Assays for endogenous components of human milk: comparison of fresh and frozen samples and corresponding analytes in serum.

Breast milk is a primary source of nutrition that contains many endogenous compounds that may affect infant development. The goals of this study were to develop reliable assays for selected endogenous breast milk components and to compare levels of those in milk and serum collected from the same mother twice during lactation (2-7 weeks and 3-4 months). Reliable assays were developed for glucose, secretory IgA, interleukin-6, tumor necrosis factor-a, triglycerides, prolactin, and estradiol from participants in a US EPA study called Methods Advancement in Milk Analysis (MAMA). Fresh and frozen (-20 degrees C) milk samples were assayed to determine effects of storage on endogenous analytes. The source effect (serum vs milk) seen in all 7 analytes indicates that serum should not be used as a surrogate for milk in children's health studies. The authors propose to use these assays in studies to examine relationships between the levels of milk components and children's health.

Expression of the spermatogenic cell-specific glyceraldehyde 3-phosphate dehydrogenase (GAPDS) in rat testis.

The spermatogenic cell-specific variant of glyceraldehyde 3-phosphate dehydrogenase (GAPDS) has been cloned from a rat testis cDNA library and its pattern of expression determined. A 1,417 nucleotide cDNA has been found to encode an enzyme with substantial homology to mouse GAPDS (94% identity) and human GAPD2 (83% identity) isozymes. Northern blotting of rat tissue RNAs detected the 1.5 kb Gapds transcript in the testis and not in RNA from liver, spleen, epididymis, heart, skeletal muscle, brain, seminal vesicle, and kidney. The rat Gapds mRNA was first detected at day 29 of postnatal testis development, an age which coincides with the initial post-meiotic differentiation of round spermatids. When isolated rat spermatogenic cell RNA was probed for Gapds expression, transcripts were detected only in round spermatids and condensing spermatids, but not in pachytene spermatocytes, demonstrating haploid expression of the Gapds gene. However, immunohistochemical staining of rat testis sections with anti-GAPDS antisera did not detect GAPDS in round spermatids, but localized the protein only to stage XIII and later condensing spermatids as well as testicular spermatozoa, indicating that Gapds expression is translationally regulated. The current results are similar to those previously obtained for mouse GAPDS and human GAPD2, suggesting that reliable comparisons can be made between these species in toxicant screening and contraceptive development.