Current topics of physiology and pharmacology in the lymphatic system

We have reviewed physiological significance of rhythmical spontaneous contractions of collecting lymph vessels, which play a pivotal role in lymph transport and seem to control lymph formation through changing the pacemaker sites of the rhythmic contractions and contractile patterns of the lymphangions. A characteristic feature that the rhythmic pump activity works in vivo physiologically under the specific environment of lower oxygen tension in lymph (25-40 mm Hg) has been evaluated. With the characteristic feature, generation of endogenous nitric oxide (NO) from lymphatic endothelial cells and/or activation of ATP-sensitive potassium channels (K(ATP)) are reviewed to play crucial roles in the regulation of lymph transport at physiological or pathophysiological conditions. Chemical substances released from malignant tumor cells and tumor-derived parathyroid hormone-related peptide (PTHr-P) are also shown to cause a significant reduction of lymphatic pump activity through generation of endogenous NO and activation of K(ATP) channels. Finally, we have discussed physiological significance and roles of the lower oxygen tension in lymph, generation of endogenous NO, and activation of K(ATP) in lymph formation, lymph transport, and the functions of lymph nodes.     

Neurotoxicity of endocrine disruptors: possible involvement in brain development and neurodegeneration

Environmental chemicals that act as endocrine disruptors do not appear to pose a risk to human reproduction; however, their effects on the central nervous systems are less well understood. Animal studies suggested that maternal exposure to endocrine-disrupting chemicals (EDC) produced changes in rearing behavior, locomotion, anxiety, and learning/memory in offspring, as well as neuronal abnormalities. Some investigations suggested that EDC exert effects on central monoaminergic neurons, especially dopaminergic neurons. Our data demonstrated that EDC attenuate the development of dopaminergic neurons, which might be involved in developmental disorders. Perinatal exposure to EDC might affect neuronal plasticity in the hippocampus, thereby potentially modulating neuronal development, leading to impaired cognitive and memory functions. Endocrine disruptors also attenuate gender differences in brain development. For example, the locus ceruleus is larger in female rats than in males, but treatments with bisphenol-A (BPA) enlarge this region in males. Some reports indicated that EDC induce hypothyroidism, which might be evidenced as abnormal brain development. Endocrine disruptors might also affect mature neurons, resulting in neurodegenerative disorders such as Parkinson's disease. The current review focused on alterations in the brain induced by EDC, specifically on the possible involvement of EDC in brain development and neurodegeneration.     

The immortalized cell lines with differentiation potentials: their establishment and possible application

Approximately 200 types of the cells are qualified as differentiated cells in the human body. If these different types of cells can be separated from each other (or cloned) and obtained in sufficient quantity, it will be beneficial for studying development, morphogenesis, tissue maintenance, cancer and aging, and for reconstructing functional tissues in vitro for regenerative medicine. We produced the transgenic mouse and rat harboring SV40 T-antigen gene to make the immortalized cell lines in the primary tissue culture and succeeded in establishing many functionally active cell lines from various tissues. Many immortalized cell lines from various tissues are shown to exhibit the unique characteristics of tissue functions and they should be useful as an in vitro model of various tissues for physiological and pharmacological investigations. Future application of these cells to drug screening is discussed.     

Role of Tyr306 in the C-terminal fragment of Clostridium perfringens enterotoxin for modulation of tight junction

We previously reported that the C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) is a novel type of absorption enhancer that interacts with claudin-4 and that Tyr306 of C-CPE plays a role in ability of C-CPE to modulate barrier of tight junctions. In the current study, to investigate effects of Tyr306 on the C-CPE activity, we prepared some C-CPE mutants substituted Tyr306 with Trp (Y306W), Phe (Y306F) and Lys (Y306K). We found that Y306W and Y306F mutants of C-CPE had claudin-4 binding affinities and effects on the barrier function of tight junctions, whereas both of these properties were greatly reduced with the Y306K mutant. Finally, the Y306K but not the Y306F and Y306W mutants had reduced abilities to enhance absorption in rat jejunum. These results indicate that aromatic and hydrophobic properties, not hydrogen bonding potential, of Tyr306 are involved in the interaction of C-CPE with claudin-4 and in the modulation of the tight junction barrier function by C-CPE.     

Regulation of neurotensin-containing neurons in the rat striatum and substantia nigra. Effects of unilateral nigral lesion with 6-hydroxydopamine on neurotensin content and its binding site density

The effect of unilateral lesion of the rat substantia nigra with 6-hydroxydopamine (6-OHDA) was investigated on the endogenous contents of neurotensin (NT) and its binding site densities in the striatum and substantia nigra. Tyrosine hydroxylase (T-OH) activity, γ-aminobutyric acid (GABA) content, binding site densities of dihydrotetrabenazine (TBZOH), a marker of dopaminergic synaptic vesicles, and of iodosulpride, a ligand for dopamine D₂ receptors, were also determined. Fourteen days following nigral lesions, these markers were analyzed by means of radioimmunoassay for NT levels, fluoremetric method for GABA content, radiochemical method for T-OH activity and quantitative autoradiography for NT, TBZOH and iodosulpiride binding site densities. Unilateral nigral lesion with 6-OHDA provoked only ipsilateral modifications in dopamine markers. T-OH activity and TBZOH binding site densities significantly decreased in both the ipsilateral striatum and substantia nigra. Iodosulpiride binding sites decreased in the substantia nigra and increased in the striatum on the ipsilateral side. In contrast to these unilateral changes observed for dopamine markers, dramatic increases in NT contents were found in both the ipsi- and contralateral striata. No change was found in nigral NT levels on either side. On the other hand, NT binding sites decreased in the ipsilateral striatum and substantia nigra, which reflected the destruction of dopaminergic elements in these regions. The present results strongly suggest a dopaminergic control of striatal NT systems and demonstrate that a unilateral loss of this control may lead to strong bilateral alterations in NT levels.