Characterization of metabolic changes during a protocol for inducing lactation ketosis in dairy cows

During the 5 wk immediately after parturition, five high producing cows that were overfed prepartum completed a protocol for inducement of ketosis. By 12 d postpartum, hepatic glycogen decreased by 75% and hepatic triglyceride, beta-hydroxybutyrate, and acetoacetate increased by 6, 4, and 2.5 times. The protocol, initiated at 2 wk postpartum, consisted of a 15 to 20% decrease from ad libitum feed intake plus dietary supplementation with 1,3-butanediol, a ketogenic substrate. Severity of the ketotic state increased gradually, and four cows developed clinical signs of ketosis at an average of 36 d postpartum. Glycogen was 90% depleted, and triglycerides, beta-hydroxybutyrate, and acetoacetate concentrations in liver were increased to 10, 10, and 15 times above average prepartum concentrations. In plasma, beta-hydroxybutyrate increased and glucose decreased. Plasma insulin exhibited an initial postpartal decrease (40%) but then was stable at that concentration through 36 d. After treatment for ketosis, glucose and insulin concentrations of plasma were greater than prepartal concentrations. Results indicate that a relatively simple protocol of prolonged energy deficit combined with an influx of ketone body precursors can induce experimental lactation ketosis in overfed cows. The protocol should be a valuable tool for ketosis research.

Cholesterol transport and uptake in miniature swine fed vegetable and animal fats and proteins. 1. Plasma lipoproteins and LDL clearance

In a 2 X 2 factorial arrangement, miniature pigs were fed four diets containing vegetable protein/fat (soybean) and animal protein (egg white)/fat (beef tallow) to demonstrate the effects of protein and fat source on total plasma cholesterol, lipoprotein distribution, low density lipoprotein (LDL) composition, and plasma clearance of LDL-cholesterol and protein. Beef tallow consumption resulted in greater plasma cholesterol concentration, decreased LDL-cholesterol concentration, and a lower LDL-cholesterol to LDL-protein ratio than did consumption of soybean oil. High density lipoprotein (HDL)-cholesterol concentration was increased by beef tallow consumption. Cholesterol percentage by weight in LDL was significantly greater in pigs consuming soybean oil than those consuming beef tallow. Percentages by weight of protein, triglyceride and phospholipid in LDL were not significantly different in any group. Dietary protein source had no significant effect on total plasma cholesterol concentration, lipoprotein concentration or LDL composition. Egg white consumption decreased fractional catabolic rate and irreversible loss of LDL-cholesterol and LDL-protein when compared with consumption of soy protein. Dietary fat source had no consistent effect on LDL clearance from plasma. Dietary fat and protein seemed to influence lipoprotein metabolism by different mechanisms. Fat source altered lipoprotein concentration and LDL composition, whereas protein source affected the removal rate of LDL from plasma.

Cholesterol transport and uptake in miniature swine fed vegetable and animal fats and proteins. 2. LDL uptake and cholesterol distribution in tissues

In a 2 X 2 factorial arrangement, miniature pigs were fed four diets containing vegetable protein/fat (soybean) and animal protein (egg white)/fat (beef tallow) to demonstrate the effects of protein and fat source on tissue cholesterol concentrations, uptake of intact low density lipoproteins (LDL) and free cholesterol exchange from LDL to tissues. Soybean oil feeding, compared with beef tallow feeding, resulted in greater concentrations of cholesterol in aorta, heart, and large and small intestines. Similar trends were seen in liver, adipose tissue and skeletal muscle. Dietary protein source had little or no effect on tissue cholesterol concentrations. Uptake of intact LDL, as measured by using [14C]sucrose-LDL, tended to be greater in pigs fed soybean oil or soy protein. Net exchange of free cholesterol from LDL, as measured with [3H]cholesterol, tended to be greater when vegetable products were fed. Relative contributions of whole tissues to total uptake by either mechanism were not influenced by diet. Mechanisms in addition to uptake of cholesterol from LDL seem to be involved in the greater accumulation of tissue cholesterol resulting from polyunsaturated fat feeding.

Changes in hormone and metabolite concentrations in plasma of steers during a prolonged fast

Two Brown Swiss and two Holstein steers, average weight of 226 kg, were fasted 8 d. Two days before the fast, jugular vein catheters were installed. Blood samples were collected every 15 min from 0800 to 1400 h on d 0, 2, 5 and 8 of fasting. Plasma from each sample was analyzed for concentrations of growth hormone, and from selected samples for insulin, glucagon, glucose, beta-hydroxybutyrate, free fatty acids, urea N and glycerol. Both growth hormone and insulin concentrations decreased by d 2 of the fast and remained at that concentration. Glucagon, however, remained constant. From d 0 to 2, concentrations of beta-hydroxybutyrate, free fatty acids and glycerol increased but then changed little for d 5 and 8. From d 0 to 2, glucose decreased and urea N increased. In contrast to the other metabolites, glucose and urea N concentrations stabilized between 3 and 5 d of fasting. The ratio of growth hormone to insulin decreased threefold and the ratio of glucagon to insulin decreased fivefold from d 0 to 2; both ratios remained constant during the rest of the fast. The data indicate that fasting cattle adapt by decreasing concentrations in plasma of growth hormone and insulin but not glucagon. These endocrine changes, therefore, seem responsible for greater rates of free fatty acid mobilization and glucose sparing during an energy deficit.

