 2.5-, 5-, 10- (2- and 24-hour groups pooled), and 15-mg dose groups, respectively, within 8 days of therapy. Doses > or = 5 mg were significantly superior to the 2.5-mg dose level (P < .05). There was no significant difference in the minimum CSCC achieved between the 2- and 24-hour infusions of the 10-mg dose. Based on an intent-to-treat analysis of all randomized patients, the overall complete response rate was 74% for dose levels greater than 2.5 mg. For assessable patients who responded to > or = 5 mg of alendronate, the estimated median duration of normocalcemia was 10 days (range, 1 to 25). The estimated median time to relapse (CSCC > 11.5 mg/dL) was 15 days from initial treatment and 12 days from initial response, respectively. Adverse events included a transient febrile response in 34% of patients and eight episodes of reversible elevations in serum transaminase levels among treated patients. CONCLUSION: While a statistically significant dose-response relationship was not clearly evident at doses greater than 5 mg, single doses of > or = 5 mg alendronate sodium effectively lowered serum calcium concentrations and were well tolerated in the treatment of cancer-associated hypercalcemia.

Adult↗
PubMed1993

Amino-terminal parathyroid hormone-related protein: specific binding and cytosolic calcium responses in rat insulinoma cells.

PTH-related protein (PTHrP), originally identified through its causative role in human humoral hypercalcemia of malignancy, is now known to be a normal gene product expressed in a wide variety of neuroendocrine, epithelial, and mesoderm-derived tissues. PTHrP gene expression has recently been demonstrated in fetal and adult, benign and malignant, as well as human and rodent pancreatic islets. As in other tissues, the role of PTHrP expression in the normal islet is only beginning to be explored. In the current report, PTHrP expression in the normal rat pancreatic islet was confirmed using an affinity-purified antiserum directed against the N-terminal, biologically active region of the molecule. The effects of PTHrP on the islet were then explored using rat insulinoma (RIN m5F) cells. Synthetic PTHrP-(1-36) bound specifically, but with low affinity (Kd, approximately 10(-7) M) to RIN cell membranes. PTHrP-(1-36) failed to stimulate cAMP production in RIN cells, although RIN cells displayed a normal adenylate cyclase response to glucagon-like peptide-1-(7-36). In contrast, PTHrP-(1-36) induced a rapid dose-dependent rise in intracellular calcium in RIN cells in doses as low as 10(-12)-10(-10) M. These findings 1) confirm that PTHrP is expressed by islet cells, 2) demonstrate that the effects of PTHrP on the pancreatic islet are mediated, as in keratinocytes and lymphocytes, by a receptor related to but distinct from the PTH receptor, and 3) suggest that PTHrP functions in the islet as an autocrine or paracrine factor. Further studies are required to determine the physiological consequences of PTHrP expression by the pancreatic islet.

Animals↗
PubMed1992

Parathyroid hormone-related protein. Evidence for secretion of a novel mid-region fragment by three different cell types.

The cDNA-predicted amino acid sequence of parathyroid hormone-related protein (PTHrP) contains multiple basic amino acid motifs, suggesting that PTHrP undergoes extensive post-translational processing prior to secretion. The secretory forms of the peptide are currently unknown. To identify these secretory forms, medium was harvested from three cell types: human renal carcinoma (SKRC-1) cells, human keratinocytes, and rat insulinoma cells stably transfected with the cDNA for PTHrP(1-141) (RIN-141 cells). Amino-terminal species were immunopurified using an anti-PTHrP(1-36) column, and mid-region species using an anti-PTHrP(37-74) column. PTHrP peptides in medium and in cell extracts were further resolved by reverse phase high performance liquid chromatography (RP-HPLC) and identified using region-specific immunoassays. SKRC-1 and RIN-141 cells secreted three distinct amino-terminal species and a novel, non-amino-terminal, mid-region fragment. Sequence and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that the RIN-141 cell mid-region fragment begins at amino acid 38 of the cDNA-predicted sequence and is approximately 70 amino acids in length. Comparison of RP-HPLC elution patterns suggests that SKRC-1 cells and keratinocytes secrete a similar or identical mid-region fragment. Immunofluorescence studies revealed a Golgi pattern for the amino-terminal species and a secretory granule pattern for the mid-region fragment. These studies indicate that 1) multiple PTHrP species are secreted, including a novel mid-region fragment; 2) Arg37 serves as a cleavage site in at least three cell types; 3) PTHrP(1-36) is likely to be an authentic secretory form of PTHrP; and 4) the mid-region fragment appears to be packaged into secretory granules. The marked interspecies conservation of this mid-region PTHrP suggests that it will have important biological functions.

