Modulation of Testicular and Whole Blood Trace Element Concentrations in Conjunction with Testosterone Release Following Kisspeptin Administration in Male Rabbits (Oryctolagus cuniculus)

The present study investigated the role of kisspeptin-10 on reproductively significant trace elements in relation to testosterone release in male rabbits, Oryctolagus cuniculus. Groups of rabbits were exposed to single 1 μg kisspeptin dose (i.v., saphenous vein), while simultaneous groups were pretreated with a kisspeptin antagonist, peptide-234 (50 μg) 20 min before administering kisspeptin. Sequential blood sampling was done through marginal ear vein puncture at staggered time intervals: 0, 0.5, 1, 2, 4, and 24 h to determine serum testosterone. Testes and whole blood were collected at 4 and 24 h post dosage to determine trace element concentrations through atomic absorption spectrophotometry. In testes, zinc (Zn), manganese (Mn), and Fe concentrations showed significant increases at 24 h, while copper (Cu) concentration was found elevated at 4 and 24 h both (P?<?0.001). In whole blood, Zn and Cu concentrations were significantly elevated at 4 and 24 h, while Mn and cobalt (Co) concentrations showed increases only at 24 h (P?<?0.001). Blood iron concentration was not altered in the blood. In contrast, no change occurred in testicular Co, and chromium or nickel concentrations in either testes or blood. Compared to control and predose groups, serum testosterone levels increased gradually and peaked at 2 h (P?<?0.001) post kisspeptin treatment but declined thereafter. Pretreatment with antagonist abolished all increases in trace elements and testosterone concentrations. The present study provides first evidence that reproduction- and fertility-related peptide “kisspeptin” modulates testicular and blood trace elements and that this action is likely GPR54-dependent.     

Plasma Concentrations of Testosterone in the Male Dog and Plasma Testosterone Profile Following Single Intramuscular Injection of HCG

The spontaneous variation in plasma testosterone was studied in 4 dogs in a 24 h period. Blood samples were taken with 1½ h interval. A variation of 26–62 % was found in the plasma testosterone concentration and the values ranged from 2.7–15.6; 0.7–10.4; 4.2–17.3; 8.7–23 nmol/l. No effect of intramuscular injection of 150 i.u. HCG could be seen on the plasma testosterone levels in samples taken 5, 10, 20 or 30 min post injection. Thereafter plasma testosterone levels increased to reach levels equal to peak concentration in the control period 1½ h post injection. The variation in the plasma testosterone concentration 1½, 3 and 4½ h post HCG injection was reduced to 8.95 ± 2.8 % (mean ± s). Plasma testosterone in a sample taken 3 h after HCG injection might thus be indicative of a Leydig cell dysfunction in the dog. An additional increase (P &lt; 0.001) in plasma testosterone levels was observed 21–30 h post injection. Thereafter levels of testosterone fell to pre-stimulation values.     

Comparison of changes in testosterone concentrations after strength and endurance exercise in well trained men

Changes in the testosterone concentrations after single sessions of endurance and strength training were measured in seven well trained men, experienced in both forms of training. Both training sessions were rated as hard to very hard on the Borg scale. Blood samples for testosterone measurements were taken before, immediately after, and 2, 4 and 6 h after the training sessions as well as the next morning. The mean testosterone concentration increased 27% (P less than 0.02) and 37% (P less than 0.02) during the strength and endurance training session, respectively. Two hours after the training sessions the mean testosterone concentration had returned to the pre-training level and remained at that level for the length of the observation period. There were no significant differences in the changes in testosterone concentration after strength and endurance training but there were large differences in the testosterone response at the level of the individual. A high correlation (r = 0.98; P less than 0.001) for individuals was found between increases in testosterone concentration after strength and after endurance training. It was concluded that the changes in mean testosterone values followed the same timecourse after single sessions of strength and endurance training of the same duration and perceived exertion. The interindividual differences in testosterone response may be of importance for individual adaptation to training.     

Seasonal pattern of luteinizing hormone and testosterone pulsatile secretion in young adult red deer stags (Cervus elaphus) and its association with the antler cycle.

