Effect of enhancement of cholesterol catabolism in guinea pigs after weaning on subsequent response to dietary cholesterol.

Cholesterol catabolism was stimulated (by cholestyramine) in post-weaned guinea pigs for a 4-wk period. The animals were then switched to regular Chow diet for another 4 wk. When subsequently challenged with 0.25% cholesterol-containing Chow, plasma cholesterol level was significantly (p less than 0.05) lower in cholestyramine pretreated guinea pigs when compared to control guinea pigs and this "hyporesponder" pattern was maintained throughout the study period. Cholestyramine pretreated animals continued to excrete significantly (p less than 0.05) higher bile acids even at 4 wk after switching to regular Chow diet. This study demonstrates that stimulation of cholesterol catabolism even at postweaning stages can still be as effective in improving subsequent cholesterol handling capacity as noted previously after manipulation at the neonatal stage.

Cholestyramine treatment during pregnancy in the rat results in hypercholesterolemia.

Timed pregnant (8 days) Sprague-Dawley rats were fed ground stock diet (CON) or ground stock diet with 4% cholestyramine (CTR) until day 20 of gestation. Animals in both groups gained weight equally well during the study period (CON (n = 7), 308 +/- 7 g; CTR (n = 6), 315 +/- 7 g, mean +/- SEM). At the end of the study period, plasma cholesterol in the CTR group was significantly greater than that in the control group (CON n = 7, 91 +/- 4 mg/dl; CTR (n = 6), 108 +/- 5 mg/dl, P less than 0.05). The fecal excretion of both neutral steroids and bile acids, studied for 3 days between days 15 and 18 of gestation, was significantly enhanced by CTR treatment. (Neutral steroids: CON, 3.9 +/- 0.3; CTR, 10.4 +/- 0.3, P less than 0.05. Bile acids: CON, 7.6 +/- 0.4; CTR, 25.8 +/- 1.7, P less than 0.05, mg/100 g body wt/day). Bile acid pool size, measured at day 20 of gestation, however, was not significantly different. Consistent with these results was the finding that hepatic cholesterol 7 alpha-hydroxylase activity (the rate-limiting enzyme of bile acid biosynthesis) measured at day 20 of gestation was significantly enhanced by CTR treatment (CON (n = 4), 14.7 +/- 1.7; CTR (n = 4), 34.8 +/- 3.3, pmoles/mg/min, P less than 0.05). The atypical finding of hypercholesterolemia, despite the CTR-induced enhanced turnover of cholesterol, may be due to changes in the homeostatic mechanisms of cholesterol and bile acid metabolism during pregnancy.

Cholestyramine feeding in weaned rats. Increase in plasma corticosterone levels and bile acid synthesis following adrenalectomy.

Feeding cholestyramine to weaned rats increased the bile acid pool and activity of cholesterol 7 alpha-hydroxylase as expected. Following adrenalectomy, cholestyramine still increased the activity of cholesterol 7 alpha-hydroxylase but the magnitude of increase was lower (P less than 0.01) than noted in intact rats. Surprisingly, cholestyramine feeding to both intact and adrenalectomized rats increased plasma levels of corticosterone.

Persistent enhancement of bile acid synthesis in guinea pigs following stimulation of cholesterol catabolism in neonatal life.

Cholesterol catabolism to bile acids was stimulated in neonatal guinea pigs by feeding 1.11% cholestyramine (CT)-containing diet for 8 weeks. The animals were then switched to standard laboratory diet for an additional 4 weeks. At the end of the laboratory diet period: a) CT-pre-treated guinea pigs continued to excrete significantly higher (p less than 0.05) amounts of bile acids, b) the activity of hepatic 7 alpha-hydroxylase was significantly elevated (p less than 0.01) in CT-pre-treated animals, and c) isolated hepatocytes from CT-pre-treated guinea pigs secreted significantly higher (p less than 0.05) amounts of bile acid when compared to controls during a 4-hour incubation. These data provide biochemical support for our contention that stimulation of cholesterol catabolism during neonatal life can have effects that persist into adult life.

