Leptin expression in offspring is programmed by nutrition in pregnancy

Birth weight is a determinant of blood leptin concentrations in adults. Since nutrition during pregnancy can affect birth weight, the hypothesis that feed intake during pregnancy alters leptin expression in progeny was examined. Leptin mRNA was measured in subcutaneous adipose tissue and leptin protein was measuredin blood plasma from 59 day old female pigs whose mothers were fed at the same restricted rate except that half were permitted to consume 35% more feed during the second quarter of pregnancy. Leptin mRNA abundance in adipose tissue (P=0.015) and plasma leptin concentration (P=0.01) were higher in progeny from mothers provided with more feed. Body weight at birth was negatively correlated with the abundance of leptin mRNA in subcutaneous fat at 59 days of age (P=0.01). This study shows for the first time that maternal nutrition during pregnancy programs postnatal leptin expression in offspring.

Effects of L-carnitine fed during lactation on sow and litter performance

Sows of differing parities and genetics were used at different locations to determine the effects of feeding added L-carnitine during lactation on sow and litter performance. In Exp. 1, sows (n = 50 PIC C15) were fed a lactation diet (1.0% total lysine, .9% Ca, and .8% P) with or without 50 ppm of added L-carnitine from d 108 of gestation until weaning (d 21). No differences in litter weaning weight, survivability, sow ADFI, or sow weight and last rib fat depth change were observed. Number of pigs born alive in the subsequent farrowing were not different (P>.10). In Exp. 2, parity-three and -four sows (n = 115 Large White cross) were used to determine the effect of feeding 0, 50, 100, or 200 ppm of added L-carnitine during lactation (diet containing .9% total lysine, 1.0% Ca, and .8% P) on sow and litter performance. No improvements in the number of pigs or litter weights at weaning were observed (P>.10). Sows fed added L-carnitine had increased weight loss (linear; P<.04), but no differences (P>.10) were observed in last rib fat depth change or subsequent reproductive performance. In Exp. 3, first-parity sows (n = 107 PIC C15) were fed a diet with or without 50 ppm of added L-carnitine during lactation (diet containing 1.0% total lysine). Sows fed added L-carnitine tended (P<.10) to have fewer stillborn and mummified pigs than controls (.42 vs .81 pigs). No differences were observed for litter weaning weight, survivability, or subsequent farrowing performance. Feeding 50 to 200 ppm of added L-carnitine during lactation had little effect on sow and litter performance.

Epinephrine transiently increases amino acid disappearance to lower amino acid levels in humans

BACKGROUND

Infusion of epinephrine decreases plasma amino acid concentrations. However, the mechanism by which this decrement occurs is not well characterized.

METHODS

Epinephrine was infused (40 ng/kg/min) for 2 hours into eight normal healthy adults. The essential amino acid tracers L-[1-(13)C]leucine and L-[phenyl-2H5]phenylalanine were infused before and during the epinephrine infusion and blood samples obtained to determine amino acid rates of appearance and disappearance from the time course of change in amino acid concentration and tracer enrichments.

RESULTS

Epinephrine infusion decreased plasma leucine and phenylalanine concentrations over a period of 30 to 90 minutes after the start of the epinephrine infusion. Epinephrine infusion induced an immediate decrement in tracer enrichments. These changes defined sharp increases in both rate of appearance and rate of disappearance. By 30 minutes of epinephrine infusion, the rate of amino acid appearance from proteolysis had returned to baseline, but the rate of amino acid disappearance remained elevated for 90 minutes before returning to baseline. It was the protracted increase in amino acid disappearance that was responsible for the lowering of plasma amino acid concentrations. After this acute response, rates of amino acid appearance and disappearance returned to normal whereas plasma amino acid levels remained suppressed.

CONCLUSIONS

Epinephrine transiently affects both rates of amino acid appearance and disappearance, with the net effect being increased in amino acid disappearance. However, epinephrine lowers amino acid concentrations beyond the period that it affects kinetics. These results suggest that the effect of epinephrine on amino acid metabolism is not detrimental and that epinephrine allows amino acid metabolism to proceed normally but at lower concentrations of amino acids.

The relationship between endogenous insulin-like growth factors and growth in pigs

Previous studies have reported conflicting data on gender differences in plasma IGF-I in postnatal pigs. There is also debate over the role of IGF-II in regulation of postnatal growth. We have, therefore, determined the concentrations of plasma IGF-I, IGF-II, and IGF-binding protein-3 (IGFBP-3) in boars, barrows, and gilts and related these to postnatal growth characteristics. Plasma concentrations of IGF-I were higher in boars than in gilts or barrows from 13 wk. of age, and plasma IGF-II levels were generally higher in barrows than in boars or gilts. Plasma IGFBP-3 levels were higher in boars than in gilts or barrows at most ages. Between 15 and 23 wk. of age, IGF-I and IGFBP-3, but not IGF-II, were positively associated with growth rate, voluntary feed intake, and gain:feed ratio. Plasma IGF-II, but not IGF-I or IGFBP-3, was positively associated with backfat depth during this period. These results support the hypothesis that circulating IGF-I and IGF-II are regulators of lean and adipose tissue growth, respectively.

