Single injection techniques in determining age-related changes in porcine renal function

Subclinical kidney injury induced by repeated cisplatin administration results in progressive chronic kidney disease

Cisplatin is used to treat many solid cancers, but its dose-limiting side effect is nephrotoxicity, causing acute kidney injury in 30% of patients. Previously, we have developed a mouse model that better recapitulates the cisplatin dosing regimen humans receive and found that repeated dosing of cisplatin induces interstitial renal fibrosis. Chronic kidney disease is progressive and is characterized by chronic inflammation, worsening interstitial fibrosis, development of glomerulosclerosis, and endothelial dysfunction. To determine if damage caused by repeated cisplatin dosing results in bona fide chronic kidney disease, mice were treated with our repeated dosing regimen and then aged for 6 mo. These mice had progressive, chronic inflammation and worsened interstitial fibrosis compared with mice euthanized after day 24. Mice aged for 6 mo developed glomerular pathologies, and endothelial dysfunction was persistent. Mice treated with only two doses of cisplatin had little inflammation or kidney damage. Thus repeated dosing of cisplatin causes long-term effects that are characteristic of chronic kidney disease. This translational mouse model of cisplatin injury may better represent the 70% of patients that do not develop clinical acute kidney injury and can be used to identify both biomarkers for early injury, as well as novel therapeutic targets for the prevention of cisplatin-induced chronic kidney disease.

The pharmacokinetics and acute renal effects of oral microemulsion ciclosporin A in normal pigs

BACKGROUND

The use of ciclosporin A (CsA) is limited by nephrotoxicity. Anatomic and physiologic similarities to humans make the pig a potential important animal model for research in effects and adverse events of CsA. In a long-term study CsA 10 mg/kg/day for 6 months did not cause deterioration in renal histology or function in pigs. For ideal CsA dosage in future long-term studies of nephrotoxicity we performed this study to describe pharmacokinetics and acute effects on renal function of CsA in normal pigs.

MATERIALS AND METHODS

Three groups of 5 piglets comprised the material, a control group and 2 groups receiving 5 days treatment with CsA (Neoral) 15 or 30 mg/kg/day, respectively. CsA whole blood concentration (B-CsA) (hourly), renal blood flow, glomerular filtration rate (GFR) and serum creatinine were measured. The area under the curve from time 0 to 12 h was calculated using the Trapezoidal Rule. Pharmacokinetic calculations were performed using the KINFIT non-linear curve fitting module.

RESULTS

B-CsA reached peak in median at 0.90 and 0.96 h (633 and 914 ng/ml) in the 15 and 30 mg/kg/day groups, respectively, and median AUC was 5055 and 6275 h ng/ml, respectively. Trough levels were 338 and 475 ng/ml. The distribution of CsA followed a 2-compartment model. Serum creatinine was 111 (control), 112 (15 mg/kg/day) and significantly increased to 168 ìmol/l in 30 mg/kg/day group, which also had a reduction in GFR compared to the other 2 groups.

CONCLUSIONS

CsA causes acute nephrotoxicity in piglets. The distribution follows a 2-compartment model similar to humans, but higher doses are necessary in pigs.

Renal blood flow measurement by positron emission tomography using 15O-labeled water

BACKGROUND

Only few noninvasive methods have the potential to quantitate renal blood flow (RBF) in humans. Positron emission tomography (PET) is a clinical imaging method that can be used to measure the tissue blood flow noninvasively. The purpose of this study was to validate PET measurement of RBF using 15O-labeled water (H215O), a tracer that allows repeated measurements at short time intervals.

METHODS

RBF was measured in six pigs by PET and by radioactive microspheres (MS). Three measurements were performed in each pig at baseline (BL), during vascular expansion and dopamine infusion (DA; 20 microg. kg-1. min-1 intravenously), and during angiotensin II (Ang II) infusion (50 ng. kg-1. min-1 intravenously). RBF was estimated from aortic and renal tracer kinetics using a model adapted from the blood flow model described by Kety and Smith.