Blood from stages aged 15 months (n = 6) was sampled at monthly intervals every 30 min for 24 h for 12 months, at 45 degrees S in New Zealand. Three extra samplings each for 24 h were carried out at about the anticipated time of antler casting. All samples were analysed for luteinizing hormone (LH) and testosterone and the resulting data further analysed by the Pulsar pulse detection routine. The animals were kept indoors under natural daylength and were fed ad libitum. All animals were weighed, antler status and size recorded and testes diameter was measured on each sampling day. Mean LH and testosterone pulsatily and plasma concentration varied seasonally. LH pulse frequency was low during autumn (2.5 pulses in 24 h), winter (1.0-1.5 pulses in 24 h) and early spring (1 pulse in 24 h) and lowest in late spring (0.2 pulse in 24 h) before rising in summer (1.0-4.0 pulses in 24 h). LH pulse amplitude and mean plasma concentration were low (< 1 ng ml-1) from March to November (autumn-spring); both rose to a peak in January (summer) of 3.4 and 1.6 ng ml-1, respectively. Testosterone pulse frequency was generally similar to LH except that slightly more pulses of testosterone than of LH were detected from March to November and more pulses of LH from November to February (summer). Testosterone pulse amplitude fell from March to November (5.3 ng ml-1 to undetectable) although there was a conspicuous peak in July (midwinter) of almost 5 ng ml-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Melatonin administration increased plasminogen activator activity in ram spermatozoa

The aim of the present study was to investigate the effect of melatonin on plasminogen activator activity (PAA), plasminogen activator inhibition (PAI) and plasmin inhibition (PI) in ram spermatozoa and seminal plasma, in correlation with changes in blood testosterone. Melatonin implants (18 mg) were placed subcutaneously in sixteen Chios rams in autumn and spring. Semen samples for spectrophotometrical assays were collected 36 h before the implantation of melatonin and thereafter once a week, for 17 weeks. Blood samples for testosterone assay (RIA) were collected 8h before implantation (one sample/30 min x 7.5 h) and thereafter every 15 days for 105 days after implantation. For each ram, six parameters of testosterone were estimated: mean value, basal level, number of peaks, peak amplitude, peak duration and mean testosterone concentration during peaks. Melatonin implantation during autumn induced an increase in PAA and t-PAI in spermatozoa; melatonin implantation in spring induced an additional increase in u-PAI and PI; no change in PAA, PAI or PI was found in seminal plasma, during autumn or spring. The melatonin-induced increase of PAA, PAI and PI in spermatozoa was in positive correlation with the increase of testosterone mean value, basal level and number of peaks; the increase of testosterone parameters was greater in autumn compared to spring. Changes of PAA, PAI and PI of spermatozoa, under the influence of melatonin, might indicate changes in the fertilizing ability of spermatozoa, since plasminogen activators and their inhibitors are present on the plasma and the outer acrosomal membrane of spermatozoa and are released during the acrosome reaction.     

Peripheral plasma testosterone concentration and sexual behavior in young prenatally stressed boars

The purpose of this study was to examine the effects of stress induced physiological changes in the gestating sow on postnatal sexual and endocrine development of male offspring. Ten boars, ranging from 160 to 185 days of age, were randomly chosen from sows which had been maintained under either stress or control conditions during mid-gestation. Blood samples were collected weekly from each boar (minimum of four weeks) at 30 min intervals over a common six-hour period via an indwelling anterior vena cava cannula. Plasma testosterone concentrations were determined by radioimmunoassay. In order to ascertain degree of sexual behavior, boars were exposed weekly to gilts in estrus and a subjective score assigned. No differences (P>.10) were found between prenatally stressed and control boars in overall mean testosterone concentration or libido score. A significant (P<.05) decrease in plasma testosterone concentration was detected in boars over age. Results suggest that mid-gestational stress of gestating sows does not affect the testosterone concentration or sexual behavior of boar off-spring.     