Hyponatremia in ultradistance triathletes

PURPOSE

Hyponatremia ([plasma sodium] <135 mmol x L(-1)) is a potentially serious complication of ultraendurance sports. However, the etiology of this condition is still uncertain. This observational cohort study aimed to determine prospectively the incidence and etiology of hyponatremia in an ultradistance triathlon.

METHODS

The subjects consisted of 605 of the 660 athletes entered in the New Zealand Ironman triathlon (3.8-km swim, 180-km cycle, and 42.2-km run). Subjects were weighed before and after the race. A blood sample was drawn for measurement of plasma sodium concentration after the race.

RESULTS

Complete data on pre- and postrace weights and plasma sodium concentrations were available in 330 race finishers. Postrace plasma sodium concentrations were inversely related to changes in body weight (P = 0.0001). Women (N = 38) had significantly lower plasma sodium concentrations (133.7 vs 137.4 mmol x L(-1); P = 0.0001) than men (N = 292) and lost significantly less relative weight (-2.7 vs -4.3%; P = 0.0002). Fifty-eight of 330 race finishers (18%) were hyponatremic; of these only 18 (31%) sought medical care for the symptoms of hyponatremia (symptomatic). Eleven of the 58 hyponatremic athletes had severe hyponatremia ([plasma sodium] < 130 mmol x L(-1)); seven of these 11 severely hyponatremic athletes were symptomatic. The relative body weight change of the 11 severely hyponatremic athletes ranged from 2.4% to +5%; eight (73%) of these athletes either maintained or gained weight during the race. In contrast, relative body weight changes in the 47 athletes with mild hyponatremia ([plasma sodium] 130-134 mmol x L(1)) were more variable, ranging from -9.25% to +2.2%.

CONCLUSIONS

Hyponatremia is a common biochemical finding in ultradistance triathletes but is usually asymptomatic. Although mild hyponatremia was associated with variable body weight changes, fluid overload was the cause of most (73%) cases of severe, symptomatic hyponatremia.

Epinephrine produces a prolonged elevation in metabolic rate in humans

BACKGROUND

Epinephrine increases the metabolic rate and contributes to the hypermetabolic state in severe illness.

OBJECTIVE

We sought to determine the effect of prolonged elevation of epinephrine on resting energy expenditure (REE).

DESIGN

Thirteen healthy men were placed on a well-defined diet for 5 d. Beginning on the morning of the second diet day, the subjects were infused for 24 h with saline, then for 23 h with epinephrine (0.18 nmol x kg(-1) x min(-1)) to increase plasma epinephrine concentrations into the high physiologic range (4720 +/- 340 pmol/L). REE and the respiratory quotient (RQ) were measured by indirect calorimetry in the postabsorptive state at the same time every morning.

RESULTS

Infusion of epinephrine significantly increased heart rate and systolic blood pressure, but the response was transient (values after 23 h of epinephrine infusion were not significantly different from those on the day saline was infused). Infusion of epinephrine significantly increased REE by 12% and increased the RQ. These changes were apparent at the end of the 23-h infusion (REE: 97.5 +/- 2.3 kJ x kg(-1) x d(-1) with saline infusion and 108.9 +/- 2.3 kJ x kg(-1) x d(-1) with epinephrine infusion; RQ: 0.832 +/- 0.012 with saline infusion and 0.879 +/- 0.013 with epinephrine infusion). REE returned to baseline by 24 h after the epinephrine infusion ended, but the postabsorptive RQ remained modestly elevated. Infusion of epinephrine also produced a transient increase in urine flow and in urinary nitrogen excretion. This diuresis was compensated for by a drop in urine volume and nitrogen excretion after the epinephrine infusion was stopped.

CONCLUSIONS

Epinephrine produced a prolonged increase in REE in healthy subjects. The fuel for this increase in REE, determined by the RQ, was from increased carbohydrate oxidation, not from that of fat or protein.

