Effect of erythropoietin on hematocrit and blood pressure in normotensive and hypertensive rats.

Treatment with recombinant human erythropoietin (rHuEPO) successfully reverses anemia in uremic patients. Of major concern, however, are blood pressure (BP) increases during rHuEPO therapy, observed particularly in persons with a history of hypertension. To determine whether preexisting hypertension enhances BP increases to rHuEPO, BP responses to 2 wk of rHuEPO or placebo were observed in spontaneously hypertensive rats (SHR) and their normotensive genetic controls (Wistar-Kyoto [WKY] rats. In addition, the role of endothelial-released nitric oxide (NO) in BP alterations caused by rHuEPO through i.v. infusions of endothelium-dependent and independent vasoactive agents were indirectly examined. At trial completion, rHuEPO elevated hematocrit, hemoglobin, and mean cell volume more in SHR than in WKY rats (P less than 0.001). Despite the considerable increase in hematocrit, rHuEPO did not alter BP in either strain. An infusion of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of NO formation, elevated BP more in rHuEPO-treated SHR than in identically treated WKY rats (P less than 0.05). Further, the administration of L-arginine caused a greater decrease in blood pressure in SHR than in WKY rats, independent of treatment condition (P less than 0.01). Because changes in BP with endothelium-independent agents were similar across groups, responses to L-NMMA and L-arginine were specific to the endothelium and probably independent of basal BP. Thus, rHuEPO provoked greater erythropoiesis in SHR than in WKY rats but did not elevate BP. L-NMMA stimulated higher BP in SHR treated with rHuEPO, suggesting a compensatory increase in vasodilatory NO synthesis to protect against a hypertensive effect of the drug in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adverse effects of sucrose-rich diets on uraemic rats

The nature of carbohydrate may affect the tolerance and progression of uraemia. The effects of three diets differing only in their carbohydrate source: namely corn starch (C), glucose (G) or sucrose (S) were examined. Study 1 examined the effects of the three carbohydrate diets on unilaterally nephrectomised control rats and severely uraemic rats. The three carbohydrates produced similar nutritional effects in uninephrectomised rats, whereas sucrose rapidly induced anorexia, stunting and slightly accelerated renal damage in uraemia. Study 2 examined the long-term effects of the three carbohydrates in moderate uraemia under conditions of high and identical carbohydrate intakes. Hyperphagic Zucker uraemic rats (F rats) received a daily allotment of each diet plus pure carbohydrate. Lean uraemic rats (L rats) received the same dietary allotment without the carbohydrate supplement. The F rats fed sucrose showed greater morbidity and mortality but little renal deterioration. Their plasma triglycerides increased dramatically. The L rats fed sucrose had the greatest urinary protein, the least creatinine clearance and the most severe renal damage. Thus, sucrose-rich but not glucose-rich diets have two adverse effects in uraemia: a deterioration in nutritional status, perhaps related to abnormal fructose utilisation, and a long-term effect on the kidney, resulting in accelerated renal deterioration.     

Fatigue and fitness modelled from the effects of training on performance

Summary The purpose of this study was to compare two ways of estimating both fatigue and fitness indicators from systems model of the effects of training on performance. The model was applied to data concerning the training of a hammer thrower. The variations in performance were mathematically related to the successive amounts of training. The model equation was composed of negative (NF) and positive (PF) functions. The NF and PF were associated with the fatigue and fitness estimated in previous studies. Using another method, fatigue and fitness indicators were estimated from a combination of NF and PF. The influence of training on performance was negatively associated with fatigue (NI), and positively to fitness (PI). The changes in performance were well described by the model in the present study (r = 0.96,N = 19,P<0.001). Significant correlations were observed between NF and NI (r = 0.93,P < 0.001) on the one hand and between PF and PI (r = 0.90,P < 0.001) on the other. The absolute values and the time variations of PI and NI were closer to the change in performance than NF and PF. The NF and PF were accounted for mainly by the accumulation of amounts of training. On the other hand, NI and PI were accounted for rather by the impact of these amounts of training on performance.     

Effects of training on iron status in cross-country skiers

Summary Haematological changes were studied in cross-country skiers during a 33-week training season (7 h a week). The daily amounts of training were calculated from the duration and the intensity of the exercise and then used to estimate training responses associated with a first order transfer function. The profile of system training responses (STR) was determined by convolution between the amounts of training and a first-order transfer function. Linear regressions were used to determine correlation coefficients between STR and iron status indices. Among the values for the time constants of decay, the one giving the best fit between STR and iron status indices was chosen. A relationship was noted between on the one hand STR and changes in serum ferritin concentration ([FERR]) and on the other hand STR and change in mean cell volume (MCV). The [FERR] was decreased and MCV was increased by training. It is suggested that a decrease in [FERR] could have been related to a decrease in total body iron stores. However, large and rapid changes in [FERR] could not have been a reflection of changes in total body iron stores. Equilibrium between [FERR] and total body iron stores could have been temporarily altered by the effects of training. Moreover, iron stores did not seem to have been sufficiently depleted to restrict erythropoiesis. The MCV increased slightly in response to intense training suggesting that training enhances the proportion of young erythrocytes.     

