RELAXIN REDUCES THE NUMBER OF CIRCULATING PLATELETS AND DEPRESSES PLATELET-RELEASE FROM MEGAKARYOCYTES - STUDIES IN RATS

In previous studies we have shown that relaxin (RLX), a peptide hormon e produced predominantly during pregnancy, is a powerful inhibitor of platelet aggregation, The current study shows that RLX, given systemic ally to rats, also affects the number of circulating platelets and the ir release by spleen megakaryocytes, Male albino rats were treated acu tely or chronically with RLX, and the effects of the peptide evaluated by platelet count and morphological analysis of spleen megakaryocytes , The results obtained show that RLX causes a decrease of circulating platelets, which is already appreciable 1 h after a single administrat ion and becomes significant upon a 4-day treatment with the peptide (7 90 000 +/- 18 000/ml in the RLX-treated rats versus 865 000 +/- 23 000 /ml in the controls; P < 0.01), Coincidentally, spleen megakaryocytes show clearcut changes consistent with a depression of platelet release , namely the appearance of a thick peripheral cytoplasmic halo, filled with actin microfilaments and without platelet territories, and a vir tual absence of images of thrombocytopoiesis. Based on the properties of RLX in inhibiting hemostasis, recognized in previous investigations and further proved by the present study, a role of the peptide is pro posed in counteracting the hypercoagulable state which currently takes place during normal pregnancy.