Determination of anaerobic threshold in rats using the lactate minimum test

The break point of the curve of blood lactate vs exercise load has been called anaerobic threshold (AT) and is considered to be an important indicator of endurance exercise capacity in human subjects. There are few studies of AT determination in animals. We describe a protocol for AT determination by the "lactate minimum test" in rats during swimming exercise. The test is based on the premise that during an incremental exercise test, and after a bout of maximal exercise, blood lactate decreases to a minimum and then increases again. This minimum value indicates the intensity of the AT. Adult male (90 days) Wistar rats adapted to swimming for 2 weeks were used. The initial state of lactic acidosis was obtained by making the animals jump into the water and swim while carrying a load equivalent to 50 percent of body weight for 6 min (30-s exercise interrupted by a 30-s rest). After a 9-min rest, blood was collected and the incremental swimming test was started. The test consisted of swimming while supporting loads of 4.5, 5.0, 5.5, 6.0 and 7.0 percent of body weight. Each exercise load lasted 5 min and was followed by a 30-s rest during which blood samples were taken. The blood lactate minimum was determined from a zero-gradient tangent to a spline function fitting the blood lactate vs workload curve. AT was estimated to be 4.95 ± 0.10 percent of body weight while interpolated blood lactate was 7.17 ± 0.16 mmol/l. These results suggest the application of AT determination in animal studies concerning metabolism during exercise

Effects of protein malnutrition on glucose tolerance in rats with alloxan-induced diabetes

Protein-calorie malnutrition produces glucose intolerance and reduced insulin release in response to glucose. Rats adapted to low- or high-protein diets show an increased resistance to the diabetogenic action of a single dose of streptozotocin or alloxan. To determine the effects of dietary protein level on pancreatic function, we measured serum glucose levels under basal conditions and during the oral glucose tolerance test (GTT) perfomed before and after a single dose of alloxan adminsitered to rats fed a 25 percent or a 6 percent protein diet for a period of 8 weeks. The incidence of mild hyperglycemia (serum glucose > 250 mg/dl) was greater among the rats fed the 25 percent protein diet (81 percent) than among those fed the 6 percent protein diet (42 percent). During the GTT performed before alloxan adminsitration the serum glucose levels of the rats fed the 6 percent protein diet were not found to be significantly different from those of rats fed the 25 percent protein diet. During the GTT performed after alloxan injection all rats showed intolerance to the substrate (serum glucose > 160 mg/dl 120 min after glucose adminsitration) regardless of whether basal serum glucose was normal or high. In summary, alloxan was less effective in producing basal hyperglycemia in the rats fed the 6 percent protein diet than in those fed the 25 percent protein diet but caused glucose intolerance during the oral GTT in both groups. Thus, it seems that feeding a 6 percent protein diet to rats offers only partial protection against the toxic effects of alloxan

Effects of intrauterine and postnatal protein-calorie malnutrition on metabolic adaptations to exercise in young rats

The effect of intrauterine and postnatal protein-calorie malnutrition on the biochemical ability to perform exercise was investigated in young male rats. Malnourished rats were obtained by feeding dams a low-protein (6 percent) casein-based diet prepared in the laboratory during pregnancy and lactation. Control rats received and isocaloric diet containing 25 percent protein. The low-protein diet contained additional starch and glucose. At 45 days of age, malnourished rats showed lower body weight, serum protein, albumin and glucose levels, hematocrit values and heart glycogen content but higher circulating free fatty acids and gastrocnemius muscle gycogen than control rats. In response to exercise (50 min of swimming), control rats displayed lower heart, gastrocnemius and liver glycogen levels whereas malnourished rats showed low glycogen levels only in the gastrocnemius muscle. Both control and malnourished rats showed high serum glucose and free fatty acid levels after exercise. In conclusion, protein-calorie malnutrtion improved muscle gycogen storage but this substrate was broken down to a greater extent in response to exerceise. Malnourished rats were able to perform exercise maintaining high blood glucose levels, as observed in control rats, perhaps as a consequence of the elevated availability of circulating free fatty acids