Porcine somatotropin, dietary protein and energy effects on arginase and transaminase activities in pigs

Two experiments were conducted with cross-bred barrows to determine the effect of somatotropin administration on liver enzyme activities. In the first experiment, pigs growing from 26 to 55 kg body weight were given two doses of pituitary porcine somatotropin (pST; 0 and 100 micrograms per kg body weight) and three levels of dietary energy (60, 80 and 100% of free choice intake). In the second experiment, pigs growing from 30 to 60 kg body weight were given two doses of recombinant porcine somatotropin (rpST; 0 and 100 micrograms per kg body weight) and five levels of dietary crude protein (110, 150, 190, 230 and 270 g crude protein/kg diet). Liver arginase (ARG, EC 3.5.3.1) and aspartate aminotransferase (AAT, EC 2.6.1.1) activities were then determined in organ samples taken at slaughter time. Dietary energy did not change liver ARG. Activities of both ARG and AAT increased as dietary crude protein increased. Both pST and rpST decreased ARG, AAT and serum utrea nitrogen. There was a lack of interaction between rpST therapy and dietary protein on either ARG or AAT activities, suggesting that set nutritional states are not required for expression of pST effects.

Interrelationships between dietary ractopamine,energy intake, and sex in pigs

A major constraint to protein deposition in the pig is energy intake. Ractopamine (RAC) isa b-agonist which has been shown to increase protein deposition under both ad libitum and restrictive feeding regimes. To assess the interactions between energy intake, sex, and dietary RAC, 104 crossbred pigs (52 boars and 52 gilts) were used in a slaughter-balance experiment conducted over the growth phase of 60-90 kg liveweight. To obtain initial body composition, 4 pigs of each sex were slaughtered at 60 kg. The remaining 96 pigs were allocated to a 2 6 2 factorial experiment. The respective factors were sex (boar or gilt), dietary digestible energy (DE) intake (21·2, 24·7, 28·2, 32·7, 36·7MJ DE/day and ad libitum), and dietary RAC (0 and 20 mg/kg of ractopamine.HCl). Average daily gain increased with DE intake and was faster for boars than gilts. Dietary RAC increased averagedaily gain in both boars and gilts independent of DE intake. Neither dietary RAC nor sex had any effect on ad libitum feed intakes while effects on feed : gain ratio reciprocated growth rates. Protein deposition increased with DE intake and was higher in boars than in gilts. Although protein deposition was increased by dietary RAC in both boars and gilts across the range of DE intakes investigated,ad libitum feed intakes were necessary to maximise protein deposition. Fat deposition increased with DE intake and was greater in gilts than in boars. Whereas dietary RAC had no effect on the rateof fat deposition or backfat depths, the fat content of the empty body was lower due to increased protein deposition and lower fat : protein ratio. Dietary RAC improves growth performance and carcass composition in both boars and gilts independent of DE intake. However, ad libitum feed intakes maybe necessary if responses are to be maximised.

The effect of dietary lysine and valine fed during lactation on sow and litter performance

Sows (98 first parity and 104 second parity) were used to determine the effects of dietary lysine and valine on lactation performance. Treatments were arranged in a 2 x 3 factorial with two levels of lysine (.80 or 1.20%) and three valine:lysine ratios (80, 100, or 120% of lysine). For all sows, increasing dietary lysine increased litter weaning weight (P < .001) and litter weight gain (P < .002) and reduced sow weight loss (P < .001). Litter weight gain tended (P = .22) to increase with increasing dietary valine, but the increase was not significant. Data were separated into two groups: sows that weaned 10 or more pigs and sows that weaned fewer than 10 pigs. For sows that weaned 10 or more pigs, litter weaning weight (P < .001) and litter weight gain (P < .001) increased and sow BW loss decreased (P < .001) when dietary lysine increased from .80 to 1.20%. For sows that weaned fewer than 10 pigs, increasing lysine had no effect (P < .77) on litter growth rate. For sows weaning 10 or more pigs, litter weaning weights (linear, P < .04; quadratic, P < .06) and litter weight gain increased (linear, P < .04; quadratic, P < .02) as dietary valine increased. For sows that weaned fewer than 10 pigs, maximum litter weight gain was observed at a valine:lysine ratio of 100% (quadratic, P < .13). These results demonstrate the need to increase dietary lysine and valine as litter weaning weights increase. High-producing sows that wean 10 or more pigs require increased dietary lysine and valine to maximize litter growth rate and minimize sow weight loss compared with sows weaning fewer than 10 pigs. The independent increases in litter weaning weights from adding lysine and valine suggest separate modes of action for these amino acids in high-producing sows.

Hyponatremia and weight changes in an ultradistance triathlon

OBJECTIVE

To describe the weight changes and the incidence of hyponatremia during an ultradistance triathlon in the athletes who attend medical care after the race.

DESIGN

Descriptive research.

SETTING

The 1996 New Zealand Ironman Triathlon in which each athlete swam 3.8 km, cycled 180 km, and ran 42 km.

PARTICIPANTS

Ninety-five athletes attending for medical care after the race were studied. One hundred sixty-nine athletes who did not attend for medical care were also weighed before and after the race.

