Assessment of Systemic Effects of  Non-ionic and Ionic Contrast Agents Following Intravenous Urography in Healthy Dogs

Canine urolithiasis is a condition of urinary system requiring emergency attention with a rapid definitive diagnosis for immediate surgical and medical therapy. In dogs, urocystoliths are difficult to palpate with no significant findings on physical examination unless the urethral passage is partially or completely obstructed. Complete blood cell count (CBC) and serum biochemical analysis are usually normal and the clinical signs are not definitive. Survey radiography is the initial step in the sequential evaluation of the urinary system problems. But it provides insufficient information regarding upper urinary tract disorders due to lack of contrast between organs. So, contrast radiography was necessary to overcome the inherent limitations of survey radiography to identify non-radiopaque uroliths and free or attached soft tissue filling defects (Fromsa and Saini, 2019). Intravenous urography was a contrast radiographic enhanced procedure that substantially improved the visualization of the renal parenchyma, pelvis, ureter as well as urinary bladder (Sharma et al., 2015) which were detected by obtaining a timed series of abdomen and pelvis imaging after intravenous injection of positive contrast agent i.e. water soluble iodinated contrast agent which were excreted from kidney to the urinary tract. In intravenous urography, the contrast agent is injected into convenient vein and a series of radiograph are taken. Thus, kidneys, ureters and urinary bladder are visualized by excretion of urine containing the contrast agents and provides information about functional and anatomical status of urinary system which includes morphometric measurement, shape, size, location of both kidneys, patency of ureters and filling defects of urinary bladder. The iodinated contrast agents used in diagnostic imaging are ionic (sodium and meglumine diatrizoate; Sodium and meglumine iothalamate) and non-ionic (iohexol and iopamidol) agents. Both these agent are same except that non-ionic do not dissociate in a solution and therefore have less osmotic pressure. The difference in the osmolarity of the contrast media has non-significant effect on the contrast study in most organs because the changes in iodine concentration in these organs are influenced mainly by tissue blood flow. On the other hand, in kidney, which consisted of blood vessels and renal tubules, the contrast effects were influenced by the osmolarity of the media because changes in iodine concentration were influenced by both renal blood flow and excretion of iodine to tubules (Kishimoto et al., 2007). The contrast substance can penetrate in the renal pelvis, which allowed assessing its shape, size and integrity. Urinary excretion of the contrast agent ensured a verification of the urinary tract functionality regarding the propagation, permeability, filling and evacuation of the urinary bladder (Ghergariu et al., 2018). Although intravenous urography was not a quantitative measurement of renal function, it can be used to assess the relative function of kidney, ureter and urinary bladder. In addition, the information gained can sometimes be used to assess the pathophysiologic mechanisms of renal failure (Heuter, 2005). Various workers have compared different contrast media at different dose rates for intravenous urography as dose of contrast agent plays an important role in density of urogram. Increasing the dose of contrast agent, to a certain limit, increases the density and thus visualization of urinary system. Therefore, Kirberger et al., (2012) evaluated the effects of repeated intravenous iohexol @ 1290 mgI/kg on renal function in healthy five Beagle dogs and reported that there was non-significant effects of repeated administration of contrast medium. Similarly, Sharma et al., (2015) had also used ionic and non-ionic contrast agent @ 600 mgI/kg body weight respectively for obtaining urogram of correct density in dogs while Gowtham, (2017) injected iohexol @800 mgI/kg intravenously in 8 healthy dogs and documented non-significant variation in haemato-biochemical and urine parameters. Because of high atomic number, iodine was toxic in different degree in different forms. Moga et al., (1972) reported that both Conray-420 and Diaginol were toxic to renal system after estimation of blood urea nitrogen and urine analysis but the toxicity was non-clinical and within tolerable limits. Almen, (1969) postulated that toxicity of contrast agent was not due to its chemotoxicity but due to hypertonicity of the solution. However, the information regarding systemic effect of iodinated non-ionic and ionic positive contrast agent is limited in veterinary practice. Therefore, the aim of present investigation was to compare the systemic effect of non-ionic and ionic contrast agent @ 1100 Img/kg in terms of physiological, haemato-biochemical and urine analysis parameters in dogs.

