Movements of the luminal contents in two different regions of the caput epididymidis of the rat in vitro.

Transport of the epididymal contents was studied in vitro by filming, for 1-2.5 h, the movements of tiny, stained oil droplets injected through a micropipette into two regions of the lumen of the caput epididymidis: the most proximal part, with the widest outer diameter (region I), and the neighbouring, narrowest portion (region II). The movements of the oil droplets were pendular. Displacement, caused by a contraction of the wall spreading in either direction, was followed by a shorter, usually passive reflux leading to a small net displacement, delta l. The distance of transport during 5 min periods varied between 0.09 and 16.79 mm (median 1.0 mm) in region I and 0.05 and 3.62 mm (median 0.42 mm) in region II. Transport divided into periods when little or no net transport took place (slow transport) and periods when the transport was effective (fast transport). Although the periods of fast transport were infrequent, their significance in transport towards the ductus deferens was high. During 5 min sampling periods of fast transport, the pendular movements were longer in both regions: delta l was longer in region I and the probability of delta l being in the direction of transport was higher than during slow transport in both regions. The mean probability of delta l being in the direction of the ductus deferens was 0.63 in region I and 0.57 in region II. Higher frequency of pendular movements, longer delta l values and higher probability of delta l being towards the ductus deferens in region I than II suggest that the transport speed is higher in region I than II. Transport consisting of short steps occurring with variable probabilities in both directions is a stochastic process.