Evaluation of provocative tests in suspected medullary carcinoma of the thyroid:heterogeneity of calcitonin responses to calcium and pentagastrin

Abnormal calcitonin secretion provides a reliable marker for the presence of medullary carcinoma of the thyroid (MCT) and its precursor form, C-cell hyperplasia (CCH). Since this tumor may be transmitted by a dominant autosomal gene, the coincidence of a sensitive marker and an easily identified "at risk" population affords an unusual opportunity for cancer prophylaxis. To evaluate the specificity and sensitivity of provocative tests used for detection of C-cell disease, we have compared the calcitonin (hCT) responses to calcium (3 mg/kg body weight over 10 minutes intravenously), pentagastrin (0.5 microgram/kg body weight), and injection of calcium (1.0 mg/kg body weight) plus pentagastrin (0.25 microgram/kg body weight) over 60 seconds in 13 patients with subsequently proven MCT or CCH and in 31 normal volunteers. The ranges of hCT observed in normals after injection of pentagastrin and combined calcium and pentagastrin were lower than those seen in all nine patients with MCT. One subject, the only MCT patient with normal basal hCT values, had a normal response to calcium whereas all others achieved supranormal levels. Basal hCT levels were normal in the four patients with CCH but the hCT response to calcium was to a value in excess of 300 pg/mL, a level exceeded by only 3 of 31 normal subjects; the hCT response to pentagastrin in CCH and in normal subjects was indistinguishable. Combined calcium and pentagastrin administration was associated with abnormal hCT responses in two of the CCH patients and in the MCT patient with a normal response to calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Excretion of ouabain by Malpighian tubules of Oncopeltus fasciatus

An in vitro preparation of Malpighian tubules was used to investigate the excretion of the polar cardiac glycoside, ouabain, in Oncopeltus fasciatus. Tubules were found to consist of at least two morphologically and physiologically distinct segments, both of which metabolized ouabain. The distal segment (segment II) secreted primary urine and ouabain. Secretion of ouabain by segment II was not observed to occur against a concentration gradient and increased with increasing fluid secretion. The proximal segment (segment I) reabsorbed fluid and ouabain but not metabolites. Ouabain was reabsorbed against a strong concentration gradient (23-fold), was independent of fluid reabsorption, and increased with increasing fluid secretion by segment II. In rapidly secreting Malpighian tubules (a situation of high cardiac glycoside secretion by segment II), the presence of segment I reduced the excretion of ouabain by 84-93%, mainly by reducing ouabain concentration. It appears excretory loss of cardiac glycosides can be reduced in O fasciatus and thus may be a factor in the sequestration of cardiac glycosides in this insect.

Validated extraction and cleanup procedures for polychlorinated biphenyls and DDE in human body fluids and infant formula

As part of an epidemiology study, extraction methods and extract cleanup procedures were developed and validated for polychlorinated biphenyls (PCBs) and DDE, an ubiquitous metabolite of DDT, in human milk, blood serum, and infant formula. Studies included quantitative and reproducible recovery of total lipids, and reproducible and reasonably high recoveries of these chlorinated compounds from the human body fluids and infant formula, including levels of environmental health interest. An extensive quality control and assurance program was designed for use with these methods. Some validation work on serum was done using radiolabeled 14C-Aroclor 1254. Dilution assays were developed to permit use of a constant procedure, which should minimize variability in results. Methods are based on selected organic solvent extraction and column chromatographic cleanup techniques and quantitation by electron capture gas chromatography (EC/GC). Using these extensively researched extraction and cleanup methods, the limits of detection for GC measurements were 10.0 and 2.00 ppb for PCBs and DDE, respectively, in milk and 4.00 and 0.80 ppb in serum.

Isopropanol enhancement of cytochrome P-450-dependent monooxygenase activities and its effects on carbon tetrachloride intoxication

