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Revista chilena de anatomía

versión impresa ISSN 0716-9868

Rev. chil. anat. v.18 n.2 Temuco  2000 



* Eliane Terezinha Rocha Mendes
** Manuel de Jesus Simões
** Oswaldo Alves Mora
*** Ricardo Martins Oliveira-Filho
** Luiz Kulay Jr.




Mendes, E. T. R.; Simões, M. J.; Mora, O. A.; Oliveira-Filho, R. M. & Kulay Jr. L. Hepatic and renal effects of propoxyphene napsylate on pregnant rats. Rev. Chil Anat., 18(2):259-263, 2000.

SUMMARY: As a less potent opioid analgesic and CNS depressant than morphine, propoxyphene abuse constitutes a potential risk among pregnant women. Since literature data indicate the possibility of serious side effects on liver compartment, in this work we examined the effects the chronic administration of this drug on both pregnant rats and their concepts.

Female rats were treated during the entire pregnancy (from day 0 up to day 20) with 5, 15 or 45 mg/kg of propoxyphene napsylate once daily, by gavage. Controls received the drug vehicle. At term, samples from both maternal and foetal kidneys and livers were taken and prepared for optical and electron microscopy examination.

Upon optical microscopy or electron microscopy examination, no morphological alterations were seen on either maternal or foetal livers of propoxyphene-treated pregnant rats. However, maternal and foetal kidneys showed signs of toxicity mainly in the group of rats treated with the highest dose of the drug, especially at the proximal convoluted tubules.

Our results suggest that, in the rat, the physiological modifications inherent to pregnancy shifted the main focus of toxicity of propoxyphene from the liver to the kidney. The mechanisms involved in such phenomenon are at present unresolved.

KEY WORDS: 1. Propoxyphene; 2. Toxycology; 3. Kidney; 4. Liver; 5. Rat; 6. Pregnancy. INTRODUCTION

The chronic use of dextropropoxyphene, a methadone-related opioid analgesic, may result in some degree of tolerance and dependence. Among drug addicts, this drug either alone or in association with others, was once accounted for by up to 33% of the causes of death due to the abuse of CNS depressant drugs (FINKLE et al., 1975). Besides, the toxic effects which are shared with other opioids (CNS and respiratory depression, delusions, hallucinations, confusion, etc.), the use of propoxyphene has been related to other concomitant events like liver function impairment, endocarditis, tetanus, sexually-transmitted diseases, infections and thromboembolic disease (LORETTA et al., 1983).

The chronic treatment (3_6 months) of rats with that drug caused reduction of body weight gain besides to liver steatosis and hepatocyte hypertrophy (EMMERSON et al., 1971a, b).

DUE et al. (1981) treated pregnant rats by oral route twice a day with 10 mg/kg of propoxyphene napsylate from the `day 0' until the 20th day of pregnancy and showed that the concentrations of this drug and of its main metabolic product (norpropoxyphene) were higher in the foetal than in the maternal blood.

The administration of propoxyphene by oral route to rats (5, 15 or 45 mg/kg) once daily during the entire period of pregnancy caused significant, dose-related reductions of foetal and placental weights (MENDES et al., 1998).

Since several papers reported jaundice and other signs of hepatotoxicity after the use of dextropropoxyphene, (DAIKOS & KOSMIDIS, 1975; FORD et al., 1977; LEE & REES, 1977; BESSARD et al., 1978; WOODY et al., 1980), we studied the morphology of maternal and foetal livers of rats treated with propoxyphene napsylate during the entire pregnancy, by means of light and electron transmission microscopy. On the other hand, since the half-life of norpropoxyphene is about 30 h and its accumulation may have some renal effects (CHAN & MATZKE, 1987), both maternal and foetal kidneys were also included in this study.


