Conjugated linoleic acid depresses the delta9 desaturase index and stearoyl coenzyme A desaturase enzyme activity in porcine subcutaneous adipose tissue

Conjugated linoleic acid (CLA) has been shown to have an effect on subcutaneous fatty acid composition and has been reported to decrease stearoyl coenzyme A desaturase (SCD) activity by decreasing mRNA expression and(or) catalytic activity in rodents and rodent cell lines. This investigation was designed to study the effects of CLA, corn oil, or beef tallow supplementation on s.c. adipose tissue fatty acid composition, adiposity, SCD enzyme activity, and the delta9 desaturase index in piglets. Eighteen crossbred barrows 16 to 18 d of age were adapted to diet for 1 wk and then assigned randomly to one of three treatments: 1.5% added CLA, 1.5% added corn oil, or 1.5% added beef tallow. Barrows were penned individually and fed the supplemental oils for 35 d (to 25.6 +/- 0.6 kg BW). Subcutaneous adipose tissue samples were obtained after slaughter. Fatty acid composition of the s.c. adipose tissue differed for each fatty acid measured due to diet with the exception of 18:3. The concentrations of CLA trans-10, cis-12 and cis-9, trans-11 were elevated from nondetectable to 1.62 and 2.52 g/100 g lipid, respectively (P < 0.001 for both isomers). Conjugated linoleic acid decreased the delta9 desaturase index (P < 0.01) and SCD enzyme activity, expressed as nanomoles of palmitate converted to palmitoleate/(7 min x g of tissue) (P = 0.075) and nanomoles of palmitate converted to palmitoleate/(7 min 105 cells) (P= 0.056). Tallow-fed pigs had a greater proportion of large adipocytes (> 700 pL) and the greatest SCD activity. These data provide the first direct evidence that dietary CLA depresses SCD enzyme activity in porcine adipose tissue, which may in part be responsible for the depression of adiposity by CLA observed by others in market weight pigs.     

Postnatal development of glucose transporter proteins in bovine skeletal muscle and adipose tissue.

Facilitated diffusion of glucose across the plasma membrane is mediated by a family of glucose transporter (GLUT). GLUT1 is ubiquitously present in all tissues and involved in cellular glucose uptake, while GLUT4 plays a key role in cellular glucose uptake stimulated by insulin in skeletal muscles and adipose tissue. To examine the postnatal change in the GLUTs of ruminants, the protein levels of GLUT1 and GLUT4 were measured by Western blot analysis of skeletal muscles, adipose tissue and brain of Holstein male calves aged from 0 to 12 months. Analysis of rumen short chain volatile fatty acids revealed that rumen fermentation increased around 2-3 months old. The GLUT1 level did not change in all tissues examined during the postnatal period, while the GLUT4 levels in skeletal muscle and subcutaneous adipose tissue decreased gradually, and at 12 month old, it was about 40% of those seen at 0 month old. These results are contrast to those in non-ruminant species, in which GLUT4 increases during postnatal development, and may be related to the insulin-resistance seen in adult ruminants.     

Stearoyl-coenzyme A desaturase gene expression during growth in adipose tissue from obese and crossbred pigs.

