Effect of acetate on glucose utilization by isolated rat thymocytes

The effects of acetate and ammonium salts on glucose metabolism, aminoisobutyric acid influx, and radioiodinated insulin binding in isolated thymocytes were studied. Acetate in the concentration range, 0.1–30 mm, was found to inhibit basal and insulin-stimulated CO₂ production whereas ammonium chloride at concentrations greater than 0.3 mm was slightly stimulatory. Ammonium salts inhibited glucose incorporation into glycogen and aminoisobutyric acid influx only at high concentration (30 mm). Neither acetate nor ammonium salts had significant effects on glucose incorporation into glycogen or aminoisobutyric acid influx at lower concentrations. No effect on insulin binding was observed. The observation that very low concentrations of acetate can perturb these biological assay systems suggests that other biological functions may be affected by trace amounts of buffer salts carried over from protein isolation steps.     

Effects of coprophagy on serum urea and the weight of the gastrointestinal tract of fed or fasted rats

Coprophagy can be minimized by fitting rat cages with metal grids which allow faecal pellets to pass through to the floor of the cage. When bedding was omitted overnight, the extent of coprophagy could be estimated from the weight of the droppings on the cage floor or the weight of the gastrointestinal (GI) tract removed from rats housed with or without grids. The effect of coprophagy was also demonstrated by the elevation of serum urea nitrogen in rats that consumed faeces. Therefore, precautions against coprophagy, or their absence, should be specified in all experimental protocols and reports.     

Effects of prevention of coprophagy on pregnant mice--is coprophagy beneficial on a balanced diet?

The effects of prevention of coprophagy on reproductive performance were examined in ICR mice. Females were treated with restrainers in order to prevent them from ingesting their feces from day 1 through day 17 of pregnancy. The restrained animals fed a commercial diet did not show any clear adverse effects. In contrast, restrained dams fed a purified diet deficient in vitamin B12 exhibited stillbirths (14%) and abortions (7%). Restrained dams fed a diet lacking in vitamin B12 and folic acid also experienced frequent abortions (27%). In addition, six out of 14 restrained dams (43%) aborted when fed a vitamin B complex-deficient diet. Sham-restrained animals, fed the vitamin B complex deficient-diet, but able to ingest their feces trapped by smaller-mesh floors, escaped these adverse effects. Sham-restrained animals fed the commercial diet, however, showed only a slight improvement in their reproductive performance. In conclusion, coprophagy has nutritional significance as long as the diet is lacking at least B vitamins, especially vitamin B12 and folic acid, whereas it almost entirely loses its nutritional significance when the mouse has access to a balanced diet such as the one made available to the laboratory mice in the present study.     

Effect of glycerin and urea on rat skeletal muscle twitches]

The dynamics of changes in the amplitude of isometric twitches of isolated EDL and SOL muscles of young rats influenced by low molecular non-electrolytes has been studied. Incubation of EDL in hypertonic glycerol or urea solution (400 mM) leads to a 80 and 60% decrease of twitches, respectively, within 15 minutes. During the following 1--2 hours the twitches restore the initial level or exceed it by 60% (urea). Removal of glycerol or urea causes a stable reduce of contraction up to 5--10% within 1 hour. Reincubation in these non-electrolytes increases twitches 3--4 fold during 1.5--2 hours. Alterations of SOL twitches in urea are the same as of EDL, while glycerol even in concentration of 600 mM produces only small changes. This appears to be determined by a higher permeability of slow muscle fibers to glycerol as compared to EDL. It is suggested that the decrease of twitches and their restore in non-electrolyte solution are determined by the hypertonic effect of the latter while reduction of twitches during non-electrolyte removal is caused by alteration of T-system.     

Effect of developmental stage on arginase and urea production in the liver of rat

Arginase activity in the liver, brain, and testis of rats was examined during the different phases of life span. When expressed as specific activity (micromoles of L-arginine hydrolyzed per minute per gram of whole homogenate protein), the enzyme activity in the brain and testis decreased markedly during the early stage of life and stayed low during the remainder of the life span. On the other hand, the arginase in the liver showed a great dependency on the developmental phase of the animal, showing two distinct peaks: one during the early phase (20 days after birth) and the other at a later time (3 months of age). This pattern of change in the hepatic arginase activity closely coincided with the pattern of the rate of urea synthesis determined with liver slices and expressed in terms of micromoles of urea formed per hour per gram of tissue slice. In contrast to the above observations, however, curves obtained by plotting the total liver arginase or urea synthetic activity vs the developmental stage of rats showed no measurable discontinuity. Further studies revealed that the observed pattern of specific activity of hepatic arginase was, in part, due to the change in the relative concentration of arginase protein in the liver.     

Effect of alanine on in vitro glucose utilization by rat interscapular brown adipose tissue

The rates of either glucose or alanine incorporation into tissue and oxidation to CO2 were studied in rat interscapular brown adipose tissue in order to evaluate the mutual influence of both substrates on their uptake and utilization. Tissue fragments were incubated in vitro in the presence of 1-10 mM glucose and 0.3-1.5 mM alanine. The highest glucose oxidation rate was obtained with the lowest alanine concentrations tested. This suggests that alanine inhibits glucose utilization by this tissue at concentrations that are within the physiological plasmatic range. Glucose levels had little effect upon alanine oxidation, but glucose had a permissive effect on the utilization of alanine. On the basis of these results, it is postulated that this glucose conservation effect of alanine on brown adipose tissue can help to prevent glucose wastage in postprandrial situations.     

Effect of glucose on the utilization of palmitate 1 14C by rat kidney cortex slices.

The authors studied the effect of glucose on the uptake and utilization of palmitate 1 14C by rat kidney cortex slices. They found that its inhibitory effect on free fatty acid (FFA) uptake was caused by inhibition of the incorporation of 1 14C-labelled palmitate into the total lipids and FFA and by reduced oxidation to 14CO2. Glucose has a regulative function in the utilization of FFA by the kidneys.