The present study was conducted during January 2020 to December 2020 on 12 apparently healthy adult dogs presented for routine health check up and vaccination to the Department of Veterinary Surgery and Radiology and Teaching Veterinary Clinical Complex, College of Veterinary Science and A.H. Anjora, Durg (C.G.). Institutional Animal Ethical Committee’s approval was obtained before undertaking study.
 
Experimental design
 
Twelve dogs were randomly divided into two groups I and II, consisting 6 animals of either sex in each. The animals of group I underwent intravenous urography with non-ionic low osmolar agent (Iohexol) @ 1100 mg I/kg body weight while animals of group II received ionic high osmolar agent (sodium and meglumine diatrizoate) @ 1100 mg I/kg body weight. For intravenous urography study, the dogs were kept off fed for 12 hours before the commencement of the radiography. Free accesses to water were allowed before the study. Laxative, Bisacodyl (Dulcolax^®) 2 ml were given to each dog of both the groups, a day before the study. Prior to administration of contrast agents, chlorpheniramine maleate @ 1 mg/kg body wt. intramuscularly was administered to animals of group I and group II. Thereafter, intravenous urography was done under general anaesthesia using atropine sulphate @ 0.04 mg/kg body wt., xylazine hydrochloride @ 1 mg/kg body wt. and ketamine hydrochloride @ 15 mg/kg body wt. administered intramuscularly followed by maintenance with xylazine and ketamine at dose @ of 1 mg: 2 mg intravenously. Before administration of contrast agents two abdominal survey radiographs (ventro-dorsal and right lateral) were taken. The animal was restrained in dorsal recumbency on X-ray table just under the x-ray tube. Cephalic vein of animal was catheterized for administration of contrast agent. Contrast agents (ionic and non-ionic) @ 1100 mg Iodine/kg body wt. were diluted with an equal amount of 5% dextrose saline solution and infused intravenously over a period of 10-15 minutes without abdominal compression. Care was taken that dose should not exceed 35 gm of iodine (Kealy et al., 2011).
 
Physiological parameters
 
Rectal temperature (^oF), Heart rate (beats/minute) and Respiration rate (breaths per minute) were recorded before (0 hr) and at 1 hr, 6 hr and 24 hrs interval after administration of contrast agents.
 
Haemato-biochemical parameters
 
About 1 ml and 2 ml blood was collected from cephalic or saphenous vein in EDTA coated vial and sterile vial for estimation of haematological and biochemical parameters respectively. Blood collection was done before (0 hr) and after administration of contrast agent at 1, 6 and 24 hr intervals. Haemoglobin (gm/dl), Packed Cell Volume (%), Total Erythrocyte Count (10⁶ /mm³), Total Leukocyte Count (10³ /mm³) were analyzed using automated haematology blood cell counter. Differential leucocyte count (DLC) was done manually by blood smear prepared immediately after blood collection and stained with Leishman stain. The count was expressed in percentage. Serum was separated for the estimation of Serum glucose (mg/dl), Total serum proteins (gm/dl), Serum urea nitrogen (mg/dl), Serum creatinine (mg/dl), Aspartate aminotransferase (U/L), Alanine aminotransferase (U/L) and Alkaline phosphatase (U/L) using semi-automated biochemistry analyzer.
 
Urine analysis
 
For urine examination, 5 ml of urine was collected aseptically in a sterile tube by urinary catheterization before and after administration of contrast agents at 6 and 24 hour interval. Urine was analyzed for Color, Clarity, Sediments (centrifugation), pH, Specific gravity and Glucose using Mission Urinalysis Regent Strips.
 
Statistical analysis
 
The mean and standard error of the recorded values were calculated. Paired t-test was used to compare the mean values at different intervals with base value in each group as outlined by Snedecor and Cochran, (1994) and statistical calculation was done using SPSS 17.0 statistical software at 95% confidence.

