[Effect of calcium overload and platelet activating factor on calcitonin gene related peptide release from lung...

The level of calcitonin gene related peptide (CGRP) in plasma and pulmonary lavage fluid was tested by radio-immunoassay on intestinal ischemia/reperfusion (I/R) injured rat. The results showed that plasma CGRP after I/R was 161.3% more than control, and 117.8% when pre-treated with platelet activating factor (PAF) receptor antagonist SR27417A before injury but no obvious changes were observed in the sham group. Meanwhile, CGRP was reduced by 17.4% in pulmonary lavage fluid in I/R animal and elevated by 97.9% in SR27417A pre-treated animal, compared with normal control. Furthermore, it was demonstrated that CGRP release from lung tissue was enhanced concentration-dependently by calcium ionophores A23187 or PAF, as a result of blockage by phospholipase A2 inhibitor p-BPB or SR27417A respectively. In vitro experiment, CGRP in pulmonary lavage fluid was 144.6% more than control when pre-treated with SR27417A and 114.6% less than that treated with A23187 only, even 14.8% less than control. Much the same, CGRP release was 13.7% less than that treated with PAF and was 55.6% more than control when pre-treated with SR27417A only. All these results indicated that (1) CGRP was significantly increased in plasma but without obvious changes in pulmonary lavage fluid following I/R injury; (2) lung tissue CGRP release may be related with Ca2+ increase in cells or phospholipase A2 activation as well as PAF increase; (3) SR27417A was a kind of strong reagent, which may promote CGRP release in vivo and in vitro, but block the effect of PAF on CGRP release.