Monitoring of the cardiac and vascular response to LBNP during the 14 day spaceflight "Cassiopee"

The objective of the present experiment was to monitor in real time the cardiac and the peripheral response to inflight LBNP. The second objective was to detect and quantify hemodynamic signs of orthostatic tolerance inflight by measuring the heart rate, blood pressure, cardiac and regional hemodynamics during LBNP.     

Adaptation of plasma volume in humans to prolonged head-down bed rest

Changes in plasma volume were studied in subjects who underwent 42 days of head-down bed rest or a one hour change in posture between upright and head-down tilt. Changes in hematocrit and heomoglobin concentration were also measured. Results are presented and discussed in terms of physiological adaptation to postural changes.     

Cardiovascular and hormonal response during a 4-week head-down tilt with and without exercise and LBNP countermeasures

To determine whether exercise and Lower Body Negative Pressure (LBNP) during 28 days of -6 degrees head-down tilt (HDT) would modify orthostatic tolerance and blood volume regulating hormones, twelve healthy men were assigned to either a no- countermeasure (No-CM, n=6), or a countermeasure (CM, n=6) group. LBNP sessions consisted of 15 minutes exposure to -30 mm Hg, on days 16, 18, 20 and 22-28 of HDT. Muscular exercise began on day 8 and consisted of combined graded dynamic and isometric resistance bilateral leg exercise on a specially designed supine ergometer, in two sessions of 15-20 min. each, every day, 6 days per week. A tilt test was performed before and at the end of HDT. Changes in resting plasma volume from control day (D-5) to HDT day 24 were -11.2% for No-CM and -2.2% for CM. After HDT three among the 6 subjects of the No-CM group presented presyncopal or syncopal symptoms, no tilt test was interrupted in CM group. Atrial Natriuretic Peptide (ANP) decreased at day 7 for the two groups and remained low during all the HDT period for No-CM group only. Plasma Renin Activity and Aldosterone increased at day 7 and remained elevated for the two groups. Norepinephrine and epinephrine were unchanged. Elevated diuresis and natriuresis were evident during the first day of HDT. However, renal excretory patterns were different between the two groups: indeed, a decrease of Na+, ANP and cGMP was observed only in No-CM at Day 13 during HDT. Our data showed that the subjects of the No-CM group experienced a greater increase in heart rate and a decrease in systolic blood pressure during tilt tests after HDT; nevertheless, after HDT, blood pressure was better maintained in CM group during the tilt test. The plasma volume decrease measured at the end of HDT was significantly lower in CM group, in contrast, these countermeasures were ineffective in preventing at least certain changes in blood volume regulating hormones.     

Fluid regulatory hormone response to exercise after coca-induced body fluid shifts

Favier, R., E. Caceres, B. Sempore, J. M. Cottet-Emard, G. Gauquelin, C. Gharib, and H. Spielvogel. Fluidregulatory hormone response to exercise after coca-induced body fluidshifts. J. Appl. Physiol. 83(2):376-382, 1997.To determine the effect of coca chewing on heartrate (HR), mean arterial blood pressure (MAP), and plasma volume andtheir relationship with the hormones regulating cardiovascular and bodyfluid homeostasis, 16 male volunteers were examined at rest and during1 h of cycle exercise at ~75% of their peak oxygen uptake in twotrials separated by 1 mo. One trial was performed after the subjectschewed a sugar-free chewing gum(Coca trial), whereas theother was done after the subjects chewed 15 g of coca leaves(Coca⁺), with the order of theCoca andCoca⁺ trials being randomized.Blood samples were taken at rest, before (R₁) and after 1-h chewing(R₂), and during the 5th, 15th,30th, and 60th min of exercise. They were analyzed for hematocrit,hemoglobin concentration, red blood cell count, plasma proteins, andfor the fluid regulatory hormones, including plasma catecholamines [norepinephrine (NE) and epinephrine], renin, argininevasopressin, and the atrial natriuretic peptide (ANP). During thecontrol trial (Coca),from R₁ toR₂, there was no significantchange in hematologic, hormonal, and cardiovascular status except for asmall increase in plasma NE. In contrast, it can be calculated thatcoca chewing at rest induced a significant hemoconcentration(3.8 ± 1.3% in blood and 7.0 ± 0.7% in plasmavolume), increased NE and MAP, and reduced plasma ANP. Chewing cocabefore exercise reduced the body fluid shifts but enhanced HR responseduring exercise. These effects were not accompanied by changes in NE,epinephrine, renin, and arginine vasopressin plasma levels. Incontrast, plasma ANP response to exercise was lower during theCoca⁺ trial, suggesting thatcentral cardiac filling was reduced by coca use. It is likely that thereduction in body fluid volumes is a major contributing factor to thehigher HR at any given time of exercise after coca chewing.

