Effects of palmitate and oleate on the respiratory quotient during acute feeding

Objective: Using tracers, we showed, over 9 hours, that palmitic acid (PA) is oxidized at a lower rate than oleic acid (OA). Our subsequent clinical trial showed that enriching the diet for 28 days with PA, relative to OA, lowered fatty acid (FA) oxidation. However, because this conclusion was based on indirect calorimetry for 7 hours after a test meal, transient differences in the kinetics of oxidation of OA and PA could explain these results. Thus, we hypothesized that increasing PA vs. OA would decrease FA oxidation during the first day of feeding the diets. Research Methods and Procedures: A double‐masked trial was conducted in 20 adults, who, after a baseline diet, were randomized to one of two experimental formula diets: high (HI) OA (PA = 1.7% kcal, OA = 31.4% kcal; N = 11) or HI PA (PA = 16.8% kcal, OA = 16.4% kcal; N = 9). Respiratory quotient (RQ) was measured over the first 14 hours of feeding the experimental diets (7:00 am to 9:00 pm ). To determine whether these subjects were representative of the subjects in the previous trial, we assessed RQ 28 days after beginning either diet. Results: During the first 14 hours of feeding the diets, time (p = 0.026) but not diet group had an effect on the difference between the RQ post‐feeding and the fasting pre‐value. However, RQ in the fed state was significantly higher in the HI PA group after 28 days of feeding. Discussion: Chronically increasing dietary PA for 28 days, but not acute meal feeding, lowers total FA oxidation.     

Peripheral nervous control of cold-induced reduction in the respiratory quotient of the rat

Cold-exposed rats show a reduction in the respiratory quotient which is indicative of a relative shift from carbohydrates to lipids as substrates for oxidative metabolism. In the present study, the effects of food deprivation and cold exposure on the respiratory quotient were observed. In addition, the involvement of the three main branches of the peripheral nervous system (sympathetic, parasympathetic, and somatic) was investigated by means of synaptic blockade with propranolol, atropine, and quinine, respectively. Both propranolol and quinine blocked the cold-induced decrease in respiratory quotient and increase in heat production, whereas atropine had only minor and very brief effects. It is concluded that both the sympathetic and somatic branches are involved in the metabolic changes associated with cold-induced thermogenesis and that the increase in metabolic heat production involves a shift from carbohydrate to lipid utilization irrespective of which of the two branches is activated.     

Effects of cold shock on the susceptibility of white lupins to fungal diseases

Experiments in controlled environments tested interactions between freezing soil (a compost-vermiculite mixture) and below-ground infection of white lupins with each of three pathogenic fungi (Botrytis cinerea, Fusarium avenaceum or Pleiochaeta setosa) on plant disease and death. Whilst soil freezing (up to 4 days at – 1^oC) caused slight necrosis and increased the severity of disease symptoms, incidence of plant death was increased only after inoculation, before freezing, of the lower hypocotyl of the youngest plants (soil frozen at less than 17 days old) with P. setosa. It is concluded that the contribution of below-ground infection by pathogenic fungi to overwinter losses in autumn-sown white lupin crops is exacerbated to a negligible extent by soil freezing, the main primary cause of such losses.     

Effects of post-weaning environment on learning in the rat

Rats were reared in three different kinds of post-weaning environment: (1) with litter-mates and a variety of playthings (objects/social), (2) without either litter-mates or playthings (no-objects/isolates), (3) with litter-mates, but without playthings (no-objects/social). The animals were subsequently tested on a variety of learning tasks. In one task, the rats had to remove an obstacle from an alley in order to enter a food compartment; subsequently they were required to remove the obstacle in a different way from the one they had learned. Another task was to open a door leading to a food compartment; when the rats and learned this, the floor of the apparatus was lowered so they had to reach the door by climbing a ladder. Object-deprived/isolates were slower than the objects/social group in the transfer phase of the above tasks, though not in original acquisition. Object-deprived/social animals were not inferior to an objects/social group. Isolates had a higher free feeding weight than social animals, were more active in an open field, and ran faster for food reward when deprived.     

