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Biomedical subjects

T J Martin

Publications and source records attributed to T J Martin.

At least 271 records · Page 15Linked to original sources
PubMed1990

Ionization and hemodynamic effects of calcium chloride and calcium gluconate in the absence of hepatic function.

Serial serum ionized calcium concentrations were measured before and after administration of either calcium chloride or calcium gluconate during the anhepatic stage of liver transplantation in 15 patients to determine the release of ionized calcium in the absence of hepatic function. When hypocalcemia (Ca++ less than 0.8 mM) occurred during the anhepatic stage, patients were randomly assigned to treatment with chemically equivalent doses of either calcium chloride (10 mg/kg, n = 8) or calcium gluconate (30 mg/kg, n = 7). Serum concentrations of ionized calcium and citrate, hematocrit, arterial blood gas tensions, acid-base state, and hemodynamic profiles were determined before and up to 10 min after calcium therapy. In both groups of patients initial similar and rapid increases in Ca++ (0.98 +/- 0.14 mM in the calcium chloride group and 1.05 +/- 0.10 mM in the calcium gluconate group) were followed by gradual decreases over the next 10 min. Measured hemodynamic values were similar in the two groups, and neither group showed improvement in cardiovascular function after calcium therapy, possibly because of the decrease in preload that occurred during the anhepatic stage. Equally rapid increases in Ca++ after administration of calcium chloride and gluconate in the anhepatic state suggest that calcium gluconate does not require hepatic metabolism for the release of Ca++ and is as effective as calcium chloride in treating ionic hypocalcemia in the absence of hepatic function.

Adult↗
PubMed1990

Fetal magnesium homeostasis in the sheep.

The fetal plasma magnesium concentration exceeds that of the mother but the difference is small compared to that of ionized calcium concentration. Although not fully independent of changes in maternal magnesaemia, fetal magnesaemia showed a high degree of autonomy during both hypermagnesaemic and hypomagnesaemic changes induced in the ewe. As with calcium, the placental gradient is reversed after fetal thyroparathyroidectomy (TXPTX) with thyroxine replacement. During perfusion in situ of the placenta from such TXPTX fetuses isolated from the fetus itself, a stable positive placental gradient of magnesium concentration could be re-established between the perfusing blood and the maternal circulation. As with calcium, this gradient could be increased by fetal calf parathyroid extract, parathyroid hormone-related protein (PTHrP 1-141), PTHrP (1-84) but not by PTHrP (1-34). It was concluded that a mid-molecule portion of PTHrP can stimulate a putative placental pump which is responsible for the gradients of both calcium ions and magnesium across the ovine placenta.

Animals↗
PubMed1990

Parathyroid hormone-related protein and calcium homeostasis in lactating mice.

Parathyroid hormone (PTH)-related protein has been shown to be a factor responsible for hypercalcemia of malignancy. Recent studies have shown the presence of mRNA for PTH-related protein in lactating breast tissue, suggesting a physiological role for this peptide during lactation. In the present study, we evaluated the effect of neutralization of PTH-related protein activity in lactating mice (by passive immunization) on various parameters of maternal and neonatal calcium homeostasis. PTH-related protein bioactivity, as tested in the adenylate cyclase assay, was present in mouse milk, and this activity was completely neutralized by the antisera used in the present study. In lactating mice, the effects of injection of PTH-related protein antisera on maternal serum calcium concentrations, milk calcium and phosphorus concentration, pup growth, dam femur calcium content, and pup calcium content were similar to those of the injection of normal rabbit serum. Therefore, maternal PTH-related protein does not appear to have a role in calcium homeostasis during lactation.

Animals↗
PubMed1990

Identification of parathyroid hormone-related protein in canine apocrine adenocarcinoma of the anal sac.

