Effect of calcium on absorption of fatty acid by rat jejunum in vitro.

The effect of Ca++ on jejunal osmiophilic particles was studied in a recirculating system which was not contaminated with plasma lipoproteins. An isolated, infused segment of rat jejunum was suspended in a bath of liquid paraffin. Transudate, containing osmiophilic particles, appeared like beads of sweat on the serosal surface, and fell to the bottom of the bath. In the range of 25-38 C, 30 C proved to be optimal for histological preservation of villous architecture. Production of transudate, 20 mg/min/g of jejunum, and transport of [14C] oleate proceeded nearly linearly after the first 30 min. Necrosis of mid-villus and crypt cells became obvious by light microscopy after one hour. Therefore, transudate was collected between the period of 30-60 min. Shadow casting of transudates, produced when saline was infused, revealed that 86 +/- 9 (SD) % of osmiophilic particles was less than 800 A in diameter; 13 +/- 8% was 800-1000 A; 0.4 +1- 0.5% was 1000 - 2000 A. Corresponding values were 58 +/- 10, 25 +/- 5, and 16 +/- 5% when 5 mM [14C] oleate + 2.5 mM monoolein was infused; 75% of the transported [14C] appeared in triglyceride. Adding 2 mM Ca++ to the infusion doubled the transport of [14C] triglyceride without increasing particle size further. We conclude that luminal Ca++ increases the absorption of luminal fatty acid by rat jejunum in vitro.