Bile acid metabolism. I. Studies on the mechanisms of intestinal transport.

Open Access
Publisher Website
Google Scholar
Abstract
Transport phenomena that result in bile salt absorption from the small intestine is analyzed. Under in vitro conditions the active transport of taurocholate and cholate occurs at nearly identical rates equaling 1,380 [plus or minus] 350 and 1,490 [plus or minus] 110 [mu][mu]moles/min./cm, respectively. Similarly, the passive ionic diffusion of taurocholate and cholate ions occurs at similar rates (89 [plus or minus]12 and 83 [plus or minus] 7 [mu][mu]moles/min./cm for a 1.0 mM gradient), whereas at physiologic pH in the intestine, only unionized cholic acid penetrates the intestinal mucosa by nonionic diffusion (610 [plus or minus] 95 [mu][mu]moles/min./cm for a 1.0 mM gradient). In the intact animal similar transport mechanisms were identified and quantitated. The maximal transport rate in vivo for taurocholate is 1,920 [plus or minus]190 [mu][mu]moles/min./cm and for cholate equals 1.900 [plus or minus] 87 [mu][mu]moles/min./cm. Passive ionic diffusion of both the conjugated and unconjugated bile salts occurs at the nearly equal rates of 440 [plus or minus] 59 and 400 [plus or minus] 80 [mu][mu]moles/min./cm for a 1.0 mM gradient, respectively, whereas nonionic diffusion of un-ionized cholic acid takes place at a rate of 2,320 [plus or minus] 280 [mu][mu]moles/min./cm. The quantitative importance of these phenomena in the overall process for bile salt absorption is discussed.