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PubMed1977

Metabolism of thyroid hormones by the isolated perfused rabbit kidney.

The metabolism of thyroxine and triiodothyronine in the isolated perfused rabbit kidney was monitored by specific radioimmunoassay for each hormone. The amount of thyroxine catabolised was proportional to the amount added initially and no saturation effects were observed over a wide range (3.9-82 nmol). After addition of thyroxine alone, triiodothyronine could be detected in the perfusion medium within 10 minutes but only much later in the urine. It was proposed that circulating thyroxine contributes indirectly to the level of urinary triiodothyronine.

Animals↗
PubMed1975

Jejunal factor stimulating insulin release in the isolated perfused canine pancreas and jejunum.

In the present study using an isolated perfused preparation of canine jejunum and pancreas, an insulin-releasing factor was found in the venous effluent of the jejunum. Insulin secretion by the pancreas rose twofold after 10% glucose was infused in the lumen of the jejunum and remained at a high level even after the stimulus was discontinued. No modification of the exocrine pancreatic secretion occurred during the insulin release, and therefore it seems unlikely that gastrin, secretin or cholecystokinin-pancreozymin were released by the jejunal mucosa. In control experiments the values of hyperglycaemia observed previously and intraluminal hyperosmolarity were tested: at these levels, they did not affect insulin secretion. The nature of this intestinal insulin-releasing factor remains unknown however, but may be identifiable when intestinal hormones in blood can be assayed reliably.

Animals↗
PubMed1979

The influence of zinc status on the levels of metallothionein in isolated perfused rat liver.

The levels of cadmium and zinc metallothionein in isolated perfused livers of zinc depleted and repleted rats were investigated. Rats (160-200 g or 90-120 g) were fed either a zinc-deficient or zinc-supplemented diet for 62 or 42 days. The 90 to 120 g rats were repleted with 30 ppm Zn2+ in the drinking water for 1, 4 and 10 days after 35 days of depletion, and another group after depletion for 21 days was repleted for 15 days on a 21% casein diet. At appropriate times livers were cannulated, removed and perfused +/- 25 mug Cd2+ as CdCl2, for 2 hours through the portal vein in a perfusion apparatus. Zinc depletion resulted in significant decreases in growth rate (1.4 versus 5.7 g/day) and liver weights. Repletion with Zn for 10 days increased the weight gain to 7.1 g/day. Depletion decreased the incorporation of Zn and Cd into metallothionein by 57 to 60%, while repletion for 1, 4 and 10 days increased the incorporation to nearly 500% of control levels. But, as repletion progressed, zinc in metallothionein fell to normal levels after 15 days. Cadmium in metallothionein did not decrease between 1 and 10 days of repletion. Zinc deficiency also reduced the zinc content of the liver by 44%, which increased to normal levels after 10 days of repletion. These data suport the conclusion that zinc status can influence the incorporation of cadmium and zinc into metallothionein.

Animals↗
PubMedDate not supplied

alpha 1- and alpha 2-adrenoceptor stimulation in the isolated perfused hindquarters of the rat: an in vitro model.

In the isolated perfused hindquarters of rats pretreated with reserpine, vasoconstrictor responses were induced by activation of postjunctional alpha 1- and alpha 2-adrenoceptors. B-HT 920 and methoxamine were used as selective stimulants of alpha 2- and alpha 1-adrenoceptors, respectively. Prazosin (pA2 8.83) exhibited a competitive antagonism toward methoxamine-induced vasoconstrictor responses, whereas yohimbine (pA2 8.95) effectively antagonized B-HT 920-induced vasoconstriction in a competitive manner. When calcium was omitted from the perfusion fluid, no vasoconstriction via alpha 2-adrenoceptors could be evoked. On the other hand, raising the extracellular calcium concentration in the perfusion fluid enhanced the alpha 2-adrenoceptor-mediated vasoconstrictor effects. Vasoconstriction via postjunctional alpha 1-adrenoceptors seemed hardly, if at all, dependent on extracellular calcium. The calcium entry blockers Co2+, La3+, and nisoldipine selectively inhibited the alpha 2-adrenoceptor-induced vasoconstriction in a noncompetitive manner. The results further support the concept that extracellular calcium is a prerequisite for the process of vasoconstriction induced by activation of postjunctional alpha 2-adrenoceptors.