The presence of parathyroid hormone-related protein (PTHrP) in the apocrine adenocarcinoma tumor line (CAC-8) derived from a hypercalcemic dog was demonstrated by western and northern blot analyses. Western blots of CAC-8 tumor extracts revealed a major protein with a molecular weight of approximately 18,000 daltons that cross-reacted with antiserum to human PTHrP. Northern blots demonstrated multiple-sized messenger RNA transcripts in CAC-8 that hybridized to a full-length cDNA probe to human PTHrP. Adenocarcinomas derived from apocrine glands of the anal sac also were stained immunohistochemically for antigens that cross-react with antiserum to human PTHrP. The tumor line (CAC-8) maintained in nude mice stained positively for PTHrP in 13 of 24 tumors. Three of ten apocrine adenocarcinomas from dogs with hypercalcemia stained for PTHrP, whereas zero of ten tumors were positive from normocalcemic dogs. Normal canine epidermal keratinocytes and areas of squamous metaplasia in a perianal gland carcinoma also were positive for PTHrP. These data demonstrated that canine tissues contained a homologue to human PTHrP that likely is important in the pathogenesis of humoral hypercalcemia of malignancy.

Adenocarcinoma↗
PubMed1990

Leukemia inhibitory factor: a novel bone-active cytokine.

A number of cytokines have been found to be potent regulators of bone resorption and to share the properties originally attributed to osteoclast-activating factor. One such activity, differentiation-inducing factor (DIF, D-factor) from mouse spleen cells, shares a number of biological and biochemical properties with the recently characterized and cloned leukemia inhibitory factor (LIF). We have assessed the effects of recombinant LIF on bone resorption and other parameters in neonatal mouse calvaria. Both recombinant murine and human (h) LIFs stimulated 45Ca release from prelabeled calvaria in a dose-dependent manner. The increase in bone resorption was associated with an increase in the number of osteoclasts per mm2 bone. The osteolytic effect of hLIF were blocked by 10(-7) M indomethacin. hLIF also stimulated incorporation of [3H] thymidine into calvaria, but the dose-response relationship was distinct from that for bone resorption, and this effect was not blocked by indomethacin. Similarly, hLIF increased [3H]phenylalanine incorporation into calvaria, and this was also not inhibited by indomethacin. It is concluded that LIF stimulates bone resorption by a mechanism involving prostaglandin production, but that a distinct mechanism is responsible for its stimulation of DNA and protein synthesis. The primary structure of LIF differs from that of other fully characterized, bone-active cytokines, and it, thus, represents a novel factor which may be involved in the normal regulation of bone cell function.

Animals↗
PubMed1990

Tumor resection and antibodies to parathyroid hormone-related protein cause similar changes on bone histomorphometry in hypercalcemia of cancer.

Bone resorption is increased in both humoral hypercalcemia of malignancy (HHM) and primary hyperparathyroidism. On the other hand, bone formation parameters are increased in primary hyperparathyroidism and decreased in HHM. Recently, a PTH-related protein (PTHrP) has been shown to be responsible for the hypercalcemia in the syndrome of HHM. In the present study we evaluated the effects of a neutralizing antiserum to PTHrP on bone histomorphometric parameters in hypercalcemic athymic mice bearing a human squamous cell lung cancer. These effects were compared to those of tumor resection. Similar to the effects of tumor resection, the antiserum to PTHrP resulted in a decrease in serum Ca levels, a decrease in bone resorption, and an increase in bone formation parameters. The studies, therefore, indicate that PTHrP is the major factor responsible for all of the features, including the decreased bone formation seen in HHM.

Animals↗
PubMed1990

Comparison of the effects of parathyroid hormone (PTH) and recombinant PTH-related protein on bicarbonate excretion by the isolated perfused rat kidney.

The isolated perfused rat kidney was used to study the effects of amino-terminal fragments of human parathyroid hormone, hPTH(1-34), bovine parathyroid hormone, bPTH(1-84) and of PTH-related proteins, PTHrP(1-34), PTHrP(1-84), PTHrP(1-108) and PTHrP(1-141) on urinary bicarbonate excretion. PTHrP(1-34) (7 nmol/l), bPTH(1-84) (5.5 nmol/l) and hPTH(1-34) (7 nmol/l) had similar effects in increasing bicarbonate excretion with respect to the control. At lower concentrations (0.7 nmol/l) all PTHrP components, but not hPTH(1-34) or bPTH(1-84) increased bicarbonate excretion significantly. Infusions of PTHrP(1-108) and PTHrP(1-141) at 0.7 nmol/l, while associated with a rise in urinary bicarbonate concentration and excretion during the early stages of perfusion, produced a sharp decline in bicarbonate concentration and excretion in the latter part of perfusion. The different peptides produced no significant differences in glomerular filtration rate, fractional excretion of sodium or urine volume. The absence of substantial differences between the effects of hPTH(1-34) and PTHrP(1-34) are as noted in previous studies. The differences between PTHrP(1-108)/PTHrP(1-141) and PTHrP(1-34) demonstrated here are consistent with (1) the clinical manifestations of acidosis in hyperparathyroidism and alkalosis in humoral hypercalcaemia of malignancy, and (2) an independent action of a component of PTHrP beyond amino acids 1-34.