RESULTS

PET and MS values correlated strongly (y = 0.79x + 42, r = 0.93, P < 0.0001) over the RBF range from 100 to 500 mL. min-1. 100 g-1. Pharmacologically induced changes were significant and were measured equally well by PET and MS: 38 and 39%, respectively, below BL (P < 0.005 and P < 0.05) under Ang II, and 47 and 48%, respectively, above BL (P < 0.005 and P < 0.01) under DA. A Bland and Altman representation showed a low average difference of -17 +/- 45 mL. min-1. 100 g-1 (mean +/- SD).

CONCLUSION

To our knowledge, this study provides the first validation of RBF measurement by PET using H215O over a large range of RBF values (100 to 500 mL. min-1. 100 g-1), which correspond to RBF values in both healthy subjects and in patients suffering from chronic renal failure.

Use of a three-blood-sample plasma clearance technique to measure GFR in horses

Measurement of renal function in horses poses a particular challenge because plasma creatinine is influenced by muscle mass which is highly developed and variable between individuals, while conventional clearance methods involve potentially daunting problems, particularly urine collection and bladder washout. This paper provides data which enable technetium-diethyleneaminopentacetic acid (Tc-DTPA) clearance to be used to calculate glomerular filtration rate (GFR)/extracellular fluid volume (ECFV) as an expression of GFR in horses, as previously validated in humans, dogs and calves. Apart from being arguably a more physiological expression of GFR than using derivatives of body weight, the use of GFR/ECFV eliminates a source of delay and error, namely measurement of the injected dose, and offers the convenience of requiring only three blood samples. It therefore has advantages for both research and clinical applications.

A simple method for measuring glomerular filtration rate in dogs

A technique for measuring glomerular filtration rate (by six-sample plasma clearance) and extracellular fluid volume is described. The results obtained for glomerular filtration rat per extracellular fluid volume with a three blood sample technique are also presented. Concurrently with the blood sample techniques measuring plasma clearance, glomerular filtration rate per extracellular fluid volume was also measured using an external radiation detector and no blood samples. The validity of expressing glomerular filtration rate per extracellular fluid volume (rather than per body weight or surface area) and the clinical utility of the results obtained with the external radiation detector are discussed.

Influence of a low protein diet on radiation nephropathy in the pig

Nine mature, approximately 45-week-old pigs, were fed a standard diet (SD) containing 16% protein; 10 pigs were fed an isocaloric low protein (LP) pig feed containing 4% protein 2 weeks prior to and 16 weeks after renal or sham-irradiation. The pigs then received the SD for a further 4 weeks. Both kidneys of seven pigs fed the LP diet, and six pigs fed the SD, were irradiated with a single dose of 9.8 Gy of 60Co gamma-rays. The remaining pigs received sham-irradiation. The individual kidney glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and the haematocrit were serially measured before and up to 20 weeks after irradiation. The radiation-induced reduction in mean individual kidney GFR, expressed as either absolute values or as a percentage of the respective sham-irradiated controls, was significantly greater in pigs fed the SD compared with pigs fed the LP diet (p < 0.05). In contrast, the radiation-induced reduction in mean individual kidney ERPF, expressed as absolute values, observed in pigs fed the SD was not significantly different from that seen in pigs fed the LP diet. However, if these data were expressed as a percentage of the respective sham-irradiated controls, then a significantly greater reduction in ERPF was seen in pigs fed the SD compared with pigs fed the LP diet (p < 0.001). Morphological analysis of renal tissue removed 20 weeks after irradiation showed that the extent and severity of the glomerular lesions seen in pigs fed the SD were significantly reduced in pigs fed the LP diet. Thus dietary protein restriction appears to reduce some of the signs of radiation nephropathy in the pig.

