Effects of central administration of distinct fatty acids on hypothalamic neuropeptide expression and energy metabolism.

OBJECTIVE: To investigate the differential effects of acute central administration of distinct fatty acids (FA) on food intake, body weight and energy metabolism. DESIGN: Male Sprague-Dawley rats were treated with bolus intracerebroventricular injections of control hydroxypropyl-ß-cyclodextrin (HPB) or HPB complexed with 30 nmol of saturated palmitic acid (PA), monounsaturated oleic acid (OA) or polyunsaturated ω-3 docosahexaenoic acid (DHA). Food intake, body weight, neuropeptide expression and various serum parameters were assessed. RESULTS: When compared with controls, rats injected with either OA or DHA had significantly reduced food intake and body weight for 48 h following injections. No significant changes in food intake or body weight were observed in the PA group. In conjunction with reduced food intake, hypothalamic anorexigenic pro-opiomelanocortin (POMC) gene expression was significantly augmented in the OA and DHA groups, with essentially no changes observed in the PA group. Changes in serum measures of energy metabolism also changed coinciding with the observed differences in food intake. Moreover, central administration of SHU9119, a melanocortin-4-receptor (MC4R) antagonist, completely abolished the anorexigenic actions of OA, suggesting a role for OA-induced augmentation of hypothalamic POMC expression in mediating its central inhibition of food intake. CONCLUSIONS: The hypothalamus differentially senses FA and, specifically, that OA and DHA, but not PA, reduce food intake and body weight, which may be mediated through POMC/MC4R signaling.

Effects of intravenous triacylglycerol emulsions on hepatic metabolism and blood metabolites in fasted dairy cows.

The objective was to determine the effects of intravenous infusion of triacylglycerol (TAG) emulsions derived from different lipid sources on energy metabolism during a 4-d fast. Six nonpregnant, nonlactating multiparous Holstein cows were randomly assigned to treatments in a replicated 3 x 3 Latin Square design. Treatments included intravenous infusion of tallow, linseed oil, or fish oil emulsions at a rate of 0.54 g of TAG/kg of body weight per day; infusions were concurrent with a 4-d fast. The emulsions were administered for 20 to 30 min every 4 h throughout the 4-d fast. Cows were fed ad libitum for 24 d between the fast/infusion periods. Infusion of tallow, linseed oil, or fish oil emulsions increased plasma concentrations of palmitic acid, linolenic acid, and eicosapentaenoic and docosahexaenoic acids, respectively. Infusion of linseed oil emulsion decreased plasma TAG concentrations compared with tallow and fish oil treatments, which were similar. Infusion of the tallow emulsion resulted in the highest concentrations of plasma nonesterified fatty acid (NEFA), insulin, and glucose, whereas the infusion derived from linseed oil had the lowest NEFA and beta-hydroxybutyric acid concentrations. The different TAG emulsions had no effect on total or peroxisomal oxidation of [1-(14C)]oleic acid in liver homogenates. Liver TAG content increased 12.0, 7.8, and 14.1 microg/microg of DNA during the fast for tallow, linseed oil, and fish oil treatments, respectively; linseed oil was different from fish oil and tended to be different from tallow.

Effects of a four-day hyperinsulinemic-euglycemic clamp in early and mid-lactation dairy cows on plasma concentrations of metabolites, hormones, and binding proteins.

The effects of insulin, using a 4 d hyperinsulinemic-euglycemic clamp, on plasma concentrations of hormone, metabolites, and binding proteins were evaluated in four Holstein dairy cows during wk 4 and 17 of lactation. Insulin was infused at 1 microg/kg/hr for 96 hr during the clamp period. Compared with the pre-clamp period, plasma insulin concentrations increased 7-fold and 4-fold during the clamp periods in early and mid-lactation, respectively. The total amount of glucose infused was higher (P < 0.05) during the clamp in early lactation. The clamp decreased plasma concentrations of non-esterified fatty acids (P < 0.001) during early lactation while differences in mid-lactation were minor. The clamp also decreased plasma concentration of beta-hydroxybutyrate (P < 0.001), plasma urea nitrogen (P < 0.001), and true protein (P < 0.01) although the patterns of decline differed between early and mid-lactation. Growth hormone (GH) concentrations decreased (P < 0.001) and insulin-like growth factor-1 (IGF-1) increased (P < 0.01) during the clamp period suggesting a direct effect of insulin on the un-coupling of the GH/IGF-1 axis. Levels of IGF binding protein-2 (IGFBP-2) decreased (P < 0.01) during the clamp period. The relative proportion of IGFBP-2 decreased (P < 0.001) and that of IGFBP-3 increased (P < 0.001) during the clamp period. There were no interactions between the clamp period and stage of lactation on GH, IGF-1, or IGFBPs. Overall, most plasma variables measured were affected in the same way during the two clamps, but the pattern of change often varied with stage of lactation.

Peripartum responses of dairy cows to partial substitution of corn silage with corn grain in diets fed during the late dry period.

We randomly assigned 189 cows in a commercial dairy farm to dietary treatments with supplemental corn grain (SC) or without supplemental corn grain (NC) approximately 3 wk before expected parturition. Diets formulated were similar except that dry ground corn replaced 21% of the corn silage in one diet. Cows fed SC had reduced plasma beta-hydroxybutyrate and tended to have increased plasma insulin concentrations prepartum compared with cows fed NC. Treatment did not affect nonesterified fatty acid concentrations prepartum, any blood variables postpartum, or incidences of health disorders. Effects of treatment on production responses were highly dependent on parity as indicated by parity x treatment x time interactions for milk and protein yields. Primiparous cows fed SC had lower milk protein yield, higher somatic cell count and days open compared with cows fed NC. The SC diet resulted in lower milk yields in early lactation and increased somatic cell count and days open for cows in second parity. However, cows in third parity or greater fed the SC diet yielded more milk and protein in early lactation, and had decreased somatic cell counts and days open. Increasing the corn grain concentration of the diet fed prepartum was advantageous to third and greater parity cows in this experiment, but showed no benefits during lactation for cows in first or second parities.