This investigation addressed the hypothesis that, as a marker of adipocyte differentiation, stearoyl-coenzyme A desaturase (SCD) gene expression would be greater during growth in obese pigs than in crossbred, contemporary pigs. Suckled pigs from a single litter were removed from the sow for sampling at 0, 3, 10, and 17 d. The number of litters at 0, 3, 10, and 17 d of age was zero, two, three, and three (obese sows) and four, two, three, and three (crossbred sows), respectively. Postweaning pigs were removed from the sow at 14 d of age. One set of postweaning pigs was fed a high-fat, milk-based diet from d 28 to 49; pigs were killed on d 28 and 49 for sampling. The grain-fed pigs were switched to a pelleted, grain-based grower diet at d 28, and samples were obtained at 31, 35, or 49 d of age. Adipose tissue from all pigs in a litter for preweaning and postweaning pigs was pooled for the measurement of cellularity and SCD mRNA. There were significant genetic and age effects for adipocyte diameter and volume; overall, adipocytes from obese pigs were larger than those from crossbred pigs. Stearoyl-coenzyme A desaturase mRNA was barely detectable at 0 d of age and increased (P < .01) by 20-fold by 49 d of age. There was a significant genetic x age interaction (P = .026); there was more SCD mRNA in adipose tissue from obese pigs than in that from crossbred pigs during the suckling period, whereas crossbred pigs exhibited greater SCD gene expression than obese pigs during the postweaning period. The lesser SCD gene expression in postweaning obese pigs was caused by a strong depression in SCD gene expression in the grain-fed obese pigs. The data indicate that SCD gene expression provides a marker for terminal differentiation, especially in preweaning pigs. Furthermore, these results provide additional evidence that SCD gene expression is up-regulated by diets high in saturated fatty acids.     

Subcutaneous and intramuscular adipose tissue stearoyl-coenzyme A desaturase gene expression and fatty acid composition in calf- and yearling-fed Angus steers

We proposed that stearoyl-CoA desaturase (SCD) activity dictates fatty acid composition of adipose tissue and muscle in beef cattle, regardless of ruminal or hepatic fatty acid hydrogenation or desaturation. Twelve Angus steers were assigned to a calf-fed (CF) group and slaughtered at weaning (8 mo of age; n=4), 12 mo of age (n=4), or 16 mo of age (n=4). Twelve steers were assigned to a yearling-fed (YF) group and slaughtered at 12 mo of age (n=4), 16 mo of age (n=4), and 17.5 mo of age (n=4; 525 kg, market weight). Data were analyzed based on time on the corn-based finishing diet, with terminal age as a covariate, and orthogonal polynomial contrasts were tested on the main effects of treatment group and time on the finishing diet. Fatty acids from duodenal digesta, plasma, liver, LM, and subcutaneous and intramuscular adipose tissue were measured, and SCD gene expression was measured in intramuscular and subcutaneous adipose tissues. In duodenal digesta, palmitic and linoleic acids increased by 100% over the sampling period, α-linolenic acid decreased over the sampling period, and trans-vaccenic acid was greater in YF than in CF steers (all P < 0.01). The proportion of α-linolenic acid decreased over time in all tissues, including liver. The SCD index (ratio of SCD fatty acid products to SCD fatty acid substrates) increased over time in LM and in intramuscular and subcutaneous adipose tissues. The SCD:glyceraldehyde 3-phosphate dehydrogenase mRNA ratio was virtually undetectable at the initial sampling periods in subcutaneous adipose tissue of YF and CF steers, and it increased over time (P < 0.01). The SCD index and SCD:glyceraldehyde 3-phosphate dehydrogenase ratio were greater in intramuscular adipose tissue of CF steers than in that of YF steers. The SCD index did not change over time in liver and decreased over time in duodenal digesta. We conclude that, unlike essential fatty acids, the SFA and MUFA composition of adipose tissue is regulated by adipose tissue fatty acid desaturation, with little contribution from hepatic or duodenal fatty acids.     

Ovine adipose tissue monounsaturated fat content is correlated to depot-specific expression of the stearoyl-CoA desaturase gene

