A reduced protein diet induces stearoyl-CoA desaturase protein expression in pig muscle but not in subcutaneous adipose tissue: relationship with intramuscular lipid formation.

A reduced protein diet (RPD) is known to increase the level of intramuscular lipid in pig meat with a smaller effect on the amount of subcutaneous adipose tissue. This might be due to tissue-specific activation of the expression of lipogenic enzymes by the RPD. The present study investigated the effect of a RPD, containing palm kernel oil, soyabean oil or palm oil on the activity and expression of one of the major lipogenic enzymes, stearoyl-CoA desaturase (SCD) and on the level of total lipids and the fatty acid composition of muscle and subcutaneous adipose tissue in pigs. The RPD significantly increased SCD protein expression and activity in muscle but not in subcutaneous adipose tissue. The level of MUFA and total fatty acids in muscle was also elevated when the RPD was fed, with only small changes in subcutaneous adipose tissue. A positive significant correlation between SCD protein expression and total fatty acids in muscle was found. The results suggest that an increase in intramuscular but not subcutaneous adipose tissue fatty acids under the influence of a RPD is related to tissue-specific activation of SCD expression. It is suggested that the SCD isoform spectra in pig subcutaneous adipose tissue and muscle might be different.

Manipulation of the n-3 polyunsaturated fatty acid content of muscle and adipose tissue in lambs.

Fifty Suffolk-crossbred wether lambs, with an initial live weight of 29 +/- 2.1 kg, were allocated to one of five concentrate-based diets formulated to have a similar fatty acid content (60 g/kg DM), but containing either linseed oil (high in 18:3n-3); fish oil (high in 20:5n-3 and 22:6n-3); protected linseed and soybean (PLS; high in 18:2n-6 and 18:3n-3); fish oil and marine algae (fish/algae; high in 20:5n-3 and 22:6n-3); or PLS and algae (PLS/algae; high in 18:3n-3 and 22:6n-3). Lambs were slaughtered when they reached 40 kg. Growth performance and intake were similar (P > 0.35) among treatments. By contrast, gain:feed was higher (P < 0.05) in lambs fed the fish oil compared with the linseed oil or PLS/algae diets. Total fatty acid concentration (mg/100 g) in the neutral lipid of the longissimus muscle was not affected by treatment (P > 0.87) but was least (P < 0.05) in the phospholipid fraction in lambs fed the linseed oil diet. Lambs fed either diet containing marine algae contained the highest (P < 0.05) percentage of 22:6n-3 in the phospholipid (mean of 5.2%), 2.8-fold higher than in sheep fed the fish oil diet. In lambs fed the fish/algae diet, the percentage of 20:5n-3 was highest (P < 0.05), contributing some 8.7, 0.8, and 0.5% of the total fatty acids in the muscle phospholipid, neutral lipids, and adipose tissue, respectively. The percentage of 18:3n-3 in the phospholipid fraction of the LM was highest (P < 0.05) in lambs fed the linseed oil diet (6.9%), a value double that of sheep fed the PLS diet. By contrast, lambs fed the PLS diet had twice the percentage of 18:3n-3 in the muscle neutral lipids (3.8%) than those offered the linseed oil diet, and 5.5-fold greater than lambs fed the fish/algae treatment (P < 0.05), an effect that was similar in the adipose tissue. The percentage of 18:2n-6 was highest (P < 0.05) in lambs fed the PLS diet, where it contributed 33.7, 10.1, and 11.2% in the muscle phospholipid, neutral lipids, and adipose tissue, respectively. The highest (P < 0.05) muscle PUFA-to-saturated fatty acid (P:S) ratio was obtained in lambs fed the PLS diet (0.57), followed by the PLS/algae diet (0.46), and those fed the fish oil or linseed oil diets had the lowest ratios (0.19 and 0.26, respectively). The favorable P:S ratio of lambs fed the PLS/algae diet, in conjunction with the increased levels of 20:5n-3 and 22:6n-3, enhanced the nutritional qualities of lamb to more closely resemble what is recommended for the human diet.

The polyunsaturated fatty acid composition of beef and lamb liver.

