Rehydration with fluid of varying tonicities: effects on fluid regulatory hormones and exercise performance in the heat.

This study examined the effects of rehydration (Rehy) with fluids of varying tonicities and routes of administration after exercise-induced hypohydration on exercise performance, fluid regulatory hormone responses, and cardiovascular and thermoregulatory strain during subsequent exercise in the heat. On four occasions, eight men performed an exercise-dehydration protocol of approximately 185 min (33 degrees C) to establish a 4% reduction in body weight. Following dehydration, 2% of the fluid lost was replaced during the first 45 min of a 100-min rest period by one of three random Rehy treatments (0.9% saline intravenous; 0.45% saline intravenous; 0.45% saline oral) or no Rehy (no fluid) treatment. Subjects then stood for 20 min at 36 degrees C and then walked at 50% maximal oxygen consumption for 90 min. Subsequent to dehydration, plasma Na(+), osmolality, aldosterone, and arginine vasopressin concentrations were elevated (P < 0.05) in each trial, accompanied by a -4% hemoconcentration. Following Rehy, there were no differences (P > 0.05) in fluid volume restored, post-rehydration (Post-Rehy) body weight, or urine volume. Percent change in plasma volume was 5% above pre-Rehy values, and plasma Na(+), osmolality, and fluid regulatory hormones were lower compared with no fluid. During exercise, skin and core temperatures, heart rate, and exercise time were not different (P > 0.05) among the Rehy treatments. Plasma osmolality, Na(+), percent change in plasma volume, and fluid regulatory hormones responded similarly among all Rehy treatments. Neither a fluid of greater tonicity nor the route of administration resulted in a more rapid or greater fluid retention, nor did it enhance heat tolerance or diminish physiological strain during subsequent exercise in the heat.     

Menstrual status and plasma vasopressin, renin activity, and aldosterone exercise responses

The effects of menstrual cycle phase (early follicular vs. midluteal) and menstrual status (eumenorrhea vs. amenorrhea) on plasma arginine vasopressin (AVP), renin activity (PRA), and aldosterone (ALDO) were studied before and after 40 min of submaximal running (80% maximal O2 uptake). Eumenorrheic runners were studied in the early follicular and midluteal phases determined by urinary luteinizing hormone and progesterone and plasma estradiol and progesterone assays; amenorrheic runners were studied once. Menstrual phase was associated with no significant differences in preexercise plasma AVP or PRA, but ALDO levels were significantly higher during the midluteal phase than the early follicular phase. Plasma AVP and PRA were significantly elevated at 4 min after the 40-min run in the eumenorrheic runners during both menstrual phases and returned to preexercise levels by 40 min after exercise. Plasma ALDO responses at 4 and 40 min after exercise were higher in the midluteal phase than the early follicular phase. Menstrual status was associated with no significant differences in preexercise AVP or PRA; however, ALDO levels were significantly higher in the amenorrheic runners. After exercise, responses in the amenorrheic runners were comparable with the eumenorrheic runners during the early follicular phase. Thus, submaximal exercise elicits significant increases in plasma AVP and PRA independent of menstrual phase and status. However, plasma ALDO is significantly elevated during the midluteal phase, exercise results in a greater response during this menstrual phase, and amenorrheic runners have elevated resting levels of ALDO.     

Use of specific monoclonal and polyclonal antibodies to define distinct antigens of the porcine zonae pellucidae

Specific monoclonal and polyclonal antibodies to solubilized porcine and rabbit zonae pellucidae (ZP) and to purified ZP glycoprotein components have been used to define distinct ZP antigens. These studies demonstrate that the individual ZP glycoproteins contain both unique and shared determinants. One monoclonal antibody (R5) has been used to demonstrate that the major porcine ZP glycoprotein, which has multiple charge species ranging in molecular weight from 42,000 to 120,000, is composed of two distinct polypeptide antigens unique to this glycoprotein class. These distinct antigens can be differentiated by immunoblotting after high-resolution two-dimensional polyacrylamide gel electrophoretic separation of trypsin-treated or deglycosylated glycoproteins. The two polypeptides also differ in their staining properties with the silver-based color stain and in their susceptibility to proteolysis. A second monoclonal antibody (PSI) has been used to define a determinant shared by all three major porcine ZP glycoprotein classes. This determinant appears to involve either a carbohydrate moiety or some other molecular feature related to post-translational modification, since the antibody recognizes only the acidic species of each glycoprotein class, and does not recognize the deglycosylated forms of the proteins. This work demonstrates that there are both unique and shared antigenic determinants present in the individual components of the ZP, but that the immunodominant determinants appear to be unique to each glycoprotein.     

