Discipline: Veterinary Medicine
S100, a multigenic family of low molecular weight protein exclusively found in vertebrates, has been involved in the regulation of a variety of intracellular and extracellular biological functions mediated by its calcium modulating activity. This study investigated the location of S100 immunoreactive structures in the ovary of 5-8 years old, 10 apparently healthy, nonpregnant Philippine water buffalo (Bubalus bubalis) using polyclonal rabbit anti-S100. S100 immunoreactivity was observed in the endothelium and subendothelial layer of the wall of arteries, endothelial lining of veins and capillaries, erythrocytes and interstitial endocrine cells. Negative immunoreaction, however, was noted in the oocyte and ovarian follicular cells. The differential localization of S100 immunoreactive structures in the ovary of the Philippine water buffalo underline assumptions suggesting its multifunctional role, especially in the regulation of angiogenesis and vascular tone, and its distinct expression from that in bovine and other domestic species of animals implying high tissue and cell specificity in vertebrate animals.