The effect on liver fatty acids of two typical beef production systems, steers fed grass (grazing) and bulls fed concentrates, was investigated. Liver fatty acids were also studied in lambs grazing grass. Total fatty acid content of liver in the beef animals was not affected by production system, being 3.5% for grass and 3.7% for concentrates although carcasses of the latter animals were leaner. The percentages of the major non polyunsaturated fatty acids (PUFA) were also similar: (concentrates in parentheses) 18:0, 25.2% (25.1%); 16:0, 13.3% (14.5%); 18:1 12.6% (14.0%). Total liver PUFA contents were similar for the two production systems and much higher than in muscle from the same animals. All n-3 PUFA were present in greater amounts in liver from grass fed animals and n-6 PUFA were higher in concentrate fed animals: mg/100g liver, 18:3n-3 92 (32); 20:5 n-3, 151 (17); 22:5 n-3, 283 (108); 22:6 n-3, 83 (32); 18:2 n-6, 172 (444); 20:4 n-6, 194 (270). The P:S ratios were 0.20 (grass) and 0.32 (concentrates) and the n-6:n-3 ratios were 0.71 and 4.8, respectively. Livers from grass-fed lamb had a higher fat content, 4.9%, than the beef livers and a lower percentage of 18:0, (21%); but more 16:0, (16%) and 18:1 (21 %). Total PUFA content of lamb's liver resembled that of beef liver and the composition was similar to that of the steers fed grass. However the concentrations of 18:3 n-3 and 22:6 n-3 were higher in lamb and contributed to a lower n-6: n-3 ratio of 0.46 although the P:S ratio of 0.18 was similar to that in beef liver. Ruminant liver is potentially a good source of C20 and C22 PUFA in the human diet particularly from grass fed animals, with a highly desirable n-6:n-3 ratio and this may be more important nutritionally than the low P:S ratio since people can offset this elsewhere in the diet.

Fatty acid content and composition of UK beef and lamb muscle in relation to production system and implications for human nutrition.

Although ruminant meats normally have a low ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (P:S ratio), the muscle contains a range of C(20) and C(22) PUFA of both the n-6 and n-3 series of potential significance in human nutrition. However, information on the amounts of these fatty acids in muscle and how they are modified by production system is limited In this study, the content and composition of fatty acids was determined in several muscles from beef steers fed grass (grazed) and bulls fed cereal concentrates. These are the two main types of beef production in the UK and Europe. Muscle fatty acids were also determined in lambs fed grass (grazed on pasture). The total fatty acid content of all muscles studied was less than 35 g kg(-1). The percentages in total fatty acids of all n-3 PUFA were higher in muscles from steers fed grass than from bulls fed concentrates whereas all n-6 PUFA were higher in the latter. The gluteobiceps muscle contained the largest amounts of fatty acids including PUFA and the m. longissimus dorsi the least amounts of PUFA in beef and lamb, and m. longissimus contained the lowest percentages of PUFA. Arachidonic acid was the major fatty acid in the C(20) + C(22) PUFA in beef from both production systems with twice as much in muscles from bulls fed concentrates. The P:S ratios were higher in the latter animals, range 0.21-0.34 compared with 0.08-0.13 in the steers fed grass. However, the n6:n-3 ratio was much less desirable in the bulls, 15.6-20.1 compared with 2.0-2.3 in the steers fed grass. These effects of production system in ruminants are larger than previously reported. Lamb muscle P:S ratios resembled those in grass-fed beef but the n-6:n-3 ratios were lower. The percentage of trans unsaturated 18:1 fatty acids was similar in both cattle production systems but lamb muscles contained twice as much as beef. Although the concentrations of the C(20) and C(22) PUFA are much lower than in fish, maintaining high n-3 levels in ruminant meats through grass feeding may be advantageous in human nutrition since meat is more widely consumed.

Changes in the levels of growth hormones, insulin, cortisol, thyroxine and somatomedin-C/IGF-1, with increasing gestational age in the fetal pig, and the effect of thyroidectomy in utero.