Positron emission tomography: a new method for determination of renal function

Positron emission tomography (PET) is a newly evolving diagnostic modality that has been widely used in many facets of clinical medicine, but whose use in the diagnosis and management of disorders of the kidney has not been previously described. Employing the radiotracer N-13 ammonia, flow-dependent extraction of this compound after intravenous injection was used to measure renal blood flow (RBF) in a swine model (N = 10). A mean baseline value of 3.16 ml./min./gm. kidney was obtained with this method, in close agreement with values previously reported using established invasive techniques. Four conditions known to affect RBF were also studied to determine the ability of PET to detect changes in RBF. Kidneys were subjected to varying durations of warm ischemia, demonstrating a progressive decrease in RBF with increasing ischemic insult, with return to normal significantly impaired in animals exposed to the greatest degree of ischemia (180 minutes versus 150 or 120 minutes ischemia). Cross-transplant between animals produced acute allograft rejection and a corresponding marked decrease in RBF that failed to normalize. After unilateral nephrectomy, RBF increased two-fold in the remaining kidney by 7 days (R = 0.79), as predicted for compensatory renal hypertrophy. Lastly, there was an inverse, linear relationship between toxic cyclosporine level and RBF (R = 0.68), indicative of vascular-mediated cyclosporine nephrotoxicity. Positron emission tomography is safe and efficient, and yields an accurate measurement of RBF in several important physiologic states. The development of PET as a quantitative measure of renal function is promising.

Resistance and pulsatility Doppler indices: how accurately do they reflect changes in renal vascular resistance

Doppler indices such as the resistance (RI) and pulsatility indices (PI) are generally thought to indicate the resistance of the vascular bed supplied by the artery under investigation. However, this association remains uncertain; some studies have demonstrated an excellent correlation between alterations in vascular resistance and changes in Doppler indices, while others have shown no consistent change. In order to assess the validity of these two indices in estimating alterations in renal vascular resistance, 12 female Large White pigs, 45 weeks old, were entered into a double blind study. In nine of the pigs both kidneys received a single dose of 9.8 Gy 60Co gamma-rays; the remaining three served as sham-irradiated controls. Renal haemodynamics were measured using 131I-hippuran renography and Duplex Doppler prior to and at 8, and 12 weeks after kidney (sham-)irradiation. The sham-irradiated animals exhibited no significant changes in any of the parameters. In contrast, the animals in which both kidneys were irradiated exhibited a significant decrease (p < 0.001) in renal blood flow (RBF) 8 and 12 weeks after irradiation. In addition, both PI and RI were increased following kidney irradiation; however, this increase was not significant until 12 weeks after irradiation (p < 0.01). This suggests that the reduction in RBF was not simply a reflection of an increased vascular resistance and/or that PI and RI do not truly represent alterations in vascular resistance. Further studies are required to confirm the applicability of PI and RI in the assessment of renal haemodynamics.

Functional changes in the pig kidney following irradiation with fractionated doses of fast neutrons (42 MeVd-->Be)

The right kidney of female Large White pigs, approximately 14 weeks old, was irradiated with fractionated doses of fast neutrons (42 MeVd-->Be). The total doses used were 6.6-9.2 Gy. Changes in kidney function, assessed as the functional index (FI, where FI = irradiated kidney function/unirradiated kidney function) or as individual kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF), were serially determined up to 104 weeks after irradiation using 99Tcm-DTPA and 131I-hippuran renography. The animals were then euthanized, the kidneys removed and weighed. A dose-dependent reduction in FI was seen within 13 weeks of irradiation. Measuring individual kidney function revealed a hyperaemic response in both irradiated and unirradiated kidney 4 weeks after irradiation. This was followed by a dose-dependent reduction in irradiated kidney GFR and particularly ERPF. The ED50 value for the impairment in ERPF, assessed as the percentage of irradiated kidneys exhibiting a > or = 50% reduction in ERPF, was significantly lower than that for GFR, i.e. 7.20 +/- 0.10 Gy compared with 8.44 +/- 0.07 Gy (p < 0.001). A dose-related reduction in irradiated kidney weight was also observed. These fast neutron-induced changes in renal function and weight are qualitatively similar to those observed following photon irradiation of the pig kidney.