Diurnal variations in plasma testosterone concentrations in the male lesser mouse lemur (Microcebus murinus)

In 6 isolated adult male lesser mouse lemurs, concentrations of testosterone in plasma were determinated at 6-h intervals over a 24-h period. Blood samples were collected at monthly intervals and for a period of 12 months under natural photoperiod. In this nocturnal prosimian, there were no apparent diurnal changes in testosterone concentrations during the non-breeding season (autumn). During seasonal sexual activity (January-August), diurnal changes in testosterone concentrations were characterized by a significant rise during the light phase. The daily testosterone peak occurred about 8.5 h after sunrise from February to July, but at the beginning (January) or at the end (August) of the breeding season, the daily testosterone peak was displaced to the morning. A circannual testosterone rhythm occurred with the highest testosterone values in May/June and the lowest values 6 months later. The dramatic fall in testosterone concentrations after the summer solstice may be associated with a change in the peripheral metabolism of testosterone.     

Plasma testosterone during nocturnal sleep in normal men

Plasma testosterone was measured by a competitive protein binding procedure at 10 to 20 minute intervals in five normal adult men during two nights of sleep. Blood samples were obtained by means of an indwelling venous catheter while sleep was monitored polygraphically. There were 1–4 abrupt elevations of plasma testosterone concentration per night in each of the subjects with an average increase of 244 ng/100 ml ± 45.5 (SE) or 59% above the values present at the onset of the episode. The fluctuations in plasma testosterone were superimposed on a nocturnal rise of the hormone observed in seven of the nights. The average of all samples taken during each hour period through the ten nights revealed a highly significant (P<0.001) nocturnal increase in plasma testosterone. The findings did not support the existence of a relation between REM sleep and an increase in testosterone levels.     

Circularly polarized,sinusoidal, 50 Hz magnetic field exposure does not influence plasma testosterone levels of rats

We exposed rats to circularly polarized 50 Hz magnetic fields to determine if plasma testosterone concentration was affected. Previous experiments indicate that magnetic fields suppress the nighttime rise in melatonin, suggesting that other neuroendocrine changes might occur as well. Male Wistar-King rats were exposed almost continuously for 6 weeks to magnetic flux densities of 1,5, or 50 μT. Blood samples were obtained by decapitation at 12:00 h and 24:00 h. Plasma testosterone concentration showed a significant day-night difference, with a higher level at 12:00 h when studied in July and December, but the day-night difference disappeared when concentrations were studied in April. In three experiments, magnetic field exposure had no statistically significant effect on plasma testosterone levels compared with the sham-exposed groups. These findings indicate that 6 weeks of nearly continuous exposure to circularly polarized, 50 Hz magnetic fields did not change plasma testosterone concentration in rats. © 1994 Wiley-Liss, Inc.     

Plasma concentrations of testosterone and LH in the male dog

Blood samples were withdrawn every 20 min from 3 conscious intact and 2 castrated mature males during non-consecutive periods of 12 h during the light and dark phases of the lighting schedule (intact dogs) and of 11 h during the light period (castrated dogs). In the intact dogs testosterone concentrations ranged from 0.4 to 6.0 ng/ml over the 24-h period. LH concentrations varied from 0.2 to 12.0 ng/ml. In all animals, LH peaks were clearly followed, after about 50 min, by corresponding testosterone peaks, but no diurnal rhythm could be established. LH concentrations in the castrated dogs were high (9.8 +/- 2.7 (s.e.m.) ng/ml), and still showed an episodic pattern in spite of the undetectable plasma testosterone levels.     

Endocrine Effects of Heat Stress in Boars

The purpose of this study was to describe the temporal changes in peripheral plasma levels of testosterone and Cortisol in boars during and after heat stress. A total of 8 boars were utilized, 4 of them were exposed to 35°C, for 100 h in a climatic room, and 4 served as controls and were kept at 20 °C for 100 h in the climatic room. Blood samples were obtained via permanent vein catheters 3 times daily from 5 days before heat stress until 20 days after termination of heat stress. Testestorone levels were determined by radioimmunoassay and Cortisol by a competitive protein binding technique. For both hormones the pre-exposure levels were similar in both groups of boars. The control boars had significantly higher testosterone levels, while being in the climatic room, than during any other period. The experimental boars had slightly increased testosterone levels during the first day of heat stress and thereafter continuously decreased levels. In the control boars the testosterone levels returned to pre-exposure levels immediately after removal from the climatic room, whereas in the experimental boars the testosterone levels were dramatically increased during the first 5 days after exposure. The differences in Cortisol levels, between the 2 groups of boars were restricted to the period spent in the climatic room. During this period the experimental boars had significantly higher Cortisol levels.     