Intestinal absorption and lymphatic transport of cholesterol and beta-sitostanol in the rat.

The intestinal absorption of cholesterol and beta-sitostanol (the saturated analogue of beta-sitosterol) were measured and their absorptions compared in the presence and absence of cholestyramine. After test meals containing [(3)H]cholesterol and [(14)C]beta-sitostanol without added cholestyramine, 4-day fecal collections yielded an average of 51% of the fed cholesterol and 83% of the fed beta-sitostanol. In separate lymph transport studies without cholestyramine, 36% of the fed cholesterol was recovered in lymph in 24 hours compared to only 2% of the fed beta-sitostanol. Thus, while total recoveries of the two labeled compounds in feces plus lymph were nearly identical (51% + 36% = 87% for cholesterol and 83% + 2% = 85% for beta-sitostanol) their distribution in the two compartments was markedly different, reflecting the relative nonabsorbability of beta-sitostanol. Adding cholestyramine to the test meal caused fecal excretion of cholesterol to increase to 73%, independent of the dose of cholestyramine used. Cholestyramine had no effect on the fecal excretion of beta-sitostanol (average excretion after cholestyramine, 85%). The relative non-absorbability of beta-sitostanol compared to cholesterol is clearly evident in this study and leads us to suggest its possible use as a lipid-soluble, nonabsorbable reference compound for measurement of the absorption of cholesterol and other lipids. Further data are presented to justify its use for this purpose.-Hassan, A. S., and A. J. Rampone. Intestinal absorption and lymphatic transport of cholesterol and beta-sitostanol in the rat.

Effect of feeding beta-sitosterol alone or in combination with cholestyramine during early life on subsequent response to cholesterol challenge in adult life in guinea-pigs.

The effect of feeding 20 g beta-sitosterol/kg alone or in combination with cholestyramine (20 g/kg) during neonatal life of guinea-pigs on their subsequent response to a dietary cholesterol challenge in adult life was examined. 2. beta-Sitosterol pretreated animals showed higher plasma cholesterol values following 2 weeks on a cholesterol challenge (2-5 g/kg) diet, but did not differ significantly from control values for the remainder of the cholesterol challenge period. 3. Guinea-pigs pretreated with beta-sitosterol plus cholestyramine, on the other hand, showed a marked increase in plasma cholesterol levels over those of controls during the cholesterol challenge period, and this "hyper-responder" behaviour was maintained throughout the study period. 4. Despite the increase in plasma cholesterol, beta-sitosterol plus cholestyramine pretreated animals excreted significantly (P less than 0.05) greater amounts of bile acids and total sterols. 5. These findings demonstrate that neonatal pretreatment with beta-sitosterol plus cholestyramine has detrimental effects on the handling of a cholesterol challenge in adult life, and does not achieve the beneficial effect previously noted with pretreatment with cholestyramine alone.

A model system for studying the bioavailability of intestinally administered microcystin-LR, a hepatotoxic peptide from the cyanobacterium Microcystis aeruginosa.

Sprague-Dawley rats were used to evaluate a model system for studying the hepatotoxicity caused by microcystin-LR (MCYST-LR), a toxin produced by the cyanobacterium (blue-green alga) Microcystis aeruginosa, and for evaluating the in vivo therapeutic potential of cholestyramine resin (CTR) which was found to bind the toxin in vitro. Female rats were treated with either toxin or an equivalent volume of the saline vehicle by direct administration into the lumen of an in situ isolated ileal loop. Male rats were dosed with toxin as described above, and then animals were dosed in the ileal loop with either cholestyramine resin (CTR, 50 mg/rat) or an equivalent vehicle. The survivors in both studies were killed six hours after dosing and hepatotoxicity was assessed by change in relative liver weights. In all groups given toxin alone, there was a significant increase in liver weight and males and females were equally susceptible. Liver weights of the toxin plus CTR treated rats were similar to those in vehicle-treated rats. When the toxin was administered into a similarly isolated jejunal loop, liver weight was significantly less than that found when an equivalent dose was administered into the ileal loop suggesting an intestinal site specificity for toxin absorption.