Amino Acid Sequence↗
PubMed1992

At least three promoters direct expression of the mouse glucocorticoid receptor gene.

We have characterized the gene for the mouse glucocorticoid receptor. The gene spans approximately 110 kilobases, and glucocorticoid receptor transcripts are assembled from nine exons. Expression of the gene is controlled by at least three promoters, resulting in glucocorticoid receptor transcripts with different 5' nontranslated exons. One promoter is cell-specific, found to be active only in T lymphocytes. The other two promoters are active to various degrees in all cell lines and tissues so far analyzed and are located in a CpG island. The promoter activities are accompanied by DNase I hypersensitivity sites in chromatin. In contrast to a conservation of exon-intron structure, differences in promoter organization suggest a divergence between the evolution of regulatory and coding regions among members of the steroid receptor super-family.

Animals↗
PubMed1992

Analysis of PTHRP binding and signal transduction mechanisms in benign and malignant squamous cells.

We have explored a potential autocrine role for parathyroid hormone-related protein (PTHRP) in malignant squamous carcinoma cells (SqCC) and their nonmalignant counterpart, human epidermal keratinocytes (HK). Specific binding of Tyr36 human PTHRP-(1-36)NH2 (125I-[Tyr36]hPTHRP-(1-36)NH2) was identified in 75% of unselected SqCC lines. In contrast, no binding was detected on the mouse keratinocyte line BALB-MK or on five different HK lines. Although each SqCC and keratinocyte line secreted immunoreactive PTHRP into its medium, there was no correlation between PTHRP concentration and number of binding sites. Inhibition of binding by [Tyr36]hPTHRP-(1-36)NH2 yielded half-maximal inhibitory concentration values of approximately 100 nM in all SqCC lines. Affinity cross-linking of SqCC cells revealed 98- and 70-kDa binding proteins with similar affinity (approximately 100 nM). Exposure of fura-2-loaded SqCC cells to PTHRP and PTH resulted in equivalent, dose-dependent transient increases in intracellular calcium [half-maximal effective concentration (EC50) = 0.08 nM]. PTHRP also increased intracellular calcium in HK (EC50 = 0.05 nM). No adenosine 3',5'-cyclic monophosphate (cAMP) response to PTHRP or PTH was elicited in either SqCC or HK, despite brisk isoproterenol responses in both. We conclude that high-capacity low-affinity binding sites for PTHRP are detectable in the majority of SqCC lines but not in HK. These low-affinity binding sites are unlikely to represent receptors. The sensitive intracellular calcium response suggests the additional presence of high-affinity receptors on SqCC as well as on HK. However, the failure of PTHRP or PTH to stimulate cAMP production in otherwise cyclase-competent cells suggests that these are not classical PTH receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed1992

A pharmacological comparison of parathyroid hormone receptors in human bone and kidney.

