Increase in intracellular calcium induced by stimulating histamine H1 receptors in macrophage-like P388D1 cells

On the role of histamine receptors in regulating pigmentary responses in Oreochromis mossambicus melanophores

PURPOSE

The present work was carried out to reveal the involvement of histamine receptors at the neuro-melanophore junction of teleost, Oreochromis mossambicus.

METHODS

The isolated scale melanophores were assayed using the mean melanophore size index and their responses were recorded in presence of various concentrations of histamine along with H(1) and H(2) receptor specific agonists and antagonist and potentiator compound 48/80.

RESULTS

Melanophores showed high sensitivity to histamine and its specific agonists. Histamine caused a dose-dependent pigment aggregation, whereas 2-(2-Pyridyl) ethylamine (PEA), a specific H(1)R agonist also caused aggregation in a similar manner. Conversely, amthamine, a specific H(2)R agonist resulted in pigment dispersion. The effects were antagonized by mepyramine; specific H(1)R antagonist and ranitidine a specific H(2)R antagonist.

CONCLUSION

It is concluded that O. mossambicus melanophores have both H(1) and H(2) receptors which mediate melanophore aggregation and dispersion respectively. Compound 48/80 augmented the melanin-aggregating and dispersing effects of PEA and amthamine. It is suggested that the effect of histamine is directly mediated through H1 and H2 receptors, whereas H1Rs may be predominantly involved in the aggregatory responses.

Regulation of interleukin-10 secretion by histamine in TH2 cells and splenocytes

Interleukin-10 is a potent suppressive factor that down-regulates cellular immune response via inhibition of the production of TH1 cytokines. Histamine shifts the TH1/TH2 balance from TH1 to TH2 cytokines making the effects of histamine on IL-10 secretion an important factor in this switch. This study was designed to assess the role of histamine in the regulation of IL-10 production and the involvement of PKA and STAT factors in this process. TH2 cells (D10.G4.1) and AKR/j splenocytes were pretreated with histamine at a concentration range of 10(-8)-10(-5) M for 1 h and then activated with PMA + ionomycin or anti-CD3 for 24 h. The supernatants were collected and tested for IL-10 content by ELISA. Histamine stimulated IL-10 production in TH2 cells in a dose-dependent manner that was reversed by both H1- and H2-receptor antagonists and by PKA inhibitors H8 and Rp-cAMPS. Tyrphostin also reversed the stimulation of IL-10 secretion by histamine, indicating that STAT factors were involved in this process. The up-regulation of IL-10 production by histamine in splenocytes was accompanied by inhibitory effects of histamine on IFN gamma production. The pretreatment of splenocytes with histamine in the presence of anti-IL-10 abrogated histamine-mediated inhibition of IFN gamma production suggesting that the effects of histamine on IFN gamma secretion were regulated by IL-10 in multi-cell system.