Renal fluoride excretion during and after enflurane anaesthesia: dependency on spontaneous urinary pH-variations

Appropriate real-time PCR reference genes for fluoride treatment studies performed in vitro or in vivo

OBJECTIVE

Quantitative real-time PCR (qPCR) is routinely performed for experiments designed to identify the molecular mechanisms involved in the pathogenesis of dental fluorosis. Expression of reference gene(s) is expected to remain unchanged in fluoride-treated cells or in rodents relative to the corresponding untreated controls. The aim of this study was to select optimal reference genes for fluoride experiments performed in vitro and in vivo.

DESIGN

Five candidate genes were evaluated: B2m, Eef1a1, Gapdh, Hprt and Tbp. For in vitro experiments, LS8 cells derived from mouse enamel organ were treated with 0, 1, 3 and/or 5mM sodium fluoride (NaF) for 6 or 18 h followed by RNA isolation. For in vivo experiments, six-week old rats were treated with 0 or 100 ppm fluoride as NaF for six weeks at which time RNA was isolated from enamel organs. RNA from cells and enamel organs were reverse-transcribed and stability of gene expression for the candidate reference genes was evaluated by qPCR in treated versus non-treated samples.

RESULTS

The most stably expressed genes in vitro according to geNorm were B2m and Tbp, and according to Normfinder were Hprt and Gapdh. The most stable genes in vivo were Eef1a1 and Gapdh. Expression of Ddit3, a gene previously shown to be induced by fluoride, was demonstrated to be accurately calculated only when using an optimal reference gene.

CONCLUSIONS

This study identifies suitable reference genes for relative quantification of gene expression by qPCR after fluoride treatment both in cultured cells and in the rodent enamel organ.

Anions and the anaesthetist

Anions are the negative components of most chemical structures and play many important physiological and pharmacological roles that are of interest to the anaesthetist. Their relevance is reviewed with a particular emphasis on the inorganic anions (halides, bicarbonate, phosphate and sulphate) and the significance and limitations of the anion gap. Organic anions (albumin, lactate) are also discussed, albeit briefly. The suitability of anions for their role in neurotransmission and acid-base balance is outlined.

The physiological and toxicological characteristics of fluoride

The metabolism and toxicity of fluoride are discussed with emphasis on new scientific findings. The gastric absorption, tissue distribution, and renal excretion of the ion are all influenced by the magnitude and direction of the pH gradient between adjacent body fluid compartments. This mechanism explains the asymmetric distribution of fluoride across cell membranes, and the manipulation of transmembrane pH gradients has proven efficacious in acute fluoride toxicity. The comparative metabolism and relative toxicities of ionic fluoride and monofluorophosphate are discussed. It is no longer certain that there is a difference between the acute toxic potentials of sodium fluoride and those of MFP. It is concluded that the "probably toxic dose" or PTD of fluoride--the dose which should trigger therapeutic intervention and hospitalization--is 5 mg/kg of body weight. As currently packaged, many dental products contain sufficient fluoride to exceed the PTD for young children. There is a need for additional research into the sources, effects, and fate of strongly bound or organic fluoride compounds. Attention is drawn to the fact that, while the metabolic characteristics and effects of fluoride in young and middle-aged adults have received considerable research attention, there is a paucity of such information for young children and the elderly. The increasing prevalence of dental fluorosis is addressed. It is concluded that nondietary sources of fluoride, mainly fluoride-containing dental products, are a major source of ingested fluoride. The article concludes with 12 recommendations for future research.

