Willem G. Linscheer

Hepatotoxicity and metabolism of acetaminophen in male and female rats

This present study was designed to assess the role of metabolic and pharmacokinetic factors in the lower susceptibility of female rats compared to male rats to xenobiotics metabolized by the cytochrome P-450-dependent mixed-function oxidase (MFO) system. Adult intact male and female Sprague-Dawley rats were administered labeled acetaminophen (1 g/kg body weight + 5 microCi [3H]acetaminophen) after an overnight fast. They were bled and killed at 0.5, 1, 2, 3, 6, 12, 24, and 36 h after drug administration. The percentage of [3H]acetaminophen radioactivity remaining in blood, liver, GI tract, and excreted in the urine was determined at all time intervals. Plasma prothrombin time and serum transaminases were determined as indices of hepatotoxicity. Hepatic GSH and glycogen were assayed. Total urinary acetaminophen and its metabolites and the molar percent of various metabolites excreted during the first 6 h were determined. Castrated male and ovariectomized female rats and their respective controls were also given acetaminophen (APAP) and were killed 24 h later to determine hepatotoxicity. The extent of hepatic damage in the intact male rats was greater and appeared sooner than in the female rats. Hepatic GSH and glycogen were depleted earlier in female rats. The percent of the administered dose excreted in the urine during the first 6 h was 17.5 for the male rat versus 24.5 for the female rat. While the APAP glucuronide conjugate concentration was significantly higher, the APAP sulfate conjugate concentration was lower in the female than it was in the male rat. Although peak radioactivity in serum was reached by 30 min in both male and female rats, suggesting quick intestinal absorption, it was significantly higher in female rats and was associated with decreased intestinal and hepatic levels and increased urinary excretion when compared to male rats. While castration of male rats decreased susceptibility to hepatotoxicity, ovariectomy of female rats tended to increase susceptibility to hepatotoxicity in comparison to their respective controls. Our data suggest that aside from the reported sex differences in the cytochrome P-450-dependent MFO enzymes, there are significant differences in GSH utilization. There are also significant changes in glucuronidation and sulfation pathways, as well as in the pharmacokinetics of acetaminophen, which tend to protect female rats against acetaminophen hepatotoxicity.

Comparative Effects of Soy and Casein Protein on Plasma Cholesterol Concentrations

The effects of soy and casein protein on cholesterol metabolism were determined under normocholesterolemic and hypercholesterolemic conditions in male Wistar rats and in Swiss White mice. Hypercholesterolemia was induced by feeding cholesterol and cholic acid in the diet for a period of 2 weeks. Our results demonstrate that there are significant species differences. The hypercholesterolemic effect of exogenous cholesterol was more pronounced in the mouse than in the rat. The rats fed the basal (no cholesterol, no cholic acid) semisynthetic diet containing either soy or casein had plasma cholesterol concentrations similar to those observed in chow-fed controls. However, plasma cholesterol concentrations in the mice fed the basal semisynthetic diet containing either of the two proteins were significantly elevated compared to the control mice fed commercial chow. Rat data demonstrate that the hypercholesterolemia induced by exogenous cholesterol administration is of a lesser magnitude in the presence of soy compared to casein as a dietary protein source. The mice data show that the concentrations of hepatic and biliary cholesterol and plasma triglycerides and in response to exogenous cholesterol are significantly lower in the soy protein diet compared to the casein protein diet.

Failure of exogenous prostaglandin to afford complete protection against acetaminophen‐induced hepatotoxicity in the rat

The protective effect of 16, 16-dimethylprostaglandin E2 (dm-PGE2) against acetaminophen-induced hepatotoxicity was determined in the rat. The dm-PGE2 was administered at two dose levels both before and after acetaminophen administration. The hepatotoxicity was evaluated by a rise in serum transaminases 24 h after acetaminophen administration and by histological examination of liver preparations. The urinary acetaminophen and its metabolites were determined by high-pressure liquid chromatography. The results suggest that exogenous dm-PGE2 administration had a modest protection against acetaminophen-induced hepatotoxicity, in contrast to its well established cytoprotective effect against many noxious agents in the gastrointestinal tract. Prostaglandin treatment had little effect on acetaminophen metabolites excretion in the urine, suggesting that it did not affect the cytochrome P-450-dependent mixed-function oxidase drug-metabolizing enzyme system. The livers from dm-PGE2-acetaminophen-treated rats showed less advanced necrosis compared to those from saline-acetaminophen-treated rats. Whereas only 2 of 13 rats died in the prostaglandin-treated group, 4 of 13 rats died in the saline-treated group.