The basis for the variation in fatty acid composition in different ovine adipose tissue depots was investigated. The proportion of stearic (C18:0) and oleic (C18:1) acids vary in a site-specific fashion; abdominal depots (omental and perirenal) contain relatively more C18:0 than C18:1, and carcass depots, especially sternum, have a markedly higher proportion of C18:1. Additionally, expression of a number of lipogenic enzyme genes (stearoyl-CoA desaturase [SCD], acetyl-CoA carboxylase-alpha [ACC-alpha], lipoprotein lipase [LPL]) and the cytoskeletal protein gene alpha-tubulin vary among depots, although the pattern of variation differs for each mRNA. When these expression data were related to the mean cell volume of adipocytes pooled from all depots, a significant pattern emerged: expression of the ACC-alpha, LPL, and alpha-tubulin genes was highly correlated with the size of adipocytes. In contrast, when the expression of SCD mRNA was assessed as a function of mean cell volume, two populations of adipocytes emerged: no significant correlation was found between the expression of SCD mRNA per adipocyte and mean cell volume for the abdominal depots, although a highly significant correlation was observed between SCD gene expression and mean cell volume for the carcass and epicardial depots. Similarly, a highly significant correlation was found for the amount of C18:1 per adipocyte and the abundance of SCD mRNA per adipocyte for the carcass and epicardial depots, whereas no significant correlation was observed for these traits for the omental and perirenal depots. Thus, the SCD gene seems to be regulated in a depot-specific fashion and in a manner distinct from that of the ACC and LPL genes.     

Size and lipolytic capacity of bovine adipocytes from subcutaneous and internal adipose tissue

Adipose tissue samples were taken from five dairy cows in early lactation. Various external and internal sites were chosen, and after isolation of the adipocytes, their size and lipolytic capacity were measured. It was found that cells from all the sites showed high lipolytic activity, although there was a four-fold difference between cells from perirenal fat and those from omental fat, which showed the highest activity. It was not possible to detect any relationship between diameter and lipolytic capacity of the adipocytes.     

Effect of breed on fatty acid composition and stearoyl-CoA desaturase protein expression in the Semimembranosus muscle and subcutaneous adipose tissue of cattle

The present study investigated (i) the effect of breed on the expression of stearoyl-CoA desaturase (SCD) protein and fatty acid composition in Semimembranosus muscle and subcutaneous adipose tissue of beef cattle and (ii) the relationship between SCD expression, cis-9, trans-11 conjugated linoleic acid (CLA) content, and monounsaturated fatty acid (MUFA) level. The study was conducted on the following breeds: Longhorn (L), Charolais cross with Holstein–Friesian (CX), Hereford (H), Belted Galloway (BG) and Beef Shorthorn (BS). Significant breed differences in the total fatty acid content, saturated fatty acid (SFA) level, MUFA and n−3 PUFA content were observed in subcutaneous adipose tissue but not in muscle. In the case of CLA, the breed differences were observed in both muscle and subcutaneous adipose tissue, with the highest level in L and the lowest level in H. In the case of subcutaneous adipose tissue, the breed with the highest CLA content (L) also had the highest SCD protein expression. The breed-specific pattern of SCD expression in subcutaneous adipose tissue was similar to the breed-specific pattern of one of the products of an SCD-catalysed reaction, C16:1 (BS < BG < H < CX < L). It has been concluded that (i) the mechanisms regulating SCD protein expression and CLA level in beef cattle are tissue-specific; (ii) breed-specific variations in SCD expression might contribute to breed variations in MUFA and CLA content in subcutaneous adipose tissue but not in Semimembranosus muscle.     

Lipogenesis in acute and 48-hour cultures of bovine intramuscular and subcutaneous adipose tissue explants

In this study, the interactions among breed of cattle, adipose tissue site and specific incubation conditions were investigated. Subcutaneous and i.m. adipose tissues were obtained from 10 Angus and 9 Santa Gertrudis steers immediately postmortem. Adipose tissue explants were incubated acutely for 2 h immediately at slaughter or after being cultured 48 h with or without 1 mU/ml insulin and 30 mg/ml bovine serum albumin; the incorporation of 14C-labeled acetate and glucose (5 mM, plus 5 mM unlabeled lactate) into lipid fractions was measured. AT the same chronological age, Angus steers had a more youthful lean maturity score, higher USDA marbling score and higher USDA quality grade (P less than .05) than did carcasses from Santa Gertrudis steers. The lower marbling score of the Santa Gertrudis steers was paralleled by smaller i.m. adipocytes (P less than .05) relative to Angus steers. Pentose cycle reductase and NADP-malate dehydrogenase activities were greater in Angus i.m. adipose tissue than in Santa Gertrudis i.m. adipose tissue, which would provide more reducing equivalents (NADPH) and glycerol for fatty acid biosynthesis and triacylglycerol esterification. Correspondingly, Angus i.m. adipose tissue exhibited a greater rate of lipogenesis from acetate and glucose (P less than .05) than did Santa Gertrudis i.m. adipose tissue in acute incubations. The presence of insulin resulted in higher rates of lipogenesis from acetate in Angus s.c. adipose tissue than in Santa Gertrudis s.c. adipose tissue after 48 h of explant culture. These data indicate that i.m. and s.c. adipose tissues exhibit aspects of lipid metabolism unique to each tissue and suggest that breed-related differences in adipose tissues may explain the divergent responses to insulin observed in different laboratories.     

