Evaluation of complete and partially obstructed kidneys using Gd-DTPA enhanced dynamic MRI in adolescent swine.

PURPOSE: Aim of this study was to evaluate the dynamic changes in renal relative signal intensity (RSI) following the administration of Gd-DTPA in adolescent pigs with complete and partial unilateral ureteric obstruction. METHODS: Pigs were divided into 3 groups: partial and complete unilateral ureteric obstruction and controls. Complete unilateral ureteric obstruction (CUUO) was created by ligating the left ureter, whereas partial unilateral ureteric obstruction (PUUO) was created in pigs of 2 weeks of age by embedding the left ureter into the psoas muscle. Dynamic MRI was performed before and at 0 - 60 min after an intravenous bolus injection of Gd-DTPA. Mean RSI of the renal cortex, medulla and pelvis was measured and interpreted as an indirect measure of the renal function. In addition, renography was performed, and renal morphology was examined IN VITRO. RESULTS: Three phases of RSI were identified. The dynamic RSI patterns differed markedly between obstructed and control kidneys. In PUUO kidneys, Phase 1 of the mean RSI of the cortex and medulla demonstrated a decreased amplitude and prolonged duration, whereas in Phase 2 the mean RSI of the pelvis was increased. In acute CUUO kidneys, the mean RSI patterns were similar to those of controls, except for a significant increase of the pelvic mean RSI. CONCLUSIONS: Gd-DTPA enhanced dynamic MRI allowed a characterization and differentiation of renal function and morphology of normal and obstructed kidneys, and secondly, provided potentially important information on renal concentrative and filtration availability.

Norepinephrine inhibits the pelvic pressure increase in response to flow perfusion.

PURPOSE: We evaluated the effects of norepinephrine on transport pressures in the normal upper urinary tract of the pig during increasing perfusion rates. MATERIALS AND METHODS: Anesthetized Danish landrace Yorkshire pigs weighing 38 to 40 kg were studied. Transparenchymally 2, 6Fr catheters were introduced into the left renal pelvis for pressure measurements and perfusion, respectively. An ultrasonic flow probe was inserted around the left renal artery to record blood flow. A 10Fr catheter was placed transurethrally for bladder drainage and the bladder was maintained empty during the entire study. In the 5 group 1 pigs the pelvic pressure increase was examined at increasing perfusion rates of the renal pelvis (2, 4, 6, 8, 10 and 15 ml per minute) in response to endoluminal administration of increasing concentrations of norepinephrine (0, 5, 50 and 100 microg/ml) in saline. In the 5 group 2 pigs the pressure flow study was also done 4 times per animal using isotonic saline. RESULTS: Endoluminal norepinephrine had a dose dependent effect on the pressure flow relationship. Perfusion with 5 and 50 microg/ml norepinephrine caused a delayed increase and a decrease in pelvic pressure in response to increasing flow rates, whereas perfusion with 100 microg/ml norepinephrine significantly inhibited and almost eliminated the pressure increase at all perfusion rates compared with saline perfusion. Importantly there were no changes in blood pressure, the heart rate or renal arterial blood flow. In group 2 perfusion with isotonic saline resulted in the same pressure response to increasing flow rates each time. CONCLUSIONS: Endoluminal administration of norepinephrine caused a dose dependent inhibition on the pressure phases of the pressure flow relationship of the upper urinary tract in pigs. No systemic changes were observed. These observations may provide a useful adjuvant treatment strategy for upper urinary tract stone treatment and endoscopy.

Partial unilateral ureteropelvic junction obstruction induced in 2-week-old piglets.

PURPOSE: We examined effects on kidney function and morphology of a partial ureteropelvic junction obstruction induced late in the postnatal nephrogenesis period of the pig. We compared the results to a similar study on pigs with obstruction induced early in the nephrogenesis period. MATERIALS AND METHODS: A total of 20 14-day-old pigs were included in the study. Fifteen animals were randomized to partial unilateral obstruction and 5 were sham operated. Kidney function and morphology were analyzed regarding glomerular filtration rate, renographic functional share and total kidney volume at the age of 4, 12 and 24 weeks. RESULTS: At age 4 weeks hydronephrosis was found in all obstructed kidneys included in the study. Four obstructed kidneys had renographic functional share 40% or greater and 1 deteriorated to less than 40% at 24 weeks. A total of 11 obstructed kidneys had a functional share less than 40%, 5 increased to a share greater than 40% at age 24 weeks and 3 had decreasing share from age 4 to 24 weeks. Single kidney glomerular filtration rate of the contralateral kidneys was significantly increased at all ages. Volume of the contralateral kidney was significantly increased at age 4 and 12 weeks. CONCLUSIONS: The variability and course of renographic functional share in kidneys subjected to partial obstruction at age 2 weeks was similar to findings obtained in pigs obstructed at age 2 days. In contrast to these our study showed compensatory increase in function and size of the contralateral kidney, suggesting that contralateral compensation is an ability gained late in the nephrogenesis period.

Ocular fluorescein kinetics before and after vitrectomy on swine.

PURPOSE: To study the quantitative effects of vitrectomy on fluorescein transport kinetics across the ocular barriers. METHODS: Thirty-six domestic swine were used in this study. Twenty anesthetized swine were given a standardized fluorescein intravenous injection immediately after unilateral vitrectomy. This was followed by one single central sample aspiration from the vitreous and the anterior chamber of both eyes in individual animals at increasing intervals up to 24 h after the injection. Fluorescein concentrations in the samples were determined by high-pressure liquid chromatography (HPLC). Eight swine underwent unilateral vitrectomy followed by anterior chamber and vitreous fluorophotometry on both eyes 1 month later. The fluorescein concentrations determined using this method were followed for 24 h. Similar examinations were performed in a control group of eight swine that did not undergo vitrectomy. Anterior chamber, vitreous, and plasma fluorescein concentration/time courses were analyzed kinetically by iterative nonlinear regression analysis. RESULTS: The barrier surrounding the anterior chamber of the eye was immediately impaired after vitrectomy, as evidenced by an increased area under the fluorescein concentration versus time curve, but the transport kinetics were restored within 1 month after surgery. The blood-retinal barrier was, however, persistently altered following vitrectomy. Transport rate and extent of drug penetration into the vitreous were increased, while drug elimination from the vitreous remained unchanged. CONCLUSION: Vitrectomy led to persistent kinetic fluorescein transport changes in the blood-retinal barrier resulting in faster and increased drug penetration to the vitreous, whereas similar alterations in the anterior chamber barrier transport were only transitory.