This study investigated the effects of varying dietary levels of very long-chain polyunsaturated fatty acids on growth, brain fatty acid composition and behavior in mice. Five groups of pregnant and lactating B6D2F1 mice were fed diets with either a very high (n-6):(n-3) ratio of 49 [(n-3) deficient)], a normal ratio of 4.0 or a low ratio of 0.32. The (n-6) fatty acids (FA) were provided either entirely as linoleic acid (LA) or as LA in combination with arachidonic acid (ARA), and the (n-6):(n-3) ratios were adjusted by partial replacement of the (n-6) FA with docosahexaenoic acid (DHA). Offspring were maintained on these diets after weaning. The diets with the low (n-6): (n-3) ratio had no effect on the birth weights of the pups, but after 15 d resulted in a significant 12% reduction in body weights. This effect persisted to adulthood and was apparent in both brain and body weights unless ARA was substituted partially for LA as the source of (n-6) FA. There were significant effects of diet on brain fatty acid composition. Increasing levels of DHA in the diet increased brain DHA and decreased ARA, and there was also retroconversion of DHA in EPA in the mice fed high levels of DHA. Addition of ARA to the diet increased brain ARA, and, at high levels only, decreased DHA. There were no effects of this wide variation in dietary (n-6):(n-3) ratio on the ability of the mice to learn the place of the hidden platform in the Morris water maze. However, in both the cued and the place learning, the mice fed the low (n-6):(n-3) diet swam more slowly, unless ARA substituted partially for LA as the source of (n-6) FA. There were no effects of diet on activity in the spatial open field. These findings show that the effects of a diet with a low (n-6):(n-3) ratio and (n-3) FA provided as DHA, can be overcome if LA is partially replaced by ARA as the source of (n-6) FA.
Heart rate variability (HRV) spectral analysis has been used as a tool for short-term assessment of parasympathetic (PNS) and sympathetic nervous system (SNS) control of heart rate. However, it has been suggested that the PNS and SNS indicators are superimposed on a broad-band noise spectrum in which the power spectral densities are inversely proportional to their frequency (1/f beta). In this study, we have used coarse-graining spectral analysis to extract the harmonic components for calculation of PNS and SNS indicators and to obtain the slope (beta) of the 1/f beta component to estimate fractal dimension (DF) of a trail of HRV. DF was regarded as an indicator of cardiovascular system complexity. Ten healthy young subjects (6 women and 4 men) were studied in supine rest and with sequential applications of four levels of lower body negative pressure (LBNP; -10, -20, -30, and -50 mmHg) and head-up tilt (HUT; 10, 20, 30, and 70 degrees). In the 20 tests, there were six occurrences of presyncopal symptoms that required the test to be terminated before the planned end point. At low levels of LBNP or HUT, arterial pulse pressure (PP) was not changed from rest, and calculated DF was very high (beta approximately 1.00). At the higher levels of LBNP and HUT, PP decreased. Coincident with this reduction in PP, PNS activity decreased, SNS activity increased, and DF was reduced, each with a significant linear relationship to the change in PP (PNS: r = 0.56; SNS: r = 0.57; DF: r = 0.70, P < 0.01). Each occurrence of presyncope was associated a low PNS indicator as well as DF < 2.50 (beta > or = 1.80). These data indicate that the cardiovascular system is operating at a reduced level of complexity and further suggest that reduced complexity might not be compatible with cardiovascular homeostasis.
Four groups of male Long-Evans rats were reared artificially from postnatal d 5 to 18 by being fed through a gastrostomy tube with rat milk substitutes containing oils providing 10% linoleic acid and 1% alpha-linolenic acid (g/100 g fat); with the use of a 2 x 2 design, they were fed one of two levels of arachidonic acid (AA) and docosahexaenoic acid (DHA) (0.0 and 2.5 g/100 g of fatty acids). A fifth artificially reared group was fed a diet high in saturated fat, and a sixth group was reared by dams fed a standard AIN-93M diet. The pups were weaned onto modified AIN-93G diets, with a fat composition similar to that fed during the artificial rearing period. Behavioral testing was conducted between 6 and 9 wk of age; brain lipid composition was then assessed. Relative to the unsupplemented group (0.0 g/100 g AA and DHA), dietary supplementation resulted in a wide range of AA (84-103%) and particularly DHA (86-119%) levels in forebrain membrane phospholipids. AA supplementation increased AA levels and decreased DHA levels, and DHA supplementation increased DHA levels and decreased AA levels, with the magnitude of these effects dependent on the level of the other fatty acid. DHA levels were very low in the saturated fat group. The groups did not differ on the place or cued version of the Morris water-maze, but on a test of working memory, the saturated fat group was impaired relative to the suckled control group. Further correlational analyses in the artificially reared animals did not support a relationship between the wide range of DHA and AA levels in the forebrain and working-memory performance.
The dynamics of ventilation (VE), oxygen uptake (VO2), carbon dioxide output (VCO2), and heart rate (fc) were studied in 12 healthy young men during upright and supine exercise. Responses to maximal and to two different types of submaximal exercise tests were contrasted. During incremental exercise to exhaustion, the maximal work rate, VO2max, VEmax, fc,max, and ventilatory threshold were all significantly reduced in supine compared to upright exercise (P less than 0.01-0.001). Following step increases or decreases in work rate between 25 W and 105 W, both VO2 and VCO2 responded more slowly in supine than upright exercise. Dynamics were also studied in two different pseudorandom binary-sequence (PRBS) exercise tests, with the work rate varying between 25 W and 105 W with either 5-s or 30-s durations of each PRBS unit. In both of these tests, there were no differences caused by body position in the amplitude or phase shifts obtained from Fourier analysis for any observed variable. These data show that the body position alters the dynamic response to the more traditional step increase in work rate, but not during PRBS exercise. It is speculated that the elevation of cardiac output observed with supine exercise in combination with the continuously varying work-rate pattern of the PRBS exercise allowed adequate, perhaps near steady-state, perfusion of the working muscles in these tests, whereas at the onset of a step increase in work rate, greater demands were placed on the mechanisms of blood flow redistribution.
The cardiovascular responses to a 10-min 1.22 rad (70 degrees) head-up tilt orthostatic tolerance test (OST) was observed in eight healthy men following each of a 5-min supine baseline (control), 4 h of 0.1 rad (6 degrees) head-down tilt (HDT), or 4 h 0.52 rad (30 degrees) head-up tilt (HUT). An important clinical observation was presyncopal symptoms in six of eight subjects following 4 h HDT, but in no subjects following 4 h HUT. Immediately prior to the OST, there were no differences in heart rate, stroke volume, cardiac output, mean arterial pressure and total peripheral resistance for HDT and HUT. However, stroke volume and cardiac output were greater for the control group. Mean arterial pressure for the control group was less than HDT but not HUT. Over the full 10-min period of OST, the mean arterial pressure was not different between groups. Heart rate increased to the same level for all three treatments. Stroke volume decreased across the full time period for control and HDT, but only at 3 and 9 min for HUT. There was a higher total peripheral resistance in the HDT group than control or HUT. The pre-ejection period to left ventricular ejection time ratio was less in HDT than for control or HUT groups. These data indicate a rapid adaptation of the cardiovascular system to 4 h HDT that appears to be inappropriate on reapplication of a head to foot gravity vector. We speculate that the cause of the impaired orthostatic tolerance is decreased tone in venous capacitance vessels so that venous return is inadequate.
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