Fatty acid elongation and desaturation enzyme activities of bovine liver and subcutaneous adipose tissue microsomes

Assay conditions were established for the fatty acid elongation and the delta 9 desaturase enzyme systems of bovine liver and adipose tissue microsomes; rat liver microsomes were used as a reference. Overall fatty acid elongation was determined by measuring the incorporation of [2-14C]malonyl-coenzyme A (CoA) to 14C-labeled stearate. Rat liver elongation activity was .50 +/- .02 nmol.min-1.mg protein-1; bovine liver microsomal elongation activity was substantially lower (P less than .05), with a mean value of .15 +/- .02 nmol.min-1.mg protein-1. The elongation activity of bovine s.c. adipose tissue microsomes (.42 +/- .10 nmol.min-1.mg protein-1) was not different (P greater than .05) from the activity observed in rat liver microsomes. To determine the fatty acid delta 9 desaturase activity, microsomes were incubated in the presence of [1-14C]stearoyl-CoA and nicotinamide adenine dinucleotide (reduced form) (NADH), and the production of radioactively labeled oleate was quantified. Microsomal delta 9 desaturase activity was similar in rat liver and bovine s.c. adipose tissue microsomes with rates of .15 +/- .04 and .21 +/- .05 nmol.min-1.mg protein-1, respectively. However, no desaturase activity was detected in bovine liver microsomes, indicating that the liver is not a major site of oleate synthesis in this species. To investigate differences in fatty acid metabolism relative to breed type, eight Angus and seven Braford heifers were slaughtered at approximately 12 mo of age. Subcutaneous fat thickness over the 12th-13th thoracic vertebrae was greater in the Angus heifers than in the Braford heifers. However, no differences (P greater than .05) were observed in mean adipocyte size or number of cells per gram of adipose tissue between the Angus and Braford heifers. Similarly, there were no significant differences between the Angus and Braford s.c. adipose tissues for microsomal fatty acid elongation or delta 9 desaturation, or for nicotinamide adenine dinucleotide phosphate (NADP)-malate dehydrogenase, fatty acid synthetase, or the pentose cycle reductases. The inability of bovine liver to convert stearate to oleate was in agreement with the fatty acid composition of the liver lipid, which had a smaller percentage of oleate and a higher percentage of stearate than s.c. adipose tissue.     

Adipogenic differentiation state-specific gene expression as related to bovine carcass adiposity