     

Molecular evolution of cytochrome c oxidase: rate variation among subunit VIa isoforms

Cytochrome c oxidase (COX) consists of 13 subunits, 3 encoded in the mitochondrial genome and 10 in the nucleus. Little is known of the role of the nuclear-encoded subunits, some of which exhibit tissue-specific isoforms. Subunit VIa is unique in having tissue-specific isoforms in all mammalian species examined. We examined relative evolutionary rates for the COX6A heart (H) and liver (L) isoform genes along the length of the molecule, specifically in relation to the tissue-specific function(s) of the two isoforms. Nonsynonymous (amino acid replacement) substitutions in the COX6AH gene occurred more frequently than in the ubiquitously expressed COX6AL gene. Maximum-parsimony analysis and sequence divergences from reconstructed ancestral sequences revealed that after the ancestral COX6A gene duplicated to yield the genes for the H and L isoforms, the sequences encoding the mitochondrial matrix region of the COX VIa protein experienced an elevated rate of nonsynonymous substitutions relative to synonymous substitutions. This is expected for relaxed selective constraints after gene duplication followed by purifying selection to preserve the replacements with tissue-specific functions.      

Antigravity suit inflation: kidney function and cardiovascular and hormonal responses in men

To investigate the effects of lower body positive pressure (LBPP) on kidney function while controlling certain cardiovascular and endocrine responses, seven men [35 +/- 2 (SE) yr] underwent 30 min of sitting and then 4.5 h of 70 degrees head-up tilt. An antigravity suit was applied (60 Torr legs, 30 Torr abdomen) during the last 3 h of tilt. A similar noninflation experiment was conducted where the suited subjects were tilted for 3.5 h. To provide adequate urine flow, the subjects were hydrated during the course of both experiments. Immediately after inflation, mean arterial pressure increased by 8 +/- 3 Torr and pulse rate decreased by 16 +/- 3 beats/min. Plasma renin activity and aldosterone were maximally suppressed (P less than 0.05) after 2.5 h of inflation. Plasma vasopressin decreased by 40-50% (P less than 0.05) and plasma sodium and potassium remained unchanged during both experiments. Glomerular filtration rate was not increased significantly by inflation, whereas inflation induced marked increases (P less than 0.05) in effective renal plasma flow (ERPF), urine flow, osmolar and free water clearances, and total and fractional sodium excretion. No such changes occurred during control. Thus, LBPP induces 1) a significant increase in ERPF and 2) significant changes in kidney excretory patterns similar to those observed during water immersion or the early phase of bed rest, situations that also result in central vascular volume expansion.     

Androgens positively regulate follicle-stimulating hormone beta-subunit mRNA levels in rat pituitary cells

We have shown previously that androgens negatively regulate LH alpha and beta-subunit mRNA levels, but have little or no effect on FSH beta mRNA levels in rats in vivo. In contrast, estrogen negatively regulates all three gonadotropin subunit mRNA levels in vivo. We have examined the effects of these sex steroids on gonadotropin subunit synthesis directly at the level of the pituitary gland by using cultured rat pituitary cells. Adult female and male rat pituitaries were dissected, dispersed enzymatically, and maintained in culture for 2 days. At that time, cells were treated for varying lengths of time with either medium alone or sex-steroid hormone treatments (estradiol or testosterone). Dose-response and time-course experiments were performed. Cells were then harvested and total RNA was extracted. Gonadotropin subunit mRNA levels were assessed by blot hybridization techniques. Sex-steroid hormones were added to achieve final concentrations ranging from 10(-12) to 10(-6) M for dose response experiments and 10(-8) M for time-course experiments. Testosterone treatment (10(-8) M) increased FSH beta mRNA levels 3-fold in females (P less than 0.01) and males (P less than 0.05), but had no effect on alpha or LH beta mRNA levels in either sex. Dose-related increases in FSH beta mRNA levels with increasing concentrations of testosterone were observed in both female and male pituitary cell cultures. Time-course studies revealed that the testosterone-stimulated increases in FSH beta mRNA levels are statistically significant by 12 h and 6 h after hormone addition in female and male cultures, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Laboratory evaluation of three mosquito pathogenic strains of Bacillus sphaericus isolated in Egypt

Three strains of Bacillus sphaericus H-5a5b designated Ghar. 1 & 10, Ghar. 2 & 20, and Ghar. 3 & 30 were tested for growth, virulence, and larvicidal activity against Culex pipiens in the laboratory. Incubation temperature was positively correlated (r = 0.91) to the rate of bacterial growth (strain Ghar. 2 & 20). All three strains retained their virulence through 25 successive transfers on nutrient agar. Acetone powder preparations showed high larvicidal activity against C. pipiens, although second instar larvae were more susceptible than fourth instars to all three strains. The most active strain was Ghar. 2 & 20 with LC50 values of 0.51 mg/liter (second instar) and 1.62 mg/liter (fourth instar) after 48 hr of exposure. Mortality rates in fourth instar larvae exposed to an acetone powder form of strain Ghar. 2 & 20 were significantly greater at higher than at lower temperatures.