Animals and treatments — Female adult virgin, EPM-1 Wistar rats weighing 150_200 g, under routine laboratory care, were mated in the proportion of 2 females for every male during 2 h. Pregnancy was verified according to HAMILTON & WOLFE (1938). Sixty pregnant rats were then randomly divided into 5 groups, as follows. I, naive animals (no drug or drug vehicle); II (control), treated with acacia oil (propoxyphene vehicle) by gavage; III, IV and V, animals treated respectively with 5, 15 or 45 mg/kg b.w. of propoxyphene napsylate (Eli Lilly S.A) by gavage. Drugs and/or drug vehicles were given once a day. Treatments started at the day 0 of pregnancy and extended until the 20th day of gestation.

Histological studies — At term (20th day) the animals were sacrificed by deep ether anesthesia. The abdominal cavity was opened and samples of both maternal and foetal kidneys were taken; some of them were immersed in Bouin's solution and others were immersed into a 2% glutaraldehyde solution. The same was done with maternal and foetal liver samples. The materials were then routinely processed respectively for optical (MASSON, 1956) and electron (WATSON, 1958; RICHARDSON et al., 1960; LUFT, 1961; REYNOLDS, 1963; HARVEN, 1967) transmission microscopy examination. An EM-900 model Zeiss electron microscope at 80 kV was used.


Following oral administration in humans, peak plasma concentrations of propoxyphene are attained within 1_2 h (REISINE & PASTERNAK, 1996); since there is a wide variation in the rate of clearance, its plasmatic half-life after a single dose is estimated to be from 6 to 12 h (LEE et al., 1959). The main metabolite of propoxyphene is its N-desmethylated derivative, norpropoxyphene, with a half-life of 30 h (McMAHOUN et al., 1971). After repeated administrations of propoxyphene, the plasma concentrations of norpropoxyphene progressively increase (INTURISSI et al., 1982) to reach values several times higher than those of the parent drug (CHAN & MATKZE, 1987).

Maternal livers showed no morphological alterations after treatment of pregnant rats with any dose of propoxyphene during the entire period of pregnancy, either at optical or electronic transmission microscopy (Fig. 1).

Fig. 1. Electronmicrograph of a maternal liver of the group V showing a hepatocyte with an euchromatic, spherical nucleus (N). The cytoplasm shows a well-developed, granular endoplasmic reticulum, and a great concentration of intact mitochondria (m). Magnification: 7,500 X.

Fig. 2. Electronmicrograph of a maternal kidney of the group V showing capillaries bearing a heterogeneous podocyte distribution, intercapillary areas with filaments concentrated in the periphery of the glomerulus. Basal membrane shows points of disruption (arrow heads) and is thickened by deposition of electrondense material (arrow). Magnification: 8,100 X.

Fig. 3. Electronmicrograph of a maternal kidney of the group IV showing the spacial relationships between several hepatocytes interconnected by membrane juxtaposition through desmosomes. The cytoplasm is well developed; some mitochondria are seen with deposition of electrontranslucent material (asterisk). Magnification: 8,400 X.

Fig. 4. Electronmicrograph of a foetal kidney of the group V with a lowered concentration of mitochondria (m) with few cristae. Several electrontranslucent vesicles (asterisk) can be observed. Magnification: 9,600 X.

Concerning maternal kidneys, no gross morphological effects of propoxyphene were noticed in any group. However, electron microscopy of kidneys of maternal rats treated with 45 mg/kg of propoxyphene (group V) revealed an increase in the number of translucent vesicles and of lysosomes in the cytoplasm of proximal convoluted tubule cells; in addition, the basal membrane of glomeruli, although preserved, showed some occasional widenings and deposits of small electrondense bodies (Fig. 2).

Due to its high lipid solubility and low molecular weight, the drug crosses easily the placental barrier and reaches a higher concentration in the foetal than in the maternal compartment, and the same is verified for its major metabolite, norpropoxyphene (DUE et al.).