Effects of L-dopa supplementation on concentrations of brain catechols, dopamine receptor binding and the incidence of pale, soft and exudative meat in stress-susceptible pigs

The purpose of this research was to determine if chronic dietary L-DOPA supplementation will alter differentially the brain catechol concentrations, dopamine receptor binding (KD and Bmax) and the incidence of pale, soft and exudative (PSE) meat in stress-susceptible (SS) and stress-resistant (SR) pigs. Stress-susceptible and SR pigs were assigned randomly to these four groups: SS pigs as controls, SR pigs as controls, SS pigs with L-DOPA supplementation and SR pigs with L-DOPA supplementation. The experiment began when pigs weighed 23 kg and terminated when pigs weighed 95 kg. Anatomical brain structures removed at slaughter included hypothalamus, thalamus, cortex, cerebellum, olfactory bulb, caudate nucleus, putamen and substantia nigra. Concentrations of norepinephrine and dopamine were greater in the hypothalami of SS than of SR control pigs. The L-DOPA supplementation eliminated the strain differences of brain catecholamine concentrations. Pigs fed L-DOPA had greater concentrations of dihydroxyphenylacetic acid in six of the eight brain regions analyzed than the controls. Dopamine receptor binding (Bmax and KD) of spiroperidol was similar in all four groups of pigs. Pale, soft and exudative pork developed to the same extent in SS pigs with or without L-DOPA treatment. The results suggest that L-DOPA supplementation eliminates strain differences in brain catecholamine concentrations but does not alter PSE meat development or striatal dopamine receptor binding.

Effects of dietary vitamin D3 on concentrations of vitamin D and its metabolites in blood plasma and milk of dairy cows

To determine the effect of supplemental dietary vitamin D3 on concentration of vitamin D and its metabolites in milk, 20 Holstein cows were assigned to four groups and fed either 0, 10,000, 50,000, or 250,000 IU of vitamin D3/d beginning approximately 2 wk prepartum and continuing through wk 12 of lactation. Samples of blood plasma and milk were assayed for concentrations of vitamin D, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D. Only the daily dosage of 250,000 IU caused significant increases of concentrations of vitamin D or 25-hydroxyvitamin D in plasma. Concentrations of vitamin D and 25-hydroxyvitamin D in milk were approximately equal and averaged .2 ng/ml. Little 1,25-dihydroxyvitamin D and no 24,25-dihydroxyvitamin D could be detected in milk from any of the four treatment groups. Cows fed 250,000 IU of vitamin D3/d produced milk containing 54 IU of vitamin D activity per liter, whereas unsupplemented cows produced milk containing 17 IU/L. Oral supplementation with up to 250,000 IU of vitamin D3/d does not increase effectively vitamin D activity of milk.

Effects of beef, soy and conventional diets on body composition and plasma lipids of young pigs fed restricted or liberal amounts of diet

Effects were determined of restricted and liberal feeding of beef-based, soy-based and conventional diets on growth rate, nutrient absorption, body composition and plasma lipid and urea concentrations of young pigs. Beef and soy diets contained more fat (40-50% of calories vs. 8-9%) and cholesterol (0.09 vs. 0%) than did conventional diets; calorie and protein intakes were equal across diets. Beef-fed pigs had greater average daily gain and absorption of fat and gross energy than did conventionally fed pigs; soy-fed pigs had intermediate growth rates but the greatest absorption of fat and gross energy. With restricted intakes, percentage of body fat was greater in soy-fed pigs than in pigs fed a conventional diet or beef and with liberal feeding, greater in soy- and beef-fed pigs than in pigs provided with a conventional diet. Plasma free fatty acid, triglyceride and cholesterol concentrations were greater in soy- and beef-fed pigs than in conventionally fed pigs. These results indicate that absorption and subsequent partitioning of nutrients toward body fat are influenced by composition as well as the amount of diet consumed. Our results also demonstrate that the pig can successfully be fed diets resembling human diets (i.e., high fat) and because of its physiological similarities to humans our understanding of nutrition and lipid metabolism of humans may be advanced.

Adipose tissue growth and cellularity: changes in bovine adipocyte size and number

Forty crossbred steers of similar birth date and fed the same growing-finishing diet were used to study adipocyte changes in six fat depots during growth from 11 to 19 mo of age. Steers were slaughtered at 2-mo intervals. Adipose tissue samples were obtained from kidney, mesenteric and brisket fat and subcutaneous, intermuscular and intramuscular fat from the 10th to 12th rib section. The osmium tetroxide fixation technique was used for determination of cell size and number. Except for three brisket fat samples, distributions of adipocyte diameters from six different fat depots were monophasic during the age range considered in this study. At 17 mo of age, the mean adipocyte diameter, in decreasing order, was: kidney fat greater than mesenteric greater than subcutaneous greater than intermuscular greater than intramuscular greater than brisket fat. Fat deposition during growth to 19 mo of age occurred mainly by hypertrophy of adipocytes. An apparent cell hyperplasia occurred in the intramuscular fat depot from 11 to 15 mo and in the brisket fat depot after 15 mo of age. Based on cellularity characteristics, evidence exists to classify intramuscular and brisket fat depots as late-developing ones. Cell number/gram of intramuscular adipose tissue was a better predictor of marbling score than was fat cell diameter.

