Margaret E. Beher

The Effect of Pituitary and Thyroid Hormones on Bile Acid Metabolism in the Rat

Abstract Bile acid synthesis and bile acid pool turnover rates and sizes were determined in normal (N), thiouracil-treated (TU), hypophysectomized (H), and thyroidtreated hypophysectomized (TH) female albino rats. Thiouracil treatment lowered the rate somewhat: N, 3.4 mg./day; TU, 2.2 mg./day. Hypophysectomy reduced the rate to less than one-third of normal: H, 0.96 mg./day. Five mg./day desiccated thyroid increased bile acid synthesis of hypophysectomized rats to 1.2 mg./day—still far below normal. Since bile acid pool sizes per 100 Gm. body weight were similar in the groups (N, 9.66 mg.; TU, 6.80; H, 9.39; TH, 9.59), these changes in synthesis were due largely to changes in pool half-life (N, 3.7 day; TU, 4.0; H, 8.8; TH, 6.5). It was concluded that hypophysectomy retards bile acid metabolism by decreasing end-product turnover rates. The effects of hypophysectomy differ from those of thiouracil-hypothyroidism, and moderate thyroid treatment does not restore steroid turnover or synthesis rates to normal. Thus other factors than lack of thyroid seem to cause the changes in steroid metabolism effected by hypophysectomy.

A Comparative Study of Bile Acid Metabolism in the Rat, Mouse, Hamster, and Gerbil

Summary A comparative study of bile acid metabolism was made in the rat, mouse, hamster, and gerbil. Bile acid elimination was mainly via fecal excretion; less than 7% was excreted in the urine. Little or no bile acid side-chain oxidation took place in any of the species. A study of bile acid distribution in the rodent tissue showed that from 80 to 90% was present in the small intestine plus gall bladder. The cecum was another site which contained considerable quantities of bile acids. The chief pool bile acid in each case was cholic acid. Chenodeoxycholic acid was present in significant amounts in rat and hamster, and in trace amounts in mouse and gerbil bile. Cholic acid half-lives (days) were: rat, 3.5; mouse, 5.0; gerbil, 2.3; and hamster, 1.0. Chenodeoxycholic half-lives (days) were: rat, 2.0; mouse, 2.5; gerbil, 1.3; and hamster, 1.8. The rat had the largest bile acid pool (27.2 mg); the mouse (5.6 mg) and gerbil (7.12 mg) intermediate amounts; and the hamster the smallest pool (2.3 mg). The relationship between bile acid synthesis rates and the rate of accumulation of tissue cholesterol after feeding cholesterol-supplemented diets was discussed. Positive correlations were noted but further studies are necessary to define the relative importance of this factor in maintaining cholesterol homeostasis in the various rodents.

Effects of cholesterol on bile acid metabolism in the rat.

Summary The effects of cholesterol feeding and accumulated tissue cholesterol on bile acid metabolism in normal female rats were studied. Feeding diets supplemented with cholesterol and corn oil over the entire experimental period resulted in decreases in the cholic and chenodeoxycholic acid pool half-lives of 1.6 and 0.9 days, respectively. In experiments on rats with accumulated tissue cholesterol fed unsupplemented basal rations during the experimental period, the half-lives of these acids also decreased 1.6 and 0.9 days, respectively, from the values for normal control rats. In both the dietary and accumulated tissue cholesterol experiments, the total bile acid pool concentration was unchanged but there was an important decrease in cholic acid concentration accompanied by a compensating increase in chenodeoxycholic concentration. Studies in the animals with elevated tissue cholesterol showed that the effects on bile acid turnover were not due to increased levels of sterols in the gastrointestinal tract but were due per se to the increased tissue cholesterol levels. Dietary corn oil by itself had no effect on either turnover rates or pool sizes of the bile acids.

Bile Acid and Cholesterol Metabolism in the Mouse as Affected by Gholestyramine.

