J. Vet. Med. A 37, 372-378 (1990) 0 1990 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0931 184X ~

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I Department of Animal Physiology, University of Agricultural Sciences, Keszthely, Department of Physiology and Biochemistry, University of Veterinary Sciences, Budapest

The Effect of Feed Intake and Portal Volatile Fatty Acid Infusion on Insulin and Free Amino Acid Concentrations in Plasma of Lambs F. H U S V ~ Tand H ~P. GALFI* Address of first author: F. HUWBTH,Department of Animal Physiology, University of Agricultural Sciences, H-8361 Keszthely, Deak F. u. 16., Hungary

With J figures and 2 tables (Received for publication September 29, 1989)

Summary Experiments were conducted with chronically catheterized growing lambs to study the effect of variations in rumen volatile fatty acid (VFA) supply on blood plasma free amino acids (FAA) and insulin. Five male lambs were fed, then fasted for 72 h and refed. In the second experiment 48 mmol of a VFA mixture per kg body weight was infused into the rumen vein of another 5 lambs. Rumen VFA, plasma FAA and immunoreactive insulin (IRI) concentrations were determined over the 72 h postfeeding period and during 24 h after refeeding as well as over 24 h after the VFA infusion. Both postprandial increase of rumen VFA and VFA infusion caused a significant increase of plasma FAA concentrations and an increase in IRI. Feed intake decreased the prefeeding total FAA (TFAA) concentration (2.7mmol/l) to 1.8 mmol/l at 4 h after feeding. I t rose again to 2.5 mmol/l at 24 to 72 h postfeeding. IRI seemed to have the highest concentrations when the TFAA were the lowest. VFA infusion also decreased the plasma TFAA, to about half of the preinfusional value. IRI, however, showed a five-fold increase after infusion. The results of these experiments show that variations in VFA absorption from the rumen due to different nutritional stages result in changes of the plasma FAA concentrations. Insulin seems to have an important role in the control of these changes.

Introduction Ruminal volatile fatty acids (VFA) meet a considerable part of the animal’s energy requirement and markedly affect the animal’s metabolic activities including hormonal functions (HORINOet al., 1968; TRENKLE, 1971; TAO and ASPLUND,1975). Fasting decreases VFA production in the rumen (GALYEAN et al., 1981) and diminishes the blood insulin concentration (TRENKLE, 1971; BOUCHATet al., 1981). In experiments with growing pigs REEDSet al. (1981) demonstrated that increasing the energy content of the diet enhanced protein synthesis. Conversely, during fasting increasing amounts of amino acids are used for glucogenesis (BERGMAN, 1984). Changes in protein synthesis and degradation are usually accompanied by changes in blood plasma free amino acid (FAA) concentrations (BERGER, 1979). Thus, the nutritional state affects blood FAA concentrations. In the present experiments blood FAA concentraU. S. Copyright Clearance Center Code Statement:

0931 - 184)3/90/3705 -0372$02.50/0

373

The Effect of Feed Intake and Portal Volatile Fatty Acid Infusion on Insulin

tions were examined in fed and fasted sheep, and following infusion of VFA into the ruminal vein.

Material and Methods Animals, diet and experimental procedures Ten Worsted Merino ram lambs of 25 ? 1.5 kg body mass were used. One week before starting the experiments polyethylene catheters (Clinical Plastic Products SA, 13 G) were implanted into a jugular vein. In five lambs a catheter was also placed into the vena ruminalis sinistra. The animals were offered ad libitum a concentrate consisting of (%) ground corn 50, ground wheat 10, alfalfa meal 29, sunflower meal (extracted) 10, urea 0.2, and vitamins and minerals 0.35 (net energy 7.04 MJ/kg) and 200 g alfalfa hay per animal. Salt licks and drinking water were available ad fibiturn. Experiment I : After feed was withheld overnight (12h), at 8 a.m. 5 lambs were fed 400g of concentrate and 200 g of hay for 2 h (feeding period). The lambs were then kept without bedding and fasted for 72 h (fasting period). After that time the lambs were refed with concentrate ad libitum and 200 g alfalfa hay (refeeding period). Serial blood samples were taken from the jugular vein, and rumen fluid was collected via an oesophageal tube. The times of sampling are shown in Fig. 1. Experiment 2: Five lambs were deprived of feed overnight (12 h) and were placed in individual cages. A VFA mixture was infused into the left ruminal vein with a peristaltic pump (Pharmacia, P-3), at a rate of 2ml per min for 2 h (10mmol mixture per min). The mixture contained (mol/l) sodium acetate 3, sodium propionate 1.5 and sodium-butyrate 0.5. During 2 h 28.8mmol of sodium acetate, 14.4mmol of sodium propionate and 4.8 mmol of sodium butyrate per kg body weight were infused. Blood samples were taken from the jugular vein. The times of sampling are shown in Fig. 2.

Analytical methods The rumen fluid was acidified with metaphosphoric acid and the VFA concentrations were determined by gas chromatography (HUSVFTH and G A L , 1988). The plasma obtained from heparinized blood was deproteinized with sulfosalicylic acid. FAA concentrations in deproteinized plasma were determined by ion-exchange chromatography, using an F E E 0 ~

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HUSV~TH and GALFI

LKB-4101 amino acid analyser (KEDENBURG, 1971). Immunoreactive insulin (IRI) of blood plasma was measured with a Boehringer ELISA kit (Ca. 199648). From the FAa concentration profile, total essential amino acids (TEAA = Thr + Cys + Val + Met + Leu + Ile + Tyr + Phe + Lys + His) and total non-essential amino acids (TNEAA = Asp + Ser + Glu + Glu - NH2 + Gly + Ala + Arg) were calculated. The sum of TEAA and TNEAA was the total free amino acid (TFAA) concentration. Results of both experiments were statistically analyzed by using analysis of variance procedures according to GILL(1978). In experiment 2 linear correlation analysis was performed between the values of plasma IRI, and TFAA, TEAA and TNEAA by the method of least squares.