Long-term studies of cisplatin-induced reductions in porcine renal functional reserve

Mature Large White female pigs aged approx. 10 months received single intravenous doses of 1.5, 2, or 2.5 mg/kg cisplatin. The glomerular filtration rate (GFR) and the effective renal plasma flow (ERPF) in individual kidneys were measured prior to and at 4-week intervals for up to 24 weeks after cisplatin administration by renography using [99mTc]-diethylenetriamminepentaacetic acid (DTPA) and iodohippurate sodium I 131, respectively. The left kidney of each cisplatin-treated pig and that of three age-matched control pigs was then removed, and GFR and ERPF values were measured in the remaining kidney at 4-week intervals for a further 24 weeks after unilateral nephrectomy (UN). Pigs treated with cisplatin showed no significant reduction in GFR or ERPF for up to 24 weeks after drug infusion. As measured using inductively coupled plasma mass spectrometry, the mean renal platinum concentration in the left kidney removed at UN was 77.5 +/- 9.1 ng/g kidney per mg/kg cisplatin. Histological evaluation of these kidneys revealed narrow interconnecting rays of interstitial fibrosis in the deep cortex and medulla; in these areas, glomeruli exhibited thickened Bowman's capsules and occasionally shrunken sclerotic capillaries. In cisplatin-treated pigs, UN was associated with a marked reduction in the ability of the remaining kidney to increase its function in terms of GFR and, to a lesser extent, of ERPF. The increase seen in GFR following UN in the cisplatin-treated pigs was only ca. 50%-70% of that seen in age-matched UN controls. Histologically, these kidneys revealed resolution of the peritubular fibrosis observed at UN; occasional sclerotic glomeruli were also evident. Platinum remained detectable in these kidneys, the mean levels being 18.8 +/- 4.9 ng/g kidney per mg/kg cisplatin. These findings confirm previous observations and illustrate the need for caution in considering further treatment of patients who have previously received cisplatin along with a second potentially nephrotoxic agent.

The effect of unilateral nephrectomy on the subsequent radiation response of the pig kidney

The left kidney of 14 Large White female pigs, approximately 14 weeks of age, was surgically removed. Thirty weeks after unilateral nephrectomy (UN) the remaining kidney was irradiated with a single dose of between 11.9 and 15.6 Gy of 60Co gamma-rays; three pigs received sham irradiation. Following irradiation glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and haematocrit (Hct) were determined for up to 48 weeks after irradiation. Irradiation resulted in a dose-dependent decline in GFR, evident 8 weeks after irradiation. This was followed by a gradual improvement in GFR, although after doses of 14.0 Gy GFR remained below control values throughout the study. A similar pattern of response was seen in terms of ERPF, but this was not dose-related. Doses of greater than or equal to 14.0 Gy also caused a significant reduction (p less than 0.001) in Hct within 4-8 weeks. Minimal levels were evident 16 weeks after irradiation; Hct then increased, but remained below preirradiation values. Dose-effect curves were obtained by determining the percentage of irradiated kidneys which showed a greater than or equal to 50% reduction in GFR and ERPF, fitted by probit analysis, and ED50 values (+/- SE) were calculated for each parameter. The ED50 values for GFR and ERPF were 14.49 +/- 0.27 Gy and 12.56 +/- 0.98 Gy, respectively. These values were not significantly different from those obtained from intact age-matched pigs in which the right kidney alone was irradiated; UN did not compromise or alter the radiation response of the kidney to irradiation. However, the ED50 values obtained for the UN pigs were significantly greater (p less than 0.001) than the values of 9.76 +/- 0.17 Gy and 6.19 +/- 0.93 Gy, seen for GFR and ERPF in intact age-matched pigs in which both kidneys were irradiated. Thus although both experimental situations involved irradiating the entire renal tissue, the relative radiosensitivity of the kidneys varied considerably. These findings show that the radiosensitivity of the pig kidney can vary markedly, depending on the physiological status of the kidney at the time of irradiation.

The effect of acetaminophen on pig kidneys with a 2-bromoethanamine-induced papillary necrosis

Large White pigs were used to investigate the effects of acetaminophen (paracetamol) on normal kidneys or those with an existing renal papillary necrosis. Pairs of young female animals were treated with either a single iv dose of 50 mg/kg 2-bromoethanamine (BEA), 100 mg/kg/day acetaminophen po for 28 days, or a combination of BEA followed by the acetaminophen treatment. Two pigs served as untreated controls. Kidney length, diameter and parenchymal thickness were measured by ultrasound scans, and glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) assessed by 99mTc-DTPA and 131I-hippuran renography prior to treatment and on day 26. Acetaminophen only caused no renal pathology. Despite the lack of a gross RPN, hyperplasia of the pelvic and ureteric urothelia (with extensive vacuolation) was observed following BEA, but BEA followed by acetaminophen for 28 days did not enhance the lesion. The BEA and BEA-acetaminophen groups (but not acetaminophen only) showed an increased ERPF compared with age-matched controls, but there was no significant difference in the overall GFR between the groups.