Summary Dietary cholestyramine (MK 135) increased the rate of mobilization of blood and liver cholesterol in mice. The bile acid turnover rate in normal mice was 5 days, in mice treated with 1% cholestyramine, 1¼ days, or 4 times as fast. Bile acid pool size was 5.62 ± 1.09 mg in normals, 4.58 ± 0.65 in cholestyramine-treated mice. The pool was shown to consist almost exclusively of cholic acid and this spectrum was not altered by cholestyramine. The daily rate of synthesis of bile acids in normal mice was 0.56 mg, 1.84 mg in cholestyramine-treated mice. Digi-tonin precipitable fecal sterol excretion was 5.54 mg day in normal mice, 7.58 mg/day in mice treated with 1% MK 135. No conclusion could be reached as to whether the increased rate of mobilization of accumulated cholesterol affected by MK 135 was due to the increased excretion of either the fecal bile acid or sterol fraction exclusively, or was attributable to the excretion of both these fractions. We wish to acknowledge the excellent technical assistance of Mrs. J. Bertasius. We also wish to thank Merck Sharp and Dohme Research Laboratories for a generous gift of cholestyramine.

Effects of conjugated bile acids on in vivo cholesterol metabolism in the mouse.

Summary Free and conjugated bile acids had qualitatively similar effects on mouse liver cholesterol levels and in vivo cholesterol-x-C14 synthesis rates. The effects of free bile acids on cholesterol metabolism are not due to the exhaustion of amino acids used in formation of glycine and taurine conjugates.

Effects of accumulated tissue cholesterol on bile acid metabolism in hypophysectomized rats and hamsters

Abstract The effects of accumulated tissue cholesterol concentrations on bile acid half-lives, pool sizes and excretion rates were studied in normal and hypophysectomized rats, and hamsters. High tissue cholesterol concentrations caused decreased bile acid half-lives in both normal and hypophysectomized rats. Total bile acid pool sizes remained static in both types of rats. In normal rats, there was a decrease in the cholic acid and a compensating increase in the chenodeoxycholic acid pool size. No change was observed in hypophysectomized rat pool spectra. Bile acid synthesis rates increased in both hypophysectomized and normal rats in response to elevated tissue cholesterol. Hamster bile acid net synthesis was unchanged by accumulated cholesterol, because an increase in the cholic acid half-life was compensated for by an increase in cholic acid pool size, and the chenodeoxycholic half-life and pool size were static. The relationship of these findings to comparative rates of tissue cholesterol accumulation in the three animals fed diets supplemented with cholesterol is discussed.

A Partial Dominant for Suppression of Color in the Syrian Hamster, Cricetus Mesocricetus auratus

In the last few years there have been several reports of a blind, pinkeared albino hamster, recently described by Knapp and Polivanov (1958). In contrast to the dark eared albino (designated cdcd by Robinson) in which faint grey pigmentation of the ears appears at about four weeks and develops fully to a deep grey or black by maturity, pigmentation is completely suppressed in the blind albino. In addition these animals demonstrate an incomplete optic development, while the dark-eared albinos eyes function normally. Knapp and Polivanov noted anophthalmia in all their animals, but microphthalmic albinos have been reported by other breeders. Albert Marsh reported (unpublished observations, 1955) that blind whites had appeared several years previously in Wisconsin, and had been bred to several hundred specimens. Bred to normal goldens, a golden F1 resulted, and the F2 consisted of golden and blind whites. Bred to the dark-eared albino, a golden F, was again produced, and the F2 was made up of golden, dark-eared, albino, and blind whites. Marsh, as well as Knapp and Polivanov, came to the conclusion that the factors for complete albinism and blindness could not be separated. Recently we obtained an extremely white panda, or piebald, (ss) male hamster with ruby eyes. (This dilution of eye color is often produced in the panda when the pattern of white spotting passes over the eye.) This male, bred to a normal female carrying a panda factor, produced an F1 of 16, of which nine survived. Of these three were normals, while the other six were distinguished by distinct ruby eyes and a white ventrum (WV) (in contrast to the usual ventral coloring of light grey underfur with pale cream tips). At maturity a few small clumps of white hair were discernible in the dorsal area of some WV. None exhibited the white blaze normally associated with panda. The lack of pandas may be attributed to their typical lower viability and inability to cope with competition of hardier littermates. A pair of WV were bred, resulting in the appearance of two blind pinkeared albinos (BA), along with five WV and two normals. At least one BA has occurred in all subsequent F2 (WV x WV) litters. These albinos differ from those of Knapp and Polivanov only in the matter of eye development, being characterized by microphthalmia rather than anophthalmia. Size of the eyeball at 19 days is one-half to one-third that of a normal littermate. In addition, the eyeball may be either opaque or clear. It is of interest to note

EFFECTS OF HYPOPHYSECTOMY, THYROIDECTOMY AND THYROID HORMONES ON STEROID METABOLISM IN THE RAT.