Effect of exercise during pregnancy and dam age on maternal blood chemistry and fetal growth

in order to determine the effect of maternal exercise on maternal nutritional status and fetal growth, young (Y=45-50 days old) Wistar rats were divided into 4 groups of 5 to 8 animals: control pregnant (CP), control non-pregnant (CNP), exercise-trained (swimming 1 j/day, 5 days/week, for 19 days) pregnant (TP) and exercise trained non-pregnant (TNP). Four equivalent groups of adult rats (A=90-100 days old) were also formed. Serum glucose, total protein, albumin, hematocrit and liver glycogen were determined in female rats and pups. There were no statistical differences in serum glucose, total protein and albumin levels, litter size or birth weight among exercise-trained animals, controls and their respective pups. Hematocrit was significantly lower in pups of exercise-trained young and control rats of the same age and physiological status (YCNP+4.1 ñ 0.2; YCP = 2.7 ñ 0.9; YTNP + 4.9 ñ 0.8; YTP = 2.7 ñ 0.4; ACNP = 6.1 ñ 0.6; ACP = 3.1 ñ 0.8; ATNP = 6.6 ñ 0.8; ATP = 2.2 ñ 0.9 mg/100 mg). We conclude that pups of adult female rats are spared from the effects of this kind of exercise training during pregnancy. On the other hand, it appears that maternal adaptations to exercise training in young rats are able to preserve only some aspects of pup metabolism

Effect of maternal exercise during pregnancy on maternal body components and fetal growth in young and adult rats

In order investigate the effects of exercise training on maternal adiposty and fetal development, young Wistar rats (45-50 days old) were divided into four groups: control non-pregnant, control pregnant, exercise-trained non-pregnant and exercise-trained pregnant. Four equivalent groups of adult rats (90-100 days old) were also used. Trained rats swam 1h/day, 5 day/week throughout pregnancy or for a 22-day period (non-pregnant rats). Physical activity during during the entire gestational period reduced weight gain during pregnancy. Both control and trained pregnant rats showed an increase in food intake during the 2nd week of pregnancy and increased food efficiency. Exercice training reduced perirenal fat weight in young and adult pregnant rats. Muscle protein content, litter size and birth weight of pups were similar for control and trained rats. These reults indicate that the energy expenditure required during exercise training by both young and adult pregnant rats reduces depot fat and does not seem to alter normal gestation. Conterregulatory mechanisms during pregnancy and exercice training result in increased food efficiency which probably preserves both maternal and pup metabolism

Effects of protein-calorie malnutrition on endocrine pancreatic function in young preganant rats

Oral glucose tolerance test (GTT), insulin secretion after Oral glucose load and the insulin to glucose ratio (I/G) during GTT were measusred in Young (45-50 days old) pregnant and non-pregnant rats fed a normal (25% or low (6%) protein diet during pregnancy or for a 22-day period. Fasting blood glucose was lower in protein-deficient rats and basal insulin was higher in pregnant control rats than in non pregnant controls. Protein-deficient rats were intolerant to the Oral glucose load. The I/G ratio during GTT was higher in control pregnant rats than in other rats. These results show that young malnourished pregnant rats are glucose intolerant and do not show pregnancy hyperinsulinemia probably as a result of decreased pancreatic capacity to release insulin in response to stimulation

Maternal adaptations for fetal growth in young malnourished rats

Carcass composition and serum free fatty acids were determined in young (45 days old) control and malnourished (25 and 6% protein diet, respectively) pregnant rats. Pregnant rats were sacrificed shortly after parturition and nonpregnant rats on the 22nd day of experiment. Carcas fat content increased in control pregnant rats. This alteration was not seen in the pregnant malnourished rats. Serum free fatty acids and pup bith weight were lower for malnourished than for control mothers. No significant difference was pbserved in carcass protein of Na+ and K+ ccontent among rats of all. These data appear to indicate that the inability to accumulate fat in the carcass and the preservacion of carcass protein at nonpregnant levels during pregnancy may be important factors involved in the genesis of the low birth weight seen in the pups of young malnourished rats, presumably reducing the availability of nutrient supplies for fetal growth