title: Effect of dietary calcium and photoperiod on the diurnal rhythm of active calcium transport in rat intestine.
abstract: 1. The everted gut sac technique was used to study the diurnal pattern of active calcium transport along the small intestine of adult rat. 2. In animals maintained under artificial light-dark cycle (LD 12 : 12) and fed ad libitum diets containing from 0.02 to 1% calcium, calcium transport displayed distinct rhythmic changes: it was high in dark and low in light. 3. The decrease in dietary calcium level resulted in a rise of the rhythm amplitude, of the transport maximum in darkness, as well as the mean efficiency of transport during 24 h. The length of the intestinal region with the ability for calcium transport was also increased. 4. The phase of the transport rhythm was shifted on low-calcium diet (0.02%). 5. Diurnal periodicity of calcium transport persisted in rats adapted for 25 days to constant illumination. Similar exposure to constant darkness resulted in arhythmic transport fluctuations.
mesh_terms: D000064:Acclimatization; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002136:Calcium, Dietary / Q000494:pharmacology*; D002940:Circadian Rhythm / Q000187:drug effects*; D003624:Darkness; D005260:Female; D007413:Intestinal Mucosa / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism*; D008027:Light; D051381:Rats
chemical_list: D002136:Calcium, Dietary; D002118:Calcium