Summary Steroid turnover in normal (N), hypophysectornized (H), I131-thyroidectomized (T), and hypophysectomized-thyroidtreated (HT) rats was investigated. Following injection of dl-mevalonic acid-2-C14, feces were collected for a 14-day period. When compared with normals, cumulative fecal bile acid-C14 excretion was reduced about 20% in H and T; while in HT, bile acid-C14 excretion approached normal rate. Cumulative fecal α + β-sterol-C14 excretion was reduced 28% in T, but was similar to normal in H and HT. Total fecal cholesterol plus coprostanol excretion was reduced in both H (-45%) and T (-25%). Thyroid hormone treatment of hypophysectornized rats resulted in a small increase in fecal sterol excretion, but the daily rate was still below normal (-30%). The total steroid-C14 synthesized from mevalonic acid-2-C14 was reduced from normal in both T and H. HT synthesized almost normal amounts of total steroid-C14. It was concluded that lack of the thyroid hormone in hypophysectomized rats accounts for some of the effects of hypophysectomy on steroid metabolism. However other hormones must also be important, since the effects of thyroidectomy were not the same as those of hypophysectomy and thyroid administration did not restore some aspects of steroid metabolism to normal.

Bile acid synthesis in normal and hypophysectomized rats: a rate study using cholestyramine.

Summary Two sequences are involved in the elimination of tissue sterol via the bile acid pathway: the conversion of the sterols to bile acids, and the elimination of these bile acids from their pool. Since either of these could be rate-limiting, we investigated this point in normal and hypophysectomized rats. Cholestyramine (MK-135) was used to increase the turnover rate of the bile acid pool. Since the bile acid pool sizes did not decrease when faster turnover rates were induced, the rate of bile acid elimination and not the rate of conversion of liver sterols to bile acids was shown to be the rate-limiting sequence in both types of rats. It thus appears that thyroid, adrenal, gonadal or pituitary hormones do not directly influence the rate of conversion of sterols to bile acids in this species. We wish to thank Merck-Sharp & Dohme Research Laboratories for a generous gift of chioles-tyramine.

Steroid-C14 metabolism in bile acid and cholesterol-treated mice after injection of mevalonic acid-2-C14.

Summary The effects of bile acid and cholesterol on the time-pattern of fecal steroid-C14 elimination was investigated in mice following a single injection of mevalonic acid-2-C14. In controls, excreted bile acid-C14 assayed 3 times sterol-C14 during the first 24 hours. This ratio reversed during the 2nd 24-hour period, and remained constant for the remainder of the 7-day experiment. Cholic acid depressed bile acid-C14 excretion, but failed to alter the time pattern of fecal sterol-C14 elimination. Cholesterol plus cholic acid depressed bile acid-C14 and increased α + β sterol-C14 excretion throughout the experiment. Hyodeoxycholic acid increased sterol-C14 excretion (shown to be of hepatic origin), had little effect on bile acid-C14 excretion, and increased total steroid-C14 eliminated. Lithocholic acid had a similar though smaller effect. After sacrifice, the livers of cholic acid-treated mice had twice the β-sterol-C14 concentration found in livers of controls, while those of mice treated with cholesterol plus cholic acid had β-sterol-C14 levels 4 times as high. Livers of lithocholic and hyodeoxycholic acid-treated animals showed reduced β-sterol-C14 levels. Carcass β-sterol-C14 levels were unaffected by any of the bile acids, but were lowered by the combination of cholesterol and cholic acid. The total amount of sterol-C14 synthesized from injected mevalonic acid was similar in all cases.