Influence of abomasal infusion of glucose or partially hydrolyzed starch on pancreatic exocrine secretion in beef steers

Five crossbred steers (348 +/- 12 kg) fitted with a pancreatic pouch draining the main pancreatic duct and duodenal re-entrant and abomasal infusion cannulas were used in a 5 x 5 Latin square design to determine the influence of postruminal carbohydrate source and level on pancreatic exocrine secretion in beef steers. Abomasal infusion treatments (250 mL infused/h) were water (control), 20 g/h glucose, 40 g/h glucose, 20 g/h starch hydrolysate (SH), and 40 g/h SH. Infusion periods were 8 d with 3 to 4 d of rest between periods. Pancreatic juice was collected for 6 h on d 8 of each collection period. Every 30 min a 10% subsample was composited and frozen and the remainder was infused into the duodenum via the reentrant cannula. Abomasal infusion of glucose or SH increased (P < 0.10) total secretion of pancreatic juice and decreased (P < 0.10) secretion of alpha-amylase activity. Abomasal carbohydrate infusion did not influence total secretion of protein, trypsin activity, or chymotrypsin activity. This experiment indicates that increasing postruminal glucose or SH decreases pancreatic alpha-amylase secretion.     

Exocrine pancreatic secretion in pigs fed sow's milk and milk replacer, and its relationship to growth performance

The objective of this study was to quantify and compare the effects of sow's milk and 2 milk replacer diets (containing clotting or non-clotting protein sources) on exocrine pancreatic secretion, plasma cholecystokinin, and immunoreactive cationic trypsin in pigs. In addition, the relationship between exocrine pancreatic secretion and growth in milk-fed pigs was studied. In a changeover experiment, 9 chronically catheterized pigs of 6.6 +/- 0.19 kg of BW were studied for 3 wk. Pigs were assigned to each of 3 diets. Exocrine pancreatic secretion was measured from the third to the seventh day on each diet. The protein content and trypsin activity of the pancreatic juice were measured. Blood samples were taken at 10 min before and after milk ingestion and were analyzed for cholecystokinin and immunoreactive cationic trypsin. Pancreatic protein and trypsin secretion did not differ between pigs fed sow's milk and those fed milk replacer, but the volume secreted was less for the pigs fed sow's milk (0.75 vs. 1.03 mL x kg(-1) x h(-1); P < 0.01). A postprandial response to milk intake was not observed. The 2 milk replacer diets did not affect exocrine pancreatic secretion differently. The average exocrine pancreatic secretion (volume, 0.94 mL x kg(-1) x h(-1); protein, 4.28 mg x kg(-1) x h(-1); trypsin, 1.65 U x kg(-1) x h(-1)) was intermediate between literature values for suckling and weaned pigs. Plasma cholecystokinin was elevated (approximately 18 pmol x L(-1)) and showed low correlations with the pancreatic secretion traits. Plasma immunoreactive cationic trypsin was not significantly related to any of the pancreatic secretion traits and should therefore not be used as an indicator for exocrine pancreatic function in milk-fed pigs. Exocrine pancreatic secretion varied substantially among individual pigs (protein, 0.22 to 13.98 mg x kg(-1) x h(-1)). Pancreatic protein and trypsin secretion showed a positive, nonlinear relationship with performance traits. It was concluded that neither specific sow's milk ingredients nor the protein source are responsible for a low pancreatic protein secretion in suckling pigs. Exocrine pancreatic secretion was positively correlated with ADG in pigs at an identical milk intake.     

