Initial observations on using magnesium metal in peripheral nerve repair.

Biodegradable magnesium metal filaments placed inside biodegradable nerve conduits might provide the physical guidance support needed to improve the rate and extent of regeneration of peripheral nerves across injury gaps. In this study, we examined basic issues of magnesium metal resorption and biocompatibility by repairing sub-critical size gap injuries (6 mm) in one sciatic nerve of 24 adult male Lewis rats. Separated nerve stumps were connected with poly(caprolactone) nerve conduits, with and without magnesium filaments (0.25 mm diameter, 10 mm length), with two different conduit filler substances (saline and keratin hydrogel). At 6 weeks after implantation, magnesium degradation was examined by micro-computed tomography and histological analyses. Magnesium degradation was significantly greater when the conduits were filled with an acidic keratin hydrogel than with saline (p < 0.05). But magnesium filaments in some animals remained intact for 6 weeks. Using histological and immunocytochemical analyses, good biocompatibility of the magnesium implants was observed at 6 weeks, as shown by good development of regenerating nerve mini-fascicles and only mild inflammation in tissues even after complete degradation of the magnesium. Nerve regeneration was not interrupted by complete magnesium degradation. An initial functional evaluation, determination of size recovery of the gastrocnemius muscle, showed a slight improvement due to magnesium with the saline but not the keratin filler, compared with respective control conduits without magnesium. These results suggest that magnesium filament implants have the potential to improve repair of injured peripheral nerve defects in this rodent model.

Body composition and menstrual function in athletes.

The problem of menstrual dysfunction in athletes was recognised at about the same time as a theory was developed that a critical fat level was necessary for the onset and maintenance of menstrual function (17% and 22% of bodyweight, respectively). This theory was acceptable because of the frequency of leanness in athletes experiencing menstrual dysfunction and because of the role of adipose tissue in the intraconversion of hormones which could affect hypothalamic and pituitary regulatory centres. Research on this topic has been hampered by the extensive use of surveys, confining sampling to specific sports, use of inaccurate methods of body composition assessment, and lack of data on hormonal changes. Studies using appropriate body composition measures do not support the critical fat theory, but they do not exclude a role for body composition changes in the regulation of menstrual function. The probability of finding menstrual dysfunction in very lean athletes is high, but not absolute, and there is no assurance that dysfunction will improve merely by increasing bodyweight. Perhaps of more concern, however, is recent research on very lean, long term amenorrhoeic athletes who train intensely and show a loss of bone mineral, apparently related to low oestrogen levels. This mineral deficiency is apparently a factor in stress fractures. The bone mineral content of these athletes is similar to that of post-menopausal women susceptible to osteoporosis. Although the loss of bone due to short term amenorrhoea may be reversible, the prognosis for a long term deficiency is not presently known.

Effect of recreational exercise on pregnancy weight gain and subcutaneous fat deposition.

This study was designed to test the hypothesis that continuing a regular regimen of recreational endurance exercise alters the time-specific rate of maternal weight gain and subcutaneous fat deposition during pregnancy. Serial measurements of body mass and 5-site skinfold thickness were obtained from 44 women before and during pregnancy who continued their preconceptional exercise regimen throughout pregnancy and from women who voluntarily stopped their preconceptional exercise regimen either before conception (N = 31) or reduced it below baseline fitness levels in very early pregnancy (N = 4). In the first and second trimester, the rate of weight gain and change in skinfold thicknesses were unrelated to exercise performance. However, those who continued exercise had a reduced rate of weight gain and change in skinfold thickness at specific sites in the last trimester of pregnancy. Overall weight gains were (mean +/- SEM) 13.0 +/- 0.5 kg and 16.3 +/- 0.7 kg in the exercise and control groups, respectively, and the increases in the sum of skinfolds were 22 +/- 2 mm and 31 +/- 2 mm, respectively. We conclude that continuing a regular exercise regimen throughout pregnancy does not influence the rate of early pregnancy weight gain or subcutaneous fat deposition but decreases both in late pregnancy. However, overall pregnancy weight gain remains well within the normal range.

The physiological response of instructors and participants to three aerobics regimens.

