Surface Tension in the Developing Mammal: Anisotropic Tension Generation in the Dorsal Skin of the Perinatal Rat

Abstract

It is common knowledge that skin biopsies retract following excision. The direction and the magnitude of this retraction is thought to be related to the field of tension previously experienced by the skin sections in vivo. We utilized this phenomenon to investigate the ontogeny, directionality, and regulation of skin tension in the perinatal rat from gestational day 20 to postnatal day 6. In this study, geometrically-precise biopsies (circles and rectangles) were excised from the dorsal skin of perinatal rats and placed in tissue culture media. The excised skin sections rapidly exhibited changes in shape (to ellipses and helices). These resulting conformations were characterized with regard to selected spatial attributes; i.e., the ratio of major to minor axes for elliptical figures and the "winding number" for helices. This simple methodological approach allowed the following conclusions: 1) skin retraction in the rat is anisotropic and is maximal in the rostral-caudal direction; 2) skin retraction is inversely related to postnatal age and to ambient temperature; 3) retraction is inhibited by in vivo treatment with epidermal growth factor (EGF) as well as by metabolic poisons such as sodium azide; 4) retraction is augmented in vitro by calcium chloride. Overall, these data support the hypothesis of a metabolically active, temperature-dependent, anisotropically organized retractile mechanism in the dorsal skin of the perinatal rat.