Effects of in vitro ronnel on metabolic activity in subcutaneous adipose tissue and skeletal muscle from steers

Ronnel [0,0-dimethyl 0-(2,4,5-trichlorophenyl) phosphorothioate] is an organophosphate pesticide with growth-promoting properties. Experiments were conducted to determine effects of ronnel on oxidation of and fatty acid synthesis from acetate and glucose as indices of metabolic activity in subcutaneous adipose tissue and skeletal muscle from 6-, 12- and 18-mo-old steers. Ronnel depressed metabolic activity in adipose tissue from 6- and 12-mo-old steers without concomitantly decreasing metabolic activity in skeletal muscle. Production of CO2 and fatty acids from acetate and glucose in tissues from 18-mo-old steers was influenced less by ronnel than in tissues from younger steers. Interactions of ronnel with thyroxine or growth hormone on acetate oxidation and conversion to fatty acids in adipose tissue also were investigated. Thyroxine increased acetate oxidation and decreased fatty acid synthesis. Ronnel interfered with the metabolic effects of thyroxine. Growth hormone, with or without ronnel, did not affect metabolic activity of adipose tissue. Ronnel seemingly alters the partitioning of acetate and glucose between major metabolic processes in adipose tissue and skeletal muscle.

Dietary calcium and vitamin D: risk factors in the development of atherosclerosis in young goats

Effects of supplemental dietary calcium and vitamin D on lipid distribution and aortic mineralization were examined in young goats. Twenty-four goats, 2-4 wk of age, were allotted one of four dietary treatments for a 20-wk period and fed a basal milk diet (Basal), a calcium-supplemented diet (Basal + Ca), a cholecalciferol-enriched diet (Basal + D3) or a diet with both calcium and cholecalciferol (Basal + Ca + D3). Goats in the Basal + Ca group had plasma cholesterol concentrations that were 16.6% of those of the Basal group. Percentage absorption and fecal excretion of total lipids were unaffected by dietary treatment. Generally, total lipid and cholesterol concentrations were unaltered in liver, other viscera and carcass tissues. Dietary cholecalciferol increased concentrations of cholesterol and total lipid in aortas, whereas dietary calcium decreased total lipids in aortas. Concentrations of calcium, magnesium and total ash were increased in aortas by dietary treatment, with a marked increase observed in the Basal + Ca + D3 group. Sudan IV and gross calcium staining in aortas revealed both lipid and mineral deposition that confirmed composition data. A high intake of vitamin D accompanied by excessive intake of calcium seems to accelerate the development of atherosclerosis. Supplemental calcium with normal amounts of vitamin D, however, is hypocholesterolemic and seems protective against the atherogenic process.

Inhibition by potential metabolic inhibitors of in vitro adipose tissue lipogenesis

To study the pathway of lactate utilization as a carbon source for fatty acid synthesis, the effect of (-)-hydroxycitrate, agaric acid, sodium oxamate, 2-n-butyl malonate and alpha-cyano-4-hydroxycinnamate on the rate of in vitro conversion of lactate, acetate and glucose to fatty acids was measured in bovine and rat adipose tissues. Sodium oxamate and hydroxycitrate caused less fatty acid to be synthesized from lactate in bovine adipose tissue. Hydroxycitrate depressed fatty acid synthesis from glucose in rat adipose tissue. alpha-Cyano-4-hydroxycinnamate was an effective inhibitor of lipogenesis from all substrates and may act as a specific inhibitor in adipose tissue. Although the inhibitors were absorbed poorly into adipocytes, the results indicate that conversion of lactate to fatty acids probably occurs by way of the citrate cleavage pathway.

Fatty acid biosynthesis in liver and adipose tissue from dogs

Production of CO2, fatty acids and glycerol from glucose and acetate was measured in slices of liver and adipose tissue taken from mature dogs. Acetate was the predominant carbon source for de novo fatty acid synthesis in both tissues. Fatty acid synthesis occurred at greater rates in adipose tissue than in liver. Glucose provided carbon for glycerol synthesis production in adipose tissue. Results support the concept that adipose tissue, and not liver, is the principal anatomical site for fatty acid synthesis in dogs.

An enzymatic assay for activity of lipoprotein lipase

An enzymatic method for the determination of the amount of free fatty acids released from triglyceride by lipoprotein lipase is described. The quantity of free fatty acids present in media before and after incubation is measured spectrophotometrically by the oxidation of NADH in the final reaction of a series of coupled enzymatic reactions. This assay for lipoprotein lipase is unlike previously described assays in that radioactive substrates or titration procedures are not used in the free fatty acid determination. In addition, another method for assay of lipoprotein lipase activity that involves the separation of free fatty acids from triglycerides by adsorption chromatography with Florisil as a stationary phase is described.

In vitro hepatic gluconeogenesis during experimental ketosis produced in steers by 1,3-butanediol and phlorizin

Adaptations of in vitro incorporation of gluconeogenic substrates into glucose and adaptations of metabolite concentrations of liver to subcutaneous phlorizin and dietary 1,3-butanediol were examined for liver samples from dairy steers. Later, the same adaptations were examined after 6 days of feed restriction. Feeding 1,3-butanediol significantly decreased conversion of carbon-14 of lactate and propionate to glucose and to carbon dioxide. There were no changes of concentrations of hepatic glycogen or triglyceride, and increases were only minor for beta-hydroxybutyrate concentration. Both phlorizin, with or without 1,3-butanediol, and feed restriction significantly increased rates of carbon incorporation into glucose from aspartate, lactate, and propionate but did not change rates of oxidation to carbon dioxide. Phlorizin had no effect on hepatic glycogen or triglyceride concentrations, but feed restriction decreased liver glycogen and increased triglyceride concentrations. Changes associated with either phlorizin treatment or feed restriction are consistent with a decreased ratio of insulin to glucagon of blood plasma. When combined, phlorizin and 1,3-butanediol seem to have some utility for developing a ketosis model.

