8/4/2019 The Gastrointestinal Digestion of Fat in Dogs Fed Triglycerides, Partial Glycerides and Free Fatty Acids

1/11

THE GASTROINTESTINAL DIGESTION OF FATIN DOGS FED TRIGLYCERIDES, PARTIALGLYCERIDES AND FREE FATTY ACIDSLEON K. KNOEBEL

Department of Physiology, Indiana University School of M edicine,Indianapolis

(Received for publication October 24, 1958)A number of w orkers have studied pancreatic lipase hydrolysis of triglycridefat in vitro in recent years (Frazer andSammons, '45; D esnuelle, '51; Borgstrom , '54). In general,they found that considerable quantities of m onoglycerides,d igly cerides, trig ly cridesan d free fatty acids were presen tin the test tube after relatively long periods of time. It hasalso been demonstrated that appreciable am ounts of theseglycerides and free fatty acids are present in lipid recoveredfrom the intestinal tract follow ing the feeding of triglycridefat (Mattson et al., '52; Desnuelle and Constantin, '52). It

appears that lipolysis in vivo and in vitro proceeds in a step-w ise fashion from triglycrideto diglyceride to monoglyc-eride to glycerol with the liberation of fatty acid at eachstep. However, it has been shown that hydrolysis of trig ly crid esn v itro pro ceed s so slowly th at a comp lete h ydro lysis to free fatty acids and glycerol does not occur in thetime it normally takes fat to traverse the small intestine.These results suggest that both glycerides and free fattyacids may be absorbed by the small intestine. This is contrary to the concept of fat digestion based on a completebreakdown of triglycrides to free fatty acids and theirabsorption as such (Verzar and McDougall, '36). In thepresent paper an attempt is made to determine whether aparallelism does exist betw een lipolysis in vivo and in vitro.39 3

8/4/2019 The Gastrointestinal Digestion of Fat in Dogs Fed Triglycerides, Partial Glycerides and Free Fatty Acids

2/11

394 LEON K . KNOEBEL ,

METHODST he ex perim ental procedure has been described (K noebeland N sset,'57). Dogs fasted at least 24 hours w ere fed atest m eal, k illed af ter three hours and contents rem ov ed f romthe stom ach, duodenum , jejunum and ileum . T he duodenumrepresented about S% and the jejunum and ileum each approx im ately 46% of the length of the sm all intestine.Free f atty acids w ere titrated in 95% ethanol w ith alcoholic0.1N KOH to the phenolphthalein endpoint. M onogly ceridecontent w as determ ined by the iodom etric technique of Pohleand M e hlenbacher ('50). For reasons giv en elsew here (K noebel and N sset, '57) both 1- and 2-m onogly cerides are considered to be included in the f inal v alues presented in thisw ork . T he part of the recov ered lipid not accounted for asfree fatty acids or m onogly cerides w as assum ed to consistof digly cerides and trigly c rides. T hat this assum ption isv alid for the m ost part is supported by the f inding of Des-nuelle and C onstantin ('52) that the am ounts of phospholipidand cholesterol, f ree and esterif ied, present in the lipid recov ered f rom the intestine of rats fed oliv e oil is v ery sm allcom pared to the quantities of gly cerides and free fatty acidspresent.K noebel and N sset('57) reported that the com position oflipid recov ered f rom v arious segm ents of the sm all intestineo f d og s f ed cotto ns eed o il trig ly crid esc lo se ly re semb led th atproduced by the action in v itro of pancreatic lipase on trio-lein in the presence of calcium ions and bile salts (D esnuelle,'51). T his suggested that trigly c ridesm ay be hy droly z ed inm uch the sam e m anner in v iv o as in v itro. In order to inv estigate further w hether such a relationship ex ists, 4 lipidm ix tures w ere fed to dogs. Each lipid m ix ture had a com position (table 1) sim ilar to that w hich presum ably ex ists at acertain tim e during the f irst hour of hy droly sis of trioleinin vitro as reported by D esnuelle ( ' 51). A test m eal contained25 gm of a lipid m ix ture, 25 gm of sucrose, 25 gm of caseinand 5 gm of cellulose f lour. T w o dogs w ere fed a test m eal

8/4/2019 The Gastrointestinal Digestion of Fat in Dogs Fed Triglycerides, Partial Glycerides and Free Fatty Acids

3/11

8/4/2019 The Gastrointestinal Digestion of Fat in Dogs Fed Triglycerides, Partial Glycerides and Free Fatty Acids

4/11

396 LEON K. KNOEBEL

' S ; .1B ' OJ . 2*1ogH

>*&oEG*K1-100iM

~-ElB| J o00U

s ~H0|50MisM0