Rate of Formation and Osmolality of Oviductal Fluid in the Cycling Rat1

Abstract

The rate of formation and osmolality of oviductal fluid in anesthetized 4 day cycling Sprague-Dawley rats was studied using micro and ultramicro techniques adapted from those used in renal physiology. The rate of production of oviductal fluid varied with the stage of the estrous cycle. The highest rates were observed on proestrus (84 nl/min) and estrus (81 nl/min). The rate decreased to 56 nl/min on diestrus Day 1 and further to 32 nl/min on diestrus Day 2. These results were in qualitative agreement with the work of others in larger mammals in which it was demonstrated that the rate of oviductal fluid production was greatest at estrus and reduced at other stages of the cycle and during pregnancy. In paired experiments, the osmolalities of simultaneously collected arterial plasma and oviductal fluid samples were compared. Neither plasma nor oviductal fluid osmolality varied during the estrous cycle. The mean values for the plasma and oviductal fluid were 290 .+-. 1 (SEM) [standard error of the mean]) and 287 .+-. 1 mOsm/kg H2O. A small but highly significant difference was found between the paired plasma and oviductal fluid osmolalities, (OF/P)OSM = 0.989 .+-. 0.004 (P < 0.005). The physiological significance of this small difference was not known.