Adrenergic alpha-Agonists↗
PubMed1978

Evaluation of renal preservation using the isolated perfused rat kidney. Ischaemic damage and the effects of inosine.

An isolated perfused rat kidney has been used to determine the response to prolonged warm ischaemia and to examine renal preservation procedures. All measurements of function declined to near zero after 90 min of warm ischaemia. Measurement of total sodium reabsorption (TNa) was the most sensitive indicator of renal damage. Inosine was without effect on subsequent renal function after 60 or 90 min of warm ischaemia, or after 24 hr of cold ischaemia. Surface cooling or hypertonic citrate solution, in the cold or at 37 degrees C, significantly improved renal function, and their use in clinical renal preservation rather than that of inosine was supported by the present results.

Adenosine Triphosphate↗
PubMed1971

Plasma concentration, uptake by liver, and biliary excretion of tritiated cardiac glycosides in the isolated perfused guinea-pig liver.

1. Investigations were carried out on isolated perfused guinea-pig livers. Different doses of tritiated ouabain, digoxin, and digitoxin were added to the perfusion medium and the subsequent plasma elimination, hepatic uptake, and biliary excretion quantitatively measured. After the perfusion, extracts of liver, bile and plasma were subjected to thin layer chromatography in order to detect the radioactively labelled glycosides and their metabolites.2. The ouabain concentration in the plasma approached the equilibrium stage within 45 minutes. At this time 40% of the administered dose had been taken up by the liver, and no further elimination occurred. The elimination curve for ouabain followed a simple exponential function. After 1 h the tissue medium (T/M) ratio was approximately 3. In bile hardly any radioactivity could be detected. Ouabain was therefore not excreted by the liver.3. Up to 80% of the digitoxin was eliminated from the plasma within 4 hours. The elimination of radioactive material for the dose range studied could be described by a hyperbolic function. The T/M ratio in the liver varied with time. At the beginning it was as high as 10 and after 4 h reduced to approximately 3. After 45-60 min the concentration of radioactive material in the bile was 500 times as high as that in the plasma. Almost 70% of the administered radioactivity was excreted with the bile within 4 hours. At the end of the perfusion almost all the identifiable substances in plasma and bile were polar metabolites, as shown by thin layer radiochromatography.4. Digoxin behaved similarly to digitoxin.5. The findings led to the following hypothesis: uptake of cardiac glycosides into the liver cells occurs by a passive diffusion process and is related to their lipid solubility. On the other hand excretion in the bile occurs in general if polar metabolites are formed in the liver cells.

Animals↗
PubMed1971

Effect of pretreatment with 6-hydroxydopamine on the uptake and metabolism of catecholamines by the isolated perfused rat heart.

1. Isolated rat hearts from control and 6-hydroxydopamine pretreated animals were perfused with (3)H-noradrenaline or (3)H-dopamine, either at a low perfusion concentration (1.50 x 10(-10) mol/ml (3)H-dopamine; 1.18 x 10(-10) mol/ml (3)H-noradrenaline) or a high perfusion concentration (296.69 x 10(-10) mol/ml (3)H-noradrenaline, 327.45 x 10(-10) mol/ml (3)H-dopamine) for 8 minutes.2. At the low perfusion concentration, the total activity, the radioactivity in the alumina eluates (sum of (3)H-dopamine, (3)H-noradrenaline and deaminated catechol metabolites) and the concentration of (3)H-dopamine. (3)H-noradrenaline and the deaminated catechol metabolites were decreased in the hearts of the pretreated rats as compared with the controls. The O-methylated amine metabolites were increased. The deaminated O-methylated metabolites were increased in the experiments with (3)H-noradrenaline and decreased in the (3)H-dopamine experiments.3. Uptake of (3)H-dopamine and (3)H-noradrenaline by the hearts of 6-hydroxydopamine pretreated rats was decreased to a much smaller extent when perfused with the high concentration than with the low concentration.4. At the high perfusion concentration there was a significant difference between control and pretreated animals with regard to the total radioactivity and the radioactivity in the alumina eluates only. The absolute and relative amounts of metabolites were not significantly changed by pretreatment with the exception of the deaminated catechol metabolites in the (3)H-dopamine experiments.5. It is concluded that neuronal Uptake 1 is greatly impaired in the hearts from rats pretreated with 6-hydroxydopamine, but extraneuronal Uptake 2 remains intact.

