ONTOGENY OF WATER SORPTION-DESORPTION IN THE PERINATAL RAT

In mammals, birth marks a transition to a cold and gaseous environment that requires rapid physiologic adaptations limiting heat and water loss. In this study the perinatal Sprague-Dawley rat was utilized as a model to study the behavior of water binding to the external body surface following birth. Water sorption and desorption were quantified by measurement of skin surface capacitance following water loading using a dry ring electrode system. The results indicate that the external body surface of the newborn rat is highly hydrophobic. This hydrophobicity is manifested by the rapid desorption of water (amniotic fluid) following birth as well as marked limitation of water sorption after birth. Post-natally, this hydrophobic effect is gradually lost over the first 3 d of life. Somatic growth retardation results in retention of this surface property, whereas extraction of the skin surface with acetone abolishes it. Morphologic and functional (water-binding) studies performed after stripping the stratum corneum with acrylic adhesive strongly suggest a physiologic role for the periderm in determining this postnatal hydrophobic effect. These data are interpreted as evidence for a novel thermoregulatory mechanism in the rat during adaptation to post-natal life.