Contribution of lipoprotein lipase activity to the differential growth of three adipose tissue depots in young broiler chickens

1. The growth of three distinct adipose tissue depots around the abdomen, neck and thigh was measured in a commercial strain of broiler, and related to the changes in activity of lipoprotein lipase within each depot.

2. At 10 d of age there was no significant difference between the weights of the depots. Thereafter the abdominal fat pad exhibited a much greater rate of growth than the other two depots so that by 55 d of age the abdominal fat pad was 4 times the size of the leg depot and 3.4 times the size of the neck depot.

3. Changes in total lipoprotein lipase activity for all three depots showed a similar pattern to the changes in their weight.

4. When [¹⁴C]‐VLDL was injected intravenously into birds at 15 and 57 d of age the percentage taken up into the abdominal fat pad was greater than that into the other two depots at both ages. At 57 d of age the abdominal fat pad had a 2.3‐fold greater uptake than at 15 d whereas the other two depots showed no significant differences at the two ages.

5. These results provide further evidence for a key role of lipoprotein lipase in regulating adipose tissue growth in broilers. They also demonstrate that although the abdominal fat pad has been used in a number of studies of adipose tissue metabolism it is not necessarily representative of other depots.     

Comparison of the rates of proliferation of adipocyte precursor cells derived from two lines of chicken which differ in their rates of adipose tissue development

1. Putative adipocyte precursor cells were isolated from the white adipose tissue of young broiler and layer chickens and cultured in vitro.

2. The cells from both sources were shown to have the characteristics of adipocyte precursor cells. On reaching confluence, lipoprotein lipase activity was induced and the cells from both strains accumulated large amounts of lipid in the presence of chicken serum.

3. Measurement of cell number over time in culture and calculation of cell doubling times showed that cells from broilers proliferated at a faster rate than those derived from layer‐strain chickens. This was the case whether primary or secondary cell cultures were used. Primary cultures of broiler cells had a doubling time of 22 h versus 39 h for layer cells.

4. The contribution of such a difference in proliferative rate to the differential rate of adipose tissue growth between broiler and layer strains observed in vivo is discussed.     

Effect of Escherichia coli endotoxin on tissue lipoprotein lipase activities in chickens

1. Four-week-old broiler chickens were injected intravenously with from 0.01 to 1 mg of E. coli endotoxin/kg body weight or with saline. 2. At all doses used endotoxin markedly depressed food intake and lipoprotein lipase activities in muscle and adipose tissue within 8 h. Heart lipoprotein lipase activity was significantly depressed only at doses of 0.1 mg endotoxin/kg body weight or greater. 3. Treatment of birds with 0.3 mg endotoxin/kg body weight reduced post-heparin lipoprotein lipase activity to 0.13 of that in control birds in 8 h. 4. Endotoxin generally depressed plasma very-low-density lipoprotein concentration. Plasma non-esterified fatty acid concentration was significantly elevated only in birds given 1 mg endotoxin/kg body weight. 5. Fatty acid synthetase activity in the liver of endotoxin-treated birds was significantly lower than in control birds 16 h after administration of endoxin, but not after 8 h. 6. These results show that tissue lipoprotein lipase activity in birds is very responsive to E. coli endotoxin, as in mammals. Hypertriglyceridaemia occurs only occasionally in endotoxin-treated chickens, most probably because of the particularly close relationship between food intake and hepatic lipoprotein synthesis in birds.     

Contribution of lipoprotein lipase to differences in fatness between broiler and layer-strain chickens

The growth of abdominal fat in chickens from broiler and layer-strains up to 10 weeks of age was measured and compared with changes in plasma very low density lipoprotein (VLDL) concentration and tissue lipoprotein lipase activities. The growth of abdominal fat in broilers was much more rapid than in layer-strain chickens. Plasma VLDL concentrations in the two strains were similar up to 5 weeks of age but thereafter concentrations tended to be higher in broilers. Plasma VLDL concentrations in both strains were much lower than those necessary for maximum lipoprotein lipase activity. The lipoprotein lipase activity of abdominal fat increased much more rapidly in broilers than in layer-strain chickens. In both strains the pattern of its increase relative to body weight was similar to that of abdominal fat. Differences in the lipoprotein lipase activity of abdominal fat between strains were attributed to differences in both activity/adipocyte and number of adipocytes. They were reduced or abolished if activity was expressed relative to tissue weight, or to its content of DNA or protein. The results strongly suggest that the greater lipoprotein lipase activity of the abdominal fat pad in broilers is an important factor in its rapid growth.     

Cytotoxic antibodies to chicken adipocytes and their precursors: lack of tissue specificity

1. Antisera raised in sheep against chicken adipocyte plasma membranes recognised adipocyte, liver and red blood cell membranes in enzyme immunoassays (EIA). 2. These antisera were cytotoxic when incubated with both adipocytes and their precursors grown in culture, and with red blood cells. 3. Adsorption of antisera with liver membranes completely abolished the response to liver and red blood cell membranes in the EIA. The response in adipocytes was reduced to only about 6% of the titre present in the unadsorbed sample. 4. Adsorption of antisera with liver membranes abolished the cytotoxic response to red blood cells and to adipocyte precursors, but some response to adipocytes still remained. 5. These results are in contrast to the rat for which adipocyte specific antisera were obtained which represented about 75% of the unadsorbed titre.     

Biochemical indicators of fatness in meat-type chickens: lack of correlation between lipoprotein lipase activity in post-heparin plasma and body fat

1. Possible relationships between fatness and lipoprotein lipase activity in adipose tissue and plasma from heparinised birds were examined in 7-week-old male and female broilers. 2. Total lipoprotein lipase activity in abdominal fat was significantly correlated (r = 0.5) with fat pad weight, but there was no correlation between specific activity of the enzyme and fat pad weight. 3. Lipoprotein lipase activity in post-heparin plasma showed no correlation with either abdominal fat or total body fat content. 4. The results indicate that measurements of lipoprotein lipase activity in biopsy samples or in post-heparin plasma are of no value in predicting the fat content of live birds.