Inhibition of dipeptidyl-peptidase IV does not increase circulating IGF-1 concentrations in growing pigs.

The enzyme dipeptidyl peptidase-IV (DPP-IV) inactivates a variety of bioactive peptides, including glucagon-like peptide-1 (GLP-1) and growth hormone releasing hormone (GHRH). Inhibiting DPP-IV in order to increase circulating GLP-1 is of interest as a treatment for Type II diabetes. Inactivation of DPP-IV may also increase circulating GHRH, potentially enhancing growth in domestic animals. To test the hypothesis that inhibition of DPP-IV activity will influence the growth hormone/ IGF-1 axis, growing pigs (Sus scrofa domesticus, 78 kg) were treated with a DPP-IV inhibitor (Compound 1, the 2,5-difluor-ophenyl analog of the triazolopiperazine MK0431, sitagliptin), and plasma concentrations of IGF-1 were monitored. Pigs were administered either sterile saline (0.11 ml/kg followed by a continuous infusion at 2 ml/hr for 72 hrs, controls, n = 2), Compound 1 (2.78 mg/kg followed by a continuous infusion at 0.327 mg/kg x hr for 72 hrs, n = 4) or GHRH (0.11 ml/kg sterile saline, followed by a continuous infusion of GHRH at 2.5 microg/ kg x hr for 48 hrs, n = 4). Plasma concentrations of Compound 1 were maintained at 1 microM, which resulted in a 90% inhibition of circulating DPP-IV activity. Relative to the predose 24-hr period, area under the IGF-1 concentration curve (AUC) tended to be lower (P = 0.062) with Compound 1 (.79 +/- 130 ng/ml x hr) than controls (543 +/- 330 ng/ml x hr). GHRH treatment increased the IGF-1 AUC (1210 +/- 160 ng/ml x hr, P = 0.049 vs. controls and P = 0.001 vs. Compound 1). We conclude that inhibition of DPP-IV does not alter the circulating levels of IGF-1 in the growing pig.

Administration of a nonpeptidyl growth hormone secretagogue, L-163, 255, changes somatostatin pattern, but has no effect on patterns of growth hormone-releasing factor in the hypophyseal-portal circulation of the conscious pig.

The activity of the growth hormone secretagog, L-163,255, on growth hormone (GH), growth hormone-releasing factor (GRF), and somatostatin (SRIF) levels was evaluated in a porcine model of hypophyseal portal blood (HPB) collection. Young, castrated pigs had HPB and jugular blood collected for approximately 300 min. The blood collection was divided into discrete periods: baseline (BL) approximately 180 min; GH response period (RSP) approximately 90 min; and positive control period following a GRF bolus, 30 min. RSP was divided into a dominant response period (DOM) and a tail (TL). The spontaneous relationship between HPB GRF and SRIF and peripheral GH during BL has been reported (Proc Soc Exp Biol Med 217:188-196, 1998). The apex of the GH pulse resulting from L-163,255 administration was nonrandomly associated (P < 0.05) with descending periods of SRIF troughs. Frequency and amplitude of GRF and SRIF pulses, and frequency and depth of SRIF troughs were not different between BL and the beginning of DOM (the 20-30 min of GH increase). GH AUC was significantly greater (P < 0.05) for DOM compared to BL and TL, and for TL compared to BL. GRF AUC tended to be greater (P < 0.1) for RSP compared to BL, but the majority of the increase was in the TL period. There were no significant differences in the SRIF AUCs between the sampling periods. Furthermore, in a separate experiment, fos activity (a marker of neuronal activation) in the hypothalamus of pigs was examined after either L-163,255 (1x or 4x), isotonic saline (control), or hypertonic saline (positive control) administration. There were no differences in fos activity in the GRF, SRIF, or CRH immunopositive neurons between L-163,255 treatment and control. The pituitaries of the L-163,255-treated pigs showed marked fos activation compared to the controls. In conclusion, L-163,255 in pigs has its primary effect at the level of the anterior pituitary.

Metabolism of 3H/14C-labeled 4''-deoxy-4''-epimethylaminoavermectin B1a benzoate in chickens. Identification of novel fatty acid conjugates of '4'-deoxy-4''-epimethylaminoavermectin B1a.