Serum cortisol concentration and testosterone to cortisol ratio in elite prepubescent male gymnasts during training.

Serum cortisol concentrations and testosterone:cortisol concentration ratios of eight prepubescent elite male gymnasts (mean age 10 years 11 months) and 11 controls (mean age 11 years 1 month) were examined during 5 consecutive training days. During this period, the gymnasts trained 3 h each day with moderate intensity mobility, strength and skill exercises while the controls were relatively sedentary. Blood samples were taken from all the boys in both groups before (1630 hours) and 30 min after (2000 hours) training on 4 days. Serum cortisol concentrations of the gymnasts were not significantly different from those of the controls throughout the experiment. Serum cortisol concentrations of both groups were significantly larger (P < 0.05) at 1630 hours than at 2000 hours, indicating that cortisol secretion followed the typical adult circadian change, seemingly unaltered by training. However, there was a significant decrease (P < 0.05) in the testosterone:cortisol ratio of the gymnasts when compared with controls from day 1 to day 3. After a rest on day 4 the testosterone: cortisol ratio of the gymnasts significantly increased (P < 0.05) but the ratio of the control group also increased indicating that there may have been some day-to-day change by factor(s) other than training. The most obvious factor which may have accounted for the unresponsiveness of serum cortisol concentration to the gymnastics training was that the exercise intensity was too low. However, several days of the training seemed to reduce the anabolic to catabolic balance but further experiments are needed to confirm this finding.     

Continuous light after a long-day treatment is equivalent to melatonin implants to stimulate testosterone secretion in Alpine male goats

In rams, artificial long days followed by continuous light stimulate testosterone secretion during the non-breeding season. The objective of this study was to determine whether artificial long days followed by continuous light could stimulate testosterone secretion in Alpine bucks as well as in those exposed to long days followed by a melatonin treatment. All bucks were kept in shaded open pens. Control males were exposed to natural photoperiod conditions (n=5). Males of the two experimental groups were exposed to 2.5 months of long days from 1 December (n=5 each). On 16 February, one group of males was exposed to 24 h of light per day until 30 June; the other group was exposed to natural variations of photoperiod and received two s.c. melatonin implants. Testicular weight was determined every 2 weeks, and the plasma testosterone concentrations once a week. In the control and the two photoperiodic-treated groups, a treatment×time interaction was detected for testicular weight and plasma testosterone concentrations (P<0.001). In control bucks, testicular weight increased from January and peaked in June, whereas in both photoperiodic-treated groups, this variable increased from January, but peaked in April, when the values were higher than in controls (P<0.05). In the control group, plasma testosterone concentrations remained low from January to June, whereas in both photoperiodic-treated groups, this variable remained low from January to March; thereafter, these levels increased in both photoperiodic-treated groups, and were higher than controls in April and May (P<0.05). We conclude that continuous light after a long-day treatment stimulate testosterone secretion in Alpine male goats during the non-breeding season as well as the long days followed by a melatonin treatment. Therefore, continuous light could replace the implants of melatonin.     

Testosterone increases neurotoxicity of glutamate in vitro and ischemia-reperfusion injury in an animal model.

