EFFECT OF OXYTOCIN ON TRANSEPITHELIAL TRANSPORT OF WATER AND NA-SKIN (RANA-CATESBEIANA)( IN DISTINCT VENTRAL REGIONS OF FROG)

Thoracic, abdominal, and pelvic fragments of ventral skin of Rana cate sbeiana were analysed regarding the effect of oxytocin on: (1) transep ithelial water transport; (2) short-circuit current, (3) skin conducta nce and electrical potential difference; (4) Na+ conductance, the elec tromotive force of the Nat transport mechanism, and shunt conductance; (5) short-circuit current responses to fast Na+ by K+ replacement in the outer compartment, and (6) epithelial microstructure. Unstimulated water and Na+ permeabilities were low along the ventral skin. Hydrosm otic and natriferic responses to oxytocin increased from thorax to pel vis, Unstimulated Na+ conductance was greater in pelvis than in abdome n, the other electrical parameters being essentially similar in both s kin fragments. Contribution of shunt conductance to total skin conduct ance was higher in abdominal than in pelvic skin. Oxytocin-induced inc reases of total skin conductance, Na+ conductance, and shunt conductan ce in pelvis were significantly larger than in abdomen, An oscillatory behaviour of the short-circuit current was observed only in oxytocin- treated pelvic skins. Decrease of epithelial thickness and increase of mitochondria-rich cell number were observed from thorax to pelvis, Ox ytocin-induced increases of interspaces were more conspicuous in pelvi s and abdomen than in thorax.