While abundant information is available characterizing PTH receptor properties in other species, data on human PTH receptors is very limited. We have been interested in the possibility that tissue-specific differences among human PTH receptors (i.e. bone vs. kidney) might exist. We have, therefore, compared pharmacological profiles for a wide array of PTH and PTH-related peptide (PTHrP) analogs in human osteoblast-like cells (SaOS-2) and human renal cortical membranes (RCM) using radioiodinated (Tyr36)hPTHrP(1-36)NH2 as a probe for PTH receptor function. The rank order of receptor affinity for 10 PTH/PTHrP receptor agonists tested was very similar in the bone and kidney assay systems. Binding affinity for these peptides was greater in human (h)RCMs and SaOS-2 membranes than in SaOS-2 intact cells. The relative binding affinities for (Tyr36)hPTHrP(1-36)amide, hPTH(1-34), bovine (b)PTH(1-34), and rat PTH(1-34) were similar in human RCMs, SaOS-2 membranes, and SaOS-2 cells. bPTH(1-84) and hPTHrP(1-74) both manifested lower receptor affinity than the amino-terminal analogs. Seven PTH/PTHrP receptor antagonists were also studied in this homologous human assay system. The binding affinity for hPTHrP(7-34)NH2 was 2- to 3-fold greater than that for (Tyr34)bPTH(7-34)NH2 in RCM and SaOS-2 membranes. However, in SaOS-2 cells, a striking reversal in the relative binding affinities was observed; the PTHrP(7-34) analog was nearly 3-fold less potent than (Tyr34)bPTH(7-34)NH2, underscoring a difference between intact and broken cell preparations. Two hybrid PTH-PTHrP receptor antagonists demonstrated similar relative affinity to each other in the human bone and kidney assay systems. Affinity cross-linking of receptors in human renal and skeletal tissues demonstrated an indistinguishable dominant 85-kilodalton receptor protein. We conclude that the binding and bioactivity profiles of a broad array of PTH and PTHrP peptides are very similar or identical in human renal and skeletal tissues. Differences relating to intact vs. broken cell preparations accounted for some variation in potency. These studies emphasize the importance of employing homologous assay systems to study PTH receptor function and the existence of interspecies differences among PTH receptors. The results support the possibility that PTH receptors in human bone and human kidney are very similar if not identical.

Affinity Labels↗
PubMed1992

Preliminary characterization of circulating amino- and carboxy-terminal fragments of parathyroid hormone-related peptide in humoral hypercalcemia of malignancy.

PTH-related peptide (PTHrP) immunoreactivity in plasma from six well characterized patients with humoral hypercalcemia of malignancy was characterized by gel filtration chromatography. An immunoradiometric assay directed against the N-terminal 74 amino acids of PTHrP and a RIA directed against the C-terminal region (amino acids 109-138) of the peptide were used to assay column fractions. When examined using acid (pH 5.0) nondenaturing conditions, N-terminal PTHrP immunoreactivity eluted with an apparent M(r) of 30,000-40,000. The apparent M(r) of this PTHrP fragment shifted to approximately 25,000 when gel filtration was performed at pH 9.0. The apparent M(r) shifted further, to approximately 6,500, when chromatographed under denaturing conditions in 4 M guanidine-HCl. Carboxy-terminal PTHrP immunoreactivity in plasma eluted with an M(r) of approximately 12,000 under acid nondenaturing conditions, as did the synthetic C-terminal PTHrP column marker, PTHrP (109-138). Synthetic PTHrP (1-36) and (1-74), and recombinant PTHrP (1-141) as well as native PTHrP species found in milk and keratinocyte-conditioned medium migrated in their expected positions when analyzed under alkaline nondenaturing or under denaturing condition. We conclude that native, synthetic, and recombinant PTHrP peptides may migrate anomalously when examined using gel filtration under nondenaturing conditions, and such studies should be interpreted with caution. Plasma from patients with humoral hypercalcemia of malignancy contains at least two PTHrP species. One native N-terminal fragment appears, as assessed under denaturing conditions, to have an M(r) of approximately 6,500, and to therefore comprise approximately 50-60 amino acids of full-length PTHrP. A second chromatographically and immunologically distinct C-terminal fragment with an M(r) of approximately 12,000 under nondenaturing conditions is also present.

Chromatography, Gel↗
PubMed1991

Glucocorticoids are required for establishment and maintenance of an alteration in chromatin structure: induction leads to a reversible disruption of nucleosomes over an enhancer.

Induction of the rat tyrosine aminotransferase gene (TAT) with glucocorticoid hormones leads to formation of a nuclease hypersensitive site at the hormone-dependent enhancer located 2.5 kb upstream of the start site of transcription. This enhancer comprises binding sites for the glucocorticoid receptor and additional transcription factors which are only recognized after hormone administration, as demonstrated by genomic footprinting. We show here that the alteration in chromatin structure occurs very rapidly and is also rapidly reversible after withdrawal of the hormone. At all stages nuclease hypersensitivity at this enhancer parallels the transcriptional activity of the TAT gene indicating that transcriptional stimulation requires ongoing enhancer activity. The enhancer region is nucleosomal before induction and after removal of the hormone but the nucleosomal pattern is disturbed in the presence of the hormone. The rapidity of chromatin changes implies that neither disruption nor reassembly of the nucleosomes is dependent on DNA replication. Addition of the glucocorticoid antagonist RU486 to induced cells has effects similar to washing out the glucocorticoid hormone, showing that maintenance of the hypersensitive site requires the ongoing binding of agonist by glucocorticoid receptor. These results describe an inducible enhancer which is regulated by a dynamic balance between two types of protein-DNA complexes, one of which is nucleosomal.