Glucose kinetics, plasma metabolites, and endocrine responses during experimental ketosis in steers

Phlorizin and 1,3-butanediol were used to determine effects of glucosuria and ketonemia on concentrations of metabolites in blood plasma and on kinetics of glucose metabolism. Four steers received four treatments (control; control plus dietary 1,3-butanediol; control plus phlorizin injections; and control plus phlorizin and 1,3-butanediol) in a Latin square design. Treatments lasted 14 days. All steers received a 30% grain, 70% forage ration in equal meals every 2 h. Metabolite concentrations in blood plasma and urine and glucose kinetics were measured on each of the last 3 days of each treatment period. Phlorizin caused glucosuria; decreased plasma glucose, glucose total entry rate, and glucose recycling; and increased plasma free fatty acids and glucose irreversible loss. Glucose pool size was increased by 1,3-butanediol. Phlorizin plus 1,3-butanediol caused glucosuria and ketonuria; decreased plasma glucose; and increased blood ketone bodies, plasma free fatty acids, glucose irreversible loss, and glucose pool size. Growth hormone, insulin, and glucagon were not affected by treatment. Physiological perturbations in these steers were characteristic of some of those in ketotic cows.

Infusions of parathyroid hormone in ruminants: hypercalcemia and reduced plasma 1,25-dihydroxyvitamin D concentrations

The relationship between infused synthetic bovine PTH-(1-34) and plasma concentrations of minerals and vitamin D metabolites was studied in eight calves (150-230 kg) and two thyroparathyroidectomized goats. Calves were infused iv with saline for 15-20 h. Then, calves were infused with one of three types of solution for an additional 35-h period. Three of the eight calves received 3 ng/kg X min (group H), three received 0.75 ng/kg X min (group L), and the remaining two calves received control saline over a 33-h period (group C). Blood samples were taken every 4-6 h. Plasma calcium, phosphorus, hydroxyproline, and 1,25-dihydroxyvitamin D [1,25-(OH)2D] remained relatively constant in control calves. PTH infusions into calves in group H resulted in an increase in plasma calcium from 2.4 to a plateau of 3.0 mmol/liter. PTH infusion caused no change in plasma phosphorus, but increased urinary excretion of phosphorus. Infusion of PTH caused a moderate increase in urinary calcium excretion, followed by pronounced calciuria after PTH withdrawal. Plasma concentrations of 1,25-(OH)2D decreased from about 30 pg/ml at the start of infusion to undetectable levels (less than 5 pg/ml) at the end of the infusion and for 30 h thereafter. Similar, but less pronounced, changes in plasma calcium and 1,25-(OH)2D concentration were observed in group L. Hypocalcemia and hypophosphatemia developed in the two lactating goats after thyroparathyroidectomy, and plasma 1,25-(OH)2D concentrations were decreased. PTH infusion (3 ng/kg X min) corrected the hypocalcemia and hypophosphatemia and markedly raised plasma 1,25-(OH)2D concentrations. When calcium chloride was infused in addition to PTH, the resulting hypercalcemia (3 mmol/liter) was associated with a marked reduction in plasma 1,25-(OH)2D. We conclude that the concentration of calcium in plasma has the major regulatory role on plasma 1,25-(OH)2D concentrations in ruminant species when potentially conflicting signals, such as hypercalcemia and high PTH concentrations, are present simultaneously.

Age- and genotype-dependent differences in catecholamine concentrations in the porcine caudate nucleus

Catecholamine concentrations of the caudate nucleus were determined by radioenzymatic assay in stress-susceptible and stress-resistant pigs at five different ages. Dopamine concentrations increased with age up to the time of puberty and declined thereafter in both genotypes of pigs. Generally, epinephrine concentrations increased with increasing age in both genotypes of pigs. Norepinephrine concentrations remained relatively constant for all ages of pigs except the oldest pigs. For most age groups, dopamine concentrations were lower in pigs of stress-susceptible genotype than in stress-resistant genotype.

Insulin responsiveness in non-fa/fa and fa/fa Zucker rats: effects of adipocyte size

Epididymal adipose tissue from non-fa/fa (lean) and fa/fa (obese) 14.5-week-old Zucker rats was used to study the influence of insulin and genotype on uptake of glucose and palmitate into adipocytes of different sizes. After incubation with radioactive substrate, adipocytes were inactivated and fixed by addition of osmium tetroxide; fixed adipocytes were isolated and separated by screening on the basis of size. Rates of substrate uptake into triacylglycerols were measured in adipocytes of each of ten size categories. Uptake rates of both glucose and palmitate increased as adipocyte size increased. Insulin had no effect on glucose uptake per adipocyte for fa/fa rats but had a highly significant (P less than 0.01) stimulatory effect on that for non-fa/fa rats. This stimulation became significantly greater with increasing adipocyte size. When insulin was included in the incubation media, glucose uptake rates were similar between similar sizes of adipocytes from non-fa/fa and fa/fa rats. Absence of insulin from the incubation media, however, resulted in lower rates of glucose uptake by adipocytes from non-fa/fa rats. Glucose uptake was maximal in adipocytes from fa/fa rats, even in the absence of insulin. Net uptake of palmitate into triacylglycerols was not influenced by insulin; a significant interaction was observed, however, between adipocyte size and genotype. Large adipocytes from fa/fa rats had greater rates of palmitate uptake than did adipocytes of similar size from non-fa/fa rats. The reverse was true for adipocytes less than 125 micron in diameter. The results of this study show that response to insulin of adipocytes of difference sizes varies with adipocyte size and with genotype.