Physiological parameters
 
Non-significant changes in rectal temperature, heart rate and respiratory rate were noticed throughout the observation period after contrast administration in animals of group I and II (Fig 1, 2, 3) and the mean values remained within the normal physiological range. There was marginal non-significant increase in heart rate and respiratory rate at 1 hour following administration of contrast agents in both the groups and there after returned near normalcy at 24 hour interval. Similar observations had been observed by Sharma et al., (2015) and Gowtham, (2017) after administration of contrast agents in dogs. On the other hand, Ganesh, (1995) recorded decrease in temperature after 5 minutes of iohexol @ 1000 mgI/kg administration which might be due to effect of contrast media on the pyelo motor mechanism. Iohexol causes tachycardia which could be attributed to generalized vasodilatation and subsequent hypotension involving reflex tachycardia as reported by Ganesh, (1995) and also documented that sodium diatrizoate caused bradycardia at 5 minutes after administration due to the presence of sodium cations in urografin 76% and its effect was reversed after 30 minutes following injection of dye. Marginal increase in respiration rate after 5 minutes of administration of both sodium diatrizoate (600 mgI/kg;1000 mgI/kg) and iohexol (600 mg I/kg;1000 mgI/kg) contrast media might be due to iodine particles present in the contrast media which had influenced the hypothalamic reaction and chemoreceptor of respiratory centre resulting in increased respiratory rate (Ganesh, 1995).



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Haematological parameters
 
In animals of group I and II, mean haemoglobin, packed cell volume (%), total erythrocyte count (TEC) and TLC showed non-significant decrease at 1 hr following a marginal increase up to 24 hr (Table 1) However, these values remained within normal physiological range in both the groups. There was non-significant reduction in haemoglobin value in both groups which might be due to hypervolaemia caused by haemodilution by contrast administration. This resulted in fluid shift from extravascular to intravascular compartments within a short period after the administration (Ganesh, 1995). The decrease in PCV might be attributed to haemodilution produced by both contrast agents. Haemoglobin, Packed cell volume (PCV %), TEC and TLC values showed non-significant difference between groups at various time intervals. To its contrary, Sharma et al., (2015) observed significant (p<0.05) decline in mean haemolglobin, packed cell volume and TEC at 1 hr after urografin administration. Intravenous administration of contrast agents produced transient hypervolemia because water was rapidly transported from the extravascular compartment to the circulation and caused marked fall in haematocrit (Sharma et al., 2015). The non-significant decrease in TEC and TLC might be due to more fluid in the blood volume caused by the shift of fluid from the extravascular to intravascular compartments after contrast administration. Similar pattern of non-significant decrease in TEC was seen in group II which resulted due to increase in plasma osmolality because of  intravenous injection of ionic contrast agents which was five to eight times hypertonic than that of normal body fluid. This caused water to leave the erythrocytes and enter the plasma resulting in shrinkage and deformity of the erythrocytes. These findings were in accordance with Koe and Alkan, (2002) who recorded non-significant (p>0.05) changes in white blood counts in ionic (urografin 76%) and non-ionic (Iopromide) groups 1 hr after injection of media contrast. Similar finding was reported by Gowtham, (2017) after iohexol administration at a dose rate of 800 mgI/kg body weight in both male and female dogs.


