The effects of immersion and exercise on prolactin during pregnancy

Prolactin is an important hormone during pregnancy, affecting mother, fetus, and amniotic fluid volume. Immersion is known to affect prolactin levels significantly. To determine the effect of immersion and exercise on the prolactin response during pregnancy, we examined serum prolactin levels at 15, 25, and 35 weeks' gestation and 10 weeks post partum. Twelve women completed 20 min land rest, 20 min immersion in 30 degrees C water to the xiphoid, and 20 min exercise in the water at 60% VO2max. Resting prolactin levels were 1.91 +/- 0.32, 4.55 +/- 0.5, and 5.85 +/- 0.27 nmol.l-1 +/- standard error of the mean at 15, 25, and 35 weeks' gestation, respectively. Postpartum lactating women had a resting mean prolactin level of 3.95 +/- 1.6 versus 0.22 +/- 0.4 nmol.l-1 in non-lactating women. Prolactin levels declined significantly during immersion even after correction for dilution by plasma volume shifts. The immersion response was inversely related to the duration of pregnancy with 29%, 22%, and 12% drops during 15-, 25- and 35-week trials, respectively. Compared to rest, exercise prolactin levels remained depressed during the 15th and 25th week trials. We hypothesize that immersion in water caused prolactin levels to decline.     

Investigation of the autonomic regulation of blood circulation during seven-day dry immersion

The paper presents the results of the investigation of autonomic regulation of blood circulation and regulation of the modification by peroral amlodipine and myostimulation during seven-day dry immersion. It was shown that autonomic regulation readjusted in immersion towards predominance of sympathetic mechanisms. Myostimulation and peroral amlodipine modified regulation substantially mobilizing high level suprasegmentary structures. Pharmaceutical intervention seems to have a more complex and varying effect on people, including side effects. Presumably this was the cause of the poor orthostatic tolerance of several subjects.     

Visual-manual tracking during a five-day dry immersion

The effect of low proprioceptive, tactile, and support afferentation on visual-manual tracking was determined using a five-day horizontal dry immersion, which provided support deprivation, as well as minimization of muscle activity and proprioceptive afferentation, simulating the physiological effects of microgravity. Hand-eye motor coordination was studied in the 13 subjects participating in the experiment with five-day dry immersion who tracked the jumpy and smooth movements of a point visual stimulus (linear and pendulum-like; horizontal and vertical; circular, clockwise and counterclockwise). Ocular movements were recorded using binocular electrooculography; and manual motions were recorded using a joystick with a biological visual feedback, when one of the two stimuli on the screen showed the current joystick tilt. Computerized stimulation was provided using virtual reality goggles. The following parameters were evaluated: the latent and total reaction time; the amplitudes and velocities of the eye and hand movements; and the coefficients of effectiveness (amplitude ratio) and the gain (velocity ratio). The examinations were performed before immersion, after 3 h of immersion, on days 3 and 5 of immersion, during the first hours after the termination of immersion, and three days after the immersion (in all subjects); and on days 5–7 after the immersion (in four subjects). It was shown that support deprivation and minimization of proprioceptive afferentation affected ocular tracking to a larger extent than the accuracy of manual movements following the visual stimulus. It was found that, in all subjects, manual tracking, which did not significantly change during the test sessions, was more accurate than visual tracking; in contrast, the accuracy of visual tracking changed noticeably both in the course of dry immersion and after its termination.     

Dry immersion effects on the mechanisms of metaboreflex regulation of hemodynamics during exercise

The effects of four-day dry immersion on metaboreflex regulation of hemodynamics were evaluated during local static exercise (30% of the maximum voluntary contraction) of the calf plantar flexors. One group of immersed subjects received low-frequency electrostimulation of their leg muscles to decrease the immersion effect on the EMG of exercising muscles. Metaboreflex regulation was evaluated by comparison of cardiovascular responses to physical loads with and without post-exercise circulatory occlusion. Immersion slightly increased the heart rate (HR) and reduced the systolic blood pressure in resting subjects; however, it did not have a distinct effect on blood pressure (BP) and HR during exercise or metaboreflex potentiation of hemodynamic shifts.     