Conversion of glucose, acetate and lactate to CO2 and fatty acids in liver and adipose tissue of prairie voles (Microtus ochrogaster)

Production of CO2 and fatty acids from acetate, glucose and lactate was determined in slices of liver and adipose tissue from prairie voles fed either a high-starch or a high-cellulose diet. Acetate and lactate were oxidized to CO2 and converted to fatty acids at greater rates than was glucose in both liver and adipose tissue. Fatty acid synthesis occurred at greater rates in adipose tissue than in liver. Fatty acid synthesis per adipocyte increased with increased adipocyte diameter. Fiber content of diets had only minimal effect on metabolic activities of liver and adipose tissue.

Metabolism of orally administered [3H]ergocalciferol and [3H]cholecalciferol by dairy calves

Concentrations of ergocalciferol, cholecalciferol, and their metabolites in plasma were determined after a single oral dose of [3H]ergocalciferol or [3H]cholecalciferol was given to 95- to 105-kg Jersey bull calves. One group (three calves) was given 365 muCi of [3H]ergocalciferol (1.2 Ci/mmol) per calf, and the other group (three calves) was given 365 muCi of [3H]cholecalciferol (1.2 Ci/mmol) per calf. Fourteen blood samples were taken from each calf during the 3 weeks after administration. Total plasma radioactivity was highest at 80 hours in both groups (8400 dpm/ml and 4600 dpm/ml in the [3H]cholecalciferol- and [3H]ergocalciferol-treated calves, respectively). For determination of the time-dependent appearance and disappearance of plasma vitamin D and vitamin D metabolites, the plasma 3H-labeled steroids were extracted and separated by high-performance liquid chromatography. In both groups, [3H]vitamin D peaked at 24-48 hours and was the predominant radioactive form in plasma 10-15 hours after dosing. After 15 hours, 25-[3H]hydroxyvitamin D became the predominant labeled metabolite, reaching its maximal concentration between 48 and 96 hours. Concentrations of 25-[3H]hydroxycholecalciferol were about twice those of 25-[3H]hydroxyergocalciferol. The appearance/disappearance profile of 25,26-[3H]dihydroxycholecalciferol and 1,25[3H]hydroxycholecalciferol resembled that of 25-[3H]hydroxycholecalciferol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of selenium on the subcellular distribution of glutathione peroxidase in rat liver, epididymal fat pad and seminal vesicle

The effect of dietary selenium on the subcellular distribution of selenium-dependent glutathione peroxidase (SeGSH-Px) activity in rat liver, epididymal fat pad, and seminal vesicle was determined. Tissues were fractionated by differential centrifugation, and the subcellular distribution of SeGSH-Px activity was determined by comparison with the distribution of biochemical marker enzymes. Liver SeGSH-Px activity was located in both the cytosol and mitochondria. In epididymal fat pad and seminal vesicle, SeGSH-Px activity was located primarily in the cytosol; association with another subcellular organelle, however, was indicated. In liver and epididymal fat pad, SeGSH-Px activity increased linearly, and, in the seminal vesicle, increased linearly and quadratically, with increasing dietary selenium concentration. Distribution of SeGSH-Px activity among the cellular fractions from the tissues, however, was not affected by dietary selenium supplementation.

Relationships between prepartal dietary calcium and phosphorus, vitamin D metabolism, and parturient paresis in dairy cows

Twenty Jersey cows were fed one of four prepartal diets: a)low calcium, low phosphorus (LCLP); b) low calcium, high phosphorus (LCLP); c) high calcium, low phosphorus (HCLP); or d)high calcium, high phosphorus (HCHP). Diets were fed for about 4 weeks prepartum. Blood samples were taken periodically, and the collected plasma analyzed for concentrations of calcium, phosphorus, hydroxyproline and 1,25 dihydroxyergocalciferol plus 1,25-dihydroxycholecalciferol (1,25-(OH)2D). Cows fed the LCLP and LCHP diets, when compared to cows fed the HCLP diet, had: a) greater concentrations of plasma 1,25-(OH)2D and hydroxyproline prepartum; b) greater plasma calcium concentrations at parturition; and c) less incidence (0 versus 4 cases) of parturient paresis. Thus, low calcium diets, regardless of dietary phosphorus intake, seemed to activate calcium homeostatic mechanisms before parturition by stimulating both bone and gut. Cows fed the HCLP diet had greater plasma calcium concentrations at parturition than did cows fed the HCHP, even though there was no measurable effect on plasma 1,25-(OH)2D and hydroxyproline concentrations during the prepartal period. It seems possible that the beneficial effect of low dietary phosphorus, when dietary calcium is high, may be a result of a prepartal increase in efficiency of absorption of calcium and phosphorus from the gut caused by increased binding of 1,25-(OH)2D to intestinal receptors.

