Force-fed Diets Research Articles

Peroxisome proliferator-activated receptors, estrogenic responses and biotransformation system in the liver of salmon exposed to tributyltin and second messenger activator

The mechanisms by which organotin compounds produce modulations of the endocrine systems and other biological responses are not fully understood. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10 mg/kg fish) for 72 h. Subsequently, fish exposed to solvent control and 10 mg TBT were exposed to waterborne concentration (200 μg/l) of the adenylate cyclase (AC) stimulator, forskolin for 2 and 4 h. The overall aim of the study was to explore whether TBT endocrine disruptive effects involve second messenger activation. Liver was sampled from individual fish ( n = 8) at the end of the exposures. The transcription patterns of peroxisome proliferator-activated receptor (PPAR) isotype and acyl-coenzyme A oxidase 1 (ACOX1), aromatase isoform, estrogen receptor-α (ERα), pregnane X receptor (PXR), CYP3A and glutathione S-transferase (GST) genes were measured by quantitative polymerase chain reaction (qPCR). Our data showed a consistent increase in PPARα, PPARβ and PPARγ mRNA and protein expression after TBT exposure that were inversely correlated with ACOX1 mRNA levels. Forskolin produced PPAR isotype-specific mRNA and protein effects that were modulated by TBT. ACOX1 expression was decreased (at 2 h) and increased (at 4 h) by forskolin and the presence of TBT potentiated these effects. TBT apparently increased mRNA and protein levels of cyp19a, compared to the solvent control, whereas cyp19b mRNA levels were unaffected by TBT treatment. Combined TBT and forskolin exposure produced respective decrease and increase of mRNA levels of cyp19a and cyp19b, compared with control. TBT decreased ERα mRNA at low dose (1 mg/kg) and forskolin exposure alone produced a consistent decrease of ERα mRNA levels that were not affected by the presence of TBT. Interestingly, PXR and CYP3A mRNA levels were differentially affected, either decreased or increased, after exposure to TBT and forskolin, singly and also in combination. GST mRNA was increased by TBT exposure. Exposure to forskolin alone increased GST expression with time, and combined exposure with TBT potentiated these respective effects. Overall, the present study demonstrates multiple biological effects of TBT given singly or in combination with cAMP activator. There are no studies known to us that have evaluated the endocrine disruptive effects of TBT in the presence of a second messenger activator, and our data suggest that TBT may exert endocrine, biotransformation and lipid peroxidative effects through modulation of cAMP/PKA second messenger signaling with overt physiological consequences.

Effects of tributyltin on salmon interrenal CYP11β, steroidogenic factor-1 and glucocorticoid receptor transcripts in the presence and absence of second messenger activator, forskolin

The mechanisms by which TBT produces modulations of the endocrine systems are not fully described. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10 mg/kg fish) for 72 h. Subsequently, fish exposed to solvent control and 10 mg/kg TBT were exposed to waterborne concentration of the adenyl cyclase stimulator forskolin (200 μg/L) for 2 and 4 h. Tissue and blood were sampled from individual fish ( n = 6). Gene expression patterns of CYP11β, steroidogenic factor-1 (SF-1), and glucocorticoid receptor (GlucR) were determined by qPCR. TBT generally decreased mRNA levels of CYP11β, GlucR and SF-1, compared to the solvent control and these effects were differentially modulated by the presence of forskolin. This study suggests that TBT may exert broader endocrine disrupting effects through possible modulation of cAMP/PKA second messenger systems.

Metabolizable Energy Value of Conjugated Linoleic Acid for Broiler Chicks and Laying Hens

Two experiments with broiler chicks and one experiment with laying hens were conducted to determine the MEn value of conjugated linoleic acid (CLA). In Experiment 1, for 8 d, 16-d-old chicks were fed diets in which 4, 8, or 12% of CLA Source A or 4, 8, or 12% of soybean oil (SO) was substituted for glucose. Dietary MEn increased linearly (P < or = 0.001) with increments of CLA Source A or SO. Regression analysis relating increases in dietary MEn and increments of the dietary fat sources showed that the MEn values of CLA Source A and SO, when evaluated separately, were 7,419 and 8,429 kcal/kg, respectively. In Experiment 2, feed was withheld from laying hens for 38 h and then the hens were force-fed diets containing 15% glucose, 15% CLA Source A, or 15% SO (two feedings of 30 g each). Excreta samples were collected for 36 h after the last feeding. The MEn values obtained for CLA Source A and SO were 8,517 and 8,437 kcal/kg, respectively. The MEn of CLA Source B (higher in unsaturated fatty acids than CLA Source A) was determined in Experiment 3 by feeding diets containing 4, 8, or 12% CLA Source B to 14-d-old chicks. Increases in dietary MEn with increments of CLA Source B were curvilinear, with resulting MEn of 9,375 to 9,588 kcal/kg of fat when CLA Source B was fed at 4 or 8% of the diet and 7,917 kcal/kg when fed at 12% of the diet. Results of this research show that CLA sources can contribute substantial energy to diets, but the MEn value of CLA sources for young chicks varies with fatty acid composition and dietary concentration.

GROWTH INHIBITION IN BONE AND BONE MARROW FOLLOWING TREATMENT WITH ADRENOCORTICOTROPIN (ACTH)

The action of ACTH on the tibia of immature rats has been studied by Becks, Simpson, Li and Evans (1944) and by Becks, Simpson, Marx, Li and Evans (1944). These workers observed retardation of chondrogenesis and osteogenesis to follow treatment of immature rats with ACTH. Likewise, ACTH antagonized the action of growth hormone when both were injected inbo hypophysectomized rats. The experiments now being reported supplement these observations by adding information regarding the action of ACTH on the bones of (1) adult rats, (2) under varied dietary conditions controlled by tube feeding and (3) at higher dose levels. In addition, the effect of ACTH on the bone marrow and vertebrae will be discussed. materials and methods The general plan of attack for these experiments has been outlined in detail elsewhere (Baker, Ingle, Li and Evans, 1948). Adult male rats (Sprague-Dawley strain) were force-fed diets high in carbohydrate, fat or protein.

EFFECT OF DIET ON GLUCOSE TOLERANCE AND LIVER AND MUSCLE GLYCOGEN OF HYPOPHYSECTOMIZED AND NORMAL RATS1,2

THE HYPOPHYSECTOMIZED RAT on an ad libitum or force-fed diet has been shown to exhibit an abnormal glucose tolerance curve (1, 2, 3). During the period of rapid glycogen formation the rate of removal of glucose from the blood is less than normal, but during the later period when glycogenolysis maintains the bloodsugar level in normal animals, the blood-sugar level of the hypophysectomized rat continues to fall. This appears to be the result of the rapid removal of glucose from the blood stream by the peripheral tissues as demonstrated by Greeley in the hypophysectomized rabbit (4). In balance studies on rats fed high carbohydrate and high fat diets by stomach tube for 10 to 17 days after hypophysectomy, it was found that while the carbohydrate-fed rats showed a low metabolic rate and lower carbohydrate stores than control animals on the same diet, the fat-fed animals still had a normal metabolic rate and a normal amount of carbohydrate in their bodies (5).