MAIN OUTCOME MEASURES

Weights were measured at race registration and on finishing the race. Whole-blood sodium concentration was measured in those athletes with clinical evidence of fluid or electrolyte disturbances.

RESULTS

Weights were significantly decreased at the end of the race in the athletes seeking medical care (n = 48, mean % delta wt = -2.5%, p < 0.001) and also in the athletes who did not seek medical care (n = 169, mean % delta wt = -2.9%, p < 0.001). Seventeen percent of race starters sought medical attention. Dehydration accounted for 26% of primary diagnoses and hyponatremia for 9%. One athlete with hyponatremia (Na 130 mEq/L) is described who drank 16 L over the course of the race, with a weight gain of 2.5 kg. This is consistent with the hypothesis of fluid overload as the cause of his hyponatremia. Hyponatremia accounted for four of five admissions to the hospital after the race. An inverse relationship between postrace sodium concentrations and percentage change in body weight was observed (r = -0.63).

CONCLUSIONS

Hyponatremia is an important risk to the health of athletes competing in an ultradistance triathlon, with fluid overload the likely aetiology.

Performance and body composition of finishing gilts (45 to 85 kilograms) as affected by energy intake and nutrition in earlier life: II. Protein and lipid accretion in body components

Forty-eight commercial hybrid gilts were used to investigate the response relationships between energy intake and deposition of protein and lipid in body components of finishing pigs (45 to 85 kg) as affected by previous nutrition. Two groups of 24 gilts received a single diet either at 2.2 (restricted pigs) or 3.7 (control pigs) times maintenance (M) from 20 to 45 kg. From 45 to 85 kg, pigs from each of these two groups were fed the same diet at one of six intake levels (1.7, 2.2, 2.7, 3.2, or 3.7 x M, or adlibitum). At 85 kg, the gilts were dissected and analyzed. Protein content in the whole body decreased curvilinearly from 190 to 166 g/kg (P < .001) and lipid content increased from 116 to 210 g/kg (P < .001) with increasing energy intake. The mean content of protein was 6 g/kg higher and of lipid 29 g/kg lower (both P < .001) in previously restricted gilts. Protein (PD) and lipid deposition (LD) in the whole body, organs, lean, and fat tissue increased linearly (P < .001) with increasing energy intake. In the whole body, PD increased from 83 to 187 g/d and LD from 46 to 392 g/d. The respective response relationships in grams/day were PD = 21.8 + 3.78 x DEI and LD = -193 + 13.7 x DEI(DEI is digestible energy intake, MJ/d). The LD:PD ratio increased curvilinearly from .6 to 2.2. Previous nutrition had only small effects on PD and LD. Only PD in the organs was on average 7 g/d higher (P < .001) in previously restricted gilts. Thus, the higher protein content and the lower lipid content in previously restricted gilts was not primarily the results of compensation but was almost entirely present at the end of the restriction phase at 45 kg.

Somatotropin enhances the rate of amino acid deposition but has minimal impact on amino acid balance in growing pigs

This experiment was conducted to establish the influence of porcine somatotropin on tissue distribution and deposition rates of amino acids in growing pigs. Barrows were treated daily with buffer or porcine somatotropin (100 micrograms/kg body wt) when they weighed between 30 and 64 kg (eight pigs/group). Pigs were restrictively fed so that the average food intake was 1.86 kg/d. The corn-soybean meal-skim milk-based diet contained 18% crude protein and 1.2% lysine, and was designed to meet muscle amino acid ratio profile with respect to lysine as the first limiting amino acid for growth. Tissue levels of eighteen amino acids were determined on lyophilized samples that were appropriately hydrolyzed and analyzed by HPLC. The concentrations (mg/g dry wt) of all amino acids were greater in carcass, skin, head and empty body of porcine somatotropin-treated pigs; amino acid concentration in viscera was not influenced by porcine somatotropin. However, when the concentration of each amino acid was expressed on a per unit protein basis, the amino acid profiles of control and porcine somatotropin-treated pigs were quite similar. The average deposition rate of each amino acid was increased approximately 67% by porcine somatotropin. When the deposition of each amino acid was calculated in relation to lysine, however, the pattern of amino acid utilization for growth was similar for control and porcine somatotropin-treated pigs; exceptions were arginine, glycine and tryptophan. The ratio of indispensable to dispensable amino acids that were deposited was also similar for control and porcine somatotropin-treated pigs. These data indicate that the synthesis rate of individual proteins can be influenced by porcine somatotropin, but the balance of amino acids remains largely unaffected, suggesting that the changes in protein and amino acid metabolism elicited by porcine somatotropin are consistent with normal growth processes.