Similarly to what was observed in maternal livers, the foetal livers showed no morphological alterations after treatment of their mothers with any dose of propoxyphene during the entire period of pregnancy, either at optical or electronic transmission microscopy (Fig. 3). Concerning the foetal kidneys of group V, we observed a significant reduction of lysosome population. In addition, mitochondriae were morphologically altered, with few cristae (Fig. 4); there were also myelin figures or cristae lysis, and pichnotic, fragmented nuclei.

There are several reports in the literature focusing on the hepatotoxicity of propoxyphene napsylate, both in rats (EMMERSON et al., 1971a) and in humans, either bearing (KLEIN & MAGIDA, 1971) or not (BESSARD et al.; PRAMMING & PETTERSEN, 1978) some liver pathology prior to the chronic use of the drug. Contrarily to what could be expected in this regard, our results did not show adverse effects of the drug on the hepatocytes of pregnant rats, even though the dosis used was 9 times higher than that indicated for therapeutic purposes in man.

The shorter period of treatment used herein when compared with that of other authors (3 up to 6 months) (EMMERSON et al. (1971a) may explain why the drug behaved relatively safe for both maternal and foetal liver during pregnancy. In addition, the animals used herein were perfectly healthy, and no liver diseases existed prior to experiments.

Regarding renal morphology, propoxyphene given in high doses during the entire pregnancy (group V) induced alterations suggesting an increase of local permeability, besides cell degeneration of proximal convoluted tubules. The corresponding foetuses also showed signs of cellular degeneration and accelerated apoptosis at the same renal compartment.

In conclusion, the chronic use of propoxyphene napsylate in pregnant rats leads to definite toxic renal effects, expressed mainly on the proximal convoluted tubules. Whether pregnancy may constitute a factor which shifts the main focus of toxicity of this drug from the liver onto the kidney is an interesting, but at present unresolved question.

RESUMEN: El uso del napsilato de propoxifeno (NP), fármaco analgésico opioide y depresor del SNC, involucra riesgo potencial de abuso y sus consecuencias, particularmente durante el embarazo. Como en la literatura hay datos indicando la posibilidad de serios efectos colaterales del NP sobre el hígado, el objetivo de este trabajo fue examinar los efectos del NP en ratas preñadas y sus fetos.

Ratas hembras fueron tratadas durante toda la preñez (desde el día 0 hasta el día 20) con 5, 15 ó 45 mg/kg de NP, una vez al día, por gavage. Grupos controles recibieron el líquido usado como vehículo (aceite de acacia). Al término, muestras de hígado y riñón de las ratas preñadas y sus fetos fueron extraídos. Las muestras fueron procesadas para microscopías óptica y electrónica.

No se detectaron alteraciones morfológicas en hígados de ratas preñadas o fetos con ninguna dosis de NP empleada. Los rinõnes de estos animales mostraron signos de toxicidad, particularmente, con la dosis más alta del fármaco y, especialmente, en las células de los túbulos contorneados proximales.

Nuestros resultados sugieren que, en la rata, las alteraciones fisiológicas propias de la gravidez parecen cambiar el órgano-blanco de la toxicidad del NP, es decir, los efectos se manifiestan en el riñón y no en el hígado. Los mecanismos involucrados en este cambio no son aún conocidos.

PALABRAS CLAVE: 1. Propoxifeno; 2. Toxicología; 3. Riñón; 4. Hígado; 5. Rata; 6. Preñez. * School of Medicine, Fundação ABC, São Paulo, Brazil.
** School of Medecine, Universidade Federal de São Paulo, São Paulo, Brazil.
*** Institute of Biomedical Sciences, Universidade de São Paulo, São Paulo, Brazil.

Address for correspondence:
Prof. Dra. Eliane Terezinha Rocha Mendes
Dept. Materno Infantil - Faculdade de Medicina Fundação ABC
Av. Príncipe de Gales, 821
09060-650 Santo André, São Paulo (SP)

Recibido : 07-09-2000
Aceptado: 10-10-2000


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