Genetic regulation of the site of fat deposition is not well defined. The objective of this study was to investigate adipogenic differentiation state-specific gene expression in feedlot cattle (>75% Angus; <25% Simmental parentage) of varying adipose accretion patterns. Four groups of 4 steers were selected via ultrasound for the following adipose tissue characteristics: low subcutaneous-low intramuscular (LSQ-LIM), low subcutaneous-high intramuscular (LSQ-HIM), high subcutaneous-low intramuscular (HSQ-LIM), and high subcutaneous-high intramuscular (HSQ-HIM). Adipose tissue from the subcutaneous (SQ) and intramuscular (IM) depots was collected at slaughter. The relative expression of adipogenic genes was evaluated using quantitative PCR. Data were analyzed using the mixed model of SAS, and gene expression data were analyzed using covariate analysis with ribosomal protein L19 as the covariate. No interactions (P > 0.10) were observed between IM and SQ adipose tissue depots for any of the variables measured. Therefore, only the main effects of high and low accretion within a depot and the effects of depot are reported. Steers with LIM had smaller mean diameter IM adipocytes (P < 0.001) than HIM steers. Steers with HSQ had larger mean diameter SQ adipocytes (P < 0.001) than LSQ. However, there were no differences (P > 0.10) in any of the genes measured due to high or low adipose accretion. Preadipogenic delta-like kinase1 mRNA was greater in the IM than the SQ adipose tissue; conversely, differentiating and adipogenic genes, lipoprotein lipase, PPARγ, fatty acid synthetase, and fatty acid binding protein 4 were greater (P < 0.001) in the SQ than the IM depot. Intramuscular adipocytes were smaller than SQ adipocytes and had greater expression of the preadipogenic gene, indicating that more hyperplasia was occurring. Meanwhile, SQ adipose tissue contained much larger (P < 0.001) adipocytes that had a greater expression (P < 0.001) of differentiating and adipogenic genes than did the IM adipose tissue, indicating more cells were undergoing differentiation and hypertrophy. Adipogenic differentiation state-specific gene expression was not different in cattle with various phenotypes, but adipogenesis in the SQ and IM adipose tissues seems to occur independently.     

The development and growth of subcutaneous adipose tissue in various production types of domestic fowl

Hyperplasia and hypertrophy of fat cells of the subcutaneous adipose tissue were studied in different production types of fowl in the post-incubation period. The cocks and hens of laying type were found to have fewer and smaller fat cells than the birds of broiler type. The highest hyperplasia was recorded in the first nine weeks of age, then followed a decrease, lasting until the 25th week. Hypertrophy continued step by step throughout the period of study and increased when hyperplasia decreased. The differences between sexes increase during sexual maturation: in the hens the hypertrophy of cells increases and hyperplasia does not decrease so quickly as in the cocks. Before sexual maturity, hypertrophy as well as hyperplasia are somewhat higher in the cocks.     

日粮营养对动物脂肪组织基因表达的影响

脂肪组织是一个强大的分泌器官,它能分泌许多与能量、脂肪代谢相关的酶、激素等.调控能量代谢和脂肪组织生长.本文综述了日粮对动物脂肪组织中基因表达作用的研究状况.并阐述了营养成分对这些基因上下游表达的作用机制.     

Adipogenic gene expression and fatty acid composition in subcutaneous adipose tissue depots of Angus steers between 9 and 16 months of age

We have demonstrated that among carcass adipose tissue depots, brisket subcutaneous adipose tissue contains the greatest concentration of MUFA and lowest concentration of SFA. Therefore, we hypothesized that brisket subcutaneous adipose tissue depots would exhibit greater adipogenic gene expression over time than other major subcutaneous adipose tissue depots. Four Angus steers, each at 9, 12, 14, and 16 mo of age, were harvested and fresh subcutaneous adipose tissue samples were collected from over the brisket, chuck, rib, loin, sirloin, round, flank, and plate. Relative gene expression for C/EBPβ, PPARγ, carnitine palmitoyltransferase-1 beta (CPT-1β), stearoyl-coenzyme A desaturase (SCD), AMP-activated protein kinase alpha (AMPKα), and G-coupled protein receptor 43 (GPR43) was analyzed by quantitative real-time PCR. Expression of C/EBPβ, PPARγ, and CPT-1β was greatest at 12 to 14 mo of age (all P < 0.0001) and declined to very low abundance by 16 mo of age in all depots. Expression of PPARγ and CPT-1β was greater (P < 0.03) in flank, rib, and sirloin subcutaneous adipose tissues than in brisket and round adipose tissues. The expression of the SCD gene did not differ among the 4 age groups (P = 0.95). The palmitoleic:stearic acid ratio (an estimate of SCD activity) was greater (P < 0.001) in the subcutaneous adipose tissues from brisket, plate, and round than in the loin, rib, and sirloin. Conversely, subcutaneous adipose tissue from the loin, rib, and sirloin had greater (P < 0.001) SCD gene expression than the brisket, plate, and round. In general, subcutaneous adipose tissues with the highest concentration of MUFA and least SFA consistently exhibited the least SCD gene expression and adipogenic gene expression. We conclude that MUFA in the brisket and other depots with large SCD indices were deposited before 9 mo of age, during a time when the subcutaneous adipocytes were highly differentiated.     