Examination of a lognormal distribution equation for describing distributions of diameters of bovine adipocytes

Samples of subcutaneous, intermuscular and mesenteric adipose tissues from beef steers were fixed with osmium tetroxide, and freed adipocytes were counted with an automatic particle counter to determine whether a lognormal distribution function would describe adipocyte size distributions more accurately than a normal distribution function. Modes and medians of size distributions generally were larger than means for adipocyte size distributions modeled with a lognormal distribution function. Normalized third and fourth moments of predicted lognormal distributions often were close to 0 and 3, respectively, which are expected values for a normally distributed population. Considerable variation was observed in the skewness of adipocyte size distributions. Both normal and lognormal models for adipocyte size distribution yielded similar means. The lognormal model yielded a greater standard deviation than the normal model for adipocyte size distributions. Smaller chi-square values were found for size distributions modeled with a lognormal than with a normal distribution function. Results suggest that a lognormal distribution function more accurately models the size distributions of bovine adipocytes.

1 Alpha-25,26-trihydroxyvitamin D3: an in vivo and in vitro metabolite of vitamin D3

A new metabolite of vitamin D3 has been isolated from the plasma of vitamin D3 treated cows and has been generated from 25(S),26-dihydroxyvitamin D3 with homogenates of vitamin D deficient chick kidney. This metabolite has been identified as 1,25,26-trihydroxyvitamin D3 by comigration with synthetic 1,25(S),26-trihydroxyvitamin D3 in four chromatographic systems, ultraviolet spectroscopy, mass spectrometry, and high-pressure liquid chromatography and mass spectrometry of derivatives. 1,25(S),26-Trihydroxyvitamin D3 is one-tenth as effective as 1,25-dihydroxyvitamin D3 in binding to the chick intestinal cytosol 1,25-dihydroxyvitamin D receptor. Either 25(S),26-dihydroxyvitamin D3 or 1,25-dihydroxyvitamin D3 can serve as precursor for in vitro production of 1,25,26-trihydroxyvitamin D3 by chick kidney tissue.

Blood lactate kinetics in normal and stress-susceptible pigs

In vitro rates of lactate metabolism were determined in stress-susceptible (SS) and stress-resistant (SR) pigs. Three SR and three SS pigs were given 20 muCi of [U-14C] L-lactate by a single injection method and resting blood lactate kinetics were measured. Seventeen blood samples were taken during the 60 min after injection. Lactate was separated from the deproteinized plasma by silicic acid column chromatography, and specific radioactivity was determined. Kinetic characteristics were calculated from plots of specific activity versus time. Pigs met steady-state requirements during the sampling period. There were no differences in kinetic characteristics of resting SS and SR pigs. Later, a second isotope injection was given after 5 min of electrical stress. Lactate pool sizes increased similarly in both types of pigs after stress; however, SS pigs had greater plasma lactate concentrations after stress. It is concluded that SS and SR pigs respond differently to stress but have similar capacities to metabolize lactate while resting.

Fatty acid synthesis from lactate in growing cattle

Rates of fatty acid synthesis from lactate and acetate and activities of selected lipogenic and NADPH-generating enzymes were determined in subcutaneous, intermuscular and intramuscular adipose tissues of cattle that were 11-19 months of age. Fatty acid synthesis from lactate and acetate increased from 11 to 13 months of age in subcutaneous and intermuscular adipose tissues; synthesis from lactate increased until 17 months of age. In intramuscular adipose tissue, synthesis from lactate also increased until 17 months of age while that from acetate continually increased. Activities of NADPH-generating enzymes increased in all three fat depots from 11 to 13 months of age, and little change occurred thereafter. Acetyl-CoA carboxylase activity was constant over entire growth period in all depots. Activity of ATP-citrate lyase increased from 11 to 13 months of age in subcutaneous and intermuscular adipose tissues, but did not increase until 19 months of age in intramuscular adipose tissue. In all cases, activities of ATP-citrate lyase were sufficient to support synthesis from lactate; therefore, lactate conversion to fatty acids in bovine adipose tissues seems to use the citrate cleavage pathway for generation of cytosolic acetyl-CoA.

A sensitive competitive protein binding assay for vitamin D in plasma

A sensitive protein binding assay for vitamin D is described. The vitamin D3 was extracted from plasma with diethyl ether and methylene chloride. The lipid extract was purified in Sephadex LH-20 followed by Lipidex 5000 and finally by high pressure liquid chromatography on a Zorbax Sil column (0.79 x 25 cm) developed in 0.25:99.75 isopropanol: methylene chloride. The vitamin D fraction was collected and quantitated by competitive protein binding assay with a 1/50,000 dilution of sheep plasma in 0.05 M potassium phosphate buffer (pH 7.5) containing 0.01% gelatin. [H3]-25-Hydroxyvitamin D3 was used as a radioactive tracer in the assay. We found that under these conditions, sheep plasma had equal affinity for vitamin D2 and vitamin D3 and could detect as little as 0.1 ng of vitamin D. When rat, cow, or human plasma was substituted for the sheep plasma, the decline in sensitivity to vitamin D2 was fivefold to tenfold. With this assay, we found excellent agreement (r = 0.98) between the results obtained by competitive protein binding analysis and direct U.V. absorbance analysis by high pressure liquid chromatography.