Animals↗
PubMed1990

A novel parathyroid hormone-related protein: role in pathology and physiology.

Many factors, such as interleukin 1, TGF alpha, TNF alpha, and beta and prostaglandins, have been implicated in aetiological roles in HHM (Martin and Mundy, 1987). Much interest in the past has also centered upon the likelihood of ectopic secretion of PTH in this condition. We have purified a protein (PTHrP) implicated in HHM from a human lung cancer cell line (BEN). Full-length cDNA clones have been isolated and found to encode a prepropeptide of 36 amino acids and a mature protein of 141 amino acids. Eight of the first 13 amino acids were identical with human PTH, although antisera directed to the NH2-terminus of PTHrP do not recognize PTH; this homology is not maintained in the remainder of the molecule. PTHrP therefore represents a previously unrecognized hormone, possibly related to the PTH gene by a gene duplication mechanism. In support for this notion, the PTHrP gene has been localized to the short arm of chromosome 12; it is believed that chromosome 11, containing the PTH gene, and chromosome 12 are evolutionarily related. In addition, the human PTHrP gene has been isolated, characterized, and shown to have a similar intron/exon organization as the PTH gene. It is possible that the original ancestral gene is indeed the PTHrP gene; resolution of this question awaits studies in lower species. Peptides synthesized to the predicted protein sequence have enabled detailed structure-function studies that have identified NH2-terminal sequences to be responsible for the biological effects of the molecule. Antibodies raised against the various synthetic peptides have led to the immunohistochemical localization of PTHrP in many human squamous cell carcinomas as well as in subpopulation of keratinocytes of normal skin. The availability of these antibodies has opened the way for the development of a radioimmunoassay to detect PTHrP in the sera of cancer patients at risk of developing hypercalcemia. The recent characterization of PTHrP-like activity in the ovine fetus suggests some physiological function for PTHrP. It is possible that PTHrP, as the fetal counterpart of PTH, has the role of maintaining the maternal-fetal calcium gradient. The isolation and characterization of PTHrP has added to our understanding of the mechanisms of hypercalcemia, and may contribute to the understanding of other metabolic bone diseases such as osteoporosis and Paget's disease. Finally, and perhaps most importantly, PTHrP may play a hitherto unrecognized role in fetal calcium metabolism and in normal cell physiology.

Amino Acid Sequence↗
PubMed1990

Isobolographic characterization of drug interactions incorporating biological variability.

Isobolograms have been widely used to characterize the nature of the interaction between combinations of drugs or chemicals. Some authors have applied this technique without accounting for the variability in the data or without adjusting for multiple comparisons to the line of additivity. This paper develops a graphical procedure which takes into account the variability of the data and which maintains favorable statistical properties. The isobolographic procedure utilized is illustrated by using three classical pharmacological drug combinations in female ICR mice. An additive relationship is illustrated with the loss of righting reflex after combinations of doses of sodium hexobarbital with itself. An antagonistic relationship is illustrated with the protection by mecamylamine of nicotine-induced lethality. A synergistic relationship is illustrated with the loss of righting reflex after combinations of ethanol and chloral hydrate. The procedure's statistical properties (level of significance and power) were determined using a simulation study. The isobolographic procedures developed here are applicable for quantal, continuous and count data. These procedures are applicable for identifying beneficial drug combinations, or conversely, identifying hazards resulting from exposure to multiple toxicants.