Lipogenesis and stearoyl-CoA desaturase gene expression and enzyme activity in adipose tissue of short- and long-fed Angus and Wagyu steers fed corn- or hay-based diets

Angus and Wagyu steers consuming high-roughage diets exhibit large differences in adipose tissue fatty acid composition, but there are no differences in terminal measures of stearoyl-CoA desaturase (SCD) activity or gene expression. Also, adipose tissue lipids of cattle fed corn-based diets have greater MUFA:SFA ratios than cattle fed hay-based diets. We hypothesized that any changes in SCD gene expression and activity would precede similar changes in adipose tissue lipogenesis between short- and long-fed endpoints. Furthermore, changes in SCD activity and gene expression between production endpoints would differ between corn- and hay-fed steers and between Wagyu and Angus steers. Angus (n = 8) and Wagyu (n = 8) steers were fed a corn-based diet for 8 mo (short-fed; 16 mo of age) or 16 mo (long-fed; 24 mo of age), whereas another group of Angus (n = 8) and Wagyu (n = 8) steers was fed a hay-based diet for 12 mo (short-fed; 20 mo of age) or 20 mo (long-fed; 28 mo of age) to match the end point BW of the corn-fed steers. Acetate incorporation into lipids in vitro was greater (P < 0.01) in corn-fed steers than in hay-fed steers and tended (P = 0.06) to be greater in Wagyu than in Angus s.c. adipose tissue because the rate in Wagyu was twice that of Angus adipose tissue in the corn-fed, short-fed steers. There were diet x end point interactions for lipogenesis in i.m. and s.c. adipose tissues (both P < 0.01) because lipogenesis was 60 to 90% lower in the long-fed cattle than in short-fed cattle fed the corn-based diet. The greatest SCD enzyme activity in Angus s.c. adipose tissue was observed at 24 mo of age (corn-based diet), but activity in Wagyu adipose tissue was greatest at 28 mo of age (hay-based diet; breed x diet x end point interaction, P = 0.08). For short- vs. long-fed endpoints in Angus, s.c. adipose tissue SCD activity was less (hay diet) or the same (corn diet). Conversely, SCD gene expression was greatest in long-fed Wagyu steers fed the hay- or corn-based diets (breed x end point interaction; P < 0.01). Contrary to our hypotheses, SCD activity increased over time, whereas lipogenesis from acetate decreased. However, the developmental pattern of SCD gene expression and activity differed markedly between hay-fed Angus and Wagyu adipose tissues, which may explain the differences in the MUFA:SFA ratios observed in adipose tissues from these cattle.     