Relative role of caloric restriction and exercise training upon susceptibility to isoproterenol-induced myocardial infarction in male rats

To determine the relative effect of body weight and physical inactivity on susceptibility to drug-induced myocardial infarction, randomly selected groups of 100-day-old male Sprague-Dawley rats were subjected to a 10-wk program of exercise training and (or) to caloric restriction followed by two subcutaneous injections of L-isoproterenol. Two groups of rats were fed a restricted diet consisting of minimum calories to maintain body weight and were either exercised (R-Ex) or remained sedentary (R-C), one group was fed ad libitum and subjected to exercise (Ex), and one group remained sedentary (C), but was provided only enough food to maintain body weight in a range similar to Ex rats. Initially, there was no difference between group body weights, but Ex and C rats exhibited a significantly greater final body weight. All Ex, R-Ex, and R-C rats survived the isoproterenol injections, but 50% of C rats died. Group C rats exhibited significantly greater activity of total plasma lactate dehydrogenase (LDH), whereas R-Ex rats had the lowest total LDH activity (p less than 0.05). R-Ex and R-C rats had a significantly lower activity of plasma LDH-1, the heart isozyme, than did the heavier Ex and C rats. More specifically, R-C rats exhibited a significantly decreased amount of plasma LDH-1 activity when compared with Ex rats, indicating that smaller, untrained rats had less myocardial damage than the heavier, exercise-trained rats. These data suggest that either exercise or maintenance of body weight is beneficial toward prevention of the drug-induced myocardial infarction, but when weight maintenance is combined with exercise additional protection is provided.

Vitamin D metabolites in plasma of cows fed a prepartum low-calcium diet for prevention of parturient hypocalcemia

Our objective was to characterize changes in vitamin D metabolites of plasma in Jersey cows fed a prepartum low-calcium diet. Eight cows were fed a high-calcium diet (80 g/day) and eight were fed a low-calcium diet (8 g/day) at least 14 days before parturition. Calcium concentrations in plasma decreased after initiation of feeding either diet, but cows fed low-calcium diet tended to have lower prepartum calcium and phosphorus and greater peripartal calcium in plasma. Hydroxyproline in plasma was greater during peripartal period in cows fed low-calcium diet. Prepartum 1,25-dihydroxyvitamin D in plasma tended to be greater in cows fed low calcium. Increases in 1,25-dihydroxyvitamin D were only 2 and 3 days after initiation of the low-calcium diet; during the first 2 days after parturition, however, 1,25-dihydroxyvitamin D tended to be lower in those cows fed low calcium. As parturition neared, 24,25-dihydroxyvitamin D tended to be lower in cows fed the low calcium-diet. Usual early postpartum changes in calcium phosphorus, magnesium, 1,25-dihydroxyvitamin D, and hydroxyproline were seen during first few days after initiation of feeding low calcium. Thus, we propose that the preventative action of the low-calcium diet is associated with preparation of the calcium homeostatic mechanism several days before the calcium demand of initiation of lactation.

Effect of fasting on free fatty acid, glycerol and cholesterol concentrations in blood plasma and lipoprotein lipase activity in adipose tissue of cattle

Contributing factors in the regulation of triglyceride deposition in and fatty acid release from bovine adipose tissue were investigated. Six Holstein steers were fasted for 9 days and then refed for 41 days. Blood samples from the jugular vein and adipose tissue samples from backfat biopsies were taken during fasting and refeeding periods. Concentrations of plasma free fatty aids, glycerol and cholesterol and activity of lipoprotein lipase in adipose tissue from fasted and refed steers were measured. Plasma free fatty acid concentration increased almost eightfold during fasting. After 4 days of refeeding, free fatty acids in plasma had returned to basal concentration. Fasting had no effect on plasma cholesterol concentration; during refeeding, concentration decreased slightly and then returned to the basal concentration. Lipoprotein lipase activity decreased to 37% of the basal concentration during fasting and increased to 100% above prefasting values during refeeding. Significant changes in plasma free fatty acid and glycerol concentrations and in activity of lipoprotein lipase in adipose tissue during fasting and refeeding suggest that fatty acid mobilization and triglyceride uptake by adipose tissue of cattle adapt to great changes in energy intake. Correlations of measured blood metabolites in fasted and refed steers demonstrate that changes in rates of lipolysis and of triglyceride uptake by adipose tissue vary in a reciprocal manner.

Conversion of alanine, aspartate and lactate to glucose and CO2 in liver from stress-susceptible and stress-resistant pigs

Rates of conversion of lactate, alanine and aspartate to glucose and oxidation of each to CO2 were determined in incubated liver slices from nine stress-susceptible (SS) and seven stress-resistant (SR) Yorkshire pigs ranging in body weight from 24 to 54 kg. Pigs were screened for stress susceptibility by exposure to halothane at 7 weeks of age. Stress was minimized before slaughter, and liver samples were obtained immediately after death. Rates of lactate and aspartate conversion to glucose were not significantly different between pig types. Mean rates of lactate conversion to glucose in livers of SS and SR pigs were 637 and 413 nmoles/(100 mg X 2 hours), respectively. Mean rates of aspartate conversion to glucose were 441 and 540 nmoles/(100 mg X 2 hours) in SS and SR pigs, respectively. Alanine conversion to glucose in livers of SS pigs was slower than that in SR pigs [527 and 813 nmoles/(100 mg X 2 hours), respectively]. Rates of hepatic gluconeogenesis from lactate probably do not predispose SS pigs to the lactic acidosis observed during the porcine stress syndrome. Rates of lactate, alanine and aspartate oxidation to CO2 in livers of SS pigs were 61, 59 and 76%, respectively, of the rates observed in SR pigs. Decreased rates of substrate oxidation to CO2 may contribute to the development of the syndrome in SS pigs.