Mechanism of the enhancing effect of sorbitol on ileal Ca uptake in rat enterocytes

The effect of sorbitol on Ca uptake by isolated ileal epithelial cells was investigated. Intestinal cells were isolated from rat ileum by mechanical vibration.⁴⁵Ca uptake was approximately 2 times higher in cells exposed to 200 mM sorbitol ofd-alanine than in control cells. This enhancing effect of sorbitol on percentage Ca uptake decreased with increasing Ca concentrations in the incubation medium suggesting an effect on Ca entry velocity. The addition of 10 M nifedipine or 200 M verapamil to the incubation medium was devoid of any effect on Ca uptake in ileal cells, whereas 100 M trifluoperazine or chlorpromazine abolished the stimulatory effect of sorbitol. Finally, the effect of sorbitol on isolated cells was independent of a measurable change of cellular ATP content. In conclusion, the stimulatory effect of sorbitol on ileal Ca uptake is probably exerted through mechanisms other than an increase in intracellular ATP concentration. Sorbitol may enhance enterocyte Ca transport via a direct interaction with calmodulin and/or the Ca pump. It may also exert its effect through an inhibition of the basolateral Na Ca exchanger.     

The energetics of middle-distance running

Summary In order to assess the relative contribution of aerobic processes to running velocity (v), 27 male athletes were selected on the basis of their middle-distance performances over 800, 1500, 3000 or 5000 m, during the 1987 track season. To be selected for study, the average running velocity corresponding to their performances had to be superior to 90% of the best French of the season. Maximum O₂ consumption and energy cost of running (C) had been measured within the 2 months preceding the track season, which, together with oxygen consumption at rest allowed us to calculate the maximalv that could be sustained under aerobic conditions: . The treadmill runningv corresponding to a blood lactate of 4 mmol·^–1 (v _la4), was also calculated. In the whole group, C was significantly related to height (r=–0.43;P<0.03). Neither C nor (with, in this case, the exception of the 3000 m athletes) were correlated to . On the other hand,v _{a max} was significantly correlated to over distances longer than 800 m. These were also correlated tov _la4. Howeverv _la4 occurred at 87.5% SD 3.3% ofv _{a max}, this relationship was interpreted as being an expression of the correlation betweenv _{a max} and . Calculation ofv _{a max} provided a useful means of analysing the performances. At the level of achievement studied, sustained over 3000 m corresponded tov _{a max}. The shape of the relationship ofv/v _{a max} as a function of the duration of the event raised the question of a possible change in C as a function of v during middle-distance running competitions.     

A method for assessing muscle fatigue during sprint exercise in humans using a friction-loaded cycle ergometer

This study investigated the mechanical changes induced by muscle fatigue caused by repeated sprints and determined whether a friction-loaded cycle ergometer has any advantages for assessing muscle fatigue. Nine subjects performed 15 sprints, each of 5 s with a 25-s rest, on a friction-loaded cycle ergometer. The averaged force, power and velocity of each push-off were calculated. Maximal power decreased by 17.9%, with a concomittent slowing of muscle contraction, but without any change in the maximal force. These results demonstrated that repeated sprints slow down muscle contraction, leading to a fall in maximal power without any loss of force. This would suggest that fast twitch fibres are selectively fatigued by repeated sprints. However, the ergometer used in the present study made it difficult to evaluate the relative influences of contraction velocity and sprinting time. This was certainly the most important limitation. On the other hand, it showed the advantage of measuring instantaneous power and total work dissipated in the environment simultaneously. It also permitted a force-velocity relationship to be obtained from a single sprint and this relationship is known to be closely related to the muscle fibre composition. Accepted: 5 March 1998     

Monosomy 9q and trisomy 16q in a case of congenital solitary infantile myofibromatosis

Although infantile myofibromatosis (IM) is the most common fibrous proliferation of infancy, many aspects of this benign lesion have not been explored. IM histogenesis is still poorly understood, despite immunohistochemical staining and ultrastructural features that suggest a myofibroblastic origin. IM diagnosis is often made difficult by the predominance of small primitive spindle cells over myofibrobasts and the presence of intravascular growth. Genetic information is scarce, with only one karyotyped case. Here we describe a case of solitary IM discovered at birth in an otherwise healthy girl. The tumor was well circumscribed, arranged in nodules and made up of ovoid cells without atypia, in a myxoid background. Immunohistochemical evaluation indicated a myofibroblastic differentiation. The cytogenetic and fluorescence in situ hybridization analyses revealed an abnormal chromosome 9, derived from an unbalanced whole-arm translocation between chromosomes 9 and 16. On both chromosomes, the breakpoints were located in the pericentric heterochromatic region. This clonal abnormality has not been reported in other tumors and is different from the chromosome 6q deletion reported in the single previous reported IM karyotype.