In goats and other ruminants, urea functions as a source of nitrogen for protein biosynthesis in the digestive tract. Ammonia can be absorbed in the digestive system when formed in excessive quantitites and enhance formation of urea, or it can be derived from urea of blood plasma when its formation from feed sources is small. Entry rates of urea into plasma may vary from 4 to 80 mumol/min per kg.75 body weight depending on dietary conditions. Urea formation is related to nitrogen intake of which approximately 70% passes into the urea pool of plasma. Irreversible losses of urea of plasma into the digestive tract vary between 10 and 90% depending on the protein to energy ratios of the diet. Entry of urea from plasma into the rumen appears to be a passive process which is sensitive to short-term changes of urea concentrations in plasma. Permeability of ruminal epithelium to urea may be altered by fermentation products of rumen (ammonia, carbon dioxide, volatile fatty acids). The influx of nitrogen into the rumen is related to needs for nitrogen of microbial populations and is associated with changes of renal excretion and tubular reabsorption of urea. Combined gastrointestinal and renal responses exert a synergistic effect on improved utilization of urea of plasma when uptake of dietary nitrogen is limited in goats and other ruminants.
The present study was undertaken to test the hypothesis that high ketone body concentrations suppress endogenous production of glucose and in pregnant sheep facilitate development of pregnancy toxemia. Rates of endogenous glucose production [mmol.min(-1)], and rate constants of glucose turnover [min(-1)] were measured in seven 12-h fasted sheep in the presence of normo- and hyperketonemia by use of D-2-[(3)H]-glucose. The measurements were carried out in the same sheep during the nonpregnant nonlactating state, during late pregnancy (10 +/- 7 d antepartum) and during lactation (19 +/- 6 d postpartum). Hyperketonemia (5 to 7 mmol.L(-1)), similar to that present in spontaneous ovine pregnancy toxemia, was induced by continuous intravenous 4-h infusions of DL-beta-hydroxybutyrate (DL-BHB). Glucose turnover [mmol.min(-1)] in the same 7 nonpregnant nonlactating, late pregnant, and lactating sheep was significantly greater during normoketonemia (0.80, 1.16, 1.76) than during hyperketonemia (0.66, 0.92, 1.16, respectively). The rate constants of glucose turnover were not altered by elevation of the BHB concentration. The results demonstrated that high BHB concentrations significantly suppressed endogenous glucose production but showed no effect on glucose utilization. The suppressive effect of hyperketonemia on hepatic glucose production resulted in a significant reduction of plasma glucose concentration and was qualitatively the same in all three reproductive states. The results indicate that hyperketonemia, which is regularly present in late twin pregnant hypoglycemic sheep contributes significantly to the reduction of available glucose. This effect of hyperketonemia may invoke sustained hypoglycemia and may render the ewe into a vicious cycle that probably makes the animal refractory to treatment in most cases.
The role of vitamin D in regulating placental transport of calcium and phosphate in pigs was studied using the "Hannover Pig Strain" which suffers from pseudo-vitamin D-deficiency rickets, type I. Sows and fetuses of normal phenotype (heterozygotes) and of homozygote phenotype which suffered from clinical symptoms of rickets were used. The homozygote animals are devoid of renal 25-cholecalciferol-1-hydroxylase. In the rachitic sows which normally depend on treatment with pharmacological doses of vitamin D3 at intervals of four to six weeks, vitamin D-treatment was discontinued two months before conception. Ca, P and 1.25-(OH)2D3 concentrations in plasma of sows and fetuses (Aa. umb., V. umb.) were measured in samples obtained at term during cesarian section. Mean concentrations of Ca and P in heterozygote sows at parturition were 2.34 mmol/l and 2.33 mmol/l, respectively, and were significantly higher than in homozygote sows, 1.58 mmol/l and 1.26 mmol/l, respectively. Ca concentrations in plasma of the umbilical vein of fetuses from both homozygote and heterozygote sows were normal, however, (3.23 mmol/l and 2.96 mmol/l, respectively) and statistically not different from each other. No significantly different P concentrations in arterial plasma of fetuses from heterozygote or homozygote sows were seen, either. The concentrations of Ca and P in the arterial umbilical plasma were significantly higher (p less than 0.001) than in venous plasma of both homozygote and heterozygote fetuses, indicating net placental transfer of these elements in both genotypes. The concentration of 1.25-(OH)2D3 in hypocalcemic sows at term (25.5 +/- 8.25 pg/ml) was significantly lower than that in the normocalcemic (heterozygote) sows (84.1 +/- 25.6 pg/ml). The 1.25-(OH)2D3 concentration in arterial plasma of fetuses from homozygote sows was only 46% that of fetuses from normocalcemic sows which showed transfer of calcitriol from mother to fetus. It is concluded from these studies that in pigs, renal production and physiological concentrations of 1.25-(OH)2D3 in either mother or fetus is not essential for the maintainance of the Ca and P homeostasis in the fetal-maternal system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with đź’™ for researchers
Part of the Research Solutions Family.