Results Experiment 1 During the 72 h fasting period the VFA concentration in the rumen initially rose, and then declined to about one-third of its initial value. The VFA concentration rose again after refeeding. The IRI concentration in plasma reflected the changes in rumen VFA concentration (Table 1). Both plasma TEAA and TNEAA concentrations significantly (I'< 0.001) decreased for 7 h after feeding, with the biggest drop between 4 and 7 h (Table 1). Subsequently the concentrations of TEAA and TNEAA rose. However, while the TEAA concentrations steadily increased even between 48 and 72h of fasting, the TNEAA concentration significantly (I'< 0.001) declined at that time. Refeeding again reduced the TFAA concentration, with lowest values between 4 and 7h. The decrease of the TEAA was more pronounced than that of the TNEAA. The increase of the essential amino acids (EAA) in the fasting period was the biggest for the ketogenic amino acids such as Leu, Lys and Thr (Fig. 3). In contrast to the EAA, the

Table 1. VFA concentration of the rumen fluid and IRI, TFAA, TNEAA and TEAA concentration of the blood plasma at different times of fasting (after feeding) and refeeding' Time of sampling h

VFA mmol/l

IRI

mU/I

TFAA mmol/l

TEAA mmol/l

TNEAA mmol/l

Fasting 0 2 4 7 10 14 19 24 48 72

60.9 f 10.3 121.0f 14.7 121.4 f 16.6 61.3 i 9.5 37.5 f 3.3 38.9 f 3.3 35.02 4.9 28.2 f 1.8 23.1 f 4.5 20.4k 3.5

15.1 f 1.3 25.0 f 3.0 20.1 f 2.7 18.1 f 1.9 16.1 f 2.3 16.6 f 1.2 12.2 f 1.9 7.9 f 0.3 4.2 f 1.0 3.6 f 0.5

2.7 f 0.2 2.4 f 0.3 1.8 f 0.3 1.7 f 0.2 2.1 f 0.1 2.4 f 0.4 2.5 f 0.2 2.5 f 0.3 2.4 f 0.3 2.5 f 0.2

1.1 f 0.1 1.0 f 0.1 0.6 2 0.1 0.6 f 0.1 0.7 f 0.1 0.8 f 0.1 0.9 f 0.1 0.9 f 0.2 1.3 f 0.2 1.3 f 0.2

1.6 f 0.2 1.3 k 0.3 1.2 _+ 0.2 1.1 f 0.2 1.4 f 0.2 1.6 f 0.3 1.6 f 0.2 1.6 f 0.1 1.1 iz 0.2 1.2 f 0.3

Refeeding 2 4 7 10 14 24

52.8 f 11.3 115.52 16.1 114.2 f 13.0 83.2 f 14.0 74.6 f 15.7 74.3 f 14.2

16.0 f 1.0 20.1 f 2.1 14.1 f 0.9 16.1 f 2.2 14.9 f 1.3 14.7 f0.8

2.4 f 0.3 1.6 f 0.3 1.7 f 0.3 2.2 f 0.2 2.5 f 0.2 2.7 t 0.2

1.2 f 0.2 0.6 f 0.1 0.6 f 0.1 0.8 f 0.1 0.9 f 0.1 1.0 f 0.2

1.2 f 0.1 1.0 f 0.1 1.1 f 0.2 1.4 f 0.2 1.6 f 0.3 1.6 f 0.3

0.3 0.9

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LSDZ P < 0.05 P < 0.001 I

13.7 24.3

2.3 7.8

Values listed are means f SE for 5 animals. Least significant difference.

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The Effect of Feed Intake and Portal Volatile Fatty Acid Infusion on Insulin

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Fig. 3. Changes in the blood plasma concentration of Leu, Lys and Thr in lambs (n times of fasting (after feeding) and refeeding

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concentration of important gluconeogenetic non-essential amino acids (NEAA) declined considerably from 24 h of fasting till 4 to 7 h after refeeding (Fig. 4).

Fig.4. Changes in the blood plasma concentration of Ala, Glu, Ser + Glu-NH2 and Gly in lambs (n = 5) at different times of fasting (after feeding) and refeeding

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HUSVBTH and GALFI

Experiment 2 After a 2 h intravenous infusion of VFA, the IRI concentration in plasma increased nearly five-fold, and then returned to the preinfusional values. TEAA concentration showed opposite changes (Table 2). Biometric calculations revealed a negative correlation between IRI and TFAA concentrations (y = 1.80-0.0783~; r = -0.8770; P < 0.01). This correlation was close for both TEAA (y = 1.16-0.0288~; r = -0.8379; P < 0.01) and for T N E A A (y = 1.72-0.0494; r = -0.8896; P

The effect of feed intake and portal volatile fatty acid infusion on insulin and free amino acid concentrations in plasma of lambs.

Experiments were conducted with chronically catheterized growing lambs to study the effect of variations in rumen volatile fatty acid (VFA) supply on ...
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