Swine microsomal acyl-CoA synthetase activity: effect of age and diet.

Fatty acid activation was examined by assessing the activity of acyl-CoA synthetase (ACS) in microsomal fractions of liver and adipose tissue obtained from swine of various ages. Liver ACS activity increased from ca. 200 to 800 nmol/(minute x g tissue) between birth and 25 days postpartum; enzyme activity generally remained elevated postweaning through 155 days of age. The preweaning hepatic patterns on a wet weight and protein basis were similar, but the wet weight- and protein-based patterns diverged after weaning due to an increase in microsomal protein. As in liver, adipose tissue ACS activity rose rapidly from birth to 25 days of age [20-110 nmol/(minute x g tissue)] but declined to lower levels after weaning. Expression of enzyme activity on a wet weight, protein, or cellular basis revealed similar developmental patterns for adipose tissue. The postweaning fall in adipose tissue ACS activity was partially explained by decreasing cellularity per unit tissue weight. In swine fed equal amounts of isoenergetic-isonitrogenous diets with low or high fat content, hepatic ACS activity tended to increase in pigs fed the high fat diet with no effect of diet on the adipose enzyme. Starvation elevated liver ACS activity, whereas the adipose enzyme activity was marginally decreased.

Effect of nutritional status on swine adipose tissue lipolytic activities.

Young swine (28 days of age) were fed an isocaloric and isonitrogenous diet with either a high fat or a low fat content for 3 to 4 weeks. The adipose tissue lipolytic rate was higher in the group fed the high fat diet. However, there was no effect of diet on the activities of several of the enzymes controlling the lipolytic process, i.e., adenylate cyclase, phosphodiesterase and hormone-sensitive lipase. No effect of diet on the activity of lipoprotein lipase was detected. Fasting for 72 hr, but not for 24 or 48 hr, caused an increase in the lipolytic rate. There was also a decrease in cell size after a 72-hr fast (P greater than .05) such that the increased rate was not significant when the data were expressed on a cell basis. Inexplicable transient changes in adenylate cyclase activity, as well as a decrease in the activity of the low affinity phosphodiesterase (doubtful physiological significance), were detected during starvation. Starvation depressed the adipose tissue lipoprotein lipase activity but had no effect on the hormone-sensitive lipase activity.

Ontogeny of glycerolipid biosynthetic enzymes in swine liver and adipose tissue.

Enzymes associated with glycerolipid biosynthesis were examined in microsomal fractions of liver and adipose tissue obtained from swine of various ages. Generally, liver glycerophosphate acyltransferase, phosphatidate phosphohydrolase, diglyceride acyltransferase, and choline phosphotransferase activities were substantial at birth but increased 2- to 3-fold by day 14 postpartum, decreased at day 25, then increased at the oldest ages studied (up to 155 days postpartum). In adipose tissue, enzyme activities were low at birth and developed through day 25 in a pattern generally similar to that observed in liver. In contrast to liver, the adipose enzymes were depressed immediately postweaning (day 32) with subsequent recovery. The observed decline in adipose tissue enzyme activities expressed on a tissue basis at older ages was primarily the result of increased adipocyte size, since the activities expressed on a cell basis did not decline as rapidly. In both liver and adipose tissue, phosphatidate was the major glycerolipid synthesized by the microsomal glycerophosphate acyltransferase enzymes at all ages (generally greater than 75%). The ratio of neutral lipids to phospholipids produced by acylation of glycerophosphate was increased when a microsomal--cytosolic preparation was used as a source of enzyme in contrast to a microsomal preparation.

Ontogeny of adenylate cyclase and phosphodiesterase activities in swine tissues.

The ontogenic patterns of the basal- and fluoride-stimulated adenylate cyclase and the cAMP phosphodiesterase activites as well as the tissue levels of cAMP were assessed in swine adipose tissue, heart, skeletal muscle, and liver. The developmental patterns were complex. However, there was a general tendency in all tissues toward lower enzyme activities in the oldest animals (150 days) for both enzymes. In adipose tissue, the decreased enzyme levels could partially be attributed to an increase in adipocyte size.

Factors influencing the lipolytic response of swine (Sus domesticus) adipose tissue: ontogeny.

Swine adipose tissue was not responsive to glucagon at any age and only marginally to adrenocorticotropin (ACTH). The latter response could be greatly magnified and the sensitivity increased by addition of theophylline (Theo). The maximal lipolytic activity (MAX) obtained with ACTH plus Theo was minimal in the newborn, greatly increased in young animals, and reduced during the growing period; however, the sensitivity did not change. The MAX for Theo (plus low epinephrine) yielded a pattern similar to ACTH, but the sensitivity changed (most sensitive in younger animals). The MAX and sensitivity obtained with dibutyryl cyclic adenosine monophosphate were not appreciably changed during development.