Animals↗
PubMed1984

Effect of bumetanide, frusemide and prostaglandin E2 on the isolated perfused kidney of rat and rabbit.

Rat and rabbit kidneys were isolated, perfused via the renal artery with Krebs solution and perfusion pressure monitored. Dose-response curves to noradrenaline administered as bolus doses or frequency-response curves from transmural arterial electrical stimulation were obtained. A 1 h continuous infusion of bumetanide (0.1 micrograms ml-1) increased the sensitivity of rat kidney vessels to noradrenaline, an effect also seen when bumetanide and flurbiprofen (6 micrograms ml-1) were simultaneously perfused. In the rabbit there was a decreased sensitivity to both electrical stimulation and noradrenaline. A 1 h continuous infusion of frusemide (6 micrograms ml-1) only altered the effects of electrical stimulation. An increased sensitivity in the rat (abolished by flurbiprofen) and a decreased sensitivity in the rabbit kidney was observed. A 1 h continuous infusion of prostaglandin (PG)E2 (2 ng ml-1) increased the sensitivity of rat kidney to both types of stimuli but caused a reduction in the responsiveness of the rabbit kidney to electrical stimuli only. Addition of flurbiprofen only slightly modified these results. The results emphasize and confirm the fundamental difference in reactivity of the rat and rabbit kidney. Bumetanide and frusemide, two ostensibly similar loop diuretics, show significantly different effects on these preparations suggesting that any modification by non-steroidal anti-inflammatory drugs cannot wholly be explained by similar PGE2 induced haemodynamic changes.

Animals↗
PubMed1975

Bile acid metabolism in mammals. VIII. Biliary secretion of cholylarginine by the isolated perfused rat liver.

In studies of cholic acid metabolism using the isolated perfused rat liver system, an unknown conjugate of cholic acid was observed. This conjugate comprised 15-27% of the biliary bile acids in these experiments, was less polar than cholylglycine on thin-layer chromatography using butanol, acetic acid, and water, and had an apparent molecular weight greater than that of cholyltaurine on gas-liquid chromatography. Amino acid analysis of the hydrolyzed conjugate demonstrated the presence of arginine. Perfusion studies with radioactive arginine, and mass spectrometric analysis proved that the conjugate was cholylarginine. Secretion of this conjugate does not represent a deficiency of available glycine and taurine.

Animals↗
PubMed1976

Glucose transport in isolated perfused proximal tubules of snake kidney.

Glucose transport was studied in isolated, perfused snake (Thamnophis spp.) renal tubules. When 14C-labeled and unlabeled glucose concentrations for bath and perfusate were identical, net transepithelial glucose transport occurred from lumen to bath. Maximum rates of transport were 1.24 X 10-12 and 2.17 X 10-12 mol min-1 mm-1 in proximal-proximal and distal-proximal segments, respecitvely. Glucose concentration in cells of perfused tubules of both segments was less than that of bath and lumen when tubules spontaneously stopped transporting glucose. Transepithelial glucose permeability ath leads to lumen) was about 0.25 X 10-5 cm sec-1 for both segments. Peritubular membrane permeability (bath leads to cell) was about 0.50 X 10-5 cm sec-1 for both segments. Luminal membrane permeabilities (cell leads to lumen) were 0.29 X 10-5 and 0.65 X 10-5 cm sec-1 for proximal-proximal and distal-proximal segments, respectively. Luminal membrane permeability in opposite direction (lumen leads to cell) was about 10.0 X 10-5 cm sec-1 for both segments. These results indicate that, during maximum glucose absorption, glucose enters cells down concentration gradient across luminal membrane by a mediated process and is transported out of the cells against concentration gradient at peritubular membrane.

Animals↗
PubMed1978

Fluid absorption with and without sodium in isolated perfused snake proximal tubules.