Anaesthesia for the patient with impaired renal function

Patients with renal disease are at risk of further deterioration of renal function and acute tubular necrosis when subjected to anaesthesia and surgery. Optimal fluid loading and careful selection of anaesthetic techniques and agents, appropriate monitoring and the use of mannitol and dopamine assist in the maintenance of renal blood flow and help preserve renal function in these patients. In association with renal failure, physiological changes in other systems result in reduced oxygen supply to the tissues, metabolic disturbances, impairment of the coagulation and immune defence mechanisms and an increased risk of cardiac and cerebrovascular catastrophe. Although many anaesthetic techniques including regional analgesia may be used successfully in these patients caution with most drugs, especially pethidine, phenoperidine, suxamethonium and all non-depolarising neuromuscular relaxants is recommended. Of the volatile anaesthetics currently available, halothane is the agent of choice. Oxygen therapy and close monitoring of cardiorespiratory function are necessary postoperatively.

Effects of working environment on the liver in 10 anaesthetists

Drug-metabolising ability, i.e. antipyrine half-life, in anaesthetists was significantly slowed (23%) at the end of summer vacation (2-4 weeks), as compared to prevacation values. Despite changes in either direction, the antipyrine half-lives, including four determinations within a year and a half from the ten anaesthetists, were within normal limits. Liver enzymes (aspartate aminotransferase, alanine amino-transferase, alkaline phosphatase) were also normal. In one anaesthetist the test for anti-HBsAg was positive in 1980, while in the others HBsAg and anti-HBsAg were negative in 1980 and 1981. The inorganic fluoride concentrations of serum and urine (determined four times) were at normal levels. Only in one anaesthetist was there a transient, surprisingly high, serum concentration (7.9 mumol/l), apparently unrelated to work exposure.

Effect of mannitol and furosemide on urinary fluoride excretion of surgical patients anaesthetized with enflurane or halothane

Urinary excretion of fluoride after enflurane anaesthesia has been found to correlate with urinary pH, while the correlation with urinary volume has remained unsettled. We therefore studied the effect of moderate doses of mannitol and furosemide on serum fluoride levels and urinary excretion of fluoride in surgical patients after controlled doses of enflurane (6+6+6 patients) or halothane (5+5+5 patients). The highest serum fluoride level was 31 mumol/1 in an enflurane patient (enflurane dose 1.26 end-tidal vol % x h) and 8 mumol/1 in a halothane patient (halothane dose 0.59 end-tidal vol. % x h). Mannitol caused th greatest mean excretion of fluoride (not significant (n.s)) in the enflurane patients without any marked rise in urinary pH or volume. Furosemide increased urinary output markedly but did not enhance urinary fluoride excretion or raise urinary pH. Compared with the control groups of both inhalation anaesthetic patients, the diuretics appeared to have no effect on the serum fluoride levels. In the enflurane patients there was a positive correlation between the change in fluoride clearance and the change in urinary pH, but no with the change in urinary volume during the first postoperative hours. On the other hand, in the halothane patients there was a positive correlation between the change in fluoride clearance and the change in urinary volume. A possible "fluoro-uretic" action of mannitol was also seen in the halothane patients, as in the later postoperative period fluoride excretion was greatest when mannitol had been given.

Effects of prolonged anesthesia with enflurane or halothane on renal function in dogs

Elevated serum inorganic fluoride levels (60-300 mumol/l), maintained over 6 h, influenced renal function in beagle dogs. Changes in water reabsorption were seen with an increased urine flow and free water clearance and decreased urinary concentration capacity. Possible nephrotoxicity as an effect of inorganic fluoride production during prolonged enflurane anesthesia was evaluated in a group of beagle dogs. Another group of dogs, anesthetized with halothane in equianesthetic doses, was studied for comparison. Serum inorganic fluoride levels and urinary oxalate excretion were determined and postanesthetic renal morphology was examined. Renal function was evaluated from endogenous clearances and concentration capacity before and after anesthesia. In the enflurane group, serum inorganic fluoride levels peaked at 22.5 mumol/l at the end of anesthesia and decreased rapidly in the postanesthetic period. Urinary oxalate excretion did not increase. No changes in renal morphology were found. Renal function tests did not reveal any disturbance after enflurane anesthesia. The two anesthetized groups did not differ in any of the parameters studied, except in serum inorganic fluoride levels.

