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At least 451 records · Page 25Linked to original sources
PubMed1980

Contrast media reactions: data analysis and hypothesis.

Two hundred and twenty-eight deaths due to the use of contrast media are reported, including 15 from intravenous cholangiography, 69 from angiography, 140 from urography and four other. The causes are analyzed and the various explanations for reactions to contrast media are considered. Data concerning the high incidence of cardiac death, the large number of deaths due to pulmonary edema, and the known transgression of the blood-brain barrier by contrast media are used to construct a theory that bases all reactions on the effect of contrast media on the central nervous system.

Adolescent↗
PubMed1982

Subjective vs. objective evaluation of gallbladder opacification during oral cholecystography in comparative clinical trials: implications for studies involving visual assessment.

Radiographs and CT images taken during oral cholecystography in dogs were interpreted in an independent, blind fashion by three radiologists on two occasions and visual assessment of gallbladder density compared to the actual CT values. While there was significant intra- and inter-observer variation, the mean scores for the observers' interpretations of both radiographs and prints correlated well with the actual CT values (p less than 0.05). In five out of six comparisons between first and second readings, the observers gave a lower score on the second reading. The considerable variation reflects the problems inherent in subjective evaluation of agents that produce small but measurable differences in radiographic density. Studies involving such subjective data have to be carefully designed in order to obtain meaningful results.

Administration, Oral↗
PubMed1983

Digital subtraction angiography for examination of vessels of the leg: use of a 40-cm image intensifier.

Digital subtraction angiography (DSA) using a 41-cm (16-in.) image intensifier was performed in 144 patients with peripheral vascular insufficiency. In most cases the entire peripheral vascular bed from the renal arteries to the popliteal trifurcation was demonstrated with four intravenous injections and four exposed fields: (a) aorto-iliac, (b) ilio-femoral, (c) femoro-popliteal, and (d) popliteo-tibial. In 90% of cases the procedure was diagnostic in all regions studied, while in 10 it was nondiagnostic in one or more regions for various reasons (myocardial insufficiency, inadequate contrast bolus, or technical failure). Most failures involved the distal arteries. In spite of some limitations, intravenous DSA using a large-field image intensifier may replace conventional angiography in routine preoperative evaluation of peripheral vascular disease, with intra-arterial injections being performed when the intravenous technique is nondiagnostic.

Adult↗
PubMed1981

Contrast nephropathy.

Contrast nephropathy is an adverse alteration in renal function induced by intravascular contrast media. Most cases involve transient asymptomatic episodes; yet a significant number involve oliguria and/or permanent renal damage. The incidence of contrast nephropathy in the general hospitalized population is about 5%, and is associated with preexisting renal insufficiency and diabetes mellitus. The incidence in patients with normal renal function is significantly lower - 0.6% following IVP and 2% following angiography. Angiography carries risks inherent to the technical problems of the procedure itself. Preexisting renal insufficiency is the most significant predisposing condition of contrast nephrotoxicity. As many as two-thirds of patients with chronic renal failure may experience an acute deterioration in renal function following exposure. Most of these episodes are transient and benign. Diabetic patients with preexisting renal insufficiency are at an even greater risk; about 75% of such patients will experience renal complications. The risk is even higher in JODM patients with severe renal disease; there is an over 90% incidence of nephrotoxicity with as many as half sustaining permanent renal damage. Adequate hydration does not appear to reduce the incidence of contrast nephropathy in susceptible patients, but it may reduce the likelihood of oliguria and permanent damage. In multiple myeloma the risk of contrast-induced renal failure is low, and probably involves a different pathogenesis than seen in other cases of contrast nephropathy. The incidence in myeloma patients is probably increased in the presence of dehydration and renal insufficiency. Peripheral vascular disease, hypertension, old age and large and repeated doses of contrast may increase the risk in susceptible patients. Prevention of contrast nephropathy must start with identification of patients at risk. In patients with preexisting renal insufficiency, and especially diabetic patients with preexisting renal insufficiency, the anticipated benefit should outweigh the potential risk of exposure to contrast media.

Angiography↗
PubMed1985

Inner-ring deiodination of 3,5,3'-triiodothyronine in the in situ perfused guinea pig placenta.