Net fluid absorption (JV) was studied in isolated, perfused snake (Thamnophis spp.) proximal renal tubules. With standard (150 mmol/liter Na+) bicarbonate-buffered Ringer in perfusate and standard Ringer plus dextran (4 g/100 ml) in bath, JV was about 0.9 nl min-1 mm-1. Removing dextran from bath reduced JV by about 20 percent. When sodium in perfusate was replaced with choline JV approached zero. However, when sodium in bath as well as perfusate was replaced with choline, JV returned to control level. Results were the same when sodium was replaced with tetramethyl-ammonium, sodium chloride was replaced with sucrose or lactose, or chloride was replaced with methyl sulfate. In contrast, replacing sodium in perfusate or in both perfusate and bath with lithium did not reduce JV. Fluid absorption was always isosmotic. Replacing bicarbonate with phosphate or Tris in sodium-containing media had no effect on JV, but the presence of buffer in sodium-free or low-chloride media may have been important for JV. Reducing temperature 10 degrees C reduced JV by about 35 percent with either sodium chloride or sucrose in both perfusate and bath. The results indicate that isosmotic fluid absorption can occur when lithium is substituted for sodium or when some other substitution is made for sodium, chloride, or both in perfusate and bath simultaneously.

Animals↗
PubMed1981

Urate transport by the isolated perfused S2 segment of the rabbit.

Urate transport was studied in isolated perfused S2 segments of the superficial proximal tubule of the rabbit. When urate was present in identical concentrations of 290 microM in the perfusing and bathing solutions, there was a net secretory flux of urate of 775.0 +/- 152.8 fmol.min-1.mm-1. When urate was present in varying concentrations in the bathing solution only, the bath-to-lumen flux of urate increased as the concentration of urate in the bathing solution was increased from 60 to 595 microM, but tended toward a plateau at higher concentrations. After correction of the net secretory flux for the contribution of passive permeation, an apparent Km of 238 microM and Vmax of 950 fmol.min-1.mm-1 for the secretory flux of urate was calculated. When urate was present only in the luminal perfusion solution, the lumen-to-bath flux of urate was significantly less than the bath-to-lumen flux at a similar bath concentration of urate. The lumen-to-bath flux of urate was not significantly affected by cooling the bath to 25 degrees C. These studies provide evidence for both passive and facilitated mechanisms for urate secretion in the rabbit S2 segment. The absorptive flux for urate, however, appears to be primarily a passive mechanism.

Animals↗
PubMed1979

Vascular and extravascular compartments of the isolated perfused rabbit lung.

The vascular, interstitial, and cellular compartments of 15 isolated, perfused and ventilated rabbit lungs determined by a steady-state indicator-dilution procedure. Five lungs were perfused with constant pulmonary artery flow and zero left atrial pressure for more than 1 h. Edema formation was continuous and pulmonary vascular volume (PVV) decreased initially at a time when pulmonary vascular resistance (PVR) was falling. Increases in PVR were not seen until edema formation had become severe. In 10 other lungs, increases in pulmonary artery or left atrial pressure resulted in elevation of PVV and accelerated edema formation. The initially abrupt increase in PVV was followed by a more gradual increase over a 10-min period. Return of fluid to the vasculature was never observed in these studies. Labeled albumin readily entered the extravascular space but a relatively constant fraction of the interstitium remained inaccessible to albumin. No changes were found in the cellular volume during edema formation.

Animals↗
PubMed1994

Fatigue of rapid and slow onset in isolated perfused rat and mouse diaphragms.

Muscle fatigue was studied in the isolated perfused rat (66% oxidative fibers) and mouse (99% oxidative fibers) diaphragms. Both muscles displayed two fatigue patterns when exposed to 333-ms trains of 20-Hz stimulation. A rapid fatigue pattern appeared within each contractile train as an immediate progressive twitch-by-twitch diminution in contractility [a decrease in maximal isometric twitch tension (T) and maximal rate of T development]. An intertrain slow fatigue pattern also appeared as a progressive train-by-train diminution in contractility and an increased maximal rate of relaxation normalized to T. A reduction in the stimulatory frequency from 20 to 2 Hz caused a considerable diminution in the rapid fatigue pattern. These data suggest that rapid fatigue results from the time course of mechanical restitution, the time necessary for the Ca2+ channels of the sarcoplasmic reticulum to recover from inactivation. The slow fatigue pattern, on the other hand, is thought to be due to changes in the intracellular milieu. The difference in sensitivity of the rat and mouse diaphragms to rapid and slow fatigue is apparently related to differences in their fiber type composition. Thus, as would be expected, the mouse diaphragm, composed of only oxidative fibers, is less susceptible to slow fatigue compared with the rat diaphragm. On the other hand, it is more susceptible to rapid fatigue.

