Adolescent growth, development, and psychosocial aspects of sports participation: an overview

This chapter examines sports participation in the context of adolescent growth and development. Because the nature of sports participation is highly organized and competitive, it is imperative that parents, coaches, physicians, and other clinicians remember that they may be placing increased pressures on the adolescent to perform and practice. The authors review the impact of physical growth and psychosocial development and also describe how substance abuse, depression, and aggressive behavior may or may not be influenced by sports participation.     

Prostate-sparing effects in primates of the potent androgen 7alpha-methyl-19-nortestosterone: a potential alternative to testosterone for androgen replacement and male contraception

7alpha-Methyl-19-nortestosterone (MENT) is a potent synthetic androgen that cannot be converted to dihydrotestosterone. In this study we determined the relative androgenic, antigonadotropic, and anabolic potencies of testosterone vs. MENT in the nonhuman primate M. fascicularis. In castrated monkeys, dose-response relationships were generated for the effects of testosterone and MENT on gonadotropin levels, prostate growth, body weight, and lipid metabolism. In a pilot study, four monkeys were castrated, and magnetic resonance imaging (MRI) was used to document a 50% loss of prostate volume within 8 weeks, verifying that MRI is a reliable means to measure prostate size in this species. Two additional groups of six monkeys each were then castrated and serially administered four graded dosages of testosterone or MENT via osmotic minipumps over 20 weeks. Complete suppression of LH was achieved with a minimum of 0.3 mg/day MENT, compared to 3.0 mg/day testosterone. MENT supported body weight 10 times more potently than did testosterone. Baseline prostate volumes were maintained with 0.1-0.2 mg/day MENT vs. 0.3 mg/day testosterone. Thus, in monkeys, MENT is 10 times more potent than testosterone with regard to the clinically desirable end points of gonadotropin suppression and anabolism, but only twice as potent at stimulating prostate growth. These results suggest that MENT may have a wider therapeutic index than testosterone for human androgen replacement and male contraception.     

The effect of free fatty acid on the reactivity of copper-based catalysts for the hydrogenolysis of fatty acid methyl esters

In the synthesis of fatty alcohols by hydrogenolysis of fatty acid methyl esters, small amounts of free fatty acids in the feed negatively affect the reactivity of copper-silica based catalysts. The effect of the acid was investigated in relation to the production of water, the nature of the inhibiting species, and the degree of reduction of the catalyst. Inhibition is reversible and not due to catalyst deactivation. Water is not the inhibiting species. Furthermore, formation of copper and zinc soaps was excluded. Lauric acid in the methyl ester feed reacts preferentially, but at a lower rate than the ester. Inhibition most likely stems from a preferential adsorption of the acid at the active sites of the catalyst. The consequences for practical applications are discussed.     

Modifiable gene expression in mice: kidney-specific deletion of a target gene via the cre-loxP system

With the advent of gene-targeting in mouse embryonic stem (ES) cells, the use of knockout mice to study the physiological effects of loss of gene function has become increasingly prevalent. However, there are several drawbacks with conventional gene-targeting approaches which may make phenotyping of the resultant mice difficult, if not, impossible. Conventional gene-targeting results in the loss of function of the targeted gene in all cells and tissues, which can be problematic for genes which are required developmentally, which exhibit a wide tissue-specific expression pattern, or are part of complex paracrine systems. As with mice that lack the angiotensinogen or endothelin-1 gene, loss of gene function may lead to a lethal phenotype which can be manifested during embryonic development, at birth or postnatally. These limitations could potentially be circumvented by using a system in which the loss of gene function is placed under spatial and/or temporal control. We will discuss how the cre-loxP recombinase system can be applied to delete a gene in a tissue- and developmentally regulated fashion.     

Combined Stress Effects on Growth of Zygosaccharomyces rouxii from an Intermediate Moisture Papaya Product

Stress factors studied included 0.95 a_w adjusted with sucrose and glycerol, pH (4.0, 3.5, and 3.0), potassium sorbate (0, 500, 1000, and 1500 ppm) and sodium bisulfite (0, 100, and 150 ppm). These were tested on a strain of Zygosaccharomyces rouxii isolated from an intermediate moisture (IM) papaya product. Z rouxii was very sensitive to SO₂. A combination of 100 ppm SO₂, 500 ppm sorbate and pH 4.0 is recommended to prevent spoilage of IM fruits by Z. rouxii. The minimum a_w for growth in sucrose-glycerol broth was between 0.62 and 0.64 in the absence of antimicrobials and in the range of optimal pH for this yeast.     

MEASURING the MECHANICAL PROPERTIES of APPLE TISSUE USING MODAL ANALYSIS

Along with the grade of intactness, fruit firmness is an important factor for the quality criteria on which the consumers acceptance for apples is based. Two methods for measuring the fruit firmness (a destructive one and a nondestructive one) are compared. the nondestructive method uses modal analysis to define the lower vibration modes. This enables the use of the 3-media elastic sphere model developed by Cooke and Rand (1973) to calculate the dynamic elastic moduli of the whole apples. the destructive method determines the dynamic elastic moduli of cylindrical samples of apple tissue. This method is based on the vibration characteristics of a mass-spring-damper system. This system consists of a cylindrical apple sample and a mass. Measuring the direct transfer function of this one-degree-of-freedom system results in values of its system parameters, from which the dynamic elastic moduli of the specimen can be calculated. The results of the two methods applied on Golden Delicious apples were compared, and the suitability of each model was evaluated.     

Empirical Observations and Thermodynamical Considerations on Water-Binding by Whey Proteins in Food Products

Basic protein knowledge is used to explain protein functionality in food products. Empirical observations on the water-binding capacity of whey protein concentrate and gelatin during cooling in set yoghurt and during sterilization of meat products are discussed in terms of effects of temperature on the structure and thermodynamic behavior of their main protein isolates: α-Lactalbumin and tropocollagen, respectively. It appears that the water-binding of proteins is governed by their thermally induced folding behavior. In particular, the greater tendency of whey proteins to fold at low temperature due to hydrophobic effects, and to remain dispersed at high temperatures as a result of disorder effects, keeps these proteins from water-retention in a network structure during cooling and sterilization.     

Kinetics and thermodynamics of emulsion delivery of lipophilic antioxidants to cells in culture

Oil-in-water emulsions are being used increasingly for the delivery of lipophilic drugs, but the fundamental physicochemical principles governing such delivery have not been explored. We determined the kinetics and thermodynamics of delivery from emulsions to cells in culture for two lipophilic compounds, U74006 and U74500. Two fundamental properties dominate the delivery, (a) the concentration of the compound in the lipid phase of the emulsion is directly proportional to the concentration of the compound in cells at equilibrium, and (b) the rate of transfer is directly proportional to the concentration of particles in contact with the cells. Thus, the transfer is consistent with direct partitioning from the lipid phase of the emulsion to cells and occurs by the direct collision of emulsion particles with cells. The details of the mechanism of delivery differ between the two compounds. Specifically, delivery of U74006 is first-order with respect to the drug accumulating in the cells. The transfer of U74500 is best described as a sum of two simultaneous pseudo first-order processes consistent with delivery from a single donor compartment to two receiver compartments. Furthermore, two molecules of U74500 appear to be involved in each transfer event. Our results show that relatively simple principles govern the delivery of compounds from oil-in-water emulsions to cells.