Broken cell preparations of rat and human placentas contain an inner (tyrosyl)-ring iodothyronine deiodinase enzyme with greatest activity when the substrate is 3,5,3'-triiodothyronine (T3). This report describes the deiodination of T3 in the intact placenta and the effect of sodium iopanoate (IA) and propylthiouracil (PTU) on T3 deiodination. Under nembutal anesthesia, the placenta of 60-65-d-old pregnant guinea pigs was surgically exposed, a single umbilical artery and the umbilical vein were cannulated, and the fetus was removed. In a temperature-controlled chamber (37 degrees C), the fetal side of the placenta was perfused through the umbilical artery at a rate of 1 ml/min with 3% bovine serum albumin Krebs-Henseleit buffer containing 0.14 nM outer ring labeled [125I]T3. Placenta effluent fractions were collected at timed intervals from the umbilical vein cannula throughout a 120-min perfusion period. The contents of the perfusion buffer and the various effluent fractions were analyzed for their iodothyronine content by high pressure liquid chromatography. In five experiments, the percent composition of 125I-labeled iodothyronines in the perfusion buffer and placenta effluent was 95.3 +/- 1.0 (mean +/- SE) and 70.2 +/- 2.1 for T3 (P less than 0.01), 2.5 +/- 0.7 and 20.1 +/- 1.8 for 3,3'-T2 (P less than 0.01), and 0 and 8.2 +/- 0.9 for 3'-T1. There was no difference between the percent [125I]iodide in the perfusion buffer and in the placenta effluents. When placentas were perfused with IA and [125I]T3, after perfusion with [125I]T3 alone, there was a significant increase (P less than 0.01) in the percent [125I]T3 in the placenta effluents, and a significant decrease in [125I]3,3'-T2 (P less than 0.01) and [125I]3'-T1 (P less than 0.01). In contrast, PTU did not affect the composition of labeled iodothyronines in the placenta effluents, despite the fact that the addition of PTU significantly (P less than 0.001) inhibits the inner-ring deiodination of [125I]T3 in human or guinea pig placenta microsomes in the presence of low (0.25 mM) concentrations of dithiothreitol. The present studies demonstrate that T3 is actively deiodinated in the inner ring to 3,3'-T2 by the intact guinea pig placenta. A portion of 3,3'-T2 is further deiodinated in the inner ring to generate 3'-T1. No outer ring deiodination of T3 was seen under the conditions employed. IA, but not PTU, inhibits T3 deiodination in the placenta perfused in situ. We conclude that the placenta is probably a site for fetal T3 metabolism.

Animals↗
PubMed1986

Cholecystographic agents and sulfobromophthalein inhibit the binding of L-thyroxine to plasma membranes of rat hepatocytes.

Cholecystographic agents and sulfobromophthalein (BSP) cause a major discharge of labeled T4 from the liver in man in vivo. In the present study we sought to determine if this discharge is partially due to inhibition of T4 binding to plasma membrane sites. Plasma membranes were isolated from hepatocytes of female Sprague-Dawley rats, and 5'-nucleotidase levels were measured to demonstrate plasma membrane viability. Specific binding of T4 (Ka, 1.01 X 10(8) M) was confirmed by displacement of labeled T4 by unlabeled hormone (10(-10)-10(-5) M). Displacement of labeled hormone was also produced by addition of tyropanoate, iopanoate, ipodate, or BSP. At 5-mM concentrations of inhibitor, the Ka for T4 declined to 4.00 X 10(7) M with BSP, 5.07 X 10(7) M with ipodate, 5.62 X 10(7) M with tyropanoate, and 7.43 X 10(7) M with iopanoate. Thus, a portion of the discharge of hepatic T4 after administration of these agents may be due to competitive inhibition of binding to plasma membrane sites.

Animals↗
PubMed1988

Iodothyronine 5'-deiodination in rat kidney microsomes: sensitivity to propylthiouracil.

When activated by dithiothreitol, iodothyronine 5'-deiodinase (I-5'D) activity in kidney microsomes is less sensitive to inhibition by propylthiouracil (PTU) and iopanoate (IOP) at nanomolar, compared to micromolar, substrate concentrations. The enzymatic activities at nanomolar substrate concentrations are, however, completely eliminated in the presence of a combination of 10 microM IOP and 100 microM PTU. In this report we present evidence that 1) the relative PTU insensitivity results from the residual activities of the high Km enzyme which, while being very sensitive to PTU inhibition at micromolar substrate concentrations, becomes progressively less PTU sensitive as substrate concentrations decline relative to its Km; and 2) the relative IOP insensitivity is due to the presence in kidney microsomes of a low Km enzyme which is relatively insensitive to IOP, but highly sensitive to inhibition by PTU. Classifying the deiodinases on the basis of PTU sensitivity, therefore, requires that not only the thiol concentrations, but, as in the case of the type I enzyme, also the substrate concentrations be specified. The PTU resistance of the type I enzyme at nanomolar substrate concentrations suggests a role of this enzyme in T3 neogenesis in PTU-treated animals.

Animals↗
PubMed1994

Down-regulation of type II L-thyroxine, 5'-monodeiodinase in cultured GC cells: different pathways of regulation by L-triiodothyronine and 3,3',5'-triiodo-L-thyronine.

The current consensus is that iodothyronines down-regulate type II T4 monodeiodinase (5'-DII) by an extranuclear acceleration of enzyme inactivation. We have investigated 5'-DII regulation in cultured GC cells, in which thyroid hormone responses are mediated by nuclear thyroid receptor (TR). GC cells actively converted T4 to T3, independent of propylthiouracil and with a Km of 1.4 nM, which are characteristics of 5'-DII. When GC cells were incubated with 10 nM T3, the Km was not affected. However, the maximum velocity was significantly down-regulated by 10 nM T3, from 0.15 to 0.018 pmol/mg protein.min. Dose-response studies showed that a 50% reduction in enzyme activity was achieved with either 0.25 nM T3 or 12 nM rT3. Time-course studies showed that a 50% reduction in enzyme activity occurred after 40 min of incubation with 100 nM rT3 and after 160 min of incubation with 10 nM T3. The down-regulation of 5'-DII by physiological concentrations of T3 has the characteristics of an effect that is mediated by nuclear TR. Our studies, therefore, suggest that down-regulation of 5'-DII by these iodothyronines in GC cells may occur by different mechanisms: enzyme inactivation for rT3, in agreement with the current consensus, and decreased enzyme production for T3, probably mediated by TR.

Animals↗