Reduction of Visceral Adipose Tissue and Improvement of Metabolic Indices: Effect of Dexfenfluramine in NIDDM

Increased visceral adipose tissue is thought to contribute to impaired glucose tolerance. We studied 10 men with non-insulin dependent diabetes (NIDDM) before and after a 12-week intervention study using dexfenfluramine. Subjects had a mean body mass index (BMI) of 26.4 ± 1.7 kg\m² and had an abdominal distribution of body fatness (waist-to hip ratio >0.9). Anthropometric indices, biochemistry, macronutrient intake from 7-day food records as well as a euglycaemic glucose clamp and magnetic resonance imaging (MRI) were performed at week 0 and week 12. Abdominal adipose tissue area measured by MRI was reduced from 854 ± 270 cm² to 666 ± 231 cm² (p=0.003) due mainly to a selective 32% reduction in visceral fat area from 484 ± 230 cm² to 333 ± 72 cm² (p=0.002). Insulin sensitivity improved from 0.29 ± 0.13 [min^?1 (mU/L)] to 0.54 ± 0.21 [min^?1 (mU/L)] (p=0.01) and C-peptide levels reduced from 0.77 ± 0.24 μmol/L to 0.58 ± 0.15 μmol/L (p=0.002). The reductions in fasting glucose and glycated haemoglobin failed to achieve significance. Fasting total cholesterol and triglyceride levels significantly reduced (p=<0.001 and p=0.021 respectively). There was a reduction in total energy intake (p=0.005) due to a significant reduction in calories obtained from fat (p<0.001). Thus dexfenfluramine was shown to be a useful adjunct therapy for the reduction of visceral fat in abdominally-obese men with NIDDM with an associated improvement in insulin sensitivity.     

Molecular structure and genetic stability of human hypoxanthine phosphoribosyltransferase (HPRT) gene duplications.

We have determined the genetic stability of three independent intragenic human HPRT gene duplications and the structure of each duplication at the nucleotide sequence level. Two of the duplications were isolated as spontaneous mutations from the HL60 human myeloid leukemia cell line, while the third was originally identified in a Lesch-Nyhan patient. All three duplications are genetically unstable and have a reversion rate approximately 100-fold higher than the rate of duplication formation. The molecular structures of these duplications are similar, with direct duplication of HPRT exons 2 and 3 and of 6.8 kb (HL60 duplications) or 13.7 kb (Lesch-Nyhan duplication) of surrounding HPRT sequence. Nucleotide sequence analyses of duplication junctions revealed that the HL60-derived duplications were generated by unequal homologous recombination between clusters of Alu repeats contained in HPRT introns 1 and 3, while the Lesch-Nyhan duplication was generated by the nonhomologous insertion of duplicated HPRT DNA into HPRT intron 1. These results suggest that duplication substrates of different lengths can be generated from the human HPRT exon 2-3 region and can undergo either homologous or nonhomologous recombination with the HPRT locus to form gene duplications.     

In vitro demonstration of a saturable transport system for leptin across the blood-brain barrier.

A saturable blood-to-brain transport system for leptin across the blood-brain barrier (BBB) has been observed in vivo. Since the main component of the non-fenestrated microvessels of the BBB is the endothelial cell, we established an in vitro culture system of these cerebrovascular cells to study leptin transport and to determine whether the self-inhibition of leptin transport characteristic of a saturable system occurs at this level. The results show that 125I-leptin crossed from the luminal to abluminal side of a monolayer of cerebral microvessel cells significantly faster than the albumin and lactalbumin controls. This transport of 125I-leptin across an in vitro BBB was significantly faster than in the opposite direction and was dose-relatedly inhibited by the addition of unlabeled leptin. Thus, the results establish that the saturable transport system for leptin across the BBB occurs at the level of the endothelial cells of the BBB.     

Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, and water intake

Armstrong, Lawrence E., Carl M. Maresh, Catherine V. Gabaree, Jay R. Hoffman, Stavros A. Kavouras, Robert W. Kenefick, JohnW. Castellani, and Lynn E. Ahlquist. Thermal and circulatory responses during exercise: effects of hypohydration, dehydration, andwater intake. J. Appl. Physiol. 82(6):2028-2035, 1997.This investigation examined the distinct andinteractive effects of initial hydration state, exercise-induceddehydration, and water rehydration in a hot environment. On fouroccasions, 10 men performed a 90-min heat stress test (treadmillwalking at 5.6 km/h, 5% grade, 33°C, 56% relative humidity).These heat stress tests differed in pretest hydration [2euhydrated (EU) and 2 hypohydrated (HY) trials] and water intakeduring exercise [2 water ad libitum (W) and 2 no water (NW)trials]. HY + NW indicated greater physiological strain than allother trials (P < 0.05-0.001)in heart rate, plasma osmolality(P_osm), sweat sensitivity(g / °C · min), and rectal temperature.Unexpectedly, final HY + W and EU + W responses for rectal temperature,heart rate, and P_osm were similar,despite the initial 3.9 ± 0.2% hypohydration in HY + W. Weconcluded that differences in pretestP_osm (295 ± 7 and 287 ± 5 mosmol/kg for HY + W and EU + W, respectively) resulted in greaterwater consumption (1.65 and 0.31 liter for HY + W and EU + W,respectively), no voluntary dehydration (0.9% body mass increase), andattenuated thermal and circulatory strain during HY + W.

     

Body composition and physical performance in men's soccer: a study of a National Collegiate Athletic Association Division I team

The purpose of this study was to examine the relationship between body composition (BC) and physical performance (PP) in male collegiate soccer players and differences among positions and between starters and non-starters. Twenty-seven male collegiate soccer players were tested at the beginning of the 2003-2004 season (age = 19.9 +/- 1.3 years, height = 177.6 +/- 6.3 cm, body mass = 77.5 +/- 9.2 kg, body fat (BF) = 10.6 +/- 5.8 kg, and %BF = 13.9 +/- 5.8%). BC, vertical jump (VJ), speed (S), lower-body and total body power production (TPW), and estimated Vo(2)max were measured. Values found for BC were similar than the ones in the literature. Significant correlations were found between BC and PP ranging from -0.38 to 0.61 for weight, VJ, S, TPW, and Vo(2)max. BF showed a positive correlation with S (r = 0.60) and a negative correlation with Vo(2)max (r = -0.67). The values for BC and PP were similar in starters and non-starters with only TPW showing a significantly greater value in starters. It is apparent that all members of a team train to play owing to the long seasons and substitutions, and a high level of excellence is demanded of both starters and non-starters alike. Training programs that equally benefit both groups are important in soccer.     

Relationship between the number of repetitions and selected percentages of one repetition maximum in free weight exercises in trained and untrained men

Resistance exercise intensity is commonly prescribed as a percent of 1 repetition maximum (1RM). However, the relationship between percent 1RM and the number of repetitions allowed remains poorly studied, especially using free weight exercises. The purpose of this study was to determine the maximal number of repetitions that trained (T) and untrained (UT) men can perform during free weight exercises at various percentages of 1RM. Eight T and 8 UT men were tested for 1RM strength. Then, subjects performed 1 set to failure at 60, 80, and 90% of 1RM in the back squat, bench press, and arm curl in a randomized, balanced design. There was a significant (p < 0.05) intensity x exercise interaction. More repetitions were performed during the back squat than the bench press or arm curl at 60% 1RM for T and UT. At 80 and 90% 1RM, there were significant differences between the back squat and other exercises; however, differences were much less pronounced. No differences in number of repetitions performed at a given exercise intensity were noted between T and UT (except during bench press at 90% 1RM). In conclusion, the number of repetitions performed at a given percent of 1RM is influenced by the amount of muscle mass used during the exercise, as more repetitions can be performed during the back squat than either the bench press or arm curl. Training status of the individual has a minimal impact on the number of repetitions performed at relative exercise intensity.