The new Dietary Reference Intakes in food labeling: the food industry's perspective

The food industry appreciates the complexity of applying the new Dietary Reference Intakes (DRIs) in labeling. The industry is prepared to update food labels to reflect new nutrient recommendations and views upcoming changes as an opportunity to harmonize nutrition information across the Dietary Guidelines for Americans 2005, MyPyramid.gov, and the food label. Members of the Grocery Manufacturers Association are unanimous in their belief that the food label be as useful to consumers as possible. This article raises discussion points, issues, and implications associated with implementation of the new DRIs on the food label.     

Mouse models for genes involved in impaired spermatogenesis

Since the introduction of molecular biology and gene ablation technologies there have been substantial advances in our understanding of how sperm are made and fertilization occurs. There have been at least 150 different models of specifically altered gene function produced that have resulted in male infertility spanning virtually all aspects of the spermatogenic, sperm maturation and fertilization processes. While each has, or potentially will reveal, novel aspects of these processes, there is still much of which we have little knowledge. The current review is by no means a comprehensive list of these mouse models, rather it gives an overview of the potential for such models which up to this point have generally been 'knockouts'; it presents alternative strategies for the production of new models and emphasizes the importance of thorough phenotypic analysis in order to extract a maximum amount of information from each model.     

Effect of Fetal Irradiation on Testicular Receptors and Testosterone Response to Gonadotrophin Stimulation in Adult Rats

The amount of [125I]human chorionic gonadotrophin bound by testicular membrane preparations from adult male rats with germinal cell aplasia induced by x-irradiation in utero was significantly reduced in comparison to that of normal males. The in vivo serum testosterone response to an injection of human chorionic gonadotrophin was significantly decreased in the x-irradiated rats. Paradoxically, the in vitro maximal secretory response to gonadotrophin stimulation was markedly increased. It is concluded that a decrease in the number of receptors on Leydig cells subjected to chronically elevated serum levels of LH does not limit the capacity of the testis for steroid biosynthesis.     

Regulated production of activin A and inhibin B throughout the cycle of the seminiferous epithelium in the rat

Production and regulation of activin A and inhibin B during the cycle of the seminiferous epithelium were investigated in adult rats. Immunohistochemistry localised the activin beta(A)-subunit to the Sertoli cell cytoplasm, with much weaker expression in spermatocytes and spermatids. Both activin A and inhibin B, measured by ELISA were secreted by, seminiferous tubule fragments over 72 h in culture. Activin A was secreted in a cyclic manner with peak secretion from tubules isolated at stage VIII. Tubules collected during stage VI produced the least activin A. Inhibin B secretion was highest from stage IX-I tubules and lowest from stage VII tubules. Addition of interleukin-1beta (IL-1beta) had relatively little effect on activin A or inhibin B secretion in culture. In contrast, the peak secretion of activin A by stage VIII tubules was blocked by co-incubation with an excess of human recombinant IL-1 receptor antagonist, whereas inhibin B secretion increased slightly. Dibutyryl cAMP stimulated activin A secretion by late stage VII and VIII tubules and stimulated inhibin B across all stages. These data indicate that activin A and inhibin B are cyclically regulated within the seminiferous epithelium, with endogenous IL-1 (presumably IL-1alpha produced by the Sertoli cells), responsible for a peak of activin A production subsequent to sperm release at stage VIII. These data provide direct evidence that production of activin A and inhibin B by the Sertoli cell is locally modulated by IL-1alpha , in addition to FSH/cAMP, under the influence of the developing spermatogenic cells.     

Two-dimensional gel analysis of the polypeptides precipitated by a polymorphic HLA-DR1,2,w6 monoclonal antibody: evidence for a third locus

The SDR1 monoclonal antibody reacts only with cells which express the HLA-DR1, 2,w6 or w8 allogeneic specificities. Two-dimensional nonequilibrium pH gradient/sodium dodecyl sulfate polyacrylamide gel electrophoretic analyses of SDR1 immunoprecipitates from [35S]methionine biosynthetically labeled cells revealed the typical pattern of Ia antigens, namely two polypeptides of about 34kDa and 29kDa (designated epsilon and beta-3) as well as the "basic invariant spot" of about 31 kDa. The epsilon and beta-3 polypeptides were only weakly represented in similar analyses of immunoprecipitates performed using a monomorphic HLA-DR monoclonal antibody, TDR31.1. The epsilon and beta-3 polypeptides of B lymphoblastoid cell lines homozygous for HLA-DR2 and w6 were structurally polymorphic as judged by two-dimensional gel analyses. This polymorphism was independent of the HLA-DR specificity. It is concluded that the SDR1 antibody recognizes a polymorphic set of Ia antigens that are coded by a locus other than HLA-DR. These antigens probably also express the MT1 (DC1, LB12) alloantigenic specificity and are most likely the human equivalent of the murine I-A subregion antigens.     

A sensitive and specific in vitro bioassay for activin using a mouse plasmacytoma cell line, MPC-11.

A new in vitro bioassay for activin was developed using the mouse plasmacytoma cell line, MPC-11. Human recombinant (hr) activin A dose-dependently inhibited the proliferation of these cells, whereas a range of other factors, including inhibin, follistatin and transforming growth factor-beta1, -beta2 and -beta3 had no effect. Conditioned medium containing activin B induced an inhibition similar to hr-activin A. The inhibitory influence of activin A could be blocked by follistatin, but not by hr-inhibin A. This bioassay had a sensitivity for activin A of around 0.4 ng/ml, an ED50 response of 3.5 ng/ml, and an intra-assay coefficient of variation of <11%. It offers substantial advantages over existing in vitro activin bioassays in terms of ease of use, specificity and throughput. The utility of the MPC-11 bioassay was demonstrated in the purification of activin from amniotic fluid, where an almost identical profile of bioactive activin A was detected compared with the pituitary cell bioassay of activin. Bioactive activin could also be detected in unpurified ovine allantoic and amniotic fluids and bovine follicular fluid. Measuring activin in untreated and heat-treated human sera or seminal plasma was hampered by a non-specific inhibitory effect, so that several serum samples did not run parallel with the hr-activin A standard. This inhibitory effect by serum could not be overcome by addition of follistatin, suggesting it is not activin-like bioactivity. This new bioassay for activin demonstrates widespread applicability for monitoring of purified or partially purified samples during purification procedures, bioactivity measurements, receptor-binding studies and assays of cell culture medium.