Effect of pregnancy on hepatic microsomal drug metabolism in rabbits and rats

In Dutch-belted rabbits, pregnancy caused several-fold decrease of in vitro hepatic microsomal aminopyrine, benzphetamine, and hexobarbital biotransformations. In pregnant Sprague-Dawley rats, various kinds of expressing the in vitro rates of hexobarbital biotransformation (per mg of microsomal protein, g of liver, 100 g of body weight) indicated unchanged or slightly elevated microsomal enzyme activity. In vivo, the course of hexobarbital blood levels after i. p. hexobarbital sodium, 100 mg/kg, indicated that the fate of hexobarbital was not primarily determined by the small changes of microsomal enzyme activity but, rather, by changed hexobarbital distribution. Different ways of expressing in vitro rates of aniline biotransformation showed decreased or unchanged enzyme activity during pregnancy and in vivo experiments indicated that these changes did not affect aniline metabolism in living rats. The results pointed out marked species differences in the effect of pregnancy on drug metabolism. Interpretation of in vitro biotransformation data for living animals suggested that with different substrates, microsomal enzyme activity and distribution, respectively, may exert different effects playing either significant or apparently minor role in drug disposition.Supported in part by U.S. Public Health Grant NIGMS 12,675.     

Dose-dependent actions of thyroxine on hepatic drug metabolism in male and female rats

Studies were carried out to compare the effects of various doses of thyroxine (T₄) on hepatic drug metabolism in male and female rats and to evaluate the role of the pituitary gland in the modulation of T₄ action. Administration of small amounts of T₄ (2.5 to 5 μg/100g body wt/day) to hypophysectomized rats of either sex increased hepatic ethylmorphine demethylase, benzo(a)pyrene hydroxylase and aniline hydroxylase activities. Larger amounts of T₄ (12.5 to 50 μg) reversed the stimulatory effects of the smaller doses. T₄ treatment produced dose-dependent decreases in hepatic cytochrome P-450 content and increases in NADPH-cytochrome c reductase activity in hypophysectomized rats of both sexes. Qualitatively similar effects were produced by T₄ administration to thyroidectomized male and female rats. However, larger doses of T₄ were required for maximum stimulation of drug metabolism in thyroidectomized than in hypophysectomized animals. The results indicate that physiological amounts of T₄ Uniformly stimulate hepatic drug metabolism in both male and female rats. Supraphysiological amounts, however, inhibit metabolism of some substrates and produce sex differences in T₄ actions. The effects of T₄ are demonstrable in the absence of the pituitary gland but pituitary-dependent factors appear to modulate the magnitude of the response to T₄.     

Selenium antagonism of cadmium-induced inhibition of hepatic drug metabolism in the male rat

Experiments were undertaken to examine the effect of selenium, an essential trace element, on cadmium-induced inhibition of drug metabolism in male, Sprague-Dawley derived rats. Prior administration of sodium selenite (1.6 mg Se/kg, ip) blocked the cadmium-induced (0.84 mg Cd/kg, ip) prolongation of hexobarbital-induced hypnosis and inhibition of hepatic microsomal biotransformation of ethylmorphine or aniline. Selenium also blocked cadmium-induced reduction in microsomal cytochrome P-450 content and the microsomal binding of both ethylmorphine and aniline. However, pretreatment of rats with selenium did not prevent the inhibitory effect of cadmium (10^?6 to 10^?3m) added in vitro on either ethylmorphine or aniline biotransformation. In addition, the reduction in biotransformation of both substrates following in vivo cadmium administration was not reversed following the in vitro administration of selenium but, in fact, selenium produced further concentration-dependent decreases in drug metabolism. In additional in vitro experiments it was found that the inhibition in drug metabolism induced by in vitro additions of cadmium is not affected by similar additions of selenium when added to the incubation vessel either before or after the cadmium. Thus, for selenium to prevent the cadmium-induced inhibition of hepatic drug metabolism requires in vivo administration of selenium.     

Effect of acute and chronic cadmium treatment on hepatic drug metabolism in male rats

The effect of acute and chronic cadmium administration on hepatic drug metabolism was investigated in the male rat. 3 days after the acute administration of cadmium by either the intraperitoneal (0.84 mg Cd/kg) or the oral (> 80 mg Cd/kg) route, there was a significant potentiation in duration of hexobarbital hypnosis and inhibition of hepatic microsomal metabolism of hexobarbital and aniline. Administration of cadmium in the drinking water at levels of 100 or 200 ppm Cd for periods of 2–12 weeks or at levels of 5 or 20 ppm Cd for 50 weeks did not produce alterations in either drug response or hepatic drug metabolism. Significant levels of metallothionein, a cadmium binding protein, found in the liver of the rats receiving cadmium chronically may offer an explanation for the observed differences in drug metabolism between the acute and chronic administration of cadmium. In additional studies, pretreatment of the rats with subthreshold doses of cadmium (0.21 or 0.42 mg Cd/kg) intraperitoneally produced a tolerance to the alterations in drug metabolism induced by the previous cadmium dose (0.84 mg Cd/kg, i.p.). However, chronic cadmium treatment (5 or 20 ppm Cd for 50 weeks) did not impart any such tolerance to subsequently administered Cd (0.84 mg/kg) by the intraperitoneal route. The hepatic levels of metallothionein induced by the chronic cadmium treatment were only 30–60% of those induced by the subthreshold cadmium and thus may not have bound enough of the large challenge cadmium dose to produce the tolerance phenomenon.     