Protein and lipid accretion in body components of growing gilts (20 to 45 kilograms) as affected by energy intake

Twenty-eight commercial hybrid gilts with a high genetic capacity for lean gain were used to determine the relationships between energy intake and tissue deposition and body composition between 20 and 45 kg BW. Four pigs were killed at 20 kg to determine body composition at the beginning of the experiment. The other 24 gilts received one of six intake levels (1.7, 2.2, 2.7, 3.2, and 3.7 times maintenance [M], and ad libitum) ranging from 11.3 to 27.2 MJ of DE/d. At 45 kg BW, the gilts were killed and dissected into carcass and organ fractions. Carcasses of pigs at 2.2 and 3.7 x M were dissected into lean and other carcass parts. Daily gain increased linearly (P < .001) from 371 to 1,075 g/d. Gain/feed increased (P < .01) from 500 to 600 g/kg. Deposition rates of protein and lipid increased linearly (P < .001) from 75 to 172 g/d and from 28 to 193 g/d, respectively. The ratio between lipid and protein deposition increased (P < .001) from .3 to 1.1. The relative organ mass increased (P < .001) with increasing energy intake, whereas the body lean percentage decreased (P < .01) from 53.9% at 2.2 x M to 47.4% at 3.7 x M. In the carcass and organs, protein content decreased (P < .01) and lipid content increased (P < .001) with increasing energy intake. Protein deposition increased with 5.77 g/MJ increase in DE intake, of which only approximately 40% was deposited in the lean tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary energy intake and exogenous porcine growth hormone administration on circulating porcine growth hormone concentration and response to human growth hormone-releasing factor administration in growing swine

In a 2 x 2 treatment array (n = 4 pigs/treatment), the effects of feed intake (ad libitum vs. restricted to 60% ad libitum) and the daily administration of excipient buffer or porcine pituitary-derived growth hormone (GH) at a dose of 100 micrograms/kg body weight per day on serum GH profile and human growth hormone-releasing factor (hGRF) response were examined in barrows weighing 55 kg. Feed intake treatment was implemented from 25 to 55 kg live weight. Buffer or GH treatment was implemented for 10 d before sampling. After GH treatment, the integrated serum GH concentration area was 25% greater in barrows fed restrictively. Data are consistent with the suggestion that GH dose to improve the efficiency of lean tissue deposition be adjusted according to feeding regimen. The serum GH response to hGRF was also altered by level of feed intake. The ad libitum feeding of buffer-treated animals resulted in a monophasic serum GH response to hGRF, whereas barrows fed restrictively had a biphasic response to hGRF. Together, these data suggest that feed intake pattern alters GH secretion and as such could influence the practical implementation of somatotropin as a metabolism modifier in swine.

Effect of cortisol on energy expenditure and amino acid metabolism in humans

Hydrocortisone was infused overnight into nine normal healthy adults on three occasions at 0, 80, and 200 micrograms.kg-1.h-1, producing plasma cortisol concentrations of 10.6 +/- 1.2, 34.0 +/- 2.0, and 64.9 +/- 4.3 micrograms/dl, respectively. L-[1-13C]leucine, L-[phenyl-2H5]phenylalanine, and L-[2-15N]glutamine were infused during the last 7 h of hypercortisolemia to measure amino acid kinetics. During the last 3.5 h, somatostatin, glucagon, and insulin were infused to reduce the cortisol-induced elevation in plasma insulin to basal. Hypercortisolemia increased plasma glucose, free fatty acid (FFA), and insulin concentrations. Institution of the somatostatin clamp returned insulin to basal but increased glucose and FFA. Acute hypercortisolemia increased protein breakdown 5-20%, as measured by increases in leucine and phenylalanine appearance rates. Normalizing insulin during hypercortisolemia did not alter phenylalanine flux but enhanced leucine appearance rate, the latter result indicating that insulin was affecting leucine metabolism during hypercortisolemia. The fraction of the leucine flux that was oxidized was not significantly increased with hypercortisolemia, but disposal by the nonoxidative route of leucine uptake for protein synthesis was increased. Hypercortisolemia increased cycling of amino acids by increasing protein breakdown and synthesis, but the increase in this process could have increased resting energy expenditure (REE) only 1-2%. Hypercortisolemia increased glutamine flux in a dose-dependent fashion through an increase in de novo synthesis, which presumably reflects increased release from skeletal muscle. Hypercortisolemia increased REE 9-15% at the 80 and 200 micrograms.kg-1.h-1 infusion rates. Respiratory quotient did not rise with cortisol infusion but tended to decrease, suggesting that the increase in REE was fueled by increased oxidation of fat. These data demonstrate that hypercortisolemia increases metabolic rate and may be in part responsible for the hypermetabolic state in injury.

