Previous papers have suggested that a maximum urinary radioopacity is achieved in mail when an adequate dose of contrast agent is given after suitable dehydration (Benness, 19651, and that this maximum radioopacity may be rclatrd to renal function (Henness et al., 1965). This concept has been confirmed in the laboratory using sheep (Renness, 3967), and the work has heen continued to define the influence of different urographic agents on urinary radioopacity.
MATERIALS .mi) METHODSX method of controlling the fluid balance of a young female sheep in a metabolic cage and of measuring the changes in plasma osmolality and contrast levels, urinary flow rate, osmoldity, contrast and electrolyte levels have been described (Benness, 1967). Blood samples were obtained through a percutaneous catheter inserted into the jugular vein, and urine samples were obtained by dependent drainage from a self-retaining bladder catheter. The animal was conscious and supported in a sling. The measurements on the blood and urine have been described.On separate occasions the animals were given equivalent doses of sodium or methylglucamine diatrizoate (NaD and MGD), or sodium or rnethylglucamine iothalamate (NaI and MGI). These doses had equivalent radioopacity (iodine content) rather than equivalent weight. Later they were given equivalent doses of sodium chloride 5% or methylglucamine hydrochloride 14.5% (NaC1 and MGHCl) on separate occasions.The plasma and urinary diatrizoate and iothalamate levels were measured by a spectrophotometric method (British Pharmacopoeia, 1963), calibrated with known standards, and expressed as NaD for convenient comparison. Urinary methylglucamine excretion was measured by a method of periodate oxidation (Ryan, personal communication), calibrated with known standards, and expressed as MGD for comparison. The details of the spectrophotometric estimation for the four contrast agents and the periodate estimation of methylglucamine will be reported in another paper. * Presented to the Annual Meeting, College of Radiologists of Australia and New Zealand, October, 1967.
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RESULTSThirty-three experiments were performed on four sheep, comparing the urinary response to the four contrast agents and the NaCl and MGHCl. On all occasions the sheep were given a normal dry food ration up to the time of the experiment, but they had no water for the previous three days. The large volume of the sheep's stomach was stabilized in this way and the dehydration, as measured by the urinary flow rate and osmolality, wa5 satisfactory and reproducible.The response in a dehydrated sheep to equivalent doses of contrast agents is illustrated in Figure 1. Doses equivalent to 1OOOmg. per kg. of NaD were used, containing approximately 600 mg. per kg. of iodine. This dosage scale was equivalent to a human infusion dose. Following control collections of blood and urine, the contrast agent was injected intravenously over one minute, and urine samples were collected for periods of 5, 5, 5, 10, 10, 10 and 15 minutes. Venous blood was sampled...