This study was designed to test the hypothesis that there are regimen-specific differences in the thermal, metabolic, and cardiovascular responses of nonpregnant women when they perform their chosen type of aerobics at their usual performance level. Thirty-six instructors and 53 participants were studied while performing their chosen aerobics regimen under simulated field conditions using oxygen consumption as the index of exercise intensity. Under these conditions no significant differences were observed in the physiological response to low impact, high impact, or step regimens. However, although their ratings of perceived exertion were lower, the participants worked at a much higher exercise intensity than the instructors (76 +/- 1 vs 62 +/- 2% VO2max). As a result they attained a higher respiratory exchange ratio (0.96 vs 0.90), rectal temperature (38.62 vs 38.12 degrees C), and blood levels of glucose (5.70 vs 4.95 mmol.l-1), lactate (3.65 vs 1.60 mmol.l-1), and norepinephrine (2656 vs 1191 pg.ml-1). We conclude that both intensity and physiological response to aerobics are individual specific not regimen specific and that participants consistently underestimate their level of performance.

Self-selected recreational exercise has no impact on early postpartum lactation-induced bone loss.

UNLABELLED: Although exercise is known to positively impact bone mineral density (BMD), its effect on lactation-induced BMD loss has not been previously evaluated in a case-control study. PURPOSE: The purpose of this study was to compare lactation-induced bone changes in women who engaged in regular, self-selected, recreational exercise versus those who refrained from such during early postpartum. METHODS: Subjects were 20 healthy, lactating women who either exercised regularly (exercise, E; N = 11) or refrained from such (control, C; N = 9) during the first 3 months postpartum. Although preconception VO2max was significantly higher in E than C (E = 54.1, C = 36.9 mL.min-1.kg-1), no significant group differences were observed for parity, age, height, weight (WT), % body fat, dietary calcium intake, lactation calcium loss, and serum estradiol. Total body (TB), lumbar spine (LS), and femur neck (FN) BMD were measured within 2 wk of parturition and repeated at 3 months postpartum by dual energy x-ray absorptiometry. RESULTS: Although TB was unchanged, BMD decreased significantly from baseline in both groups at LS (C = -5.4, E = -4.1%) and FN (C = -2.7, E = -2.8%). WT decreased significantly over time but was not significantly correlated with BMD loss. No significant group by time interactions were observed for WT or BMD changes. CONCLUSION: These results suggest that regular, self-selected, recreational E has no impact on early postpartum lactation-induced BMD loss.

Validity of "generalized" equations for body composition analysis in male athletes.

Equations by Durnin and Womersley [(D-W), Br. J. Nutr. 32:77, 1974], Jackson and Pollock [(J-P), Br. J. Nutr. 40:497, 1978], and Lohman [(L), Human Biol., 53:181, 1981] for estimating body density (BD) purportedly overcome the problem of specificity by accounting for age and/or the curvilinear relationship between skinfolds (SF) and BD. Their equations were validated on 265 male athletes against percent fat measured by underwater weighing [(UWW); mean +/- SD = 9.2 +/- 4.4%]. Equations by Sloan [(S), J. Appl. Physiol. 23:311, 1967], Katch and McArdle [(K-M), Human. Biol. 45:445, 1973], and Forsyth and Sinning [(F-S), Med. Sci. Sports 5:174, 1973] were included as "linear regression models" to compare to the curvilinear models of J-P, D-W, and L. Differences between UWW and estimated mean values ranged from -1.1 to +5.9%; correlations ranged from 0.58 to 0.85; SEE ranged from +/- 2.41 to +/- 3.61% and total error (E) ranged from 2.38 to 6.97%. The seven D-W equations overestimated mean percent fat by from 3.9 to 5.9%. The K-M, S, and L equations overestimated by 1.3, 0.5, and 1.7%, respectively. The F-S equations overestimated by 2.4 to 3.8%. Of the 21 equations evaluated, only 3 by J-P gave estimates not significantly different from UWW percent fat. Regression analyses of the relationship between UWW (y) and estimated (x) percent fat values from those equations were: y = 1.037x - 0.08 +/- 2.38, E = 2.38, r = 0.84; 0.869x + 1.36 +/- 2.45, E = 2.51, r = 0.83; 1.107x - 1.14 +/- 2.51, E = 2.53, r = 0.82.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction between regular exercise and selected aspects of women's health.

