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  • 1
    ISSN: 1432-2013
    Keywords: Brattleboro ; Antidiuretic hormone ; Calcitonin ; Parathyroid hormone ; Glucagon ; Electrolyte ; Micropuncture ; Electron probe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of (1-desamino-8-d-arginine) vasopressin (dDAVP) on water and electrolyte transport in the distal tubule were investigated by micropuncture. Since, in addition to antidiuretic hormone, parathyroid hormone, calcitonin and glucagon stimulate the adenylate-cyclase system in this nephron segment, experiments were performed on hormone-deprived rats, i.e. homozygous DI Brattleboro rats with reduced levels of endogenous parathyroid hormone, calcitonin and glucagon. Along the distal tubule, dDAVP enhanced water, Cl, Na and Ca reabsorption and sharply increased net K secretion. Phosphate transport was left unchanged and Mg reabsorption was not significantly altered by dDAVP between the early and late distal tubule. Antidiuretic hormone also slightly increased water filtration rate in the superficial nephron, which rose in proportion to whole kidney glomerular filtration rate. It is concluded that, in rats: 1) antidiuretic hormone stimulates water, NaCl and Ca absorption and enhances K secretion along the distal tubule and 2) the tubular effects of dDAVP on electrolyte transport in the loop and distal tubule are responsible for decreasing Mg and Ca urinary excretion.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Calcitonin ; Distal tubule ; Micropuncture ; Electron-probe ; Brattleboro rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of human calcitonin (HCT) on the distal tubule were investigated by micropuncture in hormone-deprived rats, i.e. in the absence of parathyroid hormone, antidiuretic hormone and glucagon, which might have masked these effects. Two groups of rats were studied: hormone-deprived and hormone-deprived+HCT, infused at 1.0 mU/min\100 g b.w. In the urine, HCT markedly reduced Ca and Mg excretion whereas excretion of water, Na and K was not significantly affected. Along the distal tubule, HCT strongly enhanced Na, Cl, Mg, Ca and total solute reabsorption, decreased K secretion but did not alter water or phosphate transport. It is concluded that HCT stimulated Na, Cl, Ca and Mg reabsorption. If, as suggested, HCT also stimulated the reabsorptive component of K transport, the hormone should therefore elicit the same physiological effects in the distal tubule and the thick ascending limb.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2013
    Keywords: Renal Tubule ; Phosphate Transport ; Sodium Dependence ; Micropuncture ; Microperfusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The standing droplet method has been used in combination with the peritubular perfusion of blood capillaries to determine the build up of transtubular concentration differences of phosphate (P i ) in the renal proximal convoluted tubule of parathyroidectomized rats. Electron probe analysis was used to estimate P i . At zero time both the intraluminal and the contraluminal P i concentration was 2 mM. The time dependent decrease of the intraluminal P i concentration was approximately 4 times faster in the early than in the late proximal convoluted tubule. After 45 sec an intraluminal steady state concentration of 0.20 mM P i was achieved in the early part. In the late part the intraluminal P i concentration approached a steady state value of 0.54 mM at 120 sec. When sodium free solutions were used the intraluminal P i concentration increased to 2.22 mM in the earlier and to 2.76 mM in the late part. The data indicate that in the proximal convoluted tubule 1. The rate of phosphate reabsorption is greater in the early part than in the later part, and 2. phosphate reabsorption might occur as co-transport with Na+ ions.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2013
    Keywords: ADH ; Mouse nephron ; Microperfusion ; NaCl transport ; Mg2+ transport ; Ca2+ transport ; Electron microprobe analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of antidiuretic hormone (ADH) on transepithelial Na+, Cl−, Ca2+ and Mg2+ net fluxes (JNa, JCl, JMg, JCa) was investigated in isolated perfused cortical thick ascending limb segments (cTAL) of the mouse nephron, using the microperfusion technique and the electron microprobe analysis to determine the ionic composition of the collected tubular fluid. Simultaneously, the transepithelial potential difference (PDte) and the transepithelial resistance (Rte) were recorded. Prior to the flux measurements cTAL segments were perfused for one hour. During this equilibration period PDte decreased significantly from +19.9±1.6 to +14.9±1.l mV and Rte increased from 30.6±3.5 Ωcm2 to 38.8±2.4 Ωcm2 (n=7), reflecting a decline in NaCl transport. After ADH was added to the bath solution at 10−10 mol.l−1, PDte increased from +14.4±1.1 to +18.0±1.5 mV, accompanied by a rise in JNa and JCl from 205±11 to 273±19 and from 216±12 to 283±21 pmol.min−1.mm−1 (n=7), respectively. JCa and JMg also increased from 0.81±0.07 to 1.50±0.12 and from 0.43±0.11 to 0.76±0.08 pmol.min−1.mm−1 (n=7), respectively. All these effects were fully reversible after withdrawal of the hormone. In conclusion our data indicate that ADH stimulates divalent cation transport and NaCl transport in the cortical thick ascending limb of Henle's loop of the mouse.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-2013
    Keywords: Isolated thick ascending limb ; Microperfusion ; Divalent cation and potassium transport ; Microprobe analysis ; Transepithelial voltage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Isolated segments of rat cortical (cTAL) and medullary (mTAL) thick ascending limbs were microperfused and the transepithelial net fluxes (Jx) were determined by measuring the composition of the collected fluid with an electron microprobe. When perfused with symmetrical solutions both segments showed similar JNa and jCl and lumen-positive transepithelial voltage (V te=7–8 mV). JMg, JCa and JK were not significantly different from zero. When perfused with asymmetrical solutions (lumen 50 mM, bath 150 mM NaCl), the mean Vte were 23 mV and 17 mV in the cTAL and mTAL respectively; this rise was accompanied by significant increases in JMg and JCa in the cTAL, but not in the mTAL, and a marked increase in JK in both segments. It is concluded that, in the rat, divalent cations can be reabsorbed in the cTAL, and K+ can be reabsorbed in the cTAL and mTAL. The transport is voltage-dependent. The mTAL can reabsorb neither Mg2+ nor Ca2+, whatever Vte.
    Type of Medium: Electronic Resource
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