Autofluorescence of the porcine endometrium during early pregnancy

Uteri recovered from cyclic gilts (n = 5) on Days 15-19 and pregnant animals (n = 34) on Days 13-40 were opened and examined under UV light. A line of greenish fluorescence was present in the mesometrial region in contact with embryonic membranes at Day 13. Small patches of reddish fluorescence subsequently appeared on the uterine mucosa near the embryonic disc, and these increased in intensity and size until they encompassed the entire area of contact between each conceptus and the endometrium, for lengths of about 20 cm, by Day 29. Fluorescence then diminished gradually and was almost totally absent by Day 40. Three additional gilts were unilaterally hysterectomized on Day 15 and treated with Evans blue dye 10 min before removal of the second uterine horn. Both horns were opened and compared under UV light, but no difference in the pattern of fluorescence could be detected. All fluorescence was associated with uterine rather than conceptus tissues. The occurrence of autofluorescence in uteri of pregnant pigs precludes use of Evans blue dye as an indicator of vascular permeability.