AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 1 138-G142, Copyright © 1990 by American Physiological Society
The propulsive behavior of the opossum sphincter of Oddi
R. Calabuig, M. G. Ulrich-Baker, F. G. Moody and W. A. Weems
Department of Surgery, University of Texas Medical School, Houston 77225.
This study investigates whether the phasic contractions of the opossum
sphincter of Oddi (SO) delay bile flow by acting as a resistor or
facilitate bile flow by acting as a pump. The common bile duct (CBD) and an
adjacent segment of duodenum from eight opossums were studied in a
propulsion evaluation system in vitro. This system required the production
of hydrostatic work by the SO to transfer fluid from the CBD to the
duodenum when the pressure in the duodenum was equal or greater than the
pressure in the CBD. Fluid movement from the CBD to duodenum and duodenum
to CBD was studied at pressure gradients up to 50 cmH2O before and after
sodium nitroprusside (10(-7) M) inhibition of smooth muscle contractile
activity. All preparations propelled fluid from the CBD to the duodenum
against a pressure gradient ranging from 10 to 50 cmH2O. The SO emptied the
CBD in a monoexponential fashion, with a time constant of 1.52 +/- 0.7 min,
until CBD pressure was reduced to 8.5 +/- 3.2 cmH2O, when propulsion
ceased. Superimposed on the CBD pressure waveform were pressure pulses of
1-2 cmH2O in amplitude that resulted from the contractions of the SO. CBD
pressure was higher at the start than at the end of a periodic pressure
pulse, whereas CBD pressure was stable between pulses. The frequency of the
pressure pulses was greatest at the maximal CBD pressure (9.4/min) and
decreased significantly when the basal pressure was reached (1.5/min, P
less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
