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Year : 2004  |  Volume : 36  |  Issue : 6  |  Page : 363--368

Effect of nabumetone on the renal function in conscious and anesthetized rats

I Long, GJ Rao, HJ Singh 
 Department of Physiology, School of Medical Sciences, Health Campus, Universiti Sains Malaysia, 16150, Kubang Kerian, Kelantan, Malaysia

Correspondence Address:
G J Rao
Department of Physiology, School of Medical Sciences, Health Campus, Universiti Sains Malaysia, 16150, Kubang Kerian, Kelantan
Malaysia

Abstract

OBJECTIVE: To examine the effect of nabumetone on the renal function in conscious and anesthetized rats. MATERIAL AND METHODS: For the conscious study, rats were housed individually in metabolic chambers for a duration which consisted of acclimatization, control, experimental and a recovery phase comprising 1, 1, 2 and 1 week respectively. During the experimental phase, one group of rats received nabumetone orally and the controls received an equivalent volume of saline. Water and food intake, body weight, urine output, urine osmolality, osmolal output and electrolyte excretions were estimated. In the second study, rats were anesthetized and saline diuresis in these animals was established with an intravenous infusion of 0.9% saline containing 3H-Inulin. Glomerular filtration rate (GFR) was estimated using standard inulin clearance. The study period consisted of equilibration, control, experimental and a recovery phase comprising 2, 1, 1, and 1 hour respectively. During the experimental phase, one group of rats received a bolus dose of nabumetone intravenously and the controls received the vehicle. Blood and urine samples were collected for analysis of electrolytes, microalbuminuria and GFR estimation. Data was analyzed using ANOVA for repeated measurements. RESULTS: In conscious rats, no significant differences were found between the two groups in any of the measured parameters. In anesthetized rats, however, there was a significant but reversible decrease in GFR and sodium excretion in rats receiving nabumetone. CONCLUSION: In contrast to the suggested renal-sparing effects of COX-2 inhibitors, we have observed renal function being affected with nabumetone during anesthetic stress.



How to cite this article:
Long I, Rao G J, Singh H J. Effect of nabumetone on the renal function in conscious and anesthetized rats.Indian J Pharmacol 2004;36:363-368


How to cite this URL:
Long I, Rao G J, Singh H J. Effect of nabumetone on the renal function in conscious and anesthetized rats. Indian J Pharmacol [serial online] 2004 [cited 2021 Oct 24 ];36:363-368
Available from: https://www.ijp-online.com/text.asp?2004/36/6/363/13507


Full Text

 Introduction



Non-steroidal antiinflammatory drugs (NSAIDs) produce deleterious side-effects on renal function, particularly when there is pre-existing renal disease or during hemodynamically stressful situations.[1] These effects have been attributed to the inhibition of prostaglandin synthesis in the kidney by these drugs.[2] When blood volume is compromised or renal blood flow is reduced, prostaglandins play a role in the regulation of renal circulation, renin secretion, and sodium and water excretion.[3] If vasoconstrictive forces stimulated to maintain the filtration fraction during hemodynamically-compromised situations are not balanced by prostaglandin-induced vasodilatation, renal failure may occur. Cyclooxygenase (COX) is a key enzyme regulating the formation of prostaglandins from arachidonic acid. Several years ago, it was reported to have two isoforms, namely, COX-1, the constitutive isoform whose existence was long recognized and COX-2,[4],[5] the inducible isoform. COX-1 is believed to be involved in the production of prostaglandins that help maintain renal function. COX-2, on the other hand, is primarily thought to be involved in the production of prostaglandins during inflammatory processes.[6] These assumptions formed the basis of the "COX hypothesis" which proposes that COX-1-derived prostaglandins are involved in regulating physiological functions, whereas COX-2 derived prostaglandins play a major role during inflammation or tissue damage. Thus, it was assumed that a selective COX-2 inhibition can provide potent therapeutic effects without the side-effects that are observed with the non-selective non-steroidal antiinflammatory drugs (NSAIDs).[7] However, recent reports point to the presence of COX-2 in the macula densa and surrounding cortical cells of the thick ascending limb of the loop of Henle (TALH) of a normal rat,[8] suggesting that it may have a normal physiological role. Furthermore, in the rabbit, COX-2 in TALH epithelial cells in the tubuloglomerular contact region play an important role in the control of renin secretion by macula densa.[9] In fact, COX-2 mRNA and protein expression in the mammalian kidney are among the highest observed in any tissues.[10] COX-1, on the other hand, has been shown to be involved in inflammatory reactions.[11] These observations suggest that COX-1 and COX-2 may not have such clearly demarcated roles as proposed by the "COX-hypothesis" and renal deleterious effects may still be observed with selective COX-2 inhibitors. We therefore examined the effect of nabumetone, a selective COX-2 inhibitor, on renal function in conscious and anesthetized rats.

