Influence of pregnancy and uterine weight on rat gastrointestinal transit

Orogastric feeding of a charcoal meal to rats was employed to measure whether the various stages of pregnancy could influence gastrointestinal transit. The oestrous cycle of female Sprague-Dawley rats was checked daily. If pro-oestrus occurred, the first day of pregnancy was defined to be on the next day after the copulation. Gastrointestinal transit studies were conducted on day 7 (first trimester), day 14 (second) and day 21 (third), respectively. The rats were killed 15 min after the successful feeding of a calorie-free, charcoal-containing test meal via a transiently placed orogastric catheter. Gastrointestinal transit was defined as the per cent of charcoal transit divided by the total length of the small intestine. These results were compared with the data obtained from non-pregnant female rats. Mean percentages of transit for the first, second and third trimester, and for controls were 42.8 +/- 1.9, 45.3 +/- 4.1, 35.7 +/- 1.7 and 42.6 +/- 1.4%, respectively (mean +/- s.e.). Late pregnancy elicited a marked inhibition of transit (P < 0.01). A significant negative correlation between transit and uterine weight of all pregnant rats was seen (r = -0.50, P < 0.05). The present study indicates that inhibited gastrointestinal transit occurs in the late pregnant rat.