Changes in brown adipose tissue lipoprotein lipase activity and lipogenesis rate during pregnancy and lactation in the rat

Brown fat lipoprotein lipase activity did not change in the first two weeks of pregnancy whereas it decreased on day 18 of gestation and was lower during late pregnancy and lactation. Fatty acid synthesis rate, measured in vivo with (3H)H2O, showed a progressive increase until day 18 of gestation followed by a decrease on day 20 of pregnancy and a reduced lipogenesis rate throughout lactation. The early reduction in the pathways of fatty acid uptake and synthesis in brown fat during the breeding cycle of the rat suggests the possibility that a decline in the substrate supply was a factor contributing to the reduced thermogenic activity of brown adipose tissue after parturition.     

Changes in the lipoprotein lipase (clearing-factor lipase) activity of white adipose tissue during development of the rat.

The lipoprotein lipase (clearing-factor lipase) activity of the white adipose tissue from rats aged between 1 and 145 days was determined. Five adipose-tissue sites (epididymal, uterine, subcutaneous, perirenal and intramuscular) together with serum concentrations of triacylglycerol, cholesterol and glucose were studied. The pattern of enzyme-activity change was remarkably similar in all the sites studied, although the growth of the tissues proceeded non-uniformly. After a peak of activity early in suckling, lipoprotein lipase activity fell to low values by 20 days of age. At weaning (21 days) the activity increased sharply and within 5 days high values were regained. The serum triacylglycerol and cholesterol concentrations were low at birth and reached peaks of concentration coincidentally with the minima of white-adipose-tissue lipoprotein lipase activities, seen late in suckling. The changes in enzyme activity were related to other metabolic changes in adipose tissue and with the known changes in plasma insulin concentrations occurring during development.     

Iodothyronine 5'-deiodinase activity in rat brown adipose tissue during development

Iodothyronine 5'-deiodinase activity in rat brown adipose tissue has a characteristic pattern of developmental changes that is completely different from that of the liver. Fetal brown fat exhibits an extremely high iodothyronine 5'-deiodinase activity that is approx. 10-fold that in adult rats. Even though brown fat iodothyronine 5'-deiodinase activity falls suddenly at birth, there is a new peak in the activity around days 5-7 of life, whereas it remains very low afterwards. Just after birth, brown adipose tissue iodothyronine 5'-deiodinase activity is already capable of stimulation by noradrenaline. The postnatal peak in brown fat iodothyronine 5'-deiodinase correlates with the known increase in the thermogenic activity of the tissue in the neonatal rat, thus reinforcing the suggestion that local 3',3,5-triiodothyronine generation could be an important event related to thermogenesis in brown adipose tissue. However, the high fetal activity was only slightly related to the thermogenic activity of brown fat. Moreover, the increased iodothyronine 5'-deiodinase activity of brown adipose tissue during fetal and neonatal life suggests a substantial contribution by brown fat in the overall extrathyroidal 3',3,5-triiodothyronine production in these physiological periods.     

The effect of short-term starvation on the lipoprotein lipase activity of adipose tissue and cardiac muscle during postnatal development of the rat.

When male rats of between 6 and 13 days of age were starved for 6 h the lipoprotein lipase activity of the epididymal and subcutaneous white adipose tissue did not decline as it did in adults and in animals aged 14-30 days. The lipoprotein lipase activity in the hearts of animals from 6 days of age increased in response to starvation as it did in adults. The relationship of these changes to changes in circulating hormone levels during development was considered.     

