Sexual dimorphism in counterregulatory responses to hypoglycemia after antecedent exercise.

After antecedent hypoglycemia, counterregulatory responses to subsequent hypoglycemia exhibit greater blunting in men than in women. Because physical exercise and hypoglycemia share multiple counterregulatory mechanisms, we hypothesized that prior exercise may also result in gender-specific blunting of counterregulatory responses to subsequent hypoglycemia. Thirty healthy subjects (15 women and 15 men; age, 28 +/- 3 yr; body mass index, 23 +/- 1 kg/m2) were studied during 2-d experiments. Day 1 consisted of either identical 90-min morning and afternoon cycle exercise at 50% maximum oxygen expenditure or two 2-h episodes of hyperinsulinemic euglycemia. Day 2 consisted of a 2-h morning hyperinsulinemic-hypoglycemic clamp. Endogenous glucose production was measured using [3-(3)H]glucose. Muscle sympathetic nerve activity was measured using microneurography. Day 2 insulin (540 +/- 36 pmol/liter) and plasma glucose (2.9 +/- 0.06 pmol/liter) levels were similar in men and women during the last 30 min of hypoglycemia. Compared with antecedent euglycemia, d 1 exercise produced significant blunting of d 2 counterregulatory responses to hypoglycemia. Several key d 2 counterregulatory responses were blunted to a greater extent in men than in women: glucagon (men, -105 +/- 14; women, -25 +/- 7 ng/liter; P < 0.0001), epinephrine (men, -2625 +/- 257 pmol/liter; women, -212 +/- 573; P < 0.001), norepinephrine (men, -0.50 +/- 0.12 nmol/liter; women, -0 +/- 0.11; P < 0.001), and muscle sympathetic nerve activity (men, -13 +/- 4; women, -4 +/- 4 bursts/min; P < 0.01). Cardiovascular responses (heart rate and systolic and mean arterial blood pressures) were also more blunted by antecedent exercise in men than in women. After d 1 exercise, the amount of glucose infused during d 2 hypoglycemia in men was increased 6-fold compared with that after d 1 euglycemia. This amount was significantly increased (P < 0.01) compared with the 2-fold (P < 0.01) increment in glucose infusion that was required in women after d 1 exercise. Lipolysis was unaffected by d 1 exercise in women, but was significantly blunted during d 2 hypoglycemia in men. In summary, two bouts of prolonged, moderate exercise (90 min at 50% maximum oxygen expenditure) induced a marked sexual dimorphism in key neuroendocrine (glucagon, catecholamines, and muscle sympathetic nerve activity) and metabolic (glucose kinetic, lipolysis) responses to next day hypoglycemia.

The effects of clofibrate and 3-amino-1,2,4-triazole on liver catalase and lipid metabolism in mice.

Clofibrate-treated mice showed a significant decrease in plasma triacylglycerols and a parallel elevation of liver catalase. Repeated administration of aminotriazole to clofibrate-treated mice effectively abolished the elevated catalase activity, but had no significant effect on the reduced plasma triacylglycerol levels. In mice, the hypolipidemic effect of clofibrate may be dissociated from its capacity to elevate liver catalase. Repeated administration of aminotriazole to control mice resulted in significantly lowered carcass fat and plasma triacylglycerol levels even though the liver catalase activity was greatly depressed. The livers of clofibrate-treated mice showed an increase in phospholipid content. Livers of aminotriazole-treated mice showed a decrease in total lipid content, with a profound decrease in free fatty acids and triacylglycerols and a slight increase in phospholipids. The composition of the individual free fatty acids of the liver triacylglycerols showed a shift towards the shorter fatty acids and the nutritionally essential alpha-linolenic acid in clofibrate-treated mice.

Changes in growth, appetite, food conversion efficiency and body composition in mice selected for high post-weaning weight gain on restricted feeding.

This study aimed to test the hypothesis that if animals were fed the same amount over the same time period, selection of the fastest growers would result in a change in the partitioning of metabolisable energy toward more protein and less fat deposition. Two mouse lines (S1 and S2) were selected for high 5 to 9 week weight gain corrected to mean 5 week weight. Appetite variation between mice was eliminated by feeding a fixed amount to each mouse daily. After 6 generations of selection, the lines were compared with an unselected control (C) on restricted and ad libitum levels of feeding for growth rate, appetite, food conversion efficiency and chemical body composition.Realised heritabilities of 5 to 9 week gain were 0.36+ 0.05 and 0.19±0.04 for S1 and S2 respectively. Nine week weights were increased by an average of 13% on both feeding levels. Most of this increase, particularly in S2, occurred before 5 weeks and was therefore outside the period of measurement used in selection. On ad libitum feeding, selection increased food intake per unit time by 6% but there was no increase per unit body weight. Food conversion efficiency (gain/food) increased by 12%. Compared with controls at 9 weeks, 3% more of the body weights of selected mice was fat and 1% less was protein. These differences were reduced but were still in the same direction when comparisons were made at the same body weight. Thus the expected change in energy partitioning toward greater protein and less fat deposition in the S lines did not occur.It was concluded that the increased growth and energy retention in the S lines was brought about by a reduction in maintenance requirement. To achieve the desired change in energy partitioning using a similar selection scheme, higher levels of dietary protein should be fed, and some measure of protein deposition rather than growth rate used as the selection criterion.

