The objective of this study was to measure changes in body composition, physical activity and adipose and skeletal muscle gene expression of cats fed a high-protein (HP) diet or moderate-protein (MP) diet, following ovariohysterectomy. Eight cats were randomized onto HP or MP diets and were fed those diets for several months prior to baseline. All cats underwent an ovariohysterectomy at baseline (week 0) and were allowed ad libitum access to dietary treatments for 24 weeks. Food intake was measured daily, and BW and body condition score were measured weekly. Blood, adipose and skeletal muscle tissue samples were collected, physical activity was measured, and body composition was determined using DEXA (dual-energy X-ray absorptiometry) at weeks 0, 12 and 24. Caloric intake increased soon after ovariohysterectomy, resulting in increased ( P , 0.05) BW at weeks 12 and 24 compared to week 0. Body condition score and body fat percentage increased ( P , 0.05) over time. Blood glucose increased ( P , 0.05) linearly over time. Non-esterified fatty acids were decreased ( P , 0.05) at weeks 12 and 24 compared to week 0. Blood leptin increased ( P , 0.05) over time. Total physical activity decreased ( P , 0.05) from week 0 to weeks 12 and 24 in all cats. Adipose tissue mRNA abundance of adiponectin, hormone sensitive lipase, toll-like receptor-4, uncoupling protein-2 (UCP2) and vascular endothelial growth factor decreased ( P , 0.05) linearly over time, regardless of diet. Skeletal muscle mRNA abundance for glucose transporter-1, hormone sensitive lipase and UCP2 were decreased ( P , 0.05), regardless of dietary treatment. Our research noted metabolic changes following ovariohysterectomy that are in agreement with gene expression changes pertaining to lipid metabolism. Feeding cats ad libitum after ovariohysterectomy is inadvisable.

3018 Poster Board II-994 Recent evidence from our laboratory and others suggests that a variable portion of ingested cobalamin (Cbl), either crystalline or from food, is degraded in the gastrointestinal tract. We have developed a biosynthetic method to incorporate 14C into the lower axial ligand of cobalamin that has made it possible to study the fate of this vitamin during its passage through the gastrointestinal tract and to assess the presence of Cbl or its breakdown products in biological samples. Following oral administration of an aqueous physiological tracer dose of 14C-Cbl (1.3 μg, 50 nCi), blood, urine, and feces are analyzed for 14C by accelerator mass spectrometry. In 9 subjects, the plasma response was consistent with the expected behavior of peroral Cbl: 14C-Cbl first appeared in the plasma 3h post-dose reaching a peak level within 6-8h. Confirmation that this dose appears bound to the physiological transport protein transcobalamin (TC) was obtained in a subset of subjects by an immunoaffinity method using anti-human TC antibody-coated magnetic beads which selectively bound 95-98% of plasma 14C. Urinary excretion of 14C was maximal in the first 24h, with 14C first appearing in urine as early as 1.5h after dosing. Fecal excretion occurred variably over several days. The amount of 14C found in the urine (10-50% of the dose) was 100-fold greater than in previous reports using 57Co-labeled cyanocobalamin (0.1-0.5%), and fecal excretion was lower than expected (10-20% vs 30-70%). Urinary excretion of 14C was inversely correlated with the peak plasma level of 14C attained (r2=0.610; p<0.001). The bulk of urinary 14C was not associated with intact Cbl and first appeared in the urine before peak 14C levels were attained in the plasma. The peak plasma level of 14C attained also showed a strong positive correlation with plasma holotranscobalamin concentration measured before administration of the 14C-Cbl (r2=0.571; p<0.001). No such correlation was found with total plasma Cbl. In additional experiments on normal volunteers using eggs endogenously labeled with 14C Cbl following intramuscular injection of hens with 14C Cbl, comparably high urinary excretion of 14C was also observed. We conclude that a variable fraction of ingested Cbl is degraded in the gastrointestinal tract of normal individuals. This may be an important determinant of the amount of Cbl absorbed from food or supplement sources. Additionally, our findings suggest that the concentration of holoTC in the plasma reflects absorptive capacity and may therefore be a good surrogate for Cbl absorptive status. Our findings also have implications regarding the bioavailability of Cbl and may inform pending considerations to fortify food supplies with Cbl in order to mitigate the incidence of Cbl deficiency, particularly among the elderly. Intestinal degradation, either microbial or through the action of digestive enzymes, may also be a source of Cbl analogues that have previously been detected in the plasma and tissues. Cbl analogues may interfere with the physiological function of cobalamin, resulting in some of the manifestations of cobalamin deficiency. Disclosures: Green: Vitalea Science: Research Funding. Miller:Vitalea Science: Research Funding. Lee:Vitalea Science: Research Funding. Sutter:Vitalea Science: Research Funding. Allen:Vitalea Science: Research Funding. Dueker:Vitalea Science: Employment.

Much of our understanding of vitamin B12 derives from radiocobalt tracer studies conducted decades ago. With new technologies, we can now study B12 absorption and metabolism with unprecedented resolution using almost ambient levels of 14C biosynthetically incorporated into the B12 molecule (14C‐B12). In on‐going studies, a dose of 14C‐B12 (1.3 µg, 50 nCi) in water is administered orally and blood, urine, and feces analyzed for 14C by accelerator mass spectrometry. In 6 subjects, the plasma response was consistent with the expected behavior of peroral B12: 14C‐B12 first appeared in the plasma 3h post‐dose with a peak level within 6‐8h. Urinary and fecal excretion was maximal in the first 24h. The amount of 14C found in the urine (10‐50% of the dose) was 100‐fold greater than in previous reports (0.1‐0.5%), and fecal excretion was lower than expected (<10% vs 30‐70%). Most of the urinary 14C was not associated with intact B12. These results are consistent with metabolism or degradation of the vitamin in the GI tract prior to absorption. The discrepancy between the present and previous findings may be due to the form of radioactive B12 used: 14C labeling the 5,6‐dimethylbenzimidazole moiety in the present study and radiocobalt labeling the corrin ring in previous studies. These findings provide valuable information on the fate of B12 after oral consumption that will inform considerations to fortify the food supply with B12.