Diurnal variations of active calcium transport in the intestine of pregnant and lactating rat.

Everted gut sac technique was used to study diurnal fluctuations of active calcium transport in the intestine of pregnant and lactating rats maintained under 12 hours light-dark cycle. At the second and third week of gestation an increase of calcium transport occurred in duodenum and adjacent part of jejunum at light phase, but the transport remained unchanged at darkness. Simultaneously the length of jejunal region able for active transport increased. In pregnant females around the term and in lactating mothers no diurnal differences in calcium transport were seen and at the 21st day of lactation the transport were seen and at the 21st day of lactation the transport was nearly equal in both duodenum and proximal jejunum. Restricted to darkness feeding of lactating rat evoked diurnal differences in jejunal but not in the duodenal transport.