Hypertriacylglycerolemia and adipose tissue lipoprotein lipase activity in the Nagase analbuminemic rat

In Nagase analbuminemic rats, serum triacylglycerol levels were significantly elevated. This abnormality was accompanied by decreased adipose tissue fat stores, and both were more marked in female than in male rats. Parametrial adipose tissue lipoprotein lipase activity was determined in normally fed female rats. When expressed per mg protein, the activity in analbuminemic rats was only 35% of that in control rats. The activity in analbuminemic rats, however, could be increased as in control rats by refeeding starved animals with a fat-free and carbohydrate-rich diet, and the peak values recorded were the same with the two groups. Treatment of animals with streptozotocin lowered adipose tissue lipoprotein lipase activity in both groups to similar levels. These results suggest that hypertriacylglycerolemia associated with analbuminemia may be caused, at least in part, by altered hormonal control of adipose tissue lipoprotein lipase activity.     

Purification and characterization of rat adipose tissue lipoprotein lipase.

Lipoprotein lipase (EC 3.1.1.34) extracted from adipose tissue of glucose-fed rats with 5 mM-sodium barbital, pH 7.5, containing 20% (v/v) glycerol and 0.1% (v/v) Triton X-100, was partially purified by affinity chromatography on heparin linked to Sepharose 4B. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of the partially purified enzyme preparation revealed the presence of two major Coomassie-staining bands (mol.wts. 62 000 and 56 000) as well as a number of minor bands. Treatment of partially purified enzyme with [1,3-3H]di-isopropyl fluorophosphate resulted in the incorporation of radiolabel into the band of mol.wt. 56 000, but not into the band of mol.wt. 62 000. Both the amount of the 56 000-mol.wt. polypeptide and the incorporation of [1,3-3H]di-isopropyl fluorophosphate into this band were greatly reduced in the enzyme preparations isolated from adipose tissue of 48 h-starved rats. whereas the amount of the 62 000-mol.wt. polypeptide was unaffected by starvation. Purification of lipoprotein lipase from adipose tissue of glucose-fed rats was also carried out using affinity chromatography on Sepharose 4B linked to heparin with low affinity for antithrombin-III. This procedure resulted in the presence of a single band of mol.wt. 56 000 on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. These results suggest that the polypeptide of mol.wt. 56 000 corresponds to the subunit of lipoprotein lipase, whereas the 62 000-mol.wt. polypeptide probably represents antithrombin-III.     

Degradation of lipoprotein lipase in rat adipose tissue

Pulse-chase studies have shown that the lipoprotein lipase protein of rat epididymal fat bodies is apparently rapidly degraded (43% in 3 h) during incubation at 37°C under conditions where little degradation of the total adipose tissue protein is taking place.     

Post-translational regulation of lipoprotein lipase activity in adipose tissue.

Changes in adipose-tissue lipoprotein lipase activity that are independent of protein synthesis were investigated in an incubation system in vitro. Under appropriate conditions at 25 degrees C a progressive increase in the enzyme activity occurs that is energy-dependent. Part of the enzyme is rapidly inactivated when the tissue is incubated with adrenaline or adrenaline plus theophylline. The mechanism of this inactivation appears to be distinct from, and to follow, the activation of the enzyme. A hypothesis is presented to account for the results in terms of an activation of the enzyme during obligatory post-translational processing and a catecholamine-regulated inactivation of the enzyme as an alternative to secretion from the adipocyte.     

Degradation of lipoprotein lipase in rat adipose tissue

Pulse-chase studies have shown that the lipoprotein lipase protein of rat epididymal fat bodies is apparently rapidly degraded (43% in 3 h) during incubation at 37 degrees C under conditions where little degradation of the total adipose tissue protein is taking place.     

Carnitine and brown adipose tissue metabolism in the rat during development

1. The content of carnitine, acylcarnitine and total acid soluble carnitine in brown adipose tissue of rats increases rapidly after birth, attaining a peak on about day 10 and then decreases. Similar changes with age were found for carnitine acetyltransferase activity in mitochondria from brown adipose tissue and heart. The activity of this enzyme in brain and in liver is much smaller, but also increases postnatally. 2. The activity of carnitine palmitoyltransferase in brown adipose tissue, however, decreases after birth then increases later in life. 3. Exposure of 18-day-old rats to the cold for 20 days leads to an increase in carnitine content in brown adipose tissue and raises the activity of carnitine acetyltransferase. The activity of carnitine palmitoyltransferase is not affected by cold adaptation.     

