The autohors studied the morphologic alteration in female rat spleens following intraperitoneal injection of Prostaglandin F2[alpha]. Their conclusion was that only one dose of 0,15 mg to each animal, brought within 12 hours, a sharp splenic constriction followed by a progressive and prominent desappearence of megakaryocytes from the red pulp. Based on these findings, the authors considered that such a phenomenon might be related to alteration of the platelet mechanism, which was already pointed out by some investigators through biochemical tests in animals injected intravenously with these substances.