Animals↗
PubMed1991

Interspecies comparison of renal cortical receptors for parathyroid hormone and parathyroid hormone-related protein.

Parathyroid hormone (PTH) and PTH-related proteins (PTHrP) interact with a common receptor in rat bone cells and in canine renal membranes with similar affinity, but PTHrP are substantially less potent than PTH in stimulating adenylate cyclase in canine renal membranes; in contrast, PTH and PTHrP are equipotent in stimulating adenylate cyclase in rat bone cells. This discrepancy has been largely viewed as reflecting differences in the relative efficiency of signal transduction of PTHrP between bone and kidney assay systems. To test the alternative (but not mutually exclusive) hypothesis that these differences could reflect interspecies differences in PTH receptors, we have characterized the bioactivity of amino-terminal PTHrP and PTH in rat and human renal cortical membranes (RCM) and compared them to results we previously reported in canine RCM. The stability of PTH and PTHrP peptides under binding and adenylate cyclase assay conditions was greater than 80% for each species. Competitive inhibition of [125I](Tyr36)hPTHrP-(1-36)NH2 binding to rat RCM by bPTH-(1-34) and (Tyr36)hPTHrP-(1-36)NH2 yielded nearly identical binding dissociation constants (3.7 and 3.6 nM, respectively), and binding to human RCM demonstrated slightly greater potency for PTHrP (0.5 nM) than for PTH (0.9 nM). Similarly, adenylate cyclase stimulating activity was equivalent for the two peptides in rat RCM, but PTHrP was twofold more potent than PTH in human RCM. Covalent photoaffinity labeling of protease-protected rat RCM yielded an apparent 80 kD receptor protein, and cross-linking of human RCM labeled an 85 kD receptor, indistinguishable in size from the canine renal PTH receptor. We conclude that rat, canine, and human renal cortical PTH receptors exhibit species specificity. The previously observed differences between rat bone cells and canine renal membranes in the efficiency of signal transduction by PTHrP may be explained, at least in part, by these species differences.

Adenylyl Cyclases↗
PubMed1991

Immunoaffinity purification of parathyroid hormone-related protein from bovine milk and human keratinocyte-conditioned medium.

Parathyroid hormone-related proteins (PRHrP) are a novel family of proteins that appear to be responsible for humoral hypercalcemia of malignancy. Although PTHrP derived from human tumors have been purified and their N-terminal amino acid sequence determined, and although the structure of the PTHrP gene and its alternatively spliced mRNA transcripts have been defined, the secretory and circulating form(s) of the protein are unknown. Purification of PTHrP in the past has been difficult, requiring multiple chromatographic steps and months or years to complete. To define naturally occurring PTHrP species we have developed a rapid and efficient immunoaffinity purification method. Bovine milk (250 ml) and human keratinocyte-conditioned medium (3000 ml) were affinity purified using a 300 microliters affinity-purified polyclonal anti-PTHrP-(1-36) antibody column and a single RP-HPLC step. Purification required only 7-10 days and yielded a 3-4% recovery. Quantities of PTHrP sufficient for silver-stained SDS-PAGE, Western analysis, and N-terminal amino acid sequence were obtained. In contrast to conventional purification schemes, affinity purification of PTHrP is rapid and efficient and can be applied to biologic samples that contain PTHrP in low abundance. These methods can be applied to the purification and characterization of the as yet undefined secretory and circulating forms of PTHrP.

Animals↗
PubMed1991

Structural and phylogenetic analysis of the chicken ventricular myosin heavy chain rod.