1. Blood samples were taken from 30 chronically catheterized pig fetuses in utero. Levels of growth hormone, insulin, cortisol, thyroxine and somatomedin-C/IGF-1 were measured in the plasma of intact fetuses and the plasma of thyroidectomized fetuses at various gestational ages during the latter part of pregnancy. 2. Growth hormone levels were high (mean +/- SEM: 83 +/- 9 ng/ml and remained constant throughout this period. 3. Insulin levels were also constant and ranged between 4 and 14 mU/l. 4. Cortisol levels showed a general increase from 400 nmol/l at 97 days to 1200 nmol/l at term and this increase was not affected by thyroidectomy. 5. IGF-1 levels were lower than in the sows (48.0 +/- 3.0 ng/ml) and did not change throughout this period. 6. Thyroxine levels were also unchanged at about 92 +/- 4 nmol/l. 7. Thyroidectomy resulted in lower (P less than 0.001) thyroxine levels (28 +/- 3 nmol/l) but had no effect on the levels of any other hormone.

Changes in the levels of growth hormone, insulin, somatomedin C and thyroxine in sheep during immunization against somatostatin.

The time-related changes in the plasma levels of growth hormone, insulin, somatomedin C and thyroxine following immunization against somatostatin, have been examined in sheep. In both the treated and control lambs there was a significant increase (P less than 0.01) in growth hormone levels with time from the start of the study (at three weeks of age) through until 13 weeks of age. This increase was mirrored by increasing somatomedin C (IGF-1) levels (P less than 0.001). Thyroxine levels did not change during the period of the study. Immunization against somatostatin did not produce any significant difference between treatment groups or between sexes in the levels of growth hormone or thyroxine. However, IGF-1 level were significantly increased (P less than 0.01) by the treatment in both sexes. The changes in the levels of insulin were complicated by a marked difference between the control groups; the control females being significantly different (P less than 0.001) from all the other animals.

Stimulation of fetal growth associated with decreased maternal plasma oestrogen levels.

Reduced maternal and fetal plasma oestrogen levels were produced in rats by daily administration of an LH-RH agonist (obtained from IMPERIAL CHEMICAL INDUSTRIES; ICI product 118630) to the dams from day 12 of gestation. Fetuses from the treated mothers were significantly heavier and longer at delivery on day 21 of gestation than fetuses from control mothers. Placental weights were also greater in the treated group.

Immuno-neutralization of maternal plasma oestradiol stimulates fetal growth in rats.

On day 12 of pregnancy, 7 rats were injected with 2 ml of an anti-oestradiol antiserum a quantity capable of binding 2.4 micrograms oestradiol. Seven further (control) rats were injected with an antiserum raised against human serum globulin. After sacrifice on day 21 of pregnancy, the fetuses from treated rats showed an increase in both placental weight (0.851 +/- 0.023 g, n = 98 vs 0.752 +/- 0.019 g, n = 97) and fetal weight (4.446 +/- 0.426 g, n = 98 vs 3.403 +/- 0.211 g, n = 97). There was no significant difference in protein, DNA and RNA contents between the fetuses from treated mothers and those from control mothers. This experiment confirms that oestrogens may play a role in fetal weight gain.

The effect of immunization against somatostatin on growth rates and growth hormone secretion in the chicken.

The effect of both active passive immunization against somatostatin on growth rate and growth hormone levels was studied in chickens. Passive immunization against somatostatin by administration of antiserum had no effect on rate of growth of chickens and no persistent effect on circulating growth hormone (GH) levels. In acute experiments, administration of anti-somatostatin serum caused a marked elevation of GH levels in chickens at both 4 and 8 weeks of age, but the relative stimulation was greater in the older birds. Active immunization against somatostatin significantly stimulated growth rate in chickens, but was not shown to have a clear effect on circulating GH levels. These data suggest that somatostatin control over GH secretion may not be fully developed in the chicken at 4 weeks of age, but that immuno-neutralization of somatostatin can produce an increase rate of growth in chickens similar to that seen in mammals.

Somatostatin antagonist analogue stimulates growth in rats.

The somatostatin antagonist analogue cyclo Ahep-Phe-D-Trp-Lys-Thr(Bzl) stimulates growth in young female rats, while somatostatin itself has only equivocal effects on inhibiting growth.