IN-VITRO ANALYSIS OF OOCYTE CUMULUS COMPLEX PICKUP RATE IN THE HAMSTER MESOCRICETUS-AURATUS

In mammals, the oocyte and its surrounding cumulus cells constitute an oocyte cumulus complex (OCC). During ovulation, OCCs are extruded int o the peritoneal or bursal cavity, depending on the species, and are t hen rapidly picked up by the fimbria on the outer surface of the ovidu ctal infundibulum and transported to the ampulla, where fertilization occurs. We developed a method to measure OCC pickup rates quantitative ly in vitro, and we used this method to evaluate the effects of viscos ity and temperature on pickup rates. Hamster infundibula are placed in a holding pipette in a chamber modified to study OCC pickup. Ciliary beat frequencies (CBF) can be measured in the same preparation. Pickup rates vary depending on the pathway on which the OCC travels over the surface of the infundibulum; however, rates for a given pathway are v ery consistent. The average pickup rate at room temperature calculated from three different pathways/infundibulum was 55.2 +/- 10.6 mu m/sec . Both rates between infundibula from the same female and rates among infundibula from different females were in most cases similar. Prepara tions preincubated in vitro for 2.75 hr produced rates similar to nonp reincubated samples, while longer preincubation resulted in decreased rates. Inclusion of Ficoll in culture medium to increase viscosity cau sed a concentration-dependent decrease in both OCC pickup rate and in CBF. However, a significant decrease in OCC pickup rate was only obser ved at viscosities higher than those found in bursal fluid. When trial s were run at physiological temperature (36.4 degrees C) rather than a mbient temperature, rates increased to 136.7 +/- 29.9 (SD) mu m/sec. L inear regression analysis demonstrated a strong positive correlation ( r = 0.94) between OCC pickup rate and temperature. The OCC pickup rate assay can be used experimentally, and should be valuable in evaluatin g factors that affect rate and in studies dealing with the mechanism o f OCC pickup. (C) 1997 Wiley-Liss, Inc.