Purification of rat adipose tissue lipoprotein lipase by affinity chromatography.

Lipoprotein lipase (EC 3.1.1.3) from rat adipose tissue was purified by affinity chromatography with heparin-Sepharose. Elution was carried out with buffered solutions of increasing NaCl molarity. Proteins without affinity for heparin were eluted with 0.5 M NaCl, while lipoprotein lipase activity was eluted as two peaks with 1.16 M NaCl (In earlier work on human adipose tissue (Etienne et al. (1974) C.R. Acad. Sc. Paris 279, 1487-1490) two fractions with lipoprotein lipase activity were also obtained). Phospholipase activity was detected in the fraction eluted with buffered 0.5 M NaCl and containing proteins without affinity for heparin. On feeding the fasting rats with fresh cream or glucose two peaks were also obtained, but the first peak had clearly increased while the second one had remained virtually unchanged.     

Extracellular degradation of lipoprotein lipase in rat adipose tissue

Background  

Recent studies in vivo indicate that short-term regulation of lipoprotein lipase (LPL) in rat adipose tissue is post-translational and occurs by a shift of the lipase protein towards an inactive form under the influence of another gene with short-lived message and product. It has not been possible to reproduce this process with isolated adipocytes suggesting that other cells are needed, and perhaps mediate the regulation. The objective of the present study was, therefore, to explore if explants of adipose tissue could be used for studies of the regulatory process.     

Developmental changes in the activity of lipoprotein lipase (clearing-factor lipase) in rat lung, cardiac muscle, skeletal muscle and brown adipose tissue.

The lipoprotein lipase activity of the lung, skeletal muscle, heart muscle and brown adipose tissue of the rat was studied during the period from late foetal to adult life. The enzyme activity in all four tissues emerged substantially during the first 24th after birth. Subsequently, heart and lung enzyme activity remained relatively constant per unit wet weight of tissue. The enzyme activity present in brown adipose tissue and skeletal muscle was elevated per unit weight of tissue during suckling compared with other periods of life. Delivery of near-term foetuses stimulated the emergence of enzyme activity in all four tissues with the same time course as that evoked by normal delivery. The significance of the presence of the enzyme in the tissues and the activity changes which occurred during development are discussed in relation to possible mechanisms of control.     

Regulation of lipoprotein lipase in muscle and adipose tissue during exercise.

Lipoprotein lipase (LPL) is regulated in a tissue-specific manner; exercise increases LPL activity in muscle at the same time it is reduced in adipose tissue. The purpose of this study was to determine the relationship between LPL activity and LPL mRNA in muscle and adipose tissue in rats exposed to one bout of exercise. Immediately after a 2-h swim, LPL activity [pmol free fatty acids (FFA).min-1.mg tissue-1] in the exercised animals was reduced 43% in adipose tissue (110 +/- 26 to 63 +/- 17) and increased almost twofold in the soleus muscle (203 +/- 26 to 383 +/- 59) compared with sedentary control animals. At the same time, LPL mRNA was reduced 42% in adipose tissue and increased 50 and 100% in the red vastus and white vastus muscles, respectively. Twenty-four hours after the swim, LPL activity had returned to control levels in adipose tissue and the soleus muscle. At hour 24 of recovery, LPL mRNA was still reduced 23% in the adipose tissue of exercised animals but was not significantly different between exercised and control animals in any of the muscle tissues analyzed. Changes in total RNA concentration could not account for the changes in relative LPL mRNA expression. The relationship between LPL enzyme activity and LPL mRNA in muscle and adipose tissue was +0.86 and +0.93 at 0 and 24 h postexercise, respectively. Thus the tissue-specific changes in enzyme activity induced by exercise could be mediated, in part, through pretranslational control.