Gastric handling of medium-chain triglycerides and subsequent metabolism in the suckling rat.

We have previously shown that preduodenal lipases account for 50% of the lipolytic capacity of 14-day-old rats. The present investigation was designed to study the kinetics of and optimal conditions for absorption of fat in the stomach of suckling rats and its subsequent distribution in the body. After the simultaneous instillation of medium-chain triglycerides (MCT) containing 1.25 microCi 2,3-[3H]trioctanoate and of long-chain triglycerides containing 1.25 microCi 1-[14C]glycerol trioleate into the stomach ligated at the pylorus, we were able to show that gastric absorption of fat is limited to MCT. Two and a half minutes after injection, 88.6% of the radioactivity in the wall of the stomach was associated with free fatty acids, proving that lipolysis had preceded the absorption of the majority of the MCT. The remainder of the radioactivity was found in mono-, di-, and triglycerides as well as with cholesterol ester and phospholipids. In the plasma, peak radioactivity was attained within 2.5 min and a steady state ensued which lasted at least 30 min. Over this time period, specific radioactivity continued to rise in the liver, suggesting that hepatic uptake proceeded at the same rate as gastric absorption. Uptake could also be demonstrated in the three other organs tested, the lungs, the heart, and the kidneys. Absorption of MCT at pH 3 was only 20% of absorption at pH 6, which is the physiological pH in the suckling rat stomach within the first 10 min after a feed. Both at pH 3 and at pH 6, the addition of sodium taurocholate increased absorption of MCT over threefold. It is likely that the absorption of MCT by the stomach is a physiological event in the suckling rat.