Isoproterenol-induced ultrastructural alterations in hearts of alloxan-diabetic rabbits

1. The effects of isoproterenol (ISO) on the ultrastructure of hearts from 10-week alloxan diabetic rabbits were examined. 2. Following alloxan injection, all rabbits developed severe hyperglycemia, hyperlipidemia and hypoinsulinemia. 3. Injection of ISO induced marked alterations in both control and diabetic rabbit hearts including accumulation of lipid and swelling of sarcoplasmic reticulum. 4. Myofibrils in both groups of animals were dispersed and appeared as a homogeneous mass with poorly defined Z-bands. 5. The most marked effect of ISO treatment in both groups of animals was damage to mitochondria. Mitochondria were extensively damaged and showed partial or complete disruption of their cristae network. 6. Glycogen granules were few in number or not detectable in both groups of animals. 7. The diabetic animals treated with ISO showed greater clumping and margination of nuclear chromatin, fewer intact mitochondria and a greater number of amorphous dense bodies in and around the mitochondria. 8. The presence of greater sarcolemmal damage in diabetic animals was inferred from the significantly greater accumulation of calcium and decreased magnesium in the myocardium.     

Impairment of hepatic drug metabolism in alcoholics.

1 The effects of chronic ethanol intake on the elimination kinetics of antipyrine were determined in nineteen male alcoholic subjects with comparison made to fourteen male volunteers. 2 Half-lives were longer and clearance values less in the alcoholic group. 3 Significant rank correlations were found between half-life and clearance when compared with various biochemical parameters of liver function measured in the plasma of the alcoholics. 4 These results show that a significant proportion of the alcoholics studied had impaired hepatic drug metabolizing capacity and that the activity of hepatic microsomal enzymes may be related to the extent of ethanol induced liver damage in these subjects.     

Evaluation of the involvement of a male specific cytochrome P-450 isozyme in senescence-associated decline of hepatic drug metabolism in male rats

The major "male specific" species of cytochrome P-450 (P-450ml) was purified and an antibody against it used to evaluate the involvement of this isozyme in alterations of drug metabolism in senescence. P-450ml exhibited strikingly high imipramine (IM) N-demethylase activity while it showed no IM 2-hydroxylation, which is an alternate pathway of IM metabolism in rat liver microsomes. The antibody to P-450ml inhibited 80% of imipramine N-demethylation in young male rats. In old male rats, which have been shown to have lower IM N-demethylase activity, a 60% inhibition was observed. The inhibitable portion of this activity in old male rats is about one third of that in young rats, but the remaining portion not inhibited by this antibody is almost identical in young and old rats. IM 2-hydroxylation on the other hand was not inhibited by this antibody at all. It also inhibited about 30% of diazepam(DZ) N-demethylation in young rats but showed no inhibition in old rats, resulting in the loss of the age difference in the remaining portion. DZ 3-hydroxylation was not inhibited by this antibody, in spite of the fact that it showed a markedly higher activity in young male than in young female rats with a subsequent reduction in old age in male rats. This study provides the first direct evidence that differences in the amount of the major male specific P-450 isozyme (P-450ml) are responsible for the age- and sex-associated differences in some of the drug metabolizing activities. It also became apparent that P-450ml may not be the only isozyme responsible for these differences.     

Interferon reduces hepatic drug metabolism in vivo in mice

The effects of two highly purified human leukocyte interferons (IFN-A and IFN-AD) on drug-metabolizing capacity in mice have been investigated. IFN-AD was found to produce significant changes in antipyrine half-life, assessed by analysis of 14CO2 exhalation rates following 14C-antipyrine administration. By contrast, IFN-A, which has considerably less antiviral potency than IFN-AD, was found to have no effect on antipyrine half-life. The administration regimen was found to markedly alter the effects seen with IFN-AD. When IFN-AD was given as single daily doses (5 X 10(7) units/kg/day X 3 days), the half-life of antipyrine increased by a mean of 40% (from 21.0 to 28.9 min). However, when a smaller daily dose (3 X 10(7) units/kg/day) was given as a continuous infusion, the antipyrine half-life increased by more than 3-fold (from 20.8 to 68.5 min) after 3 days of administration. Continued infusion for a further 3 days produced no additional change in antipyrine half-life. These results demonstrate that human leukocyte interferons can significantly inhibit hepatic metabolic activity in vivo.     