Effects of renal function on serum fluoride level in dogs during and after enflurane anesthesia

To study the effect of renal function on the increased serum inorganic fluoride level produced by the metabolism of enflurane, three groups of beagle dogs were exposed to prolonged enflurane anesthesia, 1.25 MAC for 8 h. One group was studied both with and without renal function, one group only without renal function, and one group on two different occasions with renal function intact. Serum inorganic fluoride levels were determined every hour during the enflurane anesthesia and on termination for a further 4 h. In dogs with no renal function, the increase rate and the peak of serum inorganic fluoride level were significantly higher than in dogs with renal function. The average peak level in dogs with renal function was 21.4 mumol/l and in dogs with no renal function 38.4 mumol/l. Renal function was found to have the same capacity to increase the inorganic fluoride elimination from serum as other routes of elimination. At corresponding serum levels, the rate of decrease after terminating enflurane anesthesia was 3.5-4.0 mumol/l/h lower without renal function. Reanesthesia after 3 weeks did not significantly change the serum inorganic fluoride levels compared to the first anesthesia.

Metabolic ability and enflurane defluorination in surgical patients

Antipyrine clearance and half-life, which are measures of the hepatic metabolic ability, were determined prior to anaesthesia in 14 surgical patients. The antipyrine results correlated neither with the highest serum fluoride concentrations nor with the fluoride excretion in urine following administration of enflurane. Enzyme induction may therefore have little influence on enflurane metabolism in man. Inorganic fluoride concentrations in serum and in excreted urine were determined following the exposure of a total of 21 surgical patients to measured doses of enflurane. In the group of 14 patients tested for metabolic ability, a mean dose of 0.4 end-tidal vol. % X h enflurane resulted in a mean peak serum fluoride concentration of 6.8 mumol/l (maximum 13.6 mumol/l) 2 h after enflurane exposure. In the material as a whole, the enflurane dose was positively correlated with both post-anaesthetic highest serum fluoride concentrations and the 24-h post-anaesthetic urine pH (P less than 0.01) as well as urinary volume and fluoride excretion in urine during that time. At a urinary pH below 5.0, the fluoride excretion was very low, while the highest excretions were associated with a urinary pH of about 7.0. Raising the patient's per- and post-anaesthetic urine pH and maintaining a good urinary output (which also tends to increase urine pH) may be enough to prevent accumulation of inorganic fluoride in the body following enflurane anaesthesia.

Enflurane anesthesia in living donor renal transplantation

Two groups of patients undergoing elective living donor renal transplantation were studied during enflurane or halothane supplemented anesthesia. The duration of anesthesia was similar in both groups. The mean administered enflurane dose was 243 vol % min; the corresponding halothane dose was 56 vol % min. In the enflurane group, the mean serum inorganic fluoride level peaked at 21.0 mumol/l 3 h after the end of anesthesia. The inorganic fluoride level in urine produced by the renal graft increased continuously, but did not peak, during the first 24 postanesthetic hours. The renal graft quickly started to function in all patients in both groups. The frequency of rejection reactions was higher in the enflurane group than in the halothane group. Serum creatinine levels decreased rapidly in both groups. Urine flow was high on the day of transplantation, but normalized on the first postanesthetic day. Renal sodium clearance decreased earlier in the enflurane group than in the halothane group. This difference was statistically significant on the first postanesthetic day. In the enflurane group, the required pancuronium dose was significantly lower than in the halothane group. In one patient in the enflurane group, the serum inorganic fluoride level increased to 37.5 mumol/l. In this patient renal tubular function may have been affected, but the change was not conclusive since a pronounced rejection of the graft became evident. Since increases in serum inorganic fluoride level approaching 75% of the threshold level for nephrotoxicity in normal kidneys may occur, enflurane should not be routinely used in anesthesia for renal transplantation.