Effects of methyl-deficient diets on methionine and homocysteine metabolism in the pregnant rat

Although the importance of methyl metabolism in fetal development is well recognized, there is limited information on the dynamics of methionine flow through maternal and fetal tissues and on how this is related to circulating total homocysteine concentrations. Rates of homocysteine remethylation in maternal and fetal tissues on days 11, 19, and 21 of gestation were measured in pregnant rats fed diets with limiting or surplus amounts of folic acid and choline at two levels of methionine and then infused with L-[1-(13)C,(2)H(3)-methyl]methionine. The rate of homocysteine remethylation was highest in maternal liver and declined as gestation progressed. Diets deficient in folic acid and choline reduced the production of methionine from homocysteine in maternal liver only in the animals fed a methionine-limited diet. Throughout gestation, the pancreas exported homocysteine for methylation within other tissues. Little or no methionine cycle activity was detected in the placenta at days 19 and 21 of gestation, but, during this period, fetal tissues, especially the liver, synthesized methionine from homocysteine. Greater enrichment of homocysteine in maternal plasma than placenta, even in animals fed the most-deficient diets, shows that the placenta did not contribute homocysteine to maternal plasma. Methionine synthesis from homocysteine in fetal tissues was maintained or increased when the dams were fed folate- and choline-deficient methionine-restricted diets. This study shows that methyl-deficient diets decrease the remethylation of homocysteine within maternal tissues but that these rates are protected to some extent within fetal tissues.     

Effects of hypoxia and cold acclimation on thermoregulation in the rat.

The effects of hypoxia (inspired O2 fraction = 0.12) on thermoregulation and on the different sources of thermogenesis were studied in rats before and after periods of 1-4 wk of cold acclimation. Measurements of metabolic rate (VO2) and body temperature (Tb) were made at 5-min intervals, and shivering activity was recorded continuously in groups of rats subjected to three protocols. In protocol 1, rats were exposed to normoxia to an ambient temperature (Ta) of 5 degrees C for 2 h. In protocol 2, at Ta of 5 degrees C, rats were exposed for 30 min to normoxia, then for 45 min to hypoxia, and finally for 30 min to normoxia. In protocol 3, in the non-cold-acclimated (NCA) rats, Ta was decreased from 30 to 5 degrees C in steps of 5 degrees C and of 30-min duration while in cold-acclimated (CA) rats at 5 degrees C for 4-wk, Ta was increased from 5 to 30 degrees C in steps of 5 degrees C and of 30-min duration. Recordings were made in normoxia and in hypoxia on different days in the same animals. The results showed that 1) in NCA rats, cold exposure in normoxia induced increases in VO2 and shivering that were proportional to the decrease in Ta; 2) in CA rats in normoxia, for a given Ta, VO2 and Tb were higher than in NCA rats, whereas shivering was generally lower; and 3) in both NCA and CA rats, hypoxia induced a transient decrease in shivering and a sustained decrease in nonshivering thermogenesis associated with a marked decrease in Tb that was about the same in NCA and CA rats. We speculate that hypoxia acts on Tb control to produce a general inhibition of thermogenesis. Nonshivering thermogenesis is markedly sensitive to hypoxia, especially demonstrable in CA rats; a recovery or even an increase in shivering can compensate for the decrease in nonshivering thermogenesis.     

The effect of cold exposure on rat liver mitochondrial respiratory capacity.

1. The effect of cold exposure on the respiratory capacity of rat liver mitochondria has been studied using succinate as the substrate. 2. The mitochondria obtained in this study were well coupled, as shown by the RCR and ADP/O ratios. 3. In addition, durohydroquinone was used to eliminate the regulation of substrate supply. Likewise, we measured uncoupled respiration to evaluate the maximal electron flow through the respiratory chain. 4. We found that oxygen consumption using succinate or durohydroquinone + FCCP as substrates, as well as ATP production were not affected by cold exposure. 5. Our results also show that, when succinate is used, the maximal capacity of the respiratory chain is measured. 6. The data obtained do not support a role of the electron transport chain as a target of cold action.