         
Neutrophil, lymphocyte and monocyte count showed non-significant decrease at 1 hr in group I and II, which further increased non-significantly at 6 hr and 24 hr following contrast administration and values remains within normal physiological range. Similar observation was reported by Sharma et al., (2015) after iohexol @ 600 mgI/kg body weight and Gowtham, (2017) after iohexol administration @ 800 mgI/ kg body weight. In contrary to our study, Sharma et al., (2015) reported a significant (p<0.05) decline in neutrophils at 1 hr after administration of urografin @ 600 mgI/kg body weight and then a gradual increase in the values was noted. This could be attributed to iodinated contrast agent which increased constitutive and inflammatory neutrophils apoptosis over a period and concentration dependent manner in vitro with ionic contrast media appearing to have a more toxic effect (Fanning et al., 2002). Non-significant decrease in neutrophils was recorded at 1 hr in both the groups which might be due to anaphylactic reaction against contrast agents of both iohexol and urografin. The anaphylaxis reaction resulting due to administration of contrast agent occurred as neutropenia by means of neutrophils sequestration causing a rapid shift to the margin pool. This neutropenia was thought to be the primary cause of the change in the total leucocyte counts (Sharma et al., 2015). Present study revealed a non-significant decrease in eosinophils count at 1 hr in group I which might be due to administration of antihistaminic prior to administration of iohexol. Whereas, animals of group II showed non-significant increase from base value till 24 hr of observation period after urografin administration but the values remained within normal physiological limits. However, Sharma et al., (2015) documented a significant (p<0.05) decrease in eosinophils at 1 hr after injection of iohexol @ 600 mgI/kg and urografin @ 600 mgI/kg body weight in dogs and values gradually increased non-significantly upto 24 hr in both goups. Basophils were not found in group I and II during study period. The observation simulated with the finding of Gowtham, (2017) following iohexol administration @ 800 mgI/kg body weight in both male and female dogs.
 
Biochemical parameters
 
The serum glucose levels fluctuated within normal physiological range without any significant difference within group and between groups at various time intervals (Table 2). Serum glucose levels showed non-significant increase at 1 hr in group I and II after contrast agent administration with a decrease at 6 hr interval thereafter returning to near normalcy at 24 hr of observation period. Similar pattern of alteration in serum glucose levels was observed by Sharma et al., (2015) after injection of iohexol @ 600 mgI/ kg and urografin @ 600 mgI/kg body weight respectively in dogs. This increase in serum glucose level might have resulted due to stress created on the body by contrast agents. In contrary to our study, Ganesh, (1995) reported significant (p<0.05) decrease in blood glucose level at 5 minutes after injection of both sodium diatrizoate (600 mg I/kg; 1000 mgI/kg) and iohexol (600 mg I/kg;1000 mgI/kg) contrast media with gradual increase to reached normal level in 30 minutes due to haemodiltuon caused by the fluid shift from extravascular to intravascular compartments. Following 1 hour of contrast administration, serum urea nitrogen and serum creatinine values showed a significant (p<0.05) increase followed by non-significant decrease till 24 hr of the observation period in both the groups (Table 2). To its contrary, Sharma et al., (2015) documented transient non-significant increase in plasma urea nitrogen at 1 hr after iohexol administration @ 600 mg I/kg body weight due to combination of hypertonicity and direct chemical toxicity to the renal parenchyma. However, a significant (p<0.05) increase in plasma urea nitrogen was recorded at 1 hr interval after urografin administration @ 600 mg I/kg body weight. Similar pattern of variation in creatinine values was also reported by Sharma et al., (2015) after iohexol @ 600 mg I/kg and urografin @ 600 mg I/kg administration in dogs. This might be due to direct effect of parenteral contrast administration leading to sudden and rapid deterioration in renal function that result in kidney failure to excrete nitrogenous waste products and regulating fluid and electrolyte homeostasis. Total serum protein showed non-significant marginal variations during the entire observation periodin both the groups. A non-significant increase of ALT, AST and ALP at 1 hr followed by very marginal decrease at 6 hr and 24 hr intervals after contrast administration in both the groups. The increase in ALT, AST and ALP level following 1 hr of contrast administration in both groups was probably as a result of detoxification in the liver. This finding was similar to Gowtham, (2017) who reported non-significant variation in ALT, AST and ALP of male and female dogs after iohexol administration @ 800 mg I/kg body weight.


