LIPID DROPLET ACCUMULATION AND LIPOPROTEIN-LIPASE ACTIVITY IN THE RATSALIVARY-GLAND DURING THE PERINATAL-PERIOD

The submandibular and sublingual glands of foetal and newborn rats age d 21 days in utero to 7 days after birth were examined morphologically and biochemically. Lipid droplets tended to be localized in secretory cells, especially in their basal cytoplasm. The degree of droplet acc umulation varied with the age of the rat. No droplets were observed be fore and immediately after birth. The number of accumulated droplets p eaked 26-48 h after birth, then gradually decreased and reached normal levels by 5 days. In the salivary glands of fasted newborn rats, no l ipid droplets were observed throughout the experiment. The amount of t riacylglycerol reached its maximum level 1 day after birth; it then de creased gradually until 5 days and after that did not change. The amou nt of cholesterol did not change during postnatal development. Lipase activity attained its maximum level in the salivary glands immediately after birth and then decreased rapidly. It was higher in the glands o f fasted than fed 1-day-old rats. Antiserum against lipoprotein lipase inhibited the salivary gland lipase activity in a dose-dependent mann er, with 5 mu l of antiserum producing 60-70% inhibition. Non-immune s erum had little effect. It was concluded that (1) accumulated lipid in the secretory cell cytoplasm of the salivary glands originates from i ngested milk; (2) the principal component of accumulated lipid droplet s is triacylglycerol; (3) 60-70% of the total lipase activity represen ts lipoprotein lipase; (4) an increase of lipoprotein lipase activity is recognizable before the accumulation of triacylglycerol.