The public health initiative to increase women's participation in regular recreational exercise to the 90% level raises multiple theoretic concerns about its impact on the reproductive health of women. However, at all points in a woman's life the overall effect of regular exercise to appetite appears to be beneficial rather than harmful, and in the absence of other stressors, exercise performance must significantly exceed usual recreational levels to have an adverse effect on any aspect of a woman's reproductive life. Therefore even in elite athletes abnormalities of any part of the reproductive process (puberty, menstrual cyclicity, pregnancy, lactation, and menopause) should not be attributed solely to exercise without complete evaluation. While generally beneficial, the interaction between exercise and skeletal integrity is influenced by hormonal status and multiple exercise variables. Thus, whereas regular exercise at all ages appears to provide both short- and long-term benefit, the characteristics of the exercise regimen need to vary at different time points.

Fetal heart rate response to sustained recreational exercise.

OBJECTIVE: We aimed to test the hypotheses that fetal heart rate increases during and after sustained exercise and that the magnitude of the increases is related to gestational age and the duration, intensity, and type of exercise. STUDY DESIGN: Maternal oxygen uptake and fetal heart rate were monitored in 120 regularly exercising women in association with routine 20-minute workouts between 16 and 39 weeks' gestation. RESULTS: In 97% of the studies fetal heart rate increased during and after exercise. This was significant at all gestational ages and with all forms of exercise with an overall increase of 15 +/- 11 beats.min-1 at 60% +/- 12% of maximal aerobic capacity (mean +/- SD). The magnitude increased with gestational age (10 +/- 8 to 20 +/- 11 beats.min-1), exercise intensity (8 +/- 7 to 21 +/- 13 beats.min-1), and exercise duration (8 +/- 4 to 16 +/- 7 beats.min-1). CONCLUSION: We concluded that the hypothesis is correct and speculate that these changes represent a maturing fetal response to a reduction in Po2.

Parallel inheritance of tissue catalase activity and immunostimulatory action of amphotericin B in inbred mouse strains.

Both amphotericin B (AmB) and its methyl ester derivative are potent immunoadjuvants that also stimulate murine B lymphocytes and macrophages in vitro. Most of the common inbred mouse strains show AmB-induced immunostimulation (AmB-high responders) but mice from the C57BL strains, regardless of H-2 genotype, are AmB-low responders. Lymphoid cells from AmB-high responder strains also exhibit greater resistance to H2O2 toxicity in vitro compared with cells from AmB-low responders. This result led to an evaluation of differences in the tissue catalase levels of AmB-high and -low responder strains. Results from several laboratories, including ours, indicate that C57BL mouse strains express low levels of tissue catalase activity in addition to low or absent immunostimulant effects of AmB. Several AmB-high responder strains have high spleen cell, macrophage, and liver catalase, and the mouse strain distribution of enzyme activity as well as the dominant inheritance of the low catalase phenotype is compatible with regulation by the Ce-1 locus in lymphoid organs as well as liver. Other evidence also suggests that H2O2 metabolism is important in lymphoid cell responses to AmB. For example, AmB stimulates a stronger respiratory burst in macrophages from AmB-high responder strains under the same conditions that inhibit burst activity in macrophages from low responders. Selective immune enhancement by AmB in high catalase mouse strains along with enhanced susceptibility to AmB toxicity in low responder C57BL mice with low tissue catalase activity suggests that cellular peroxidation is a major determinant of the genetic regulation of amphotericin-induced immunostimulation.

The effect of sustained exercise on follicular phase levels of 17 beta-estradiol in recreational athletes.

OBJECTIVE: Our purpose was to test the hypothesis that sustained exercise elevates circulating levels of 17 beta-estradiol in an intensity-dependent manner. STUDY DESIGN: Blood samples were obtained in the follicular phase of the menstrual cycle from 75 female recreational athletes before and immediately after 20 minutes of aerobics or running at their usual exercise intensity. RESULTS: The levels of 17 beta-estradiol rose after exercise 97% of the time. At exercise intensities between 50% and 88% of maximum capacity there was a direct linear relationship (r = 0.57) between exercise intensity and magnitude of increase in estradiol levels. A similar relationship was not present for cortisol. CONCLUSION: Sustained exercise produces an intensity-dependent increase in the levels of 17 beta-estradiol that probably reflects decreased hepatic clearance caused by the fall in splanchnic blood flow. Thus the magnitude of the increase in the level of 17 beta-estradiol can be used as a rough index of the exercise-induced decrease in splanchnic blood flow.

