Xu, Zhice, Calvario Glenda, Linda Day, Jiaming Yao, and Michael G. Ross. Osmotic threshold and sensitivity for vasopressin release and Fos expression by hypertonic NaC1 in ovine fetus. Am J Physiol Endocrinol Metab 279:E1207-E1215, 2000-In adults, hyperosmolality stimulates central osmoreceptors, resulting in arginine vasopressin (AVP) secretion. Nearterm fetal sheep have also developed mechanisms to respond to intravascular hyper tonicity with stimulation of in utero AVP release. However, prior studies demonstrating fetal AVP secretion have utilized plasma tonicity changes greater than those required for adult osmotic ally induced AVP stimulation. We sought to examine near-term fetal plasma osmolality threshold and sensitivity for stimulation of AVP secretion and to correlate plasma hormone levels with central neuronal responsiveness. Chronically instrumented ovine fetuses (130