DIURNAL CHANGES IN LIGHT-INTENSITY INSIDE THE PREGNANT UTERUS IN SHEEP

Penetration of light into the pregnant sheep uterus was studied in 9 e wes, gestational ages 40 to 142 days (term 147 days). Light sensors we re placed inside the pregnant horn and over the flank skin overlying t he position of the uterine horn. To perform the experiments, the ewes were placed in a study cage outdoors and light sensors were connected to a luxometer. Simultaneous measurements were obtained from the intra uterine and the external sensors in the shade at noon. The amount of l ight detected inside the uterus increased with gestational age from tw o lux at 40 days to 51.1 +/- 16.5 (n = 5) lux at 142 days (0.2 and 5.4 % of be amount of light detected at the maternal flank). Measurements through the 24 h were done in four pregnant ewes at 142 days gestation under natural photoperiod (13.5 Light:10.5 dark). in these experiment s, the intensity of intrauterine Light changed through the 24 h, refle cting the changes in the intensity of the sunlight. Maximal intrauteri ne light values were observed at noon, corresponding to 4.7% of incide nt light. Small but detectable values were observed at 0900 and 1800 h . Our data show that, at mid gestation, light reaches the pregnant ute rus and that, at late gestation, changes in intrauterine lighting thro ughout the 24 h are present reflecting the changes in external dayligh t. Therefore the sheep fetus is exposed to light-dark transitions at d awn and dusk, and to a peak of light at midday. (C) 1998 Elsevier Scie nce B.V. All rights reserved.