The complex metabolic activities of cells respond to environmental cues by sensing transmitter substances, such as ligands or hormones. Peptide hormones cannot enter the cell directly and transmit their information by recognizing and binding to receptors located on the surface of the cell. The receptor serves as the communicative link between the outside and the inside of the cell. In response to the binding of hormone, receptors activate one or more signal transduction pathways, resulting in the generation of the important second messengers, such as cAMP and diacylglycerol (DAG), that in turn activate the protein kinases A and C, respectively (1–5).

An enzyme immunoassay (EIA) originally developed for mouse beta-nerve growth factor (NGF) and commercially available was validated for human NGF. Cell culture medium containing bioactive recombinant human NGF was used as a reference, and mouse 2.5S beta-NGF as a standard. One of three human placentas contained measurable NGF (70 pg/g of tissue of mouse beta-NGF equivalents), a second detectable, and a third undetectable NGF. In three human semen samples NGF content ranged from 0.13 - 1.4 ng/ml. NGF could not be detected in normal human serum and in plasma from patients with Paget's disease, although mouse 2.5S beta-NGF added to human blood could be completely recovered from the serum.

Analysis of C57BL/6J allophenic mice for their lymphocyte composition, using H-2 antigens as external markers, and glucose phosphate isomerase (GPI) isozymes as internal markers, has led to the discovery of two unusual mice. Both mice showed heterodimers of GPI isozymes upon electrophoresis of the lymphocyte lysate. Specific anti-H-2 antisera confirmed that the cells of the mice were of C57BL/6J and origin, as expected, but that the A/J cells seemed to behave as Fj hybrids containing the Gpi-1^ and Gpi-l^ alleles. Possible origins of the Cpi-l^ allele in the A/J cells

Allophenic mice are chimeras which are produced from the aggregation of two genotypically distinct embryos. In this study, embryos from the C57BL/6J and A/J strains were used to produce C57BL/6J ↔ A/J allophenic mice. These strains were chosen because of their markedly different lifespans, their different glucose phosphate isomerase (GPI) isozymes, and their different H-2 haplotypes [C57BL/6J: long-lived, Gpi-1b, H-2b; A/J: short-lived, Gpi-1a, H-2a. The mice were bled at two month intervals and the composition of their peripheral blood lymphocytes determined at each point from analysis of GPI isozymes and H-2 antigens. It was founr that the proportion of long-lived (C57BL/6J) lymphocytes tended to increase with age. Moreover, the total lifespan of the allophenic mice was directly related to the percentage of long-lived lymphocytes in their peripheral blood.

In a comparative study of A/J (Gpi-1a) and C57BL/6J (Gpi-1b) mice, we observed that erythrocytes of A/J mice exhibited significantly higher glucose phosphate isomerase (GPI) activity compared to erythrocytes of C57BL/6J mice on a per cell, per gram of protein, or per gram of hemoglobin basis. Higher GPI activity per cell was detected for peripheral blood lymphocytes of A/J compared to C57BL/6J mice. (A/J × C57BL/6J)F1 mice expressed erythrocyte and peripheral blood lymphocyte GPI activities intermediate to those of the parental mouse strains. The GPI activities of spleen lymphocytes from A/J, C57BL/6J, or (A/J × C57BL/6J)F1 mice were not significantly different from each other. The higher activity in the A/J mice could be due to GPI of a higher catalytic rate or to the presence of more GPI molecules. In order to distinguish these two possibilities, GPI was purified to homogeneity from both strains of mice. The specific activities (activity per milligram of protein) of the purified enzymes from the two strains were found to be similar, indicating that GPI from the A/J strain was not a more active enzyme. Antibody to the purified enzymes was prepared and used in an enzyme-linked immunosorbent assay (ELISA) to compare the relative amounts of enzyme molecules in cells of A/J and C57BL/6J mice. Results of the ELISA tests on peripheral blood lymphocytes indicated that A/J mice contain more molecules of GPI per cell and, therefore, have a higher GPI activity than C57BL/6J mice.

Glucose phosphate isomerase (GPI) enzyme activity was measured in two strains of mice, A/HeNNial (Gpi-1a) and C57BL/6NNia1 (Gpi-1b). Seven solid tissues (muscle, brain, heart, kidney, liver, lung, spleen) and three cell types (peripheral blood lymphocytes, spleen lymphocytes, erythrocytes) were analyzed for GPI activity in mice from 6 to 36 months of age. No major changes in enzyme activity with age were found. The most striking observation was that A/HeNNial mice showed a significantly higher GPI activity than C57BL/6NNia1 mice in four of the solid tissues (muscle, heart, kidney, spleen) and two of the cell types (peripheral blood lymphocytes, erythrocytes) analyzed.