EFFECTS OF RELAXIN ON MAST-CELLS - IN-VITRO AND IN-VIVO STUDIES IN RATS AND GUINEA-PIGS

The results of the current study demonstrate that relaxin inhibits his tamine release by mast cells. This effect is related to the peptide co ncentrations, and could be observed in both isolated rat serosal mast cells stimulated with compound 48/80 or calcium ionophore A 23187, and in serosal mast cells isolated from sensitized guinea pigs and challe nged with the antigen. The morphological findings agree with the funct ional data, revealing that relaxin attenuates calcium ionophore-induce d granule exocytosis by isolated rat serosal mast cells. Similar effec ts of relaxin have also been recognized in vivo by light microscopic a nd densitometric analysis of the mesenteric mast cells of rats which r eceived the hormone intraperitoneally 20 min before local treatment of the mesentery with calcium ionophore. Moreover, evidence is provided that relaxin stimulates endogenous production of nitric oxide and atte nuates the rise of intracellular Ca2+ concentration induced by calcium ionophore. The experiments with drugs capable of influencing nitric o xide production also provide indirect evidence that the inhibiting eff ect of relaxin on mast cell histamine release is related to an increas ed generation of nitric oxide. It is suggested that relaxin may have a physiological role in modulating mast cell function through the L-arg inine-nitric oxide pathway.