Digestible lysine requirement of gilts with high genetic potential for lean gain, in relation to the level of energy intake

One hundred gilts were used to determine the optimal ratio between ileal digestible lysine and digestible energy in the diet, and the effect of energy intake level on this optimal ratio for gilts with high genetic potential for lean gain, between 20 and 45 kg BW. In a 2 x 15 factorial arrangement the pigs were fed either 2.5 or 3.0 times the energy requirements for maintenance. Average daily lysine intake in the treatment period ranged from 6.4 to 18.2 g/d in 15 graduated steps. The first 12 increments were .74 g/d, and the last two increments were 1.48 g/d. Average daily gain (ADG), gain/feed, and protein deposition increased curvilinearly (P < .01) with increasing lysine intake. The ADG was maximized at 606 and 768 g/d, gain/feed was maximized at .564 and .604 kg/kg, and protein deposition was maximized at 108 and 128 g/d at the low- and high-energy levels, respectively. The ratio between lipid and protein deposition decreased curvilinearly with increasing lysine intake (P < .01) and reached a minimum of .53 and .75 at the low- and high-energy levels, respectively. The lysine requirements (ileal digestible lysine/DE, grams/megaJoule), determined with a linear-plateau model, were .57 for ADG and gain/feed, and .62 for protein deposition. These estimated requirements were similar for the two energy levels. Consequently, approximately .60 g of ileal digestible lysine/MJ of DE was required to optimize performance in gilts with high genetic potential for lean gain, irrespective of the feed intake level. In addition, a factorial model to estimate the lysine/energy requirements is proposed.

Interrelationships between sex and ractopamine on protein and lipid deposition in rapidly growing pigs

Sixty pigs were used to investigate the effects of two levels of dietary ractopamine (RAC; 0 and 20 mg/kg) and three sex types (SEX; boars, gilts, and barrows) on performance over the live weight range 60 to 90 kg. Pigs were housed in individual pens and allowed ad libitum access to a diet containing 3.466 Mcal of DE and 10.7 g of lysine/kg. Control boars exhibited faster and more efficient growth and deposited more protein and less fat than gilts or barrows. The RAC increased ADG by 17 and 21% in gilts and barrows but not in boars. Feed intake was not altered by dietary RAC. Dietary RAC increased the rate of protein deposition by 15, 42, and 41% in boars, gilts, and barrows, respectively. Nevertheless, the daily rate of protein deposition was greatest in RAC-treated boars. The RAC tended to reduce the daily rate of fat deposition by 21% in boars but not in gilts or barrows. Carcass protein content increased by 5% and fat content decreased by 8% in response to RAC. These improvements in carcass composition occurred without compromising meat quality. Results show that RAC is a potent stimulator of protein deposition in finishing pigs. However, increased protein deposition is not necessarily at the expense of fat deposition.

Interrelationships between dietary protein and ractopamine on protein and lipid deposition in finishing gilts

Fifty-two gilts were used to investigate the effects of two levels of dietary ractopamine (RAC; 0 and 20 mg/kg) and six levels of dietary protein content (DPC; 8.5, 11.2, 14.0, 16.7, 19.5, and 22.2%) on performance over the live weight range from 60 to 90 kg. Pigs were housed in individual pens and restrictively fed their treatment diets according to a sliding scale related to live weight (average intake approximately 7.0 Mcal of DE/d). The ADG increased with increasing DPC for both control and RAC-treated gilts. The RAC further increased ADG at DPC > 14%; improvements were most apparent during the first 3 to 4 wk. There was a significant linear interaction between DPC and RAC for average daily carcass gain. Although carcass gain was not affected by RAC at the three lowest DPC, it was significantly increased for the three highest DPC. Feed to gain decreased with increasing DPC in a similar manner for both control and RAC-treated gilts. The relationship between empty body protein deposition and DPC could be described by a quadratic and rectilinear model. Regardless of the model employed, protein deposition increased with DPC at the same rate for both the control and RAC-treated gilts over at least the two lowest levels of DPC (< 11.2%). At higher DPC maximal rates of protein deposition were at least 21% greater in RAC-treated gilts; these rates were achieved at 3% higher DPC for RAC-treated gilts. Fat deposition decreased with increasing DPC but was unchanged by dietary RAC. Because the biological efficiency of protein use was unchanged, RAC-treated gilts have greater dietary protein requirements than controls do.

Splanchnic bed utilization of glutamine and glutamic acid in humans

To study the fate of enterally delivered nonessential amino acids, glutamine and glutamate, 14 healthy adults were infused in the postabsorptive state with [2-15N]glutamine and [15N]glutamate for 7 h by intravenous (iv) and nasogastric (ng) tube routes. The amount of enterally delivered tracer that was sequestered by the splanchnic bed on the first pass was 54 +/- 4 and 88 +/- 2% for the [2-15N]glutamine and [15N]glutamate tracers, respectively. Only 46 and 12% of the ng glutamine and glutamate tracers entered systemic blood, respectively. The relative amount of 15N transferred from glutamate to glutamine, the transaminating amino acids leucine, isoleucine, valine, and alanine, and to proline was significantly higher when the [15N]glutamate was infused by the ng vs. iv route. The same was also true for [2-15N]glutamine, which presumably transferred 15N after it was converted to glutamate. Thus we conclude that the splanchnic bed sequesters over one-half of the glutamine and almost all of the glutamate delivered to it in the postabsorptive state. There is production of transaminating amino acids in the splanchnic bed, and the splanchnic bed produces simultaneously both glutamine from glutamate and glutamate from glutamine.