Acute or chronic treatment of rats with isopropanol caused a significant increase in hepatic cytochrome P-450 content and a two- to threefold increase in aniline hydroxylase and 7-ethoxycoumarin O-deethylase activities, but no significant change in ethylmorphine N-demethylase or benzo(a)pyrene hydroxylase activity. In rats treated with isopropanol and challenged with CCl4, liver toxicity of CCl4 was characteristically potentiated, as assessed by elevation of serum glutamic-pyruvic transaminase (SGPT) levels. Isopropanol pretreatment also potentiated CCl4-induced damage to the hepatic monooxygenase system. In addition to a decrease in cytochrome P-450, rats treated with isopropanol and challenged with CCl4 showed a nonspecific decrease not only in aniline hydroxylase and 7-ethoxycoumarin O-deethylase activities, but also in ethylmorphine N-demethylase, benzo(a)pyrene hydroxylase, and NADPH-cytochrome c reductase activities. These results were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized microsomes. The electrophoretic results showed that isopropanol pretreatment markedly potentiated the CCl4-caused destruction of cytochrome P-450 hemeproteins. The data strongly suggest that isopropanol increases one or more forms of cytochrome P-450 which selectively enhance the metabolism of CCl4 to an active metabolite. This active metabolite then causes a nonselective damage to the microsomal mixed-function oxidase system.

Enhanced inhibition of hepatic microsomal calcium pump activity by CCl4 treatment of isopropanol-pretreated rats

Pretreatment of rats with isopropanol enhanced both hepatotoxicity and calcium pump inhibition after CCl4 exposure in vivo or in vitro. Animals were given isopropanol (1.25 ml/kg) 18 hr before CCl4 (0.01 to 1.0 ml/kg). CCl4 hepatotoxicity, judged as increased appearance of glutamic-pyruvate transaminase in serum, was enhanced by isopropanol pretreatment. Pretreatment of rats with isopropanol made CCl4 as much as 20- to 30-fold more potent as an inhibitor of the calcium pump. Inhibition of another endoplasmic reticulum enzyme, glucose 6-phosphatase, was also enhanced by isopropanol pretreatment. In contrast to the effect of CCl4 in control animals, in isopropanol-pretreated rats given CCl4, depletion of liver glutathione was observed. Altered CCl4 metabolism in isopropanol-pretreated animals may result in production of increased amounts of phosgene (or other metabolites) responsible for inhibition of the liver microsome calcium pump and glutathione depletion.

Duodenal microflora in infants with acute and persistent diarrhoea

The duodenal bacterial population was determined qualitatively and quantitatively in 3 groups of infants with diarrhoeal disease of varying duration. Infants with acute self limiting diarrhoea (group 1) had an abnormal overgrowth of organisms in the upper small bowel which was similar to that found in infants whose diarrhoea persisted after 4 days in hospital (group 2). The total duodenal organism count in infants with diarrhoea persisting after 7 days in hospital (group 3) was almost 100 times greater than either of the other groups. The findings may have important implications in preventing persistent diarrhoea from becoming protracted.

Enhanced hepatotoxicity and inhibition of liver endoplasmic reticulum calcium pump by CCl4 in rats fed a thiamine deficient diet

Male Sprague-Dawley rats were fed a thiamine deficient diet for three weeks, then treated with a range of CCl4 doses (0.01-1-ml/kg). Rats fed the deficient diet grew more slowly (body weight 65 percent of control) and had elevated liver glutathione (GSH) (220 percent of control). CCl4 hepatotoxicity, assessed by serum glutamicpyruvic transaminase (SGPT) activity and histological examination 24 hours after the hepatotoxin, was augmented in the group fed the thiamine deficient diet. Likewise, CCl4 inhibition of liver endoplasmic reticulum (ER) function (glucose-6-phosphatase (G6Pase) and calcium pump activities one hour after CCl4) was enhanced in rats fed the deficient diet. These results suggest that thiamine deficiency enhances CCl4 damage to membranes of the ER and enhances CCl4 hepatotoxicity.

Evidence for an osmotic effect of glucose in the in vivo rat proximal tubule

A series of micropuncture experiments were performed to assess whether phlorizin inhibition of proximal tubular glucose reabsorption inhibits proximal tubular fluid reabsorption due to a change in the transepithelial osmotic gradient for glucose. End proximal tubular filtrate reabsorption was measured, control vs experimental, in the same rat. The effects of infusing phlorizin in one group were compared to those of graded small infusions of mannitol in a second group of rats. In the phlorizin series tubular fluid and peripheral plasma were analyzed for glucose. Net renal sodium and renal oxygen consumption were measured in these same rats. In the mannitol series tubular fluid and peripheral plasma mannitol concentrations were determined. The results show that phlorizin inhibits proximal tubular fluid and glucose reabsorption without changing renal oxygen consumption. Mannitol inhibits proximal fluid reabsorption per unit transepithelial concentration difference to the same extent as does glucose during phlorizin infusion. We interpret these data as most consistent with the conclusion that the reduction in proximal tubular fluid reabsorption during phlorizin infusion is primarily due to the resultant change in the effective transepithelial osmotic gradient for glucose. Normally this gradient favors net fluid reabsorption. During phlorizin it favors retention of fluid in the proximal tubular lumen.