Cisplatin-induced reductions in renal functional reserve uncovered by unilateral nephrectomy: an experimental study in the pig

Groups of mature Large White female pigs, approximately 10 months of age, received single intravenous infusions of 1.5, 2 or 2.5 mg/kg body weight (equivalent to approximately 90, approximately 120 and approximately 150 mg/m2) cisplatin. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured before and at 4 weeks after cisplatin infusion by renography using [99 mTc]-DTPA (diethylenetriamminepentaacetic acid and iodohippurate sodium I 131, respectively. The left kidney of each cisplatin-treated animal plus that of four age-matched control pigs was then removed surgically, and GFR and ERPF were measured in the remaining kidney at 4 weekly intervals for up to 24 weeks after unilateral nephrectomy (UN). The pigs treated with cisplatin exhibited no consistent change in either GFR or ERPF at 4 weeks after treatment. A histological evaluation of kidneys from animals treated with greater than or equal to 2 mg/kg cisplatin that had been removed at UN revealed both tubular and glomerular lesions. The latter consisted of cell proliferation on the parietal surface of the urinary space; damage to the S1 portion of the proximal convolution was also noted. Following UN there was a pronounced dose-dependent reduction in the functional status of the remaining kidney such that the increase in GFR and ERPF in pigs initially receiving 2.5 mg/kg cisplatin was less than 50% of that seen in age-matched UN controls. Moreover, the glomerular lesions observed at 4 weeks after cisplatin infusion had apparently progressed to glomerular hyalinisation by 24 weeks after UN. Thus, prior treatment with cisplatin may cause a permanent reduction in renal functional reserve that may be clinically "silent" until exposure to an additional nephrotoxic insult.

The effect of age and the proportion of renal tissue irradiated on the apparent radiosensitivity of the pig kidney

In 14-week-old (immature) and 45-week-old (mature) pigs either the right kidney (unilateral irradiation, UI) or both kidneys (bilateral irradiation, BI) were irradiated. The kidneys of immature pigs received single doses of 7.0-12.6 Gy of 250 kV X-rays; mature pigs received single doses of 7.8-14.0 Gy of 60Co gamma-rays. These were assumed to be approximately equivalent to the X-ray doses using a RBE of 0.9 gamma-rays/X-rays. The glomerular filtration rates (GFR) and effective renal plasma flows (ERPF), were determined for up to 24 weeks after irradiation. From these data dose-effect curves were obtained by determining, at each dose level, the percentage of irradiated kidneys which exhibited a greater than or equal to 50 per cent reduction in GFR and ERPF. 60Co gamma-ray doses were normalised to approximately equivalent X-ray doses. The dose-effect curves were fitted by probit analysis, and ED50 values (+/- SE) calculated for both GFR and ERPF. Similar conclusions could be drawn from the results obtained following the determination of both GFR and ERPF. However, the ED50 values obtained for ERPF were significantly lower than those for GFR (p less than 0.05). In 14-week-old animals the kidney of UI animals was significantly more radiosensitive than that of BI animals, i.e. the ED50 values, in terms of GFR, were 8.74 +/- 0.31 Gy and 10.97 +/- 0.23 Gy, respectively (p less than 0.001). In 45-week-old pigs the reverse was true; the ED50 values were 12.67 +/- 0.34 Gy and 8.78 +/- 0.15 Gy (p less than 0.001) for unilateral- or bilateral-irradiated animals, respectively. The kidney of BI mature animals appeared to be as radiosensitive as the UI immature pigs. Thus the renal response to radiation was markedly influenced by the age of the animals and by the proportion of the renal tissue irradiated.