Light effects upon dry lettuce seeds

Germination of certain dry seeds (achenes) of Lactuca sativa L. cv. Grand Rapids was increased to ca. 75% after irradiation with 665 nm red light (R; 1x10³ J m^-2); this response was eliminated by far-red light (FR) following the R. The response of dry seeds required an order of magnitude more light than that of wetted seeds, and was not maximal until 48 h after irradiation. Other seeds, which could not be stimulated by R in dry state, showed a partial response after 10 min hydration. Irradiation of dry seeds (or seeds wetted 1 h) with FR (1x10³ J m^-2) reduced dark germination from 26% to 2%. Seeds dehydrated in an oven (60°C, 90 min) showed a decrease in germination if irradiated with R (1x10⁵ J m^-2) before wetting. The results show that phytochrome is present in dry lettuce seeds (and functional in some seed lots) prior to wetting; and that in other seed lots the molecule becomes functional within minutes after wetting the seeds. Transformation of the FR absorbing from of phytochrome (P_FR) to the inactive from (P_R) occurs at lower seed moisture content than the reverse reaction. It appears that dormancy in seeds ripened in sunlight might be assured during seed drying and maturation by the more effective transformation of P_FR to P_R than vice versa as phytochrome is dehydrated.Abbreviations FR far-red - R red - CAL seeds from California - NC seeds from North Carolina (see text)     

Lung volume changes in response to altered breathing gas pressure during upright immersion

Since elastic and flow-resistive respiratory work are volume dependent, changes in lung volume during immersion affect respiratory effort. This investigation examined changes in lung volume with air delivery pressure modifications during upright immersion. Static pressure-volume relaxation relationships and lung volumes were obtained from ten immersed subjects breathing air at four delivery pressures: mouth pressure, lung centroid pressure (PLC), and 0.98 kPa above and below PLC. The PLC is the static lung pressure which returns the respiratory relaxation volume (VR) to normal and was previously determined to be +1.33 kPa relative to pressure at the sternal notch. Lung volume changes observed when breathing air at mouth pressure were reversed when air was supplied at PLC. The expiratory reserve volume (ERV) and VR were reduced by 58% and 87%, respectively, during uncompensated immersion. These differences indicated an active defence of ERV and implied that additional static respiratory work was required to overcome transrespiratory pressure gradients.     

Changes in muscle sympathetic nerve activity and calf blood flow during static handgrip exercise

To test the function of sympathetic vasco-constrictor nerves on blood flow in resting limbs during static muscle contraction, muscle sympathetic nerve activity (MSNA) to the leg muscle was recorded from the tibial nerve microneurographically before, during and after 2 min of static handgrip (SHG). Simultaneously, calf blood flow (CBF) was measured by strain gauge plethysmography. An increase in MSNA, a decrease in CBF and an increase in calf vascular resistance (CVR) in the same resting limb occurred concomitantly during SHG. However, the increase in CVR was blunted in the second minute of handgrip when MSNA was still increasing. The results indicated that the decrease of CBF during SHG reflects the increase in MSNA, while the dissociation between MSNA and CVR at the later period of SHG may be related to metabolic change produced by the vasoconstriction.     

Skin blood flow during incremental exercise in a thermoneutral and a hot dry environment

Eight physically fit men performed two incremental bicycle ergometer tests, one in an ambient temperature of 25 degrees C and the other at 40 degrees C. Oesophageal temperature (Tes) increased continuously throughout the tests up to 38.0 and 38.3 degrees C, respectively. In both environments, forearm blood flow (plethysmography) was linearly related to Tes above the Tes threshold for vasodilation, but at the heaviest work loads this relationship was clearly attenuated and therefore indicated skin vasoconstriction, which tended to be more pronounced at 25 degrees C. During recovery at 25 degrees C, in some subjects the forearm blood flow increased above the levels observed at the end of the graded exercise in spite of a decreasing Tes. Skin blood flow, measured by laser Doppler flow meter at the shoulder, was quantitatively different but, on average, seemed to reveal the same response pattern as the forearm blood flow. In spite of the higher level of skin blood flow in the heat, blood lactate accumulation did not differ between the two environments. The present results suggest that there is competition between skin vasoconstriction and vasodilation at heavy work rates, the former having precedence in a thermoneutral environment to increase muscle perfusion. During short-term graded exercise in a hot environment, skin vasoconstriction with other circulatory adjustments seems to be able to maintain adequate muscle perfusion at heavy work levels, but probably not during maximum exercise.     