1,1-Dichloroethylene inhibition of liver endoplasmic reticulum calcium pump function

This study shows that 1,1-DCE promptly inhibits a calcium homeostatic function of liver ER. The correlation with GSH depletion and the effect of MFOS induction on calcium pump inhibition suggest that this is a direct effect of a 1,1-DCE metabolite on the calcium pump. As a result of calcium pump inhibition, calcium released from the ER may serve to trigger changes that result in a massive influx of extracellular calcium and, ultimately, cytotoxicity.

Carbon disulfide hepatoxicity and inhibition of liver microsome calcium pump

This work has shown that CS2 promptly inhibits the liver ER calcium pump only in those animals that subsequently develop hepatic necrosis. In this respect, inhibition of the ER calcium pump by CS2 resembles the actions of chlorinated hydrocarbon hepatotoxins. This lends further support to the suggestion that disruption of calcium homeostasis is an important early step in the action of at least some hepatotoxins [1-5]. CS2 appears to be the first example of a hepatotoxin other than chlorinated hydrocarbons that inhibit the liver ER calcium pump early in the course of intoxication. Finally, studies by others [17,18] suggest a mechanism by which CS2 can interact with and inhibit the liver ER calcium pump.

Xylose absorption in infants with severe prolonged diarrhoea

Energy supply may be a limiting factor in tissue repair when infants with severe prolonged diarrhoea are fed orally. Xylose tolerance tests were done on 8 female infants who had had severe dehydrating diarrhoea requiring treatment in hospital for 7 days. Seven infants had flat xylose tolerance curves, 5 of these being at very low levels. Very early intervention with hyperalimentation, elemental diets or antibacterial agents and basic anion exchange resins may reduce morbidity.

Nucleotide-induced alteration of rat liver microsome calcium pump activity

Rat liver microsomes sequester calcium by an energy dependent process that may be a nonmuscle cell analog of the sarcoplasmic reticulum Ca2+ pump of skeletal muscle (Moore, L., Chen, T.S., Knapp, H.R., Jr. and Landon, E.J. (1975) J. Biol. Chem. 250, 4562-4568). Homogenization of rat liver in the presence of ATP (5 mM) results in a 2-fold increase of the specific activity of the microsome Ca2+ pump. The effect of ATP is concentration dependent and is detected at ATP levels as low as 0.1 mM. ATP will produce this effect if added before homogenization, after homogenization or after any of the centrifugation steps of microsome isolation. Homogenization of rat liver in the presence of ADP and AMP also increases specific activity of the microsome Ca2+ pump, but to a lesser extent than ATP. Other nucleoside triphosphates have been tested and are in general less effective than ATP in increasing microsome Ca2+ pump activity. The phosphate group of nucleotides appears to be improtant to his effect in that adenosine does not affect Ca2+ pump activity, while sodium pyrophosphate will increase pump activity but to a smaller extent than ATP. The presence of nucleotides or pyrophosphate during microsome isolation results in the release of a small amount of protein material from microsomes. These proteins can be detected in 105 000 Xg supernatant by SDS-polyacrylamide gel electrophoresis. Three bands of molecular weight 46 000, 42 000 and 36 000 comprise the majority of protein material released from microsomes. The ability of nucleotides to release one of the these proteins, the 42 000 molecular weight band, from microsomes correlates with the ability of the nucleotide to increase microsome Ca2+ pump activity. Preliminary evidence indicates that the protein released from ATP-treated microsomes is able to suppress the stimulated calcium uptake measured in ATP-treated microsomes. It is possible that this protein functions to regulate Ca2+ pump activity in the endoplasmic reticulum of liver.

Effect of cell density on energy-dependent calcium uptake by Balb/c 3T3 membranes is independent of protein synthesis and attachment to substratum

Membranes isolated from subconfluent cultures of Balb/c 3T3 cells have low energy-dependent calcium uptake activity. Replating confluent cells at low density results in a prompt fall of energy-dependent calcium uptake by membrane fractions. The level to which uptake activity falls is a function of the density at which the cells are plated (Moore and Pastan, '77b). To determine if regulation of energy-dependent uptake of calcium by membrane fractions is dependent upon attachment to a substrate and to further characterize conditions that regulate the process, we examined calcium uptake activity of membranes isolated from cells in suspension. With cells in suspension energy-dependent calcium uptake activity of isolated membranes falls promptly if cells are diluted to a low density (less than 10(5) cells/ml) and is a function of cell density. When cells in suspension at low cell densities are concentrated to high cell densities (greater than 2 x 10(6) cells/ml), calcium uptake activity of the isolated membrane fraction is increased as a function of cell density. These changes of membrane calcium uptake activity occur promptly and do not require protein synthesis.