The metabolism of 3H/14C-labeled 4"-deoxy-4"-epimethylaminoavermectin B1a (MAB1a) benzoate, the major homologue (>/=90%) of the avermectin insecticide emamectin benzoate, was studied in laying chickens. Ten Leghorn hens (Gallus domesticus) were orally dosed once daily for 7 days (1 mg/kg of body weight/day). Eggs and excreta were collected daily, and eggs were subsequently separated into whites and yolks. Chickens were euthanized within 20 hr after the last dose, and liver, kidney, heart, muscle, fat, ovaries, gizzard, gastrointestinal tract and contents, and carcass were collected. Approximately 70 and 6% of the total administered dose were recovered in the excreta plus gastrointestinal tract and contents and in the tissues plus eggs, respectively. Two novel metabolites, i.e. the 24-hydroxymethyl derivative of the parent compound (24-hydroxymethyl-4"-deoxy-4"-epimethylaminoavermectin B1a) and the N-demethylated derivative of 24-hydroxymethyl-4"-deoxy-4"-epimethylaminoavermectin B1a (24-hydroxymethyl-4"-deoxy-4"-epiaminoavermectin B1a), were identified. In addition, eight fatty acid conjugates of each of these two metabolites, comprising 8-75% of total radioactive residues in tissues and eggs, were isolated and identified. Although this represents some of the most extensive in vivo fatty acid conjugation to a xenobiotic reported to date, potential human exposure to MAB1a residues from consumption of chicken would be extremely low, because the dosage level in this study was approximately 1000-fold greater than the MAB1a residue levels seen in crops and because the majority of the applied dose was recovered in the excreta. Based on these findings, the avian biotransformation of MAB1a differs substantially from the mammalian biotransformation.

Hypophyseal-portal concentrations of growth hormone-releasing factor and somatostatin in conscious pigs: relationship to production of spontaneous growth hormone pulses.

A method of collecting hypophyseal portal blood (HPB) in conscious pigs was used to show the relationship between GRF and somatostatin (SRIF) concentration and peripheral GH response. Six male castrate pigs (approximately 63 kg body weight) had HPB and jugular blood collected individually for an average of 175 min each. Twenty-seven spontaneous GH pulses were detected in the 1050 min of total HPB collection. Of the associations examined, the only significant finding was that GH pulse maxima occurred nonrandomly within periods of SRIF descent (63%; P = 0.005). Although 48% (13/27) of GH pulse maxima were associated with an ascent in portal GRF concentration, these associations were not determined to be nonrandom (P = 0.14). Only 7 of 27 (26%) GH pulse maxima were associated with an ascent in portal GRF concentration and a descent in SRIF concentration occurring simultaneously. A saline infusion given approximately 120 min after beginning blood collection resulted in an increase in SRIF pulse frequency and a decrease in GH-AUC and GRF-AUC. The cause of this saline effect is unknown, but it may have been related to acclimation of the pigs to the blood collection procedure. These data show the complexity of the relationship between SRIF and GRF concentrations and GH secretion and may indicate a close relationship with SRIF in GH pulse generation in the pig. In addition, these data support the hypothesis that, in the pig, mediation of GH release cannot be explained simply by antagonism between GRF and SRIF.

Transorbital approach to the porcine pituitary.

A transorbital approach to the pituitary gland is described in domestic swine weighing between 40 and 70 kg. A transpalpebral eye exenteration is performed and the optic canal is enlarged caudally, using a bone drill. An operating microscope is used to improve visualization of the surgical site as the pituitary stalk and anterior pituitary are exposed to the level of the optic chiasm. This approach exposes the pituitary sufficiently to perform either a hypophyseal stalk transection or a hypophysectomy or to implant cannulas for hypothalamic-hypophyseal portal blood sampling. This technique has been performed in more than 50 pigs without major complications. Postoperative recovery has been rapid and uneventful. The transorbital approach is a significant refinement of the frontal craniotomy and cerebral elevation technique previously described in the pig, and results in shortened surgery time, minimal brain manipulation, and greatly decreased morbidity.

Mediation by the central nervous system is critical to the in vivo activity of the GH secretagogue L-692,585.