Morphofunctional properties of red blood cells of humans in 5-day dry immersion

The blood of six healthy male volunteers sampled before, immediately after, and 7 days after 5-day dry immersion was analyzed for morphological parameters, erythrocyte metabolism, and lipid and phospho-lipid levels. The experimental 5-day exposure was shown to increase the erythrocyte count. On the first day after the experiment, upward trends were exhibited by hemoglobin and packed cell volume (PCV). The significant decrease in adenosine triphosphate and low level of reduced glutathione that were also detected on the first day after the experiment could be the result of enhanced oxidation in the cell, possibly due to the activation of lipid peroxidation. A downward trend in the phospholipid fraction of the erythrocyte membrane against constant levels of cholesterol and its ethers could be associated with a significant increase in the fraction of nonesterified fatty acids on day 1 and triglycerides on days 1 and 7 after the experiment.     

Effect of dry immersion in combination with stimulation of foot support zones upon muscle force-velocity characteristics

The complex of motor disturbances arising under conditions of real and simulated microgravity that include decrease of contractile characteristics of postural muscles is likely to be a result of withdrawal of support stimuli. Artificial stimulation of support zones of feet is shown to diminish partially or prevent completely the negative effects of microgravity on the motor system. The aim of the study was to evaluate and compare the changes of contractile properties of extensors and flexors of knee joint measured in isokinetic and isotonic regimes under conditions of simulated microgravity (7 days dry immersion).     

Muscle contraction-blood flow interactions during upright knee extension exercise in humans.

To test for evidence of a muscle pump effect during steady-state upright submaximal knee extension exercise, seven male subjects performed seven discontinuous, incremental exercise stages (3 min/stage) at 40 contractions/min, at work rates ranging to 60-75% peak aerobic work rate. Cardiac cycle-averaged muscle blood flow (MBF) responses and contraction-averaged blood flow responses were calculated from continuous Doppler sonography of the femoral artery. Net contribution of the muscle pump was estimated by the difference between mean exercise blood flow (MBFM) and early recovery blood flow (MBFR). MBFM rose in proportion with increases in power output with no significant difference between the two methods of calculating MBF. For stages 1 and 5, MBFM was greater than MBFR; for all others, MBFM was similar to MBFR. For the lighter work rates (stages 1-4), there was no significant difference between exercise and early recovery mean arterial pressure (MAP). During stages 5-7, MAP was significantly higher during exercise and fell significantly early in recovery. From these results we conclude that 1) at the lightest work rate, the muscle pump had a net positive effect on MBFM, 2) during steady-state moderate exercise (stages 2-4) the net effect of rhythmic muscle contraction was neutral (i.e., the impedance due to muscle contraction was exactly offset by the potential enhancement during relaxation), and 3) at the three higher work rates tested (stages 5-7), any enhancement to flow during relaxation was insufficient to fully compensate for the contraction-induced impedance to muscle perfusion. This necessitated a higher MAP to achieve the MBFM.     

Aspartate aminotransferase metabolism in muscles during physical exercise

It is established that the concentration of cytosolic aspartate aminotransferase decreases the first day after intensive physical exercises due to the intensification of the degradation processes, the decrease in the synthesis rate and the enzyme entry into the blood vessel. The enzyme content is normalized by the 24th hour of rest and then the supercompensatory phase takes place: the enzyme biosynthesis increases and its degradation decreases to a greater extent.     

Acute effects of cigarette smoking and inhalation of carbon monoxide during maximal exercise

The acute effect of inhaling the smoke of three cigarettes was compared to the effect of inhalation of an amount of carbon monoxide (CO), giving the same CO-saturation of the arterial blood as smoking during rest and during maximal exercise on a Krogh cycle ergometer. Sixteen male subjects were tested in the morning (1) after about 8 h without smoking (control), (2) after inhalation of the smoke of three cigarettes (smoke), and (3) after CO-inhalation (CO). It was found that the average maximal rate of O2-uptake (VO2 max) decreased during both smoke and CO by about 7%. Endurance time at VO2 max decreased 20% during smoke but only 10% during CO. A significant decrease in maximal heart rate (HR), and an increase in HR at rest, was demonstrated only during smoke. The peak lactate concentration (HLa) following maximal exercise was significantly decreased after smoke. The results suggest that the decrease in VO2 max during smoke is due to the CO-saturation of the blood, and hence to a decrease in the oxygen capacity of the blood, while the decrease in endurance time during smoke is combined effect of the CO-saturation and an increased cost of breathing caused by the smoke particles. It is further suggested that nicotine, or possibly some other components of the smoke, have an enhancing effect on the heart at rest rest, while an inhibition is seen during maximal exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of ventilation and gas exchange during supine and upright cycle exercise.

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.