Lactate as a precursor of fatty acids in bovine adipose tissue

In vitro experiments were conducted to determine the rates of lactate, acetate, and glucose conversions to glycerol, CO2, and fatty acids by subcutaneous adipose tissue of cattle. To study the pathway for lactate utilization as a carbon source for lipogenesis, the effect of each of four substates (lactate, acetate, pyruvate, and glucose) on the rate of conversion of the other three was determined. The rates of lactate conversion to fatty acids and to glycerol were greater than those for acetate and glucose. Acetate, however, was oxidized to CO2 at greater rates than either lactate or glucose. Acetate was used for fatty acid synthesis at greater rates than pyruvate was less than that from lactate but greater than that from glucose. Acetate additions to the incubation media decreased the synthetic rates from lactate, pyruvate, and glucose. Pyruvate decreased rates of fatty acid synthesis from glucose but slightly (not statistically significant) stimulated synthesis from lactate and acetate. Lactate decreased glucose and pyruvate utilization but had no effect upon that of acetate. Our results clearly demonstrated that lactate can be used for fatty acid synthesis as well as for glycerogenesis by bovine adipose tissue.

Sterol synthesis and CO2 production from mevalonate in calves

Nonruminating male Holstein calves were fed a reconstituted milk containing 11.7% nonfat-dried-milk solids and 3.5% beef tallow. Calves were slaughtered at 17 weeks of age. Samples of perirenal adipose tissue, liver, muscle, small intestine, kidney cortex, and kidney medulla were assayed in vitro for sterol synthesis and production of (14)CO(2) from [2-(14)C]mevalonate. Of the tissues tested, adipose tissue and kidney medulla produced nonsaponified lipids at the greatest rates; kidney cortex and liver at half the rate of adipose tissue; muscle and jejunum at one-eighth the rate of adipose tissue; and ileum at a negligible rate. The amount of (14)C in squalene, lanosterol, and cholesterol of the nonsaponified lipids of each tissue was determined by thin-layer chromatography. Proportions of (14)C in cholesterol to (14)C in total nonsaponified lipids ranged from 30% to 59%; squalene, from 5% to 27%; and lanosterol, from 11% to 59% of the total nonsaponified lipids present. The rate of CO(2) production by the "trans-methylglutaconate shunt of mevalonate metabolism" was determined. Kidney cortex displayed the greatest shunt activity, producing 15-80-fold more CO(2) than any other tissue tested. Ileum, jejunum, skeletal muscle, and kidney medulla had similar shunt activities; liver sections had less shunt activity, and no shunt activity was detected in adipose tissue. These data reveal a shunt for mevalonate utilization that does not lead to sterols and also show that the kidney is important in the sterol and nonsterol metabolism of mevalonate.

Gluconeogenesis from lactate in liver of stress-susceptible and stress-resistant pigs

In vitro rates of lactate conversion to glucose and oxidation to CO2 were determined in livers of stress-susceptible (SS) and stress-resistant (SR) pigs because we hypothesized that livers of SS pigs had a lower capacity than livers of SR pigs to remove lactate from blood. Stress-susceptibility was determined by reaction to halothane at 7 weeks of age. At approximately 9 weeks of age, pigs were assigned to one of three experimental diets. Pigs weighing 95 kg were slaughtered immediately after stress, and liver samples were obtained. Incorporation of lactate into glucose in liver of SS pigs was 38% of that in SR pigs. Addition of either vitamin C or vitamins C and E plus magnesium oxide and collagen extract to a corn-soy diet did not alter lactate conversion to glucose, but depressed lactate oxidation to CO2. No differences were detected in either activities of lactate dehydrogenase, HAD-malate dehydrogenase, phosphoenolpyruvate carboxykinase, fructose-1,6-diphosphatase, and glucose-6-phosphatase or concentration of glycogen in livers of SS and SR pigs. Our data indicate that livers of SS pigs possess a lower capacity to incorporate lactate into glucose and to oxidize lactate to CO2; maximal activities of enzymes measured in this study are not the cause of these differences. Reduced capacity of lactate metabolism in livers of SS pigs seems a part of the etiology of the porcine stress syndrome.

Changes in fatty acid synthesis and lipogenic enzymes in adipose tissue from fasted and fasted-refed steers

Controls of fatty acid synthesis in bovine adipose tissue were investigated. Six Brown Swiss steers were fasted for 8 days and then refed for 56 days. Biopsy samples of backfat adipose tissue were taken during the fasting and refeeding periods. Rates of acetate incorporation into fatty acids (FAS), activities of acetyl CoA carboxylase (CBX), glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and NADP:isocitrate dehydrogenase, and plasma free fatty acids (FFA) and plasma acetate were determined. FAS decreased 60% after 1 day of fasting and 99% after 8 days. FAS did not increase until day 3 of refeeding when energy intake was above maintenance, then returned to normal by 14 days. CBX followed a pattern similar to FAS, except its activity did rise above the control rate during refeeding. Plasma FFA increased 350% and acetate decreased 67% during fasting. After 4 days of refeeding, FFA returned to normal, and acetate increased to 156% of initial concentration, then returned to normal by 21 days. These data suggest that CBX limits FAS in adipose tissue of cattle.