Increasing evidence has demonstrated striking sex differences in the outcome of neurological injury. Whereas estrogens contribute to these differences by attenuating neurotoxicity and ischemia-reperfusion injury, the effects of testosterone are unclear. The present study was undertaken to determine the effects of testosterone on neuronal injury in both a cell-culture model and a rodent ischemia-reperfusion model. Glutamate-induced HT-22 cell-death model was used to evaluate the effects of testosterone on cell survival. Testosterone was shown to significantly increase the toxicity of glutamate at a 10 microM concentration, whereas 17beta-estradiol significantly attenuated the toxicity at the same concentration. In a rodent stroke model, ischemia-reperfusion injury was induced by temporal middle cerebral artery occlusion (MCAO) for 1 h and reperfusion for 24 h. To avoid the stress-related testosterone reduction, male rats were castrated and testosterone was replaced by testosterone pellet implantation. Testosterone pellets were removed at 1, 2, 4, or 6 h before MCAO to determine the duration of acute testosterone depletion effects on infarct volume. Ischemic lesion volume was significantly decreased from 239.6 +/- 25.9 mm(3) in control to 122.5 +/- 28.6 mm(3) when testosterone pellets were removed at 6 h before MCAO. Reduction of lesion volume was associated with amelioration of the hyperemia during reperfusion. Our in vitro and in vivo studies suggest that sex differences in response to brain injury are partly due to the consequence of damaging effects of testosterone.     

Seasonal variation in pituitary-gonadal function in free-ranging impala (Aepyceros melampus).

Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April-May) and nonbreeding (September-October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 microgram/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence of higher levels of testosterone during the velvet period in muntjac than in other cervids

Previous studies have shown that despite having a clear seasonal fluctuation in fecal testosterone concentration, the significantly lower testosterone levels found in velvet stags of the nonseasonal breeder muntjac (Muntiacus sp.) apparently did not stop their spermatogenesis as in other deer species. In the present study, in vitro cultivated Leydig cells isolated from adult stags of three native deer species of Taiwan were treated with androstenedione, with or without adding human chorionic gonadotropin. Results showed that, unlike the two seasonal breeders, sika deer (Cervus nippon) and sambar deer (Rusa unicolor), Leydig cells of velvet muntjac had no dramatic reduction in or even maintained the full capability of their testosterone productivity compared with the hard-antlered stage. The decrease in fecal testosterone level observed earlier in muntjac during the velvet period was probably due to a reduction of number of Leydig cells. These results support the hypothesis that testosterone production in muntjac during its velvet period might never be low enough to trigger the quiescent phase of the reproduction cycle.     

Serum Ferritin Is Inversely Correlated with Testosterone in Boys and Young Male Adolescents: A Cross-Sectional Study in Taiwan

Objective

The transition from childhood to teenaged years is associated with increased testosterone and a decreased iron status. It is not clear whether higher testosterone levels cause the decreased iron status, and to what extent, obesity-related inflammation influences the iron-testosterone relationship. The aim of the present study was to examine relationships of testosterone, iron status, and anti-/proinflammatory cytokines in relation to nutritional status in boys and young adolescent Taiwanese males.

Methods

In total, 137 boys aged 7~13 yr were included. Parameters for obesity, the iron status, testosterone, and inflammatory markers were evaluated.

Results

Overweight and obese (ow/obese) boys had higher mean serum testosterone, interleukin (IL)-1β, and nitric oxide (NO) levels compared to their normal-weight counterparts (all p<0.05). Mean serum ferritin was slightly higher in ow/obese boys compared to normal-weight boys, but this did not reach statistical significance. A multiple linear regression showed that serum ferritin (β = -0.7470, p = 0.003) was inversely correlated with testosterone, while serum IL-10 (β = 0.3475, p = 0.009) was positively associated with testosterone after adjusting for covariates. When normal-weight boys were separately assessed from ow/obesity boys, the association between testosterone and serum ferritin became stronger (β = -0.9628, p<0.0001), but the association between testosterone and IL-10 became non-significant (β = 0.1140, p = 0.4065) after adjusting for covariates. In ow/obese boys, only IL-10 was weakly associated with serum testosterone (β = 0.6444, p = 0.051) after adjusting for age.

Conclusions

Testosterone and serum ferritin are intrinsically interrelated but this relationship is weaker in ow/obese boys after adjusting for age.     

Season of the year influences semen output and concentrations of testosterone in circulation of yaks (Poephagus grunniens L.)