Cadmium inhibition of hepatic drug metabolism in the rat

Pretreatment of rats and mice of either sex with a single 2.0 mg/kg dose of cadmium acetate (840 μg Cd ion) potentiates the action of subsequently administered hexobarbital. Three days after cadmium administration to the male rat the duration of response to hexobarbital, but not that to barbital was significantly prolonged. Plasma concentrations of hexobarbital at awakening were not different from controls, indicating that cadmium treatment had not altered central nervous system sensitivity to the barbiturate. Such treatment of male rats 3 days prior to sacrifice leads to a significant inhibition of the metabolism of aminopyrine, hexobarbital, p-nitroanisole and zoxazolamine in microsomal subfractions obtained from these animals; microsomal cytochrome P-450 is reduced to 50% of control values by the cadmium treatment. Inhibition of the metabolism of these substrates by cadmium was also achieved when the metal was added to isolated microsomes in concentrations ranging from 5 × 10^?4 to 5 × 10^?7m.     

Changes in pentobarbital hypnosis and hepatic metabolism in streptozotocin-diabetic mice

The present study deals with the hypnotic effect of pentobarbital (Pento) in relation to its metabolism in hepatic microsomes in streptozotocin (STZ, 170 mg/kg, i.p.) injected mice. Liver weight (mg/10 g body wt.) of STZ-treated mice was larger than that of the controls throughout the experimental period. Although the shortening of sleeping time induced by Pento (60 mg/kg, i.p.) was always observed, Pento-metabolizing enzyme activity (by the method of Kato et al., 1964) increased in mice with diabetes for 2 and 4 weeks but decreased in mice with diabetes for 8 weeks. Induction following phenobarbital (100 mg/kg, s.c.) and inhibition by SKF 525-A (10 mg/kg, i.p.) of hepatic metabolizing enzyme were found in both control and mice with diabetes for 2, 4 and 8 weeks, but these were not definitely correlated to their hepatic Pento-metabolizing enzyme activities. STZ-induced hyperglycemia and shortening of sleeping time by Pento were completely prevented by the pretreatment with nicotinamide (500 mg/kg, i.p.). NPH-insulin injection partially decreased hyperglycemia in STZ-diabetic mice, but sleeping time by Pento was not significantly affected. These results suggest that the hyposensitivity to Pento in STZ-diabetic mice is partially related to an abnormality of metabolism in liver such as the hyperglycemic state.     

Riboflavin and drug metabolism in adult male and female rats

Oxidative metabolism of drugs in vitro in liver 9000 g supernatant fraction from riboflavin-deficient adult male and female rats was investigated. A significant decrease in overall oxidation of aminopyrine, ethylmorphine, N-methylaniline, aniline and acetanilide was observed. Studies at two deficiency levels indicate that a marked decrease in specific activities of N-demethylation of aminopyrine. ethylmorphine. N-methylaniline and hydroxylation of aniline and acetanilide occurs in both male and female rats. The levels of drugmetabolizing enzymes were further lowered with increase in deficiency. The levels of flavin, NADPH cytochrome c reductase, cytochrome P-450 and cytochrome b₅ were reduced in riboflavin-deficient (7 weeks) male rats as compared to normal rats. The activity of drug enzymes from riboflavin-deficient rats was stimulated by pretreatment with phenobarbital. A significant reversal of drug enzyme activities was noted when riboflavin was administered to deficient animals.     

Effect of dibromotetrafluoroethane inhalation on hepatic drug metabolism in mice

Inhalation of dibromotetrafluoroethane, 0.63 to 1.0%, for 5 hr daily, for 3 or 4 days, reduced hexobarbital sleeping time and zoxazolamine paralysis time 2-fold in mice. Increased metabolism of hexobarbital and zoxazolamine by the hepatic 9000 g microsomal supernatant fraction prepared from exposed mice correlated well with the effects determined in vivo. Addition of 2,4-dichloro-6-phenyl-phenoxyethyldiethylamine (SKF 525-A) to the hepatic 9000 g microsomal supernatant fraction prevented the dibromotetrafluoroethane-induced increase in hepatic drug metabolism.     

Effect of phencyclidine on hepatic drug metabolism in the rat

Phencyclidine, an anesthetic used in experimental animals, was examined for its effect on hepatic drug metabolism. Treatment of male rats for 4 days with phencyclidine (50 mg/kg/day, ip) caused significant increases in the rate of metabolism of hexobarbital, aminopyrine, and zoxazolamine in vitro by the 10,000 g hepatic supernatant fraction. Metabolism of p-nitroanisole in vitro was not altered by the drug treatment. Significant shortening of hexobarbital sleeping time was observed after phencyclidine treatment. Zoxazolamine paralysis time was increased by the drug treatment. The discrepancy between the zoxazolamine studies in vivo and in vitro appear to be due to alteration of the sensitivity of the rat to the paralyzing action of zoxazolamine since plasma concentrations at the time of recovery from zoxazolamine paralysis were lower in the treated animals.