Biomedical subjects

W J Caldicott

Publications and source records attributed to W J Caldicott.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Mechanism of the renal response to contrast medium in dogs. Decrease in renal function due to hypertonicity.

Radiographic contrast media (CM) (meglumine/sodium diatrizoate-76%; 1650 mOsm/kg) and other hypertonic solutions induce renal vasoconstriction by an unknown mechanism. In anesthetized dogs, renal blood flow (RBF) was measured with an electromagnetic flowmeter and filtration fraction (FF) and glomerular filtration rate (GFR) by the renal extraction of technetium-99m tin chelate. Ureteral pressure (UP) and wedged renal venous pressure (VP) were measured as indices of intrarenal pressure. Measurements of renal length (L), along with pressures, made it possible to examine the compliance of the system. A 4-cc intrarenal bolus of CM caused a 59% reduction in GFR (control: 0.63 +/- 0.04 to 0.26 +/- 0.04 ml/min X g, mean +/- SEM), in association with a 23% reduction in RBF (control: 3.10 +/- 0.11 to 2.39 +/- 0.26 ml/min X g) and a 44% decrease in FF (control: 0.32 +/- 0.01 to 0.18 +/- 0.03). These responses were compared with a 3-microgram intrarenal bolus of norepinephrine (NOREPI) which resulted in a 79.0 +/- 7.5% reduction in RBF, 68.3 +/- 7.3% reduction in GFR and 42.6 +/- 15.6% increase in FF. The NOREPI-induced vasoconstriction caused transient decreases in renal L, UP, and VP, whereas the CM-induced decrease in renal blood flow was associated with increases in these parameters. In studies employing ureteral occlusion to elevate intrarenal pressure, the magnitude (area, cm2) of the CM-induced decrease in renal perfusion was accentuated with increased UP (r = 0.79, n = 24, P less than 0.001). The CM-induced increase in renal L, UP, and VP must reflect osmotic forces and an increase in intrarenal pressure. The decreases in FF and GFR probably reflect Starling forces in the glomerular capillaries, with osmotic transients dominating. The results suggest a mechanical mechanism for the CM-induced decrease in RBF.

Acetylcholine↗

PubMedDate not supplied

The influence of contrast medium dose on filtration fraction in the rabbit kidney.

We have examined the effect of dose on contrast medium-induced reductions in glomerular filtration in anesthetized rabbits. The fraction of renal plasma flow that is filtered, the filtration fraction, was directly measured by the renal arteriovenous difference method using technetium-99m (99mTc) (Sn) DTPA as the tracer, arterial and renal venous extracorporeal shunts, a gamma camera and a computer. Filtration fraction (FF) was measured each 30 seconds before and after contrast medium (sodium/methylglucamine diatrizoate) was injected in 15 seconds at a dose of 0.5, 1.0 or 2.0 ml/kg, IV. In six animals that had a control FF of 0.19 +/- 0.01 there was a dose-related decrease in FF. The largest dose reduced FF by 53.3%. In three other animals that had a low control FF (0.07 +/- 0.01), the largest dose induced an even greater 71.0% decrease in FF. These data suggest that attempts at increasing contrast excretion by injecting larger doses will be offset, at least in part, by larger reductions in glomerular filtration, and that this effect may be greater when glomerular function is impaired.

Animals↗

PubMedDate not supplied

Excretion of contrast media by the immature rabbit. Comparison of Renografin and Iopamidol.

The excretion of iodinated contrast media was studied in 13 immature rabbits after the intravenous injection of 2 ml/kg (approximately 600 mg I/kg) of radio-labelled Renografin-60, a high osmolality agent (1510 mOsm/kg), or Iopamidol-300, a new agent with a much lower osmolality (616 mOsm/kg). Renografin, but not Iopamidol, induced an immediate but transient 40% fall in blood pressure, a marked diuresis that was 3.4 times greater at its maximum than for Iopamidol, and a much lower urinary iodine concentration at the time of maximum diuresis (Renografin: 90.3 +/- 9.2 microgram/ml; Iopamidol: 213 +/- 32.9 microgram/ml). No difference between the two contrast media was found for plasma iodine concentration, renal clearance from the plasma, urinary iodine excretion rate or volume of distribution. In five additional rabbit pups, formal clearance studies made using a constant IV infusion of the agents and timed collections of urine and plasma showed that Iopamidol and Renografin were cleared at the same rate by the kidneys (P greater than 0.9).

Animals↗