Seasonal changes in plasma testosterone concentration and semen quality were evaluated in yak bulls throughout a 1-year period. Blood samples were collected every week from adult yak bulls (n = 15). These blood samples were analyzed for testosterone using a highly sensitive enzyme-linked immunoassay. Ejaculates were collected from five representative bulls each week. Ejaculate volume, progressive motility, live sperm count and sperm concentrations were determined. Mean testosterone in plasma was 1.03 ± 0.25 ng/ml. Concentrations of testosterone changed throughout the year (P < 0.05) and were found to be highest during the winter. It was also higher during the autumn than in summer and spring (P < 0.05). Mean ejaculate volume, progressive motility, live sperm count and spermatozoa concentration were 2.7 ± 0.3 ml, 72.8 ± 1.4%, 82.3 ± 0.9% and 968 ± 233 × 10⁶ ml⁻¹, respectively. Ejaculate volume and sperm concentration were higher (P < 0.05) in autumn than in other seasons. To conclude, a highly sensitive EIA for testosterone was developed and validated for yak plasma. Seasonal changes in semen quality were associated with changes in the concentration of testosterone in plasma from yak bulls.     

The effects of intracerebroventricular infusion of prolactin in luteinizing hormone, testosterone and growth hormone secretion in male sheep

This study tested a hypothesis that the enhancement of the prolactin (PRL) concentration within the central nervous system (CNS) disturbs pulsatile luteinizing hormone (LH) and growth hormone (GH) secretion in rams that are in the natural breeding season. A 3h long intracerebroventricular (icv.) infusion of ovine PRL (50 microg/100 microl/h) was made in six rams during the daily period characterized by low PRL secretion in this species (from 12:00 to 15:00 h); the other six animals received control infusions during the same time. Blood samples were collected from 9:00 to 18:00 h at 10 min intervals. A clear daily pattern of LH secretion was shown in control animals, with the lowest concentration at noon and an increasing basal level around the time of sunset (P < 0.001). No significant changes in LH concentration occurred in PRL-infused animals and the concentration noted after infusion of PRL was significantly (P < 0.05) lower than after the control infusion. The frequency of LH pulses tended to decrease in rams after PRL treatment. The changes in LH secretion clearly carried over to the secretion of testosterone in the rams of both groups. The GH concentrations changed throughout the experiment in both groups of rams, being higher after the infusions (P < 0.001). However, the mean GH concentration and GH pulse amplitude noted after PRL infusion were significantly lower (P < 0.001 and P < 0.05, respectively) from those recorded in the control. The continued fall in PRL secretion observed in rams following PRL infusion (P < 0.05 to P < 0.001) indicates a high degree of effectiveness of exogenous PRL at the level of the CNS. In conclusion, maintenance of an elevated PRL concentration within the CNS leads to disturbances in the neuroendocrine mechanisms responsible for pulsatile LH and GH secretion in sexually active rams.     

Exercise-Induced Blood Lactate Increase Does Not Change Red Blood Cell Deformability in Cyclists

Background

The effect of exercise-induced lactate production on red blood cell deformability and other blood rheological changes is controversial, given heavy-exercise induces biochemical processes (e.g., oxidative stress) known to perturb haemorheology. The aim of the present study was to examine the haemorheological response to a short-duration cycling protocol designed to increase blood lactate concentration, but of duration insufficient to induce significant oxidative stress.

Methods

Male cyclists and triathletes (n = 6; 27±7 yr; body mass index: 23.7±3.0 kg/m²; peak oxygen uptake 4.02±0.51 L/min) performed unloaded (0 W), moderate-intensity, and heavy-intensity cycling. Blood was sampled at rest and during the final minute of each cycling bout. Blood chemistry, blood viscosity, red blood cell aggregation and red blood cell deformability were measured.

Results

Blood lactate concentration increased significantly during heavy-intensity cycling, when compared with all other conditions. Methaemoglobin fraction did not change during any exercise bout when compared with rest. Blood viscosity at native haematocrit increased during heavy-intensity cycling at higher-shear rates when compared with rest, unloaded and moderate-intensity cycling. Heavy-intensity exercise increased the amplitude of red blood cell aggregation in native haematocrit samples when compared with all other conditions. Red blood cell deformability was not changed by exercise.

Conclusion

Acute exercise perturbs haemorheology in an intensity dose-response fashion; however, many of the haemorheological effects appear to be secondary to haemoconcentration, rather than increased lactate concentration.