The low availability of dietary choline for the nutrition of the sheep.

1. Choline, which is present in the diet of the sheep either in the non-esterified form or combined in phospholipids, is rapidly degraded in the rumen. The ultimate product formed from the N-methyl groups is methane. 2. Analysis of the non-esterified choline and the phosphatidylcholine in ruminal and abomasal digesta indicate that the phospholipid is the main vehicle for the passage of choline to the lower digestive tract. 3. The concentration of phosphatidylcholine in abomasal digesta is lower than that of ruminal digesta, which is in line with a selective retention of protozoa in the rumen as observed by others. 4. On defaunation of the rumen to remove ciliated protozoa the concentration of phosphatidylcholine in ruminal digesta falls markedly and becomes lower than that in abomasal digesta. 5. Calculation shows that the adult sheep obtains at most only about 20--25 mg of effective choline per day from its diet (0.002--0.0025% of dietary total dry-weight intake). This is some fifty times less than the minimum required to avoid pathological lesions and death in other species investigated (0.1%+ of dietary dry-weight intake). 6. Sheep liver can synthesize choline from [14C]ethanolamine both in vitro and in vivo, but the synthesis of choline per kg body weight is many times less than it is in the rat. 7. The intact sheep oxidizes an injected dose of [1,2-14C]choline to CO2 at a rate that is several times less than that observed for the rat. This could help to explain the apparent minimal requirement of sheep for dietary choline.

Conversion of choline methyl groups through trimethylamine into methane in the rumen.

1. Choline methyl groups were rapidly metabolized to trimethylamine by rumen micro-organisms. 2. Trimethylamine was further metabolized to methane, but this system was more easily saturated by an excess of substrate, so that trimethylamine accumulated in the rumen of the fed animal. 3. Although trimethylamine was the only intermediate isolated in the conversion of the methyl groups of choline into methane, methylamine also served as a substrate for methane production. 4. The methyl group of methionine was also converted into methane by rumen fluid, but the methyl groups of carnitine were not.

Biochemical, physiological and production indices related to fat metabolism in the laying fowl at various stages of physiological development.

The significance of fat accumulation during physiological development of layers was studied using White Leghorn X Australorp pullets from 12 weeks of age. 2. Liver fat, carcass fat, liver weight and body weight increased markedly at the onset of sexual maturity. 3. Within the liver, the protein to DNA ratio did not alter significantly during development; glycogen was not consistently depleted by egg production. 4. Liver fat content was significantly correlated with carcass fat, liver weight and DNA concentration, and plasma total lipid and cholesterol, independent of stage of development; with body weight, liver protein, moisture, and protein to DNA ratio, excluding the period prior to commencement of sexual maturation; and with plasma phospholipid during lay. 5. Obesity was a feature of faster growing fowls which matured earlier, consumed more, utilised food less efficiently for egg production and produced fewer saleable eggs.

Changes in the body composition of mice selected for high and low eight week weight.

Body composition was studied in three lines of mice, one selected for high (H) and one for low (L) 8 week weight, and one maintained as an unselected control (C). After 25 generations 8 week weights were 41.2g, 30.6 g and 20.5g for the H, C and L lines. Mice were sampled from the lines and analysed for fat, protein, ash and water at generations 14 and 25. Apart from fat in the H line, there was little alteration due to selection in the relationships between individual body components and total body weight. In the H line, the contribution of fat to body weight gain was considerably increased. Although leaner than the C and L mice at low body weights, H line mice rapidly became fatter with increasing body weight. Selection appeared to reduce the body weight at which fat was deposited at its maximum rate in the H line. The H and C lines were equally fat at body weights of 29.0 g and 21.6 g at generations 14 and 25 respectively. Body weights at points of inflection of the growth curves of the H, C and L lines at generation 25 were 18.3 g, 14.3 g and 12.8 g. The implications of these findings for meat species slaughtered at set weights are discussed.

Metabolism of fatty acids by bovine spermatozoa.

The incorporation of (14)C-labelled myristic, palmitic, stearic, oleic and linoleic acids in vitro into the lipids of bovine spermatozoa was measured at intervals from 2min to 2h. All acids were rapidly incorporated into diglycerides, myristic acid being metabolized to the greatest extent. Whereas the low incorporation of acids into total phospholipids reflected the relative stability of the major phospholipid fractions in sperm, the minor phospholipids, particularly phosphatidylinositol, showed comparatively high metabolic activity. Although, in general, saturated acids were incorporated more actively than unsaturated substrates, stearic acid was poorly incorporated into all lipids except phosphatidylinositol. In regard to fatty acid composition of sperm lipids it was notable that diglycerides contained myristic acid as the major component, and this acid was also a prominent moiety of phosphatidylinositol. Docosahexaenoic acid was the principal fatty acid of the major phospholipid classes. These findings have been discussed in relation to the role of lipids in the metabolism of spermatozoa.