Direct measurement of transepithelial force: an in vivo technique

A technique for direct in vivo measurement of the intensity of absorptive force generated by an epithelial membrane is described. A quasirigid porous cartridge containing normal saline was placed in isolated intestinal segments of anesthetized rat and connected, via a catheter, to a Statham pressure transducer. Once excess fluid had been absorbed, further fluid absorption was hindered by the nonyielding character of the cartridge, leading to the development of negative (subatmospheric) pressures. Volume expansion with intravenously infused normal saline solution resulted in an abrupt fall in absorptive force, followed by a more gradual recovery to the pre-volume-challenge level. Contraction of intravascular volume by bleeding led to a prompt increment in absorptive force proportional to the amount of blood removed. Return of the blood to the circulation restored absorptive force to the prebleed level. Complete circulatory arrest (death) produced a temporary increment, lasting about 30 min, in absorptive force. Physical mechanisms that may be involved in these alterations of absorptive force are discussed.