We have isolated and characterized five overlapping clones that encompass 3.2 kb and encode a part of the short subfragment 2, the hinge, and the light meromyosin regions of the myosin heavy chain rod as well as 143 bp of the 3' untranslated portion of the mRNA. Northern blot analysis showed expression of this mRNA mainly in ventricular muscle of the adult chicken heart, with trace levels detected in the atrium. Transient expression was seen in skeletal muscle during development and in regenerating skeletal muscle following freeze injury. To our knowledge, this is the first report of an avian ventricular myosin heavy chain sequence. Phylogenetic analysis indicated that this isoform is a distant homolog of other ventricular and skeletal muscle myosin heavy chains and represents a distinct member of the multigene family of sarcomeric myosin heavy chains. The ventricular myosin heavy chain of the chicken is either paralogous to its counterpart in other vertebrates or has diverged at a significantly higher rate.

Amino Acid Sequence↗
PubMed1991

Glycosylation of parathyroid hormone-related peptide secreted by human epidermal keratinocytes.

While the gene and mRNA transcripts encoding PTH-related peptide (PTHrP) have been well characterized, the actual secretory form(s) of the peptide is unknown. Accordingly, synthetic and recombinant PTHrPs employed to date for biological and immunological characterization have necessarily been of arbitrary lengths. No prior evidence for glycosylation of PTHrPs has been described. To define the naturally occurring form(s) of this peptide secreted by human epidermal keratinocytes, we have affinity purified, using an anti-PTHrP-(1-36) antibody column, human PTHrP secreted under conditions of protease protection. Human keratinocyte-conditioned medium collected without measures to protect against proteolytic degradation contains multiple PTHrP immunoreactive and bioactive species. In contrast, under conditions of protease protection, human keratinocyte-conditioned medium contains a single 18,000 mol wt (Mr) form of the peptide. In contrast to recombinant and synthetic PTHrPs, which migrate as distinct, well focussed bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, this 18,000 Mr PTHrP displays the broad electrophoretic profile of a glycoprotein. Treatment of this peptide with trifluoromethanesulfonic acid, an agent that deglycosylates both O- and N-linked saccharides from their core proteins, shifted the Mr of the protein to approximately 10,000. In contrast, exposure of recombinant PTHrP-(1-141) to the same agent results in no change in electrophoretic mobility. These studies indicate that the 18,000 Mr species of PTHrP secreted by human epidermal keratinocytes is a glycoprotein.

Blotting, Western↗
PubMed1990

Immunochemical characterization of circulating parathyroid hormone-related protein in patients with humoral hypercalcemia of cancer.

Tumors from patients with humoral hypercalcemia of cancer produce a parathyroid hormone-related protein (PTHRP). We have developed two region-specific immunoassays capable of measuring PTHRP in plasma: an immunoradiometric assay directed toward PTHRP amino acid sequence 1 to 74 and a radioimmunoassay directed toward PTHRP amino acid sequence 109 to 138. Sixty normal subjects had low or undetectable plasma PTHRP (1 to 74) concentrations (mean, 1.9 pmol per liter) and undetectable PTHRP (109 to 138) concentrations (less than 2.0 pmol per liter). Patients with humoral hypercalcemia of cancer (n = 30) had elevated levels of both PTHRP (1 to 74) (mean, 20.9 pmol per liter) and PTHRP (109 to 138) (mean, 23.9 pmol per liter). The plasma concentrations of immunoreactive PTHRP correlated with the levels of urinary cyclic AMP excreted; in some patients, the concentrations decreased after the tumors were resected. Patients with chronic renal failure (n = 15) had plasma PTHRP (1 to 74) concentrations similar to those in the normal subjects, but their plasma PTHRP (109 to 138) concentrations were elevated (mean, 29.6 pmol per liter). The levels of both peptides were normal in patients with hyperparathyroidism and those with hypercalcemia due to various other causes. Breast milk contained high concentrations of PTHRP. An anti-PTHRP (1 to 36) immunoaffinity column failed to extract PTHRP (109 to 138) immunoactivity from plasma, suggesting that the C-terminal region circulates as a separate peptide. We conclude that plasma PTHRP concentrations are high in the majority of patients with cancer-associated hypercalcemia and that the circulating forms of PTHRP in such patients include both a large N-terminal (1 to 74) peptide and a C-terminal (109 to 138) peptide. Measuring the concentrations of PTHRPs may be useful in the differential diagnosis of hypercalcemia.

Adult↗
PubMed1990

Rapid induction of c-fos transcription reveals quantitative linkage of RNA polymerase II and DNA topoisomerase I enzyme activities.