Animals↗
PubMed1976

Glycogen regulation in isolated perfused near term monkey liver.

Glycogen metabolism was studied in the isolated perfused liver of the monkey conceptus at 90% of gestation using an in situ recirculating perfusion system. Net uptake of glucose and galactose and the activities of the enzymes, glycogen synthetase and phosphorylase, were studied in response to varied perfusate composition. Synthetase activity was expressed as %I. the percentage of total synthetase activity in the active form. Perfusate glucose concentrations as high as 700 mg/100 ml did not lead to net glucose uptake of to an increase in the baseline %I synthetase (4 +/- 1, mean +/- SEM). In the presence of 300 mg/100 ml glucose, insulin at 10(-7) M in creased %I to 8 +/- 2, and galactose greater than 75 mg/100 ml increased %I to 8 +/- 1. The combination of galactose, glucose, and insulin increased %I to 40 +/- 5. With this latter combination, synthetase activity was proportional to perfusate glucose concentration above 100 mg/100 ml. Phosphorylase activity was diminished by either galactose or insulin, and phosphorylase activity was lowest in the group receiving galactose, glucose, and insulin. Galactose was taken up by all livers, but net glucose uptake was not observed under any condition; net hexose uptake was observed in perfusions with galactose. Glycogen levels did not vary significantly with varied perfusate composition during the 30-min perfusion periods.

Animals↗
PubMed1978

The effects of calcium and calcium-ionophores (X 537 A and A 23187) on renin release in the isolated perfused rat kidney.

1. Calcium depletion from the medium of the isolated perfused kidney reduced renin release and renal perfusate flow. 2. Reintroduction of calcium increased renin release and perfusate flow. 3. The ionophore X 537 A (0.1-4 micromol/1) increased renin release both in the presence and absence of calcium in the medium. 4. The ionophore A 23187 (1-10 nmol/1) increased as well as decreased renin release. There was a positive correlation between direction of this effect and renal perfusate flow. 5. The results are compatible with the view that the effects of calcium and ionophores on renin release are the sum of direct and indirect effects of these agents, the predominant indirect effect being the modification of vascular tone.

Animals↗
PubMed1985

Pharmacokinetics of melphalan in clinical isolation perfusion of the extremities.

The pharmacokinetics of melphalan in clinical hyperthermic isolation perfusion was studied in 16 patients with malignant melanoma. Analysis by computer-generated lines of best fit showed that the loss of melphalan from perfusate conforms best to a biexponential equation. The initial loss with a half-life (t1/2) of approximately 5 to 10 min is interpreted as rapid uptake of melphalan by the tissue of the perfused extremity. The terminal portion of the curve with a half-life of approximately 35 to 50 min is interpreted as due predominantly to the hydrolysis of melphalan, with a lesser component of loss due to absorption of melphalan to the filters and tubing of the perfusion apparatus. Determination of the area under the curve suggests that there is no appreciable uptake of melphalan by the tissue of the perfused extremity after 30 min.

Chemotherapy, Cancer, Regional Perfusion↗
PubMed1979

Benzo(a)pyrene oxidation, conjugation and disposition in the isolated perfused rabbit lung: role of the glutathione S-transferases.

The isolated perfused rabbit lung metabolised 7--11 % of 20 mumol of [14C]-benzo(a)pyrene added in the perfusion medium in 1 h. The major metabolite formed was 3-hydroxybenzo(a)pyrene, both free (30--40 % of the total metabolites) and conjugated (4 % of total metabolites). Quinones comprised 15 % of the total and metabolism at the 9, 10 position accounted for a further 10 %. Forty per cent of the water-soluble metabolites was chromatographically identical to the glutathione conjugate of benzo(a)pyrene 4,5-oxide. Sulphate and glucuronide conjugates were formed in small but detectable amounts, principally from phenols, but also from dihydrodiols. After 1 h the more water-soluble conjugates had diffused from the lung into the perfusion medium, but the majority (60--90 %) of the metabolic products were still concentrated within the lung. The lung's limited ability to conjugate its major metabolites of benzo(a)pyrene with sulphuric or glucuronic acid, coupled with slow elimination of the products formed, particularly dihydrodiols may contribute to the susceptibility of this organ to polycyclic aromatic hydrocarbon-induced carcinogenesis.

Animals↗