Effects of ractopamine in pig muscles: histology, calpains and β-adrenergic receptors

Ractopamine is a G-adrenergic agonist which stimulates growth in pigs, but this effect appears to decline during prolonged treatment. This study was conducted to examine possible mechanisms for the growth-enhancing activity of ractopamine, and its attenuation. Finishing gilts (47.0 kg body weight) were allocated to one of five experimental groups: CON, control diet for 6 weeks; RAC, ractopamine (20 mg/kg feed) for 6 weeks; C/R, CON for 3 weeks and RAC for 3 weeks; R/C, RAC for 3 weeks and CON for 3 weeks; and ALT, CON for weeks 1, 3 and 5, and RAC in weeks 2, 4 and 6. All pigs were fed 2.25 kg/day of a commercial grower ration (13 MJ DE/kg, 16% crude protein, 0.6 g available lysine/MJ DE). Samples of the m. longissirnus dorsi were taken at slaughter and analysed for fibre histology, calpain activities and G -adrenergic receptor populations. Ractopamine had no effect on muscle fibre proportions, but Type II fibres were smaller in pigs treated for the first 3 weeks only (R/C; 2477 8m2, P < 0.05), and tended to be larger in pigs treated for the second 3 weeks only (C/R; 3670 8m2, P < 0.10), as compared to controls (3086 8m2). Giant fibres were also larger in C/R pigs as compared to controls (9027 v. 6917 8m2, P < 0.05). Type I fibres were unaffected by any of the treatments. Calpain II and calpastatin activities were unaffected by any treatment, but calpain I activities were reduced in C/R pigs as compared to controls (0.331 v. 0.504 U/g, P < 0.05), indicating that reduced capacity for protein degradation might partially account for the hypertrophic effect of ractopamine. Pigs treated with ractopamine for 3 weeks before slaughter had reduced numbers of G-adrenoceptors in muscle than controls (2.34 v. 3.17 fmol/mg protein, P < 0.05), which may be responsible for the observed attenuation in growth enhancement over time.

Temporal changes in growth enhancement by ractopamine in pigs: performance aspects

Ractopamine is a phenethanolamine with G-adrenergic agonist activity which stimulates growth in pigs. In order to test whether the growth-enhancing properties of ractopamine change over time, 40 Large White crossbred gilts (47.0 kg liveweight) were assigned to five treatment groups: CON, control diet for 6 weeks; RAC, ractopamine(20 mg/kg feed) for 6 weeks; C/R, CON for 3 weeks, then RAC for 3 weeks; R/C, RAC for 3 weeks, then CON for 3 weeks; ALT, CON for weeks 1, 3, and 5, and RAC in weeks 2, 4 and 6. The control diet was a commercial wheat and soy-based grower ration (13 MJ DE/kg, 16% crude protein, 0.9% lysine, 0.6 g available lysine/MJ DE); all pigs were fed 2.25 kg/day. Weekly measurements included body weight and P2 backfat (by ultrasound). Due to uncertainty about the data from the final week, results for weeks 1 to 3 and 3 to 5 are presented. Average daily gain (ADG) was increased by RAC (+16%) during the first 3 weeks, with no further improvement thereafter. C/R produced higher ADG (+21%) during weeks 3 to 5 compared with controls, and ALT tended to do the same (+12%, P < 0.10). Over the 5 week period, total weight gain was increased (P > 0.05) by RAC (+18%) and ALT (+15%), and tended to increase with C/R (+12%, P < 0.10) with no significant effect of R/C (+l0%, P > 0.05). There were no differences among groups in P2 backfat during the feeding period ( P > 0.05). With the exception of dressing percentage, which was increased by RAC, C/R and ALT ( P < 0.05), carcass and meat quality characteristics (carcass weight, P2 backfat, loin eye area, pH, colour, drip loss and protein solubilities) were unaffected by any of the treatments (P > 0.05). In conclusion, ractopamine stimulated growth in finishing pigs on restricted intakes; this effect diminished over time, and was more pronounced in older and heavier pigs. In addition, meat quality characteristics were unaffected.