To investigate the effect of hypophyseal transection (HST) on GH secretagogue activity of the non-peptidyl GH secretagogue L-692,585 in the conscious pig, male castrated swine were randomly assigned to either a hypophyseal stalk transection group (HST; n = 3) or to a sham-operated control group (SOC; n = 3). Treatments administered were L-692,585 (100 micrograms/kg), human GH-releasing factor(1-29)NH2 (GRF; 20 micrograms/kg) or L-692,585 (100 micrograms/kg) + GRF (20 micrograms/kg) on days -7 to -3 before surgery and days +3 to +8 after surgery. To evaluate the integrity of the pituitary gland, the animals were challenged with corticotropin-releasing hormone (CRH; 150 micrograms) or GnRH (150 ng/kg) both before and after surgery. Blood was collected from -60 to +180 min post treatment and assayed for GH, cortisol and LH. Before surgery, no significant difference (P > 0.05) in peak GH response (ng/ml) was present between the two groups (SOC vs HST) in response to L-692,585 (101 +/- 12 vs 71 +/- 9) or L-692,585 + GRF (171 +/- 21 vs 174 +/- 21). Only two out of three SOC vs three out of three HST pigs responded to GRF (13 +/- 2 vs 25 +/- 3) resulting in a significant difference between groups. Following surgery, significant differences were present in peak GH response (ng/ml) between SOC and HST groups following L-692,585 (79 +/- 6 vs 13.8 +/- 1.0); however, the response to L-692,585 + GRF was similar (115 +/- 8 vs 94 +/- 7). All animals responded to GRF; however, a significant difference was present between groups due to the magnitude of the responses. Whereas the cortisol responses (ng/ml) to L-692,585 in the SOC and HST groups were similar before surgery, a significant difference was present after surgery (44.4 +/- 6.4 vs 14.6 +/- 2.1). No significant difference was noted between the HST and SOC groups in response to CRH or GnRH either before or after surgery. These results indicated that L-692,585 induced an immediate GH response in the intact animal in contrast to GRF where the GH release was variable. L-692,585 also stimulated an immediate increase in cortisol levels. Transection of the hypophyseal stalk dramatically decreased but did not ablate the GH or cortisol response to L-692,585. Co-administration of L-692,585 + GRF induced an immediate GH response of similar magnitude in the intact and HST animal. We conclude that L-692,585 has a direct but limited action at the level of the pituitary and that an intact hypophyseal stalk is required for a maximal GH and cortisol response. L-692,585 acts with GRF at the level of the pituitary to induce a maximal GH response. These findings suggest that L-692,585 stimulates GH secretion by acting in combination with GRF and interrupting the inhibitory tone of somatostatin on the somatotroph.

Colostral milk fat percentage and pig performance are enhanced by feeding the leucine metabolite beta-hydroxy-beta-methyl butyrate to sows.

Three trials were conducted to test whether feeding the leucine metabolite beta-hydroxy-beta-methyl butyrate (HMB) would increase fat content of sows' milk and pig weight gain. All sows received a basal diet and were assigned at random to receive either 2 g of CaCO3/d (control) or 2 g of Ca(HMB)2/d (HMB), which was top-dressed to the basal diet. Treatment began 3 to 4 d before farrowing. In Trials 1, 2, and 3 there were 4, 19, and 11 pairs of sows, respectively. In a combined analysis that included all three trials, milk fat at d 1 was increased by 41% (P = .01) and pig weight at d 21 was increased by 7% (P = .01) for sows fed diets containing HMB compared with sows fed control diets. Sows fed HMB lost more backfat (P = .03); however, sows receiving HMB had more (P < .05) backfat depth at farrowing than control sows. At weaning there was no difference in backfat depth between the treatment groups. Sows fed HMB tended to consume less feed (P = .07) than control sows. In Trials 2 and 3, data were collected on the subsequent reproductive cycles of the sows. A combined analysis of the data revealed no differences in sow performance when sows previously fed the diet containing HMB were compared with sows previously fed the control diet. In conclusion, beta-hydroxy-beta-methyl butyrate, when fed to sows at 2 g/d, resulted in an increase in fat percentage of sow's milk and pig performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Postprandial lipoprotein composition in pigs fed diets differing in type and amount of dietary fat.

