MORPHOLOGICAL STUDY ON THE PERICYTES OF GOAT'S PLACENTOMAL CAPILLARIES

Pcricytcs arc connective tissue cells associated abluminally with capillary and postcapillary venulcs, They share a common basal lamina with endothelial cells (Majno, 1965: Schor et al., 1995). Such rnicrovcssels arc involved with the exchange
of material and extracellular space (Nehls and Drenckhahn, 1993). Perleytes were first described in the nictitating membrane of the frog by Rouget (1873). and have been seen surrounding capillaries in a wide variety of tissues
(Zimmerman, 1923: Majno, 1965: Lunam and Roger, 1981: Sims, 1986: Hirschi and D'Amore, 1996; Sundberg et al., 1996; Wisse et al., 1996). The most probable function for pcricytcs is the regulation of capillary flow by their contraction (Epling, 1966; Rhodin, 1968: Wieble, 1974: Tilton et al., 1979). A possible functional role of the pericytes is the control of material exchange through the vessel wall (lmayama and Urab, 1984) and its participation in angiogenesis has been proposed (Crocker et at, 1970; Schor et at, 1995). A further role that has been attributed to pericytcs is to stabilize the capillary wall (Cohen et al., 1980; Frank et al., 1990: Jeon et at., 1996). In rat uterus. the increase in pericytes coincides with the time of implantation (Lunam and Roger, 1983). Steven and Samuel (1979) have suggested that there arc few pericytes associated with the maternal capillaries in sheep placenta to perform an important regulatory function on the transport of material from the mother to the fetus. However, Yasear et HI. (1987) found a considerably large
number of pcricytcs in association with the maternal microvessels in sheep placenta throughout pregnancy. In the gOHt'S placenta. the materno-Ictal interface is characterized by the presence of syncytial tissue covering the maternal side of placentomes. The plcentomes arc ruminant-specific fetomatcrnal contact zones characterized by  the presence ofmicrovillar junction between syncytium and fetal trophoblastic layer (Steven, 1975; Wooding and Flint, 1994). Due to the lack of information on the distribution of pericytes in the goat's placenta the present study was initiated to evaluatethe distribution of the pericytes surrounding the materna! capillaries which are located close to the syncytium, i.e. those most closely involved in the materno-fetal exchanges throughout pregnancy.