Radiation nephropathy in mature pigs following the irradiation of both kidneys

Both kidneys in mature female Large White pigs, ca. 45 weeks old were irradiated with single doses of 7.8-14.0 Gy of 60Co gamma-rays. Radiation-induced changes in renal function were assessed on the basis of sequential individual measurements of kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) for up to 24 weeks after irradiation. At the same time intervals blood samples were taken to determine plasma renin levels and the haematological status of each animal. Two weeks after irradiation the ERPF and in particular the GFR was increased. This was followed by a pronounced, dose-dependent, decline in renal haemodynamics. Minimal functional levels were observed 8-12 weeks after irradiation. Function then somewhat recovered. There was a significant (r greater than or equal to 0.98; p less than 0.001) inverse relationship between the mean values of GFR and ERPF, determined at 4-24 weeks after irradiation, and the radiation dose. After a dose of 7.8 Gy the reduction in ERPF was greater than that for GFR. However, at higher doses both parameters were reduced to an equal extent. The resulting slope of the dose-effect curve for impaired renal function versus dose was significantly steeper for GFR than that for ERPF (p less than 0.001). There was a significant reduction (p less than 0.002) in the erythrocyte count, the haematocrit and haemoglobin levels within 6-8 weeks of irradiation; this anaemia was characterized as a normochromic normocytic anaemia. There were no marked changes in plasma renin levels as a result of renal irradiation. The pathogenesis of late radiation-induced damage to the kidney is discussed in the light of these findings.

Nephropathy in the mature pig after the irradiation of a single kidney: a comparison with the immature pig

The right kidney of 11 mature 10-month-old Large White female pigs was irradiated with single doses of 9.8-14.0 Gy of 60Co gamma rays. Individual kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured using 99mTc-DTPA and 131I-hippuran renography for periods up to 24 weeks after irradiation. Renal function was assessed either as a functional index, FI (FI = irradiated/unirradiated kidney function), or as the individual kidney GFR and ERPF. The radiation-induced changes after the irradiation of a single kidney (unilaterally irradiated--UI) of mature pigs were compared with those previously observed in 14-week-old immature pigs. Irradiation resulted in a dose-dependent reduction in the FI for both GFR and ERPF. However, these reductions were significantly less than those previously seen in immature pigs. Within 2 weeks of irradiation GFR increased in both the irradiated and the unirradiated kidneys in each animal, compared with unirradiated age-matched control kidneys. No marked changes in renal hemodynamics were seen in mature animals after a single dose of 9.8 Gy. This was in marked contrast to the pronounced reduction in the GFR and ERPF in the irradiated kidney previously observed in immature animals irradiated with an equivalent single dose of X rays. After higher doses, the irradiated kidney in mature pigs showed a dose-dependent reduction in GFR and ERPF. However, the extent of this reduction was significantly less than that seen in immature animals. There was no apparent difference in the response of the unirradiated kidneys in mature or immature pigs. The ED50 values, based on a probit fit to the data for the proportion of functional tests in which the irradiated kidney showed a greater than or equal to 50% reduction in GFR or ERPF, were higher in the mature animals; for example for ERPF the ED50 values were 11.76 +/- 0.28 Gy and 7.67 +/- 0.34 Gy for mature and immature animals, respectively. Thus, the UI kidney in mature pigs appears to be less radiosensitive than the UI kidney in immature animals.

Evaluation of Tc-99m-DTPA for renal clearance studies in the pig

Conventional creatinine clearance studies in the pig are complicated by difficulties with catheterisation, infection, accurate collection and active creatinine renal tubular reabsorption. We compared a single injection, 99mTc-DTPA elimination method with creatinine clearance. Nineteen pairs of GFR estimations were performed in 10 pigs: 7 in normal pigs and 12 following bile duct ligation and/or nephrectomy. Red cell and plasma protein binding of the isotope and its hepatobiliary excretion was assessed. Absolute and weight normalised endogenous creatinine clearances correlated significantly with 99mTc-DTPA elimination. 99mTc-DTPA red cell binding and hepatobiliary excretion were negligible. Thus, 99mTc-DTPA elimination is a valid indicator of changes in renal function in grouped porcine studies, particularly in the biliary obstruction model. However, isotope plasma protein binding was high in the 2 normal pigs assessed. Individual accuracy would be improved by routine protein binding correction, unless consistently low for a particular preparation.