Animals↗
PubMed1990

Pharmacological evaluation of the antagonism of nicotine's central effects by mecamylamine and pempidine.

The nature of mecamylamine's and pempidine's antagonism of nicotine in the central nervous system has not been defined clearly. Although these compounds are thought to be noncompetitive antagonists in the brain due to the fact that they do not compete effectively for agonist binding to brain tissue in vitro, pharmacological evidence is lacking. The alteration of nicotine's dose-response curves for depression of spontaneous activity and antinociception was determined in the presence of increasing concentrations of pempidine. Pempidine was found to increase the ED50 of nicotine (0.73 mg/kg) for depression of spontaneous activity in a dose-related manner. At a dose of 3 mg/kg, pempidine increased nicotine's ED50 4.7-fold. The maximum effect of nicotine was achieved in the presence of the highest dose of pempidine, suggesting competitive antagonism. However, pempidine did decrease the maximum effect of nicotine in producing antinociception at doses that increased the ED50 13.7-fold which suggests a noncompetitive action. The structural requirements for mecamylamine's antagonism of these nicotine effects was also determined in order to address the question of whether the antagonists are interacting at a receptor site. The structure-activity relationships of the mecamylamine analogs revealed that the N-, 2- and 3-methyl groups were important for optimal potency. Optical isomerism was found to have little effect on potency. Addition of pyridinyl groups to the nitrogen abolished the activity of these compounds. The structural requirements for the agonists and antagonists therefore appear to be quite different. The alterations produced similar results for antagonism of both effects of nicotine. Mecamylamine and pempidine therefore appear to exhibit both competitive and noncompetitive properties in antagonizing the central effects of nicotine.

Analgesia↗
PubMed1989

Atrial natriuretic peptide-dependent phosphorylation of smooth muscle cell particulate fraction proteins is mediated by cGMP-dependent protein kinase.

The atrial natriuretic peptide (ANP) stimulates cGMP production and protein phosphorylation in a particulate fraction of cultured rat aortic smooth muscle cells. Three proteins of 225, 132, and 11 kDa were specifically phosphorylated in response to ANP treatment, addition of cGMP (5 nM), or addition of purified cGMP-dependent protein kinase. The cAMP-dependent protein kinase inhibitor had no effect on the cGMP-stimulated phosphorylation of the three proteins but inhibited cAMP-dependent phosphorylation of a 17-kDa protein. These results demonstrate that the particulate cGMP-dependent protein kinase mediates the phosphorylation of the 225-, 132-, and 11-kDa proteins. The 11-kDa protein is phospholamban based on the characteristic shift in apparent Mr from 11,000 to 27,000 on heating at 37 degrees C rather than boiling prior to electrophoresis. ANP (1 microM) increased the cGMP concentration approximately 4-fold in the particulate fractions, from 4.3 to 17.7 nM, as well as the phosphorylation of the 225-, 132-, and 11-kDa proteins. In contrast, the biologically inactive form of ANP, carboxymethylated ANP (1 microM), did not stimulate phosphorylation of any proteins nor did the unrelated peptide hormone, angiotensin II (1 microM). These results demonstrate the presence of the cGMP-mediated ANP signal transduction pathway in a particulate fraction of smooth muscle cells and the specific phosphorylation of three proteins including phospholamban, which may be involved in ANP-dependent relaxation of smooth muscle.

Adenosine Triphosphate↗
PubMed1989

Purification and characterization of recombinant human parathyroid hormone-related protein.

Full-length human parathyroid hormone-related protein (PTHrP-(1-141] as well as a carboxyl-terminal shortened form (PTHrP-(1-108] have been expressed from recombinant DNA-derived clones. These proteins were expressed in Escherichia coli as fusion proteins so that cyanogen bromide cleavage yields the desired product. Both proteins were purified and then characterized by sodium dodecyl sulfate gel electrophoresis, amino-terminal amino acid sequencing, peptide mapping, and mass spectral analysis. Recombinant PTHrP-(1-141), PTHrP-(1-108), synthetic PTHrP-(1-34), and naturally derived PTHrP are all equipotent in the stimulation of cyclic AMP levels in the osteoblast-like cell line UMR 106-01. However, PTHrP-(1-141) and -(1-108) are two to four times more active than PTHrP-(1-34) in the stimulation of plasminogen activator activity from this cell line. PTHrP-(1-141) reacts equipotently with PTHrP-(1-34) in a radioimmunoassay using an antiserum prepared against PTHrP-(1-34). PTHrP-(1-141), -(1-108), and -(1-84) were used as PTHrP-specific mobility standards on sodium dodecyl sulfate gel electrophoresis to determine the approximate length of two forms of naturally derived PTHrP. The data show that PTHrP purified from the lung tumor cell line BEN contains a major form of about 108 amino acids and another form of about 141 amino acids.