The functional association between DNA topoisomerase I and gene activity has been analyzed using the tightly regulated c-fos proto-oncogene, which undergoes rapid transitions between active and inactive states of transcription. We show that the topoisomerase I inhibitor camptothecin can be used to measure topoisomerase I activity throughout the transcription cycle of the c-fos gene. Upon induction of c-fos transcription in the presence of camptothecin, topoisomerase I cleavages spread through the gene in the 5' to 3' direction and concomitantly transcriptional elongation is retarded. Parallel kinetic measurements of RNA polymerase II activity and topoisomerase I activity demonstrate a quantitative and temporal link between the two enzymes. Our results argue that topoisomerase I quantitatively relieves the torsional consequences of transcriptional elongation in intact cells.

Animals↗
PubMed1990

Quantitative evaluation of anticalciuretic effects of synthetic parathyroid hormonelike peptides.

The PTH-like peptide (PTHLP) responsible for hypercalcemia in many patients with humoral hypercalcemia of malignancy (HHM) acts on PTH receptors in bone and kidney, and large doses of PTHLPs have been shown to reduce urinary calcium excretion. However, PTHLPs have not been assessed quantitatively for effects on renal calcium excretion at concentrations (5-100 pM) now known to be found in the serum of patients with HHM. We perfused isolated rat kidneys with synthetic [tyr-36] PTHLP-(1-36)amide [PTHLP-(1-36)], PTHLP-(1-74), and synthetic bovine PTH-(1-34). The ratio of calcium to sodium clearances (CCa/CNa), a measure of distal tubular calcium transport, was reduced to the same extent by PTH, PTHLP-(1-36), and PTHLP-(1-74) (54.3 +/- 3.9, 52.9 +/- 3.9, and 52.7 +/- 1.3% reductions from control), respectively) at maximal doses (35-50 pM and higher), with half-maximal effects at 10, 18, and 32 pM, respectively. PTH, PTHLP-(1-36), and PTHLP-(1-74) all increased fractional phosphate excretion over control (p less than 0.05 each). All three peptides were natriuretic, at least doubling fractional Na excretion (p less than 0.05 or less). Urinary cAMP excretion was increased by all three. None had any effect on GFR or renal vascular resistance. These results indicate that clinically relevant concentrations of PTHLPs are anticalciuretic and natriuretic, with maximal effects similar to those of PTH. Differences in anticalciuretic potencies are small but may explain differences among patients, depending on the size(s) and concentrations of the native circulating form(s) of the peptide.

Animals↗
PubMed1990

Intraperitoneal free fatty acids induce severe hypocalcemia in rats: a model for the hypocalcemia of pancreatitis.

Indirect evidence suggests a causative role for intraperitoneal free fatty acids (FFA) in hypocalcemia associated with pancreatitis. We examined the effects of intraperitoneal injection of four naturally occurring FFAs on serum calcium in rats. Two saturated FFAs, stearate and palmitate, induced little or no hypocalcemia. Two unsaturated FFAs, oleate and linoleate, caused dramatic hypocalcemia in treated versus control rats (6.3 +/- 1.4 and 5.3 +/- 0.7 mg/dl, respectively, versus 10.1 +/- 0.6). Dose-response studies demonstrated that minute quantities of oleate (100 microliters per 250 g rat) caused marked hypocalcemia (7.2 +/- 0.3 mg/dl). Treated versus control rats also revealed a decrease in ionized calcium (3.15 +/- 0.2 versus 5.6 +/- 0.05 mg/dl) and magnesium (1.4 +/- 0.15 versus 2.0 +/- 0.10), an appropriate increase in PTH levels (1670 +/- 451 versus 396 +/- 235 pg/ml), and a fall in calcitonin levels (70.4 +/- 21.3 versus 47.5 +/- 16.4 pg/ml) but no change in albumin or phosphate levels. In vitro, the Ksp of calcium dioleate was shown to be 5.3 x 10(-8) m3/liter3; thus under physiologic conditions 100 microliters oleate binds 7.2 mg calcium, or approximately twice the total ECF ionized calcium in the rat. The amounts of intraperitoneal FFA that can easily be achieved in pancreatitis complex pathophysiologically significant amounts of calcium and may lead to severe hypocalcemia.

Animals↗