Functional recovery in the irradiated kidney following removal of the contralateral unirradiated kidney

The right kidneys of seven Large White female pigs, approximately 14 weeks of age, were irradiated with single doses of 7-12.6 Gy of 250 kV X-rays. Sequential measurements of individual kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were carried out using 99mTc-DTPA and [131I]hippuran renography for time periods up to 24 weeks after irradiation. From this data, kidneys receiving a dose of 7 Gy were found to be functioning (F), while kidneys which received greater than or equal to 8.8 Gy were assessed as having no significant function (NF). When the pigs were approximately 10 months of age the contralateral unirradiated kidney was removed; the left kidney of three age-matched unirradiated pigs was also removed. The response of the right kidney to unilateral nephrectomy (UN) in these animals was assessed in terms of changes in haemodynamics (i.e. GFR and ERPF) for periods up to 24 weeks after UN. At post-mortem, the length and weight of the remaining kidney was measured. A marked increase in renal length was observed in irradiated kidneys following UN. In addition, the weights of irradiated kidneys following UN were greater than those of irradiated kidneys in age-matched pigs where the unirradiated kidney had not been removed. Four weeks after UN there was a pronounced increase in GFR and, in particular, ERPF in previously NF irradiated kidneys. The mean increase in these parameters, measured at the end of the follow-up period, when compared with the pre-surgery values, was 350.1 +/- 84.3 and 781.8 +/- 151.0% respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of single doses of X-rays on renal function in unilaterally irradiated pigs

The right kidney of 13 Large White female pigs was irradiated with single doses of 250 kV X-rays in the range 7-12.6 Gy. Sequential measurements of individual kidney glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were carried out by means of 99mTc-DTPA and 131I-hippuran renography for periods up to 24 weeks after irradiation. GFR levels increased in irradiated and unirradiated contralateral kidneys 2 weeks after treatment compared with age-matched controls. ERPF values exhibited a small increase in a proportion of animals. Renal function then declined in irradiated kidneys in a dose-dependent manner. A dose of 7 Gy resulted in a decline followed by subsequent recovery. After doses of greater than or equal to 8.8 Gy GFR and ERPF declined rapidly, reaching minimal levels by 6-12 weeks, the time depending on the dose. The reduction in ERPF was quantitatively greater than that for GFR. In animals receiving greater than 8.8 Gy the irradiated kidney contributed in the order of only 10% of the total ERPF. The reduction in GFR resulted in a prompt functional compensatory response in GFR in the unirradiated contralateral kidney. In terms of ERPF, a compensatory response was not evident until weeks 20-24. The results indicated that the radiation tolerance dose of the pig kidney following unilateral irradiation with single doses of X-rays was approximately 8 Gy.

Techniques for the quantitative measurement of individual kidney function in the pig

A prerequisite for elucidating the effect of radiation on porcine renal function is the development of non-invasive methods for accurate quantification of unilateral glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). The techniques presented here are (a) measurement of unilateral kidney filtration fraction (FF) determined by analysis of the early rise of the kidney's time-activity curves following the injection of tubular ([131I]hippuran) and glomerular ([99mTc]DTPA) tracers, and (b) deconvolution of the respective renogram. Unilateral FF values are obtained by calculating the ratio of glomerular to tubular clearances. Results for 23 female large white pigs indicate a highly significant correlation (r = 0.91, P less than 0.001) between computed FF values and those obtained from the plasma disappearance curves of [99mTc]DTPA and [131I]hippuran. Deconvolution of the renogram allows estimation of the mean transit time (MTT) for [99mTc]DTPA and [131I]hippuran, these are 6.94 +/- 1.87 and 6.86 +/- 1.44 min respectively. In addition, FF values calculated from the H0 values are significantly correlated (r = 0.7, P less than 0.05) with estimates from plasma disappearance curves of the tracers. Therefore these techniques appear to provide accurate non-invasive methods for determining individual porcine kidney function.