Coordinate regulation of ovine adipose tissue gene expression by propionate

The current study examined the acute effects of intravenous propionate infusion on plasma hormones and metabolites and the expression of adipose tissue lipogenic genes. Four yearling rams were assigned to one oftwo groups (saline or propionate infusion) in a crossover design. All sheep were cannulated in both jugular veins and infused with 1.2 M propionate at a rate of 64 micromol x mix(-1) x kg BW(-1) for 30 min. Blood samples were collected at -10, 0, 5, 10, 20, 30, 60, and 120 min after initiation of infusion. Subcutaneous adipose tissue biopsies were obtained from the tailhead at 0 and 2 h after propionate infusion and analyzed for gene expressions of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor gamma, leptin, and uncoupling protein-2 using a nonisotopic ribonuclease protection assay. The partial cDNA of the enoyl reductase region of ovine fatty acid synthase was cloned and sequenced from s.c. adipose tissue of sheep. The deduced amino acid sequence (210 amino acids) was 86% identical to human, 88% identical to rat, 88% identical to mouse, and 72% identical to chicken. Plasma glucose and insulin concentrations abruptly increased 5 min after beginning propionate infusion and further increased up until 30 min but were unaffected in saline-infused sheep (P < 0.05). Plasma concentration of NEFA decreased (P < 0.05) during propionate infusion, whereas IGF-I levels were unaltered. The amounts of lipoprotein lipase, acetyl CoA carboxylase, fatty acid synthase, peroxisome proliferator-activated receptor gamma, and leptin mRNA increased (P < 0.05) in s.c. adipose tissue of propionate-infused sheep compared with those of saline-infused sheep. However, uncoupling protein-2 mRNA decreased (P < 0.05) in propionate-infused sheep. This study demonstrates that an acute nutrient challenge, in the form of i.v. propionate, can stimulate or inhibit the expression of various adipose tissue genes involved with lipogenesis and adipose tissue metabolism.     

Porcine somatotropin decreases acetyl-CoA carboxylase gene expression in porcine adipose tissue

Crossbred barrows were treated daily with porcine somatotropin (pST; 4 mg/d) from 79 to 127 kg BW to determine whether pST regulates the activity and gene expression of adipose tissue acetyl-CoA carboxylase (ACC), the rate limiting enzyme in de novo fatty acid synthesis. Administration of pST reduced ACC enzyme activity, protein content, and mRNA abundance in adipose tissue by 40 to 50%. When comparisons were made among all pigs, ACC enzyme activity and mRNA abundance were closely associated (r² = .94). In summary, our results indicate that pST decreases ACC enzyme activity and that this is associated with a significant reduction in ACC mRNA abundance. We speculate that decreased ACC enzyme activity results from a reduction in ACC protein and that this occurs because pST reduces the abundance of mRNA available for translation.     

Influence of bovine growth hormone and growth hormone-releasing factor on messenger RNA abundance of lipoprotein lipase and stearoyl-CoA desaturase in the bovine mammary gland and adipose tissue

Our objective was to determine the influence of bovine growth hormone (bGH) and bovine growth hormone-releasing factor (bGRF) administration on the mRNA abundance of lipoprotein lipase (LpL) and stearoyl-CoA desaturase (SCD). Primiparous Holstein cows received bGH, bGRF, or no treatment from 118 to 181+/-1 d postpartum. We hypothesized that bGH and bGRF treatment would increase the mRNA abundance of both SCD and LpL in the mammary gland with a corresponding reduction in adipose tissue. Milk yield significantly increased but milk fat percentage did not change as a result of bGH or bGRF treatment. Short-, medium-, and long-chain fatty acid concentrations in milk were not affected by either bGH or bGRF treatments, with the exception of a modest, but significant, increase in C16:1 and C18:1 following bGH treatment. Analysis was conducted on the genes encoding LpL (E.C. 3.3.1.34), a key enzyme involved in the uptake of fatty acids into tissues, and SCD (E.C. 1.14.99.5), which is the enzyme responsible for introducing delta9 double bonds in fatty acids of 16 and 18 carbons in length. In adipose tissue, treatment with bGH and bGRF reduced the mRNA abundance of LpL to 14.6 and 25.7% respectively, of that observed for control animals. Similarly, these treatments reduced the SCD mRNA abundance to undetectable levels in adipose tissue. In mammary gland, bGH and bGRF had no significant impact on LpL mRNA abundance. Bovine GH did not significantly affect SCD mRNA abundance in the mammary gland, and bGRF reduced SCD mRNA abundance. From this study to examine the role of bGH and bGRF on the expression of the genes encoding these key lipogenic enzymes in cattle, we conclude that the increased substrate required for enhanced milk fatty acid yield may have been provided through redirection of nutrients to the mammary gland away from adipose tissue and through overall increased metabolism in the mammary gland.