A new method of radioiodine labeling of polyanionic macromolecules for radioimmunoassay.

A method is described for radiolabeling polyanionic macromolecules by the formation of an electrostatic complex with a radioiodinated tyramine conjugated DEAE-dextran. Data is presented on the use of this technique for the detection and quantitation of immunospecific binding of polynitrophenylated proteins, deoxyribonucleic acids, and cell surface antigens.

The effect of regular maternal exercise on erythropoietin in cord blood and amniotic fluid.

OBJECTIVE: Our purpose was to test the hypothesis that continuing regular, high-intensity exercise until the onset of labor produces significant fetal hypoxemia, as evidenced by elevated erythropoietin levels in the fetal compartment. STUDY DESIGN: Erythropoietin levels were measured in samples of amniotic fluid and cord blood obtained from fetuses born to 31 exercising women and 29 matched controls. RESULTS: Erythropoietin levels (mean +/- SEM) in amniotic fluid obtained at the time of membrane rupture (9 +/- 2 vs 11 +/- 2 mU/ml) and in cord blood (38 +/- 6 vs 53 +/- 16 mU/ml) and amniotic fluid at delivery (9 +/- 1 vs 24 +/- 12 mU/ml) were no different in women who exercised regularly until the onset of labor. In both groups the majority of elevated cord blood levels (> 50 mU/ml) could be explained by labor events. Amniotic fluid erythropoietin levels correlated directly (r = 0.52) with cord blood hematocrit and increased slowly during labor. CONCLUSION: We conclude that the initial hypothesis is incorrect and speculate that cord blood erythropoietin reflects fetal oxygenation during labor, whereas amniotic fluid erythropoietin primarily reflects the adequacy of oxygenation before the onset of labor.

Induction of amphotericin B-specific antibodies for use in immunoassays.

High-titered antisera specific for amphotericin B (AmB) were induced by immunization with a protein conjugate of the D-lysyl AmB methyl ester. These polyclonal anti-AmB antibodies reacted preferentially with AmB or the AmB methyl ester and discriminated sharply between nystatin and AmB. A solid-phase radioimmunoassay was developed with radioiodinated immunoglobulin G fractions derived from the anti-AmB antisera. This assay was capable of detecting AmB in the sera in the same concentration range that is regularly achieved during AmB treatment of systemic fungal infections. This study demonstrated the feasibility of immunoassays in measuring the concentration of AmB in blood and tissue fluids.

Amphotericin B selectively stimulates macrophages from high responder mouse strains.

Lymphoid cells from most inbred mouse strains respond to amphotericin B (AmB)-induced immunostimulation. However, C57BL/6 mice and related strains display low or absent lymphoid cell stimulation by AmB and enhanced susceptibility to AmB toxicity. Experiments reported here show that in vitro incubation with AmB can stimulate AKR (AmB-high responder strain) macrophage proliferation. Intraperitoneal injection of AKR mice with AmB also elicits a population of macrophages primed for enhanced oxidative burst activity after triggering by zymosan particles. Under the same experimental conditions, AmB elicits a population of very weakly responsive macrophages from C57BL/6 mice. The low responsiveness of C57BL/6 macrophages correlates with previous observations that AmB is a potent immunoadjuvant and B cell mitogen in most inbred strains, but it selectively lacks immunoadjuvant effects in C57BL/6 mice and it also fails to induce polyclonal B cell stimulation in their spleen cell suspensions. Similarly, in measurements of protein synthesis in vitro, high concentrations of AmB produce a greater inhibition of protein synthesis in C57BL/6 peritoneal macrophages than in parallel cultures of AKR macrophages. These findings support the hypothesis that the macrophage is an important target cell in the mediation of AmB-induced immunomodulation.