Development of circadian variations in intestinal calcium transport during maturation of the rat.

Everted gut sac technique was used to study diurnal pattern of active calcium transport along the small intestine of developing and adult rats kept under 12:12 h light-dark cycle. In animals aged 6 weeks to 5 months calcium transport displayed essential diurnal fluctuations with maximum transport at darkness whereas in 23 days old rats diurnal fluctuations were negligible. During maturation of the rat a gradual increase in the amplitude of calcium transport rhythm was observed. Since the 10th week of life diurnal variations of the calcium transport involved both the transporting efficiency and the intestinal area participating in the transport. Nevertheless an age-dependent decrease occurred in the intestinal region capable of transporting actively calcium. Diurnal pattern of calcium transport was almost the same in 6-week-old rats either fed ad libitum or adapted from weaning to feeding restricted to darkness. Feeding restricted to light period resulted in arrhythmic transport fluctuations. A shift in the phase of the diurnal rhythm of calcium transport was observed in 6-week-old rats adapted from the 14th day of life on to reversed light dark cycle..