Inhibitory effect of propylthiouracil-induced hypothyroidism in rat on oxidative drug metabolism

The effect of propylthiouracil (PTU) pretreatment on in vivo and in vitro oxidative drug metabolism was determined in the rat. Whereas pentobarbital sleeping time (PBST) and zoxazolamine paralysis time (ZZPT) were used as indices of in vivo drug metabolizing activity, biotransformation of aminopyrine and aniline by hepatic microsomal preparations were used as indices of in vitro drug metabolizing enzymes activities. PTU pretreatment significantly prolonged both PBST and ZZPT. Whereas PTU did not affect microsomal protein concentration or cytochrome P-450 content, it significantly decreased microsomal cytochrome c reductase and aniline hydroxylase activities. These changes in enzymatic activities were observed in microsomal preparations from either non-fasted or 24-hr fasted rats. Our results suggest that PTU-induced hypothyroidism modifies the metabolism and effectiveness or toxicity of concomitantly administered drugs.

Effect of dietary composition on liver glycogen accumulation and lipid metabolism in the hypothyroid chick (Gallus domesticus)

Abstract 1. 1. Since propylthiouracil-induced hypothyroidism in the mash (commercial high carbohydrate diet) fed chick results in liver enlargement with excessive accumulation of glycogen, these studies were conducted to determine the effect of diet composition on carbohydrate and lipid metabolism in the hypothyroid chick. 2. 2. PTU (0.1%) was fed for 2 weeks in mash, high carbohydrate (HC), high fat (HF), or in high protein (HP) diets. 3. 3. Thyroid glands were significantly enlarged in all PTU treated chicks independent of the nature of dietary composition. 4. 4. Liver weight increased and glycogen accumulated in all hypothyroid chicks, the maximum in HC diet and minimum in HF diet fed group. 5. 5. Plasma glucose levels did not correlate with liver glycogen concentrations. 6. 6. Hypothyroidism significantly increased plasma triglycerides in HC and mash fed, cholesterol in mash fed and phospholipids in HC and HF diets fed groups. HP diet had a hypocholesterolemic effect. 7. 7. PTU significantly decreased bile phospholipids. Bile cholesterol was also decreased except in HF diet fed group. 8. 8. The results demonstrate profound changes in carbohydrate and lipid metabolism in hypothyroid chicks. These changes are modulated by dietary composition and liver glycogen accumulation probably is dependent on dietary carbohydrate supply.

Studies in Iron Absorption: IV. Absorption in the proximal small intestine in patients with cirrhosis

Summary Mean absorption of iron measured by means of entraluminal infusion through a 4-lumen, 2-balloon tube in an isolated jejunal loop, washed free from bile and pancreatic juice, was higher in 11 patients with cirrhosis of the liver (0.83 ± 0.14 μg. per minute) than in 10 normal control subjects (0.33 ± 0.06 μg. per minute). Changing the pH of the inf usate from 3.0 to 7.0 did not affect the rate of iron absorption. However, mean absorption rate returned to normal upon addition of the patients own duodenal juice to the infusate. In 2 patients, the absence of such an inhibiting factor was associated with higher-thannormal uptake of iron from the intestine after an oral test dose of Fe 59 as measured by the body counting technique. Thus, intraluminal as well as extraluminal factors are of importance in the regulation of iron absorption in patients with cirrhosis of the liver.

Effects of somatostatin on gastric acid secretion and on lipid and carbohydrate metabolism in the rat.