Splanchnic bed utilization of leucine and phenylalanine in humans

To study the fate of enterally delivered essential amino acids, leucine and phenylalanine, 14 healthy adults were infused in the postabsorptive state with [1-13C]leucine, [5,5,5-2H3]leucine, and [phenyl-2H5]phenylalanine for 7 h in a crossover design by intravenous and nasogastric tube routes. The amount of enterally delivered tracer that was sequestered by the splanchnic bed on the first pass was 21 +/- 1, 17 +/- 3, and 29 +/- 2 for the [13C]leucine, [2H]leucine, and [2H]phenylalanine tracers, respectively. Less than 2% of the nasogastric [1-13C]leucine tracer was oxidized on the first pass. We estimate that 40% of the nasogastric leucine tracer that was sequestered on the first pass was converted to alpha-ketoisocaproate and released, and 50% was incorporated into newly synthesized proteins. Assuming that less phenylalanine is incorporated into protein than leucine because of the lower abundance of phenylalanine in protein compared with leucine, we estimate that 80% of the extracted nasogastric phenylalanine tracer was converted to tyrosine. The study design also indicated a significant effect of duration of tracer infusion on the results, presumably due to recycling of tracer from rapidly turning over protein.

Growth hormone increases whole-body protein turnover in growing pigs

Ten pigs with an average initial live weight of 65 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone (pGH; .1 mg.kg-1.d-1) for a 13-d period on N retention and whole-body protein turnover. Feed intake was restricted to both the control (treated with excipient) and pGH-treated groups to ensure that animals in each group consumed equal amounts. Whole-body protein turnover was estimated from the excretion of 15N in urinary urea and ammonia after a single oral dose of [15N]glycine. Nitrogen balance and whole-body N flux were increased by 35 to 40% with pGH treatment (P less than .001). Protein synthesis and breakdown were increased by 56 and 59% (P less than .001), respectively, in pGH-treated pigs relative to controls. These higher rates of protein turnover seemed to lower slightly the efficiency of the metabolic process for protein deposition. However, the absolute increment in protein synthesis rate was greater than that for breakdown, leading to the increased net N retention. Thus, pGH treatment improved the utilization of dietary amino acids for protein deposition.

The effect of dietary protein intake on glutamine and glutamate nitrogen metabolism in humans

The response of glutamine and glutamate kinetics were studied in five healthy young adult men on diets containing deficient (0.1), adequate (0.8), or surfeit (2.2 g.kg-1.d-1) amounts of protein. Glutamate, glutamine, and phenylalanine kinetics were measured in the postabsorptive state at the end of each diet period. Urinary urea and ammonia excretion correlated with protein intake (the sum of the two was 2.1 +/- 0.2, 5.7 +/- 0.3, and 11.9 +/- 1.2 g N g.kg-1.d-1 for the respective 0.1, 0.8, and 2.2 g.kg-1.d-1 protein intakes). Glutamate and glutamine concentrations varied inversely with protein intake. Phenylalanine concentrations and phenylalanine flux did not change significantly with the changing protein intake. Both glutamate and glutamine fluxes varied inversely with protein intake (glutamate flux was 177 +/- 15, 120 +/- 10, and 125 +/- 11 mumol.kg-1.h-1 and glutamine flux was 373 +/- 29, 343 +/- 26, and 318 +/- 15 mumol.kg-1.h-1 at the respective 0.1, 0.8, and 2.2 g.kg-1.d-1 protein intakes). These changes in glutamine or glutamate flux in response to alterations in dietary protein intake were attributable to changes in de novo production.

Interrelationships between exogenous porcine somatotropin (PST) administration and dietary protein and energy intake on protein deposition capacity and energy metabolism of pigs

Exogenous porcine somatotropin (PST) administration stimulates protein deposition and inhibits lipogenesis, resulting in dose-related improvements in growth performance and reduction of carcass fat content. However, the associated impacts of this technology on dietary nutrient requirements and energy partitioning between maintenance, protein, and fat remain unclear. Studies with pigs between 25 and 60 kg body weight indicate that, because of unknown improvements in amino acid utilization and(or) in the energy available for protein synthesis, only marginal increases in dietary protein percentage are required to support 20 to 25% improvements in protein deposition induced by PST administration. In contrast, an increased dietary protein concentration is required to support maximal protein deposition in pigs 60 to 100 kg. Exogenous PST administration increased the maintenance energy requirement and altered the relationship between energy intake and protein deposition, although the magnitude of these changes and the consequent effects on expression of dietary protein (amino acid) requirements was influenced by gender. Albeit limited, information suggests that PST alters nutrient demand at the tissue level. Information of this type will form the basis for rational decisions concerning the method for expression of dietary nutrient requirements (% vs g/d) for PST-treated pigs. Further quantitative information is required on the effects of PST dosage on the relationship of protein deposition to energy intake and on any underlying changes in amino acid utilization and metabolism.