 Material and Methods



For experiments on conscious rats, male Sprague-Dawley rats weighing between 200-220 g were housed individually in metabolic cages for a total duration of 5 weeks. The animal unit of Health Campus, Universiti Sains Malaysia supplied the rats used in this study. The study protocol consisted of four phases, namely, acclimatization phase (1 week), control phase (1 week), experimental phase (2 weeks) and recovery phase (1 week). All animals were treated identically during the acclimatization, control and the recovery phases. No observations were made during the acclimatization phase where the animals were allowed to acquaint themselves with the metabolic cages. During the experimental phase, however, the animals in the nabumetone group (n=10) were given 15 mg/kg/day of nabumetone dissolved in 0.5 ml of saline via the oral route. The dose that was administered is equivalent to the maximum therapeutic dose used in humans. Animals in the control group (n=10) received only 0.5 ml of saline orally. Food and water intake, body weight, urine output, urine osmolality, urinary osmolal output, urinary excretions of sodium, potassium, magnesium, calcium and microalbumin were estimated in all animals over 24 h on alternate days during the control, experimental and recovery phases.

For experiments on anesthetized animals, male Sprague-Dawley rats weighing between 230-260 g, fasted overnight but with access to water ad libitum, were prepared for standard inulin clearance experiments.[12] Following anesthetization with an intraperitoneal injection of sodium thiopental (60 mg/kg, body weight), the jugular vein and carotid artery were cannulated for continuous normal saline infusion, and blood pressure monitoring and blood sampling respectively. Tracheostomy was performed to maintain a clear airway. The urinary bladder was catheterized suprapubically for urine collection. Animals were infused intravenously with 0.9% saline, containing 3H Inulin (0.5 ÁCi ml-1, Amersham, UK), at a rate of 200 Ál min-1 for the first hour to induce rapid volume expansion and diuresis. The infusion rate was then reduced to 100 Ál min-1 of 0.9% saline containing 3H Inulin (1 ÁCi ml-1) for the next five hours. The five hours were divided into four phases, namely equilibration phase (1 h), control phase (1 h) experimental phase (1 h), and recovery phase (2 h). There were two groups of rats, the experimental group (n=8), which consisted of animals receiving nabumetone intravenously (5 mg/kg body weight) at a rate of 100 Ál min-1 during the experimental phase (one hour), and the control group (n=8), which consisted of animals receiving the vehicle (0.1 ml acetone) during the same period.

Blood and urine samples were collected every 30 min for analyses of urinary osmolality, urinary osmolal output, urinary microalbumin and glomerular filtration rate (GFR) estimation. Urinary sodium and potassium concentrations were analyzed using a flame photometer (Corning 404, UK), urinary magnesium and calcium concentrations were analyzed using ion selective electrodes (Hitachi-912), urinary osmolality was estimated by the freezing point depression (Osmomat 030, Gonotec, Germany) and urinary microalbumin was estimated using a commercially available kit for human urinary microalbumin (SERA-PAK, Bayer, USA).

Statistical analysis was performed using two-way ANOVA for repeated measurements and Tukey Post Hoc for multiple comparisons to locate the differences when ANOVA revealed a significant effect. All results were presented as mean ▒ SEM and a P' Value of 0.05 or less considered as significant. The Universiti Sains Malaysia Ethics Committee approved the study protocol.

