Involvement of endogenous opioid peptides in the antinociception induced by the novel dermorphin tetrapeptide analog amidino-TAPA.

The antinociceptive effect of i.t. administered N(alpha)-amidino-Tyr-d-Arg-Phe-beta-Ala (amidino-TAPA), an N-terminal tetrapeptide analog of dermorphin, was characterized in ddY mice. In the opioid receptor ligand-binding assays using mouse brain membranes, amidino-TAPA showed a very high affinity for mu-opioid receptors, a low affinity to delta-opioid receptors and no affinity for kappa-opioid receptors. In the mouse tail-flick test, i.t. treatment with amidino-TAPA produced a potent antinociception. The antinociception induced by amidino-TAPA was significantly attenuated by i.t. pretreatment with the mu-opioid receptor antagonist beta-funaltrexamine, the kappa-opioid receptor antagonist nor-binaltorphimine and the delta-opioid receptor antagonist naltrindole. Moreover, the antinociception induced by amidino-TAPA was significantly attenuated by i.t. pretreatment with antisera against the endogenous kappa-opioid peptides dynorphin A, dynorphin B and alpha-neo-endorphin; and the endogenous delta-opioid peptide [Leu(5)]enkephalin. In mice lacking prodynorphin, the precursor of the endogenous kappa-opioid peptides, the antinociceptive effect of amidino-TAPA was significantly attenuated compared to that in wild-type C57BL/6J mice. However, there was no difference in G-protein activation by amidino-TAPA in the spinal cord membranes from prodynorphin knockout mice and C57BL/6J mice. The present results suggest that the spinal antinociception induced by the mu-opioid receptor selective peptide amidino-TAPA is mediated in part by the release of endogenous opioid peptides in the spinal cord, which is caused by the direct stimulation of mu-opioid receptors.

The distinctive effects of acute and chronic psychological stress on airway inflammation in a murine model of allergic asthma.

BACKGROUND: Psychological stress has long been recognized to be associated with asthma symptoms. There appear to be individual differences in the susceptibility to even the same kind of stress, and furthermore, stress responses are different between the types of the stress, acute and chronic, even in the same person. However, the mechanisms linking stress to asthma are not well defined. Psychological stress upregulates the expression of endogenous opioids. The opioids stimulate the hypothalamus-pituitary-adrenal axis and sympathetic and adrenomedullary system, through the activation of mu-opioid receptor (MOR) to release stress hormones, such as cortisol and catecholamines, respectively. These hormones can modulate immune responses via the induction of Th1 immunity. METHODS: Female BALB/c and C57BL/6, wild and MOR-deficient, mice sensitized with ovalbumin (OVA) were exposed to OVA with or without either acute or chronic restraint stress. Airway inflammation was evaluated by the measurement of the number of inflammatory cells and cytokine contents in bronchoalveolar lavage fluids. RESULTS: In BALB/c mice, but not in C57BL/6 mice, the number of total cells, eosinophils and lymphocytes in the acute stress group were significantly decreased compared with those in the non-acute stress group. In contrast, chronic stress significantly increased the cell numbers and the contents of IL-4 and IL-5 in both mouse strains. Furthermore, these exacerbations were abolished in MOR-deficient mice. CONCLUSIONS: These results suggest that acute stress modifies the allergic airway responses distinctively depending on the genetic background, and MOR is involved in the chronic psychological stress-induced exacerbation of allergic airway inflammation.

Inhibition of eosinophil survival by a selective inhibitor of phosphodiesterase 4 via the induction of apoptosis.

Selective inhibitors of phosphodiesterases (PDEs) have been suggested to have anti-inflammatory effects on bronchial asthma through the inhibition of chemotaxis, adhesion, degranulation, the respiratory burst, and survival prolongation of eosinophils. However, the mechanisms by which these agents inhibit eosinophil survival remain unclear. We therefore investigated the possible mechanisms of inhibitory effects of selective inhibitors of PDE 3 (cilostazol) and PDE 4 (rolipram) on granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated eosinophil survival. Purified blood eosinophils were cultured with medium alone or GM-CSF (0.01 ng/ml) in the presence or absence of the agents for up to 6 d. DNA was extracted from freshly isolated eosinophils and eosinophils cultured for 2 d with medium alone, GM-CSF, or GM-CSF in the presence of the agents, and analyzed using agarose gel electrophoresis. The presence of rolipram (10(-4), 10(-5), 10(-6) M), but not cilostazol, significantly inhibited eosinophil survival at days 2, 4, and 6. A laddering pattern was observed in the DNA of eosinophils cultured with medium alone and with GM-CSF in the presence of rolipram. The results reveal that selective PDE 4 inhibitors inhibit GM-CSF-mediated eosinophil survival through the induction of apoptosis.

In vitro permeation of beta-lactam antibiotics across rat jejunum and its correlation with oral bioavailability in humans.

AIMS: To investigate the correlation between in vitro permeation of 11 beta-lactam antibiotics across rat jejunum and their oral bioavailability in humans. METHODS: The absorptive and secretory permeation across rat jejunum was evaluated and apparent permeability coefficients (P(app)) were determined. RESULTS: A steep, sigmoid-type curve was obtained for the relationship between P(app) in the absorptive permeation and human oral bioavailability. When the ratios of P(app) in the absorptive direction to P(app) in the secretory direction were plotted against human oral bioavailability, a much improved correlation was obtained (r = 0.98, P < 0.001). The addition of glycylglycine to both mucosal and serosal media modified the permeation of ceftibuten and cephalexin from the absorptive to the secretory direction. CONCLUSIONS: For 11 beta-lactam antibiotics rat intestinal permeation correlated well with human oral bioavailability, especially when corrected for secretory transport.