 
Urinalysis parameters
 
It was observed that the urine pH and specific gravity did not alter much and remained within normal physiological limits in both groups after administration of non-ionic and ionic contrast agents (Table 3). The above findings were in concurrence with those of Sharma et al., (2015) following administration of iohexol and urografin 76% @ 600 mg I/kg respectively in dogs. Similarly, Gowtham, (2017) reported variation in urine pH from 6.5 to7.5 in male dogs and 6.5 to 8.5 in female dogs while specific gravity between 1.005 to 1.015 in male dogs and 1 to 1.015 in female dogs after iohexol administration. In contrary to our study, Ganesh, (1995) reported significant (p<0.05) decrease in urine specific gravity after 5 minutes of administration of both ionic and non-ionic contrast agent in dogs. Urine glucose was not evident in all the animals of group I and II during observation period at 0, 6 and 24 h after administration of iohexol @ 1100 mg I/ kg and urografin @ 1100 mg I/ kg body weight respectively. This finding suggests that both contrast agents did not caused any systemic effect on urine glucose profile. Ganesh, (1995) observed that glucose was absent in urine in all the animals after administration of both sodium diatrizoate (600 mg I/kg; 1000 mgI/kg) and iohexol (600 mg I/kg; 1000 mgI/kg) contrast agent in dogs. Similar observation was reported by Gowtham, (2017) after iohexol administration @ 800 mg I/kg body weight in both male and female dogs.


 
Physical examination of urine
 
Before administration of contrast agents, the colour of urine was yellow in all the dogs of both the groups except in 1 dog of group I where it was straw coloured (Table 4). Following 6 hr of contrast administration, there was no change in the urine colour in both the groups except in 1 dog of group II were it was straw coloured. At 24 h post contrast administration the urine colour was yellow in both the groups. Similarly, Sharma et al., (2015) reported no change in urine colour in both iohexol and urografin 76% @ 600 mg I/kg group respectively in pre and post contrast urine sample in dogs. Gowtham, (2017) documented similar pattern of change in urine colour after iohexol administration @ 800 mg I/kg body weight in both male and female dogs. The clarity of urine was clear in all the animals of group I and II. Similarly, Gowtham, (2017) reported clear urine in all the dogs of both groups except in 1 male dog (group I) where it was slightly turbid after iohexol administration @ 800 mg I/kg body weight. Absence of sediments in urine was noticed in both group I and II. Sharma et al., (2015) documented light deposition of sediments in both the groups following 1 hr of administration of iohexol and urografin76% @ 600 mg I/ kg body weight respectively in dogs. In accordance to the present study, Gowtham, (2017) also reported absence sediments in urine in all the dogs of both groups except in 1 male dog (group I) where sediment was present after iohexol administration @ 800 mg I/kg body weight.


 
Adverse effects of contrast agents
 
No complication was observed after intravenous urography with non-ionic and ionic contrast agents (iohexol and urografin 76%) @ 1100 mg I/kg body weight in study animals. The contrast agents both non-ionic and ionic were well tolerated by dogs as well as no mortality was reported. The reason might be that before administration of contrast agents, chlorpheniramine maleate was given and both contrast agents were diluted with equal amount of 5% dextrose solution. The care was taken that the dose did not exceed 35 g of iodine. These findings were in accordance with Ganesh, (1995) who observed no post radiographic mortality or morbidity in any of the animals regardless of drugs or dosage. Koe and Alkan, (2002) also reported that dogs did not show any adverse reactions when the ionic (urografin 76%) and non-ionic (ultravist 300) contrast media were administered. 

On the basis of present investigation, it could be concluded that intravenous urography using non-ionic and ionic contrast agents does not produce any adverse reaction or deleterious effect on vital organs. As there were no differences in physiological, haemato-biochemical and urine analysis parameters following intravenous urography by non-ionic and ionic contrast agent in dogs. However, there were transient changes which were well tolerated by dogs and clearly signify regarding the functional status of urinary system and no adverse effects were produced by contrast agents as all parameters remained within physiological limits. Thus, both non-ionic and ionic contrast agents can be safely used for intravenous urography at dose rate of 1100 mgI/kg in canine.

The present study was supported by Dau Shri Vasudev Chandrakar Kamdhenu Vishwavidyalya (DSVCKV), Chhattisgarh.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
All animal procedures for experiments were approved by the Institutional Animal Ethical Committee.

The authors declare that there are no conflict of interest regarding publication of this article.