To evaluate the effects of strain, gender and fasting in the regulation of lipoprotein lipase (LPL) and hepatic lipase (HL) activities were measured in tissues of male and female Wistar and Sprague-Dawley rats after feeding or a 24-h starvation period. It is noteworthy that an effect of gender on LPL activity was observed in Wistar, but not in Sprague-Dawley rats, not only in the basal (fed) activity in several tissues, such as white and brown adipose tissues, heart, and brain, but also in response to fasting which affected LPL activity in brown adipose tissue, heat and lung of female but not of male Wistar rats. By contrast, HL activity in liver, plasma and adrenals of Sprague-Dawley rats was higher in females than in males. No effect of gender on HL activity was observed in Wistar rats. Our results indicate that differences exist between Wistar and Sprague-Dawley rats in the regulation of both LPL and HL. Some of the contradictory results found in the literature may be explained by the differences between rat strains and gender, as well as differences in the nutritional status of the animals.

The effect of fasting on hepatic endothelial lipase activity in the liver of adult rats was investigated. We found that, both in male and female rats, fasting produced a progressive decrease of the hepatic endothelial lipase activity. Upon refeeding, the activity returned to control values in 48 h. In isolated livers from fed male rats, a sharp peak of hepatic endothelial lipase activity appeared in the perfusate upon heparin addition. It accounted for 75% of the total activity (heparin-released + residual) of the tissue. Fasting (24 h) decreased the heparin-releasable activity, and this effect was responsible for most of the decrease found in whole tissue. We suggest that the effect might be due to a decreased synthesis and/or secretion of the enzyme by hepatocytes, since isolated hepatocytes from fasted rats, incubated at 37 C, released 65% less activity to the incubation medium than hepatocytes from fed rats. Adrenaline, but not insulin, glucagon, dexamethasone, epidermal growth factor, or T3, decreased the amount of hepatic endothelial lipase activity released by hepatocytes isolated from fed rats. The effect of adrenaline appears to be mediated by alpha 1-receptors since phenylephrine but not isoprenaline reproduced, and prazosin but not propranolol blocked, the effect of the catecholamine. In the presence of cycloheximide, adrenaline also decreased the amount of activity released. We suggest that, in our incubation conditions (up to 3 h), the hormone affects the posttranslational processing of the enzyme. In vivo administration of prazosin blocked the effect of both noradrenaline and fasting on hepatic endothelial lipase activity in whole liver. Those results suggest that catecholamines are involved in the decreased hepatic endothelial lipase activity found in the liver of fasted rats, and points out the role of these hormones in the acute modulation of an enzyme involved in reverse cholesterol transport.

Lipoprotein lipase in animal tissues is known to be affected by fasting, but contradictory results have been published concerning this effect in particular tissues. For example, we reported that lipoprotein lipase activity expressed in the liver of neonatal rats was either increased or not affected by fasting. To evaluate the influence of the rat strain used as experimental animal model, we studied differences between Wistar and Sprague-Dawley rats in the development and in the effect of fasting on lipoprotein lipase and hepatic lipase activities in tissues of neonatal rats. Beside some minor differences in the development of lipoprotein lipase in some tissues like brown adipose tissue and lungs, we found quite remarkable differences between both strains in the development of lipoprotem lipase and hepatic lipase activities in the liver. In 1-day-old neonates, differences between both strains were also observed in the effect of fasting on lipoprotein lipase activity both in liver and lungs. In the liver of Wistar pups lipoprotein lipase activity was increased by fasting by 350%, but only by 50% in the liver of Sprague-Dawley pups. In contrast, in the lungs of Wistar pups lipoprotein lipase activity was increased by fasting by 280%, but by 580% in lungs of Sprague-Dawley rats. Therefore, our results indicate that quantitative differences exist between Wistar and Sprague-Dawley rats in the regulation of lipoprotein lipase.

Hepatic lipase activity is detectable in liver but also in adrenal glands, ovaries, and plasma. The subunit size of hepatic lipase in liver, adrenal glands, and nonheparin plasma was compared. Hepatic lipase in liver and adrenal glands appeared as a 55 kDa band. In liver, a faint band of lower size was also detected. In nonheparin plasma, hepatic lipase appeared as a doublet of 57 kDa and 59 kDa. When activity/mass ratio was calculated, similar values were obtained for liver and adrenal glands. In plasma this value was much lower. After heparin administration in vivo, hepatic lipase activity in plasma increased nearly 100-fold with appearance of an additional 55 kDa band in postheparin plasma. This band coeluted with activity after preparative polyacrylamide gel electrophoresis. Differences in size persisted after digestion with peptide-N -glycosidase F. A progressive increase in 57 kDa and 59 kDa in postheparin plasma followed disappearance of the 55 kDa band, suggesting that these larger bands originate from the smaller form. In plasma, both smaller and larger forms were associated with HDL, but not with LDL or VLDL. We conclude that rat plasma contains a larger form of hepatic lipase that is inactive in in vitro assay. Hepatic lipase is involved in the metabolization of remnant lipoproteins (1) and triglyceride-rich high-density lipoproteins-2 (2). As a result of triglyceride and phospholipid hydrolysis, hepatic lipase promotes the uptake of HDL cholesterol by the liver (3), and generates pre ␤ 1

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