A calcium requirement for movement of cultured cells

When calcium is removed from culture medium, motility of cultured cells is decreased. The effect is rapid, reversible and pronounced. Decreased motility is observed with normal mouse Balb/c 3T3 cells, mouse L929 cells, rat kidney fibroblasts and chick embryo fibroblasts. The calcium dependence of movement can be observed both with individual cells and with the movement of the margin of a monolayer into a wound. Magnesium will not substitute for calcium to maintain motility. Strontium will substitute, but is not as effective as calcium for maintaining cell movement. Low concentrations of the divalent cation ionophore A23187 (0.5-1 micron) partially reverse the reduced migration observed at low calcium concentrations. These results are consistent with the hypothesis that movement of non-muscle cells occurs through mechanisms similar to those important in the contraction of muscle.

The early phase of experimental acute renal failure. IV. The diluting ability of the short loops of Henle

Experiments were conducted to establish whether diminished solute reabsorption in the loop of Henle during acute renal failure could explain the loss of urinary concentration and participate in generating a tubuloglomerular feedback-mediated reduction in filtration rate. The electrolyte content of the fluid in the ascending limb of the loop of Henle was determined in situ by monitoring its electrical conductivity after propulsion into the distal tubule with a sudden burst perfusion. The value of the minimum electrolyte concentration decreased exponentially with increasing equilibration time, reaching a steady-state value equivalent to 27 +/- 9 mM NaCl in normal kidneys, 34 +/- 15 mM in mercuric chloride kidneys and 53 +/- 22 mM following ischaemia. A mathematical model was derived to describe the process of sodium chloride dilution from which it was possible to calculate both the permeability and transport velocity of the cortical thick ascending limb. In the normal kidney, the transport velocity was calculated to be 4.65 +/- 0.92 . 10(-5) cm/s, a value not significantly different from that of the mercuric chloride of ischaemic kidneys, and the estimated permeability was 1.13 +/- 0.52 . 10(-5) cm/s, not different from that of the mercuric chloride kidneys but significantly lower than that calculated for the ischaemic kidneys. It is concluded that for the more severely damaged ischaemic model, the loss of urinary concentrating ability was accompanied by a reduction in diluting ability of the ascending limb of the short loop of Henle, which appears to be due, at least in part, to an elevation of the passive permeability to sodium chloride in this segment.

Influence of glomerular filtration rate on renal PAH secretion rate in the rat kidney. Dependency of PAH extraction on renal filtration fraction

PAH secretion (TPAH) was studied in rats at spontaneously occurring glomerular filtration rate (GFR). At saturated transport, TPAH was found to be correlated to GFR. This relationship was also observed at unsaturated transport where TPAH depends upon the PAH concentration in arterial plasma. However, no significant correlation between TPAH and renal PAH load or renal plasma flow rate was found when the effects of GFR were removed by partial correlation analysis. A dependency of TPAH on GFR explains the correlations found between filtration fraction (FF) and renal PAH extraction (EPAH) or renal tubular PAH extraction fraction (EPAH--FFPAH). Thus, even at low PAH concentration in a. plasma, renal PAH extraction may only be assumed to be constant if the filtration fraction is constant.

Effect of liposomes containing cholesterol on adenylate cyclase activity of cultured mammalian fibroblasts

Liposomes prepared with cholesterol and dipalmitoyl phosphatidylcholine were incubated with a clone of normal rat kidney fibroblast of cells in culture. The cells took up [14C]cholesterol in proportion to the concentration of liposomes in the incubation medium, and the uptake increased with time over the four hours of study. Two cell membrane enzymes, adenylate cyclase and (Na+ + K+)-ATPase, exhibited decreased activity after treatment with cholesterol-containing liposomes. The decrease in adenylate cyclase activity was directly proportional to the uptake of [14C]cholesterol. When a variety of subclones of NRK 5W were examined some were found to respond to cholesterol treatment and some did not. These data are consistent with the view that membrane cholesterol content plays a role in controlling the activity of some plasma membrane enzymes.