To determine the effects of diet on postprandial lipoprotein composition, growing pigs were fed diets containing 20 or 40% of energy as soybean oil, tallow or a 50:50 blend of soybean oil and tallow. At the end of wk 6, a blood sample was drawn from pigs fasted for 12 h. Pigs were then fed, and blood samples were drawn 1 and 4 h later. In LDL, concentrations of free and total cholesterol were greater in pigs fed 40% of energy as fat than in pigs fed 20% of energy as fat (P less than 0.02). Pigs fasted for 12 h had lesser concentrations of triacylglycerol and greater concentrations of phospholipid in LDL and HDL than did pigs fasted for 1 and 4 h (P less than 0.05). In HDL, total cholesterol and phospholipid concentrations were greater in pigs fed 40% of energy as fat than in pigs fed 20% of energy as fat (P less than 0.01). A greater concentration of triacylglycerol was found in VLDL of pigs fed 40% of energy as fat than in pigs fed 20% of energy as fat (P less than 0.01). Amount of dietary fat had a greater effect than did type of dietary fat on composition of lipoproteins from postprandial pigs.

A surgical model for studying biliary bile acid and cholesterol metabolism in swine.

Techniques were developed in young growing pigs to simultaneously collect and reinfuse bile. Silastic cannulae were designed and surgically implanted in the common bile duct and the duodenum. Direct sampling of the hepatic bile was achieved by bypassing the gallbladder. The techniques allowed for steady-state studies of hepatic function to be conducted in conscious swine in two different studies. Pigs, thus surgically modified, can serve as an appropriate model for physiologic, pharmacologic, and nutritional research that involves bile sampling.

Effect of dietary fat source on lipoprotein composition and plasma lipid concentrations in pigs.

Most studies of the effects of dietary fat sources on plasma lipid components have used diets with extreme fat compositions; the current study was designed to more nearly mimic human dietary fat intake. Young growing pigs were fed diets containing either 20 or 40% of energy as soy oil, beef tallow or a 50/50 blend of soy oil and tallow. Different dietary fats did not affect concentrations of cholesterol, triacylglycerol or protein in plasma or major lipoprotein fractions. The concentration of phospholipid was less in plasma and in very low density lipoproteins with soy oil feeding than with tallow feeding. The weight percentage of cholesteryl ester in the low density lipoprotein fraction tended to be greater with 40% than with 20% tallow and tended to be less with 40% than with 20% soy oil. Phospholipid as a weight percentage of low density lipoprotein was least in pigs fed soy oil. Tallow feeding increased the percentage of myristic, palmitic, palmitoleic and oleic acids in plasma, relative to both other groups. Soy oil feeding increased the percentage of linoleic and linolenic acids. These moderate diets were not hypercholesterolemic, but they did alter plasma fatty acid composition and phospholipid concentrations in plasma and very low density lipoprotein.

Influence of dietary calcium and cholecalciferol on composition of plasma lipids in young pigs.

Young growing pigs were fed diets containing either 1 or 3 times the daily requirement of calcium and 1, 5 or 25 times the daily requirement of vitamin D (as cholecalciferol) in a completely randomized design with treatments in a 2 X 3 factorial arrangement. Excess dietary calcium increased the phospholipid concentration in the plasma, but not its partitioning among plasma lipoproteins. The level of dietary calcium had no effect on cholesterol, triacylglycerol or protein concentrations in plasma or their partitioning among plasma lipoproteins. Excess dietary calcium decreased body weight gains of pigs. The level of dietary cholecalciferol had no effect on body weight gain or on the concentrations of cholesterol, phospholipid, triacylglycerol or protein in plasma, or on their partitioning among plasma lipoproteins. Increased vitamin D intake resulted in increased plasma 25-hydroxycholecalciferol, whereas high dietary calcium decreased concentrations of 1,25-dihydroxy-vitamin D. Increased dietary calcium also increased plasma calcium concentrations of only plasma phospholipids and decreased growth rate, whereas excess dietary vitamin D had no effect on growth or lipid composition of plasma in growing pigs.

Automated enzymatic method for the determination of ammonia: application to rumen fluid, gut fluid, and plasma.

The enzymatic method for the determination of ammonia with glutamate dehydrogenase has been adapted to the AutoAnalyzer. The automated method was applicable for NH(3) measurement in sheep rumen samples, swine gut fluid samples, and bovine plasma. Results were compared with those of the Conway diffusion method and the manual enzymatic method. The automated method allows 30 samples per h to be analyzed routinely. Values were comparable with those with the manual method, but lower than those with the Conway diffusion method.