1 Studies were conducted to examine the effects of somatostatin on pentagastrin‐induced gastric acid secretion, and on bile, plasma and liver lipid composition in the rat. 2 In addition, liver glycogen and plasma glucose concentrations were measured. 3 Somatostatin was administered intravenously as a bolus (100 ug) at the start of the experiment followed by a continuous infusion (50 ug/h) for 2 h. 4 Controls were infused with isotonic saline (1 ml/h) throughout the experiment. Gastric secretions and bile were collected during the infusions. 5 Somatostatin significantly decreased the volume of gastric secretion as well as total gastric acid output but it had no effect on bile flow or bile lipid composition. 6 Plasma and liver lipids were not affected. Plasma glucose concentrations were significantly elevated but liver glycogen was not changed. 7 Our results suggest that somatostatin probably decreases glucose uptake by peripheral tissue. The effect of somatostatin on bile composition and glucose levels in the rat is different from observations reported in other species.

Effects of PEG-electrolyte (colyte) lavage on serum acetaminophen concentrations : a model for treatment of acetaminophen overdose

The purpose of this study was to evaluate whole gut lavage with polyethylene glycol electrolyte solution (Colyte), as a potentially adjunctive measure in lowering serum acetaminophen levels. The effect of bowel lavage was evaluated on serial serum acetaminophen concentrations after 2-g and 4-g doses in 7 and 12 male patients, respectively. Mean peak level of serum acetaminophen after 2 g (60 min after intake) was not significantly lowered by bowel lavage. After 4 g, peak acetaminophen serum levels were significantly lower after bowel lavage (65.4% of controls,P<0.001). Urinary concentrations of the mercapturic acid conjugate of the toxic metabolite were also significantly reduced by lavage (55% after 2 g and 45% after 4 g,P<0.01). Activated charcoal given orally after administration of 4 g of acetaminophen had no significant effect on peak serum levels and had no additive effect on lavage. These studies suggest that rapic, complete bowel lavage with a polyethylene glycol electrolyte solution may be beneficial as an adjunct to the treatment of the acetaminophen intoxication.

Prevention of acetaminophen hepatotoxicity by propylthiouracil in the glutathione depleted rat

This study was designed to investigate the protective effect of PTU pretreatment against acetaminophen hepatotoxicity in rats whose hepatic GSH had been depleted by prior diethylmaleate (DEM) administration. A single injection of DEM depleted hepatic GSH showing lowest level after 90 min in both control and PTU pretreated rats. Triple injection schedule kept the hepatic GSH concentrations consistently very low up to 6 hr. Whereas a toxic dose of acetaminophen administration did not effect SGOT and SGPT levels after 30 hr in PTU pretreated rats given either a single or multiple injections of DEM, the same dose of acetaminophen in the control rats raised these transaminases to a very high level. High activity of transaminases was associated with significant histological hepatic damage. Our results suggest that PTU pretreatment affords significant protection against acetaminophen hepatotoxicity even under conditions when hepatic GSH concentrations have been significantly depleted prior to acetaminophen administration.

Lipid and carbohydrate metabolism in euthyroid and hypothyroid chick embryo (Gallus domesticus).

1. The effect of propylthiouracil (PTU)-induced hypothyroidism on carbohydrate and lipid metabolism was studied in the chick embryo. 2. A single dose of PTU (250 micrograms/embryo) was administered on day 11 and embryos sacrificed on day 20 of incubation. 3. Thyroid glands were significantly enlarged (6 fold) by PTU administration. 4. Increased thyroid weight was associated with growth retardation and decreased plasma thyroxine levels. 5. Plasma glucose level was lower and phospholipids were significantly higher in the hypothyroid embryo. 6. Liver lipid concentrations in the control and hypothyroid embryos were not different but were significantly higher in both groups when compared to previously reported values in the young chick. 7. In contrast to PTU treatment after hatching, liver glycogen levels were not increased in the hypothyroid chick embryo. This was attributed to the high lipid nutrient condition of the chick embryo since a high lipid diet in the young chick decreased hepatic glycogen accumulation significantly.