 Results



Food intake, water intake and body weight were measured every two days. As there were no significant differences between the values in each rat in each phase, the values for each phase for each rat were averaged and the average was then used to calculate the group mean. No significant differences were evident in food and water intake when the three phases in each group were compared or when the corresponding phases of the two groups were compared ([Table:1]). Body weight increased significantly in both the groups over the period of the study, but no significant differences were evident in the rate of increase in body weight between the two groups.

Urinary parameters (urine output, sodium output, potassium output, calcium output, magnesium output, urine osmolality, osmolal output and microalbuminuria) were measured every two days. As there were no significant changes over time between the values during each phase, the values for each rat in each phase were averaged and the average was then used to calculate the group mean ([Table:2]). No statistically significant differences were evident in any of the measured urinary parameters between the three phases in each group or between the corresponding phases of the two groups.

In anesthetized rats, no significant differences were observed in the urine flow rate, osmolal output and microalbuminuria over the duration of the study in both the groups or between the two groups when the corresponding periods in the three phases were compared ([Table:3]). Calcium, magnesium and potassium excretions were found to decrease significantly with time in both the groups (PPP-1, urine output averaged between 75-85 lmin-1 in all the rats. This inability of the anesthetized animal to excrete completely the infused saline load has been reported before and the reason for this is not clearly established.[19] Administration of nabumetone intravenously to anesthetized rats significantly decreased GFR and sodium excretion, albeit transiently [Figure:1] and [Figure:2]. Both GFR and sodium excretion decreased immediately after the infusion of nabumetone. During the first half hour of the recovery phase, GFR and sodium excretion were significantly lower (Pin vivo. The reason for this discrepancy is unclear but it may reflect the severity of the procedures involved and possibly the role of some extra-renal mechanisms in the maintenance of renal function. The precise mechanism responsible for the fall in GFR following nabumetone infusion is unclear. The stress of anesthesia and surgery increases renal sympathetic activity and causes vasoconstriction in the kidney, thereby decreasing renal blood flow and consequently GFR. Normally, in the absence of COX inhibitors, prostaglandin-induced vasodilatation would have opposed the vasoconstrictor effects of the renal sympathetic nervous system[4] and attenuated the vasoconstrictor responses to norepinephrine.[3]

Recent evidence suggests that noradrenalin enhances the production of COX-2 derived metabolites, which then play an important role in modulating the renal vasoconstriction elicited by noradrenaline.[22] In the presence of nabumetone, this balance between the vasoconstrictor and vasodilators forces could have been disturbed and GFR decreased. The fall in sodium excretion was even more significant given the fact that approximately 150 mol min-[1] was continuously infused throughout the period of study. Two possible mechanisms could also explain the decreased sodium excretion evident with nabumetone infusion. The first is associated with decreased GFR, where a decrease in GFR would result in decreased filtered load and consequently a decrease in urinary excretion of sodium. The second mechanism may be due to the removal of the inhibitory effect of prostaglandins on tubular sodium reabsorption. Prostaglandins are both diuretic and natriuretic in their action.[23] They have been shown in vitro to directly inhibit tubular reabsorption of sodium[24] and water.[25] The decrease or absence of prostaglandins in the presence of nabumetone, may increase tubular reabsorption of sodium and consequently decrease its excretion in the urine. There may well be other mechanism/s that are involved in these responses, as prostaglandins also influence the regulation of medullary blood flow, which contributes to the kidney's ability to modify renal solute excretion. Clearly, further studies using different doses of these drugs are needed to elucidate the responses of the kidneys to different COX inhibitors in different situations. In addition, this makes a good point for further investigations into the expression of the isoenzyme in the rat nephron in normal and during stressful situations.

In conclusion, our study suggests that firstly, COX-2 derived prostaglandins are possibly not involved in the maintenance of renal function in the rat in normal situations. This, however, would require further confirmation with higher doses. Secondly, COX-2 derived prostaglandins are involved in the maintenance of GFR and sodium excretion, particularly in anesthetized rats. It may therefore be added that in hemodynamically stressful situations, selective COX-2 inhibitors can have similar renal effects as non-selective NSAIDs.

 Acknowledgements



This research study was supported by a short-term grant from Universiti Sains Malaysia.

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