Amino Acid Sequence↗
PubMed1989

Structure of the 5' flanking region of the gene encoding human parathyroid-hormone-related protein (PTHrP).

We have characterized a human genomic clone that contains the 5' coding and 5' flanking sequences of the human parathyroid hormone-related protein gene (PTHrP). The 5' end of the gene contains three exons separated by two small introns of 60 and 165 bp, respectively. The coding region of the PTHrP gene exhibits significant structural homology to the human parathyroid hormone gene (PTH), including the position of at least two introns. However, there is no significant nucleotide sequence homology to the PTH gene within the intragenic region nor in the flanking genomic sequences. The PTHrP gene has been localized, by chromosomal in situ hybridization to bands p11 or p12, on human chromosome 12. Analysis of the 5'-noncoding DNA reveals a complex, putative regulatory region, with multiple potential transcription start points. Nucleotide sequence analysis shows the position of one consensus TATA sequence, at -514 bp, from the start of translation whereas the other regulatory domain is located at least 1 kb further 5' to this consensus TATA sequence. Evidence from the structure of a number of cDNA clones, as well as S1 nuclease and primer extension studies supports the hypothesis that the PTHrP gene contains at least two mRNA transcription start points that define two putative regulatory domains. The result of expression from these different promoters combined with an alternative splicing event would be to produce multiple forms of PTHrP mRNA that differ in the 5'-untranslated region. This analysis of the human PTHrP gene is the first report of a PTHrP gene for any species.

Base Sequence↗
PubMed1989

Effects of calcitonin gene-related peptide on cyclic AMP formation in chicken, rat, and mouse bone cells.

Mixed bone cell cultures obtained by sequential collagenase-trypsin digestion of newborn chick, rat, and mouse calvaria responded to calcitonin gene-related peptide (CGRP) with a dose-dependent increase in cyclic AMP formation. The amplitude of response to CGRP in each species was less than that to parathyroid hormone (PTH). The CGRP effect was not the result of an action as a weak calcitonin agonist, since in most instances a calcitonin effect was not observed. Only in early digests of mouse calvarial cells were consistent stimulatory effects of calcitonin on cyclic AMP noted, and these were always considerably less in amplitude than those to CGRP. It is concluded that chick, rat, and mouse bones contain cells in osteoblast-rich populations that respond specifically to CGRP with a rise in cyclic AMP.

Animals↗
PubMed1989

Parathyroid hormone-related protein: immunohistochemical localization in cancers and in normal skin.

An immunoperoxidase method has been developed to detect parathyroid hormone-related protein (PTHrP) in histological specimens of tumors and of normal skin. A rabbit polyclonal antiserum against PTHrP-(1-16) was used that did not cross-react with PTH-(1-34) either under radioimmunoassay conditions or at the high antiserum concentrations used in neutralizing biologic activity. PTHrP antigen was detected in the keratinocyte layer of normal skin and in 100% of 34 samples of squamous cell cancers but in only one of six breast cancers, and none of 15 other adenocarcinomata. It was also detected in four of four samples of renal cortical carcinoma and two of two of melanoma, both of which can be associated with hypercalcemia, and three of three small cell carcinomata of the lung. Immunologic detection of PTHrP could be useful in the diagnosis of tumors of squamous cell origin, particularly in the cytological differentiation of lung cancers, where it may be of value in distinguishing between squamous cell and small cell carcinoma on the one hand and poorly differentiated adenocarcinoma on the other.

Humans↗