Influence of rumen escape starch on pancreatic exocrine secretion of goats

The objective of the experiment was to evaluate the effect of rumen escape starch (RES), accomplished by altering dietary starch concentrations on pancreatic exocrine secretion of goats. Four goats (36.8 ± 3.2 kg) with common bile duct re‐entrant and duodenal catheters were used in a 4 × 4 Latin square. Goats were fed diets containing 20%, 30%, 40% and 50% starch. Periods consisted of 10 day adaptation followed by 3 day of sample collection. Juice was collected in 1‐h fractions continuously for 72 h. Total juice secreted was recorded, and 3% sub samples were retained to form a composite sample. The remaining fluid was returned to the duodenum. Juice composite samples were analyzed for activities of α‐amylase, trypsin, chymotrypsin and lipase. Secretion of pancreatic α‐amylase was lower (p < 0.05) when comparing lambs fed 20% starch diet with 30%, 40% and 50% starch diets. Lipase secretion was greater (p < 0.05) in lambs fed 40% starch diet compared with the other diets. Total secretion of juice, trypsin and chymotrypin was not affected (p > 0.05) by dietary starch concentration. Rumen escape starch increased with increasing dietary starch concentration (p < 0.05). Regression analysis showed that increasing RES results in a quadratic increase (p < 0.05) in pancreatic α‐amylase and lipase secretion, and the secretion of α‐amylase and lipase is maximum when RES is 113 and 83 g/day respectively. These results suggest that optimal RES for pancreatic secretion of α‐amylase and lipase is 80–110 g/day in adult goats.     

Effects of substance P on fluid and amylase secretion in exocrine pancreas of rat and mouse

The effects of substance P on fluid and amylase secretion were examined in the exocrine pancreas of the rat and the mouse in vivo and in vitro. In the anaesthetised rat, a single intravenous injection of substance P caused an atropine resistant increase in both the basal and caerulein stimulated flow of pancreatic juice and amylase output, but reduced the secretin stimulated pancreatic juice flow. In vitro experiments using superfused mouse pancreatic fragments supported the in vivo result showing that substance P enhanced caerulein stimulated amylase output.     

Pancreatic exocrine secretion and plasma concentration of some gastrointestinal hormones in response to abomasal infusion of starch hydrolyzate and/or casein

Eight Angus steers (290 +/- 8 kg), surgically prepared with pancreatic pouch-duodenal reentrant cannulas and abomasal infusion catheters were used in a replicated 4 x 4 Latin square experiment to investigate the effects of abomasal infusion of starch hydrolyzate (SH) and/or casein on pancreatic exocrine secretion and plasma concentration of hormones. Steers were fed a basal diet of alfalfa (1.2 x NEm) in 12 equal portions daily. Abomasal infusion treatments (6-L total volume infused per day) were water (control), SH [2.7 g/(kg BW x d)], casein [0.6 g/(kg BW x d)], and SH + casein. Periods were 3 d for adaptation and 8 d of full infusion. Pancreatic juice and jugular blood samples were collected over 30-min intervals for 6 h on d 11. Weight and pH of pancreatic samples were measured, and a 10% subsample was composited and frozen until analysis of total protein and pancreatic enzyme activities. The remaining sample was returned to the duodenum. Plasma was harvested and frozen until analyzed. Pancreatic juice (67 mL/h) and protein (1.8 g/h) secretion rates were not affected by nutrient infusion. There were SH x casein interactions for all pancreatic enzyme secretions (U/h; alpha-amylase, P < 0.03; trypsin, P < 0.08; and chymotrypsin, P < 0.03) and plasma insulin concentration (P < 0.10). Secretion of pancreatic enzymes was increased by SH (trypsin) and casein (alpha-amylase, trypsin, and chymotrypsin) but not when SH + casein were infused together. Glucose (P < 0.10) and cholecystokinin octapeptide concentrations (CCK-8; P < 0.05) were increased by SH, but glucagon was decreased (P < 0.10). Casein decreased (P < 0.10) plasma CCK-8 concentrations. These data indicate that positive effects of postruminal casein on enzyme secretion were inhibited by SH, emphasizing the complexity of the regulatory mechanisms involved in dietary adaptation of pancreatic exocrine secretion. Changes in hormone concentration may not relate directly to changes in enzyme secretion.     

Influence of substrate and/or neurohormonal mimic on in vitro pancreatic enzyme release from calves postruminally infused with partially hydrolyzed starch and/or casein

Our objectives were to determine the effects of neuroendocrine challenge and substrates on in vitro alpha-amylase and trypsin release in pancreatic tissue collected from Holstein calves (n = 24; 88 +/- 3 kg) abomasally infused for 10 d with tap water (control), partially hydrolyzed starch (SH; 4 g/[kg of BW x d]) and/ or casein (0.6 g/[kg of BW x d]). The caudal portion of the pancreas was removed, rinsed with ice-cold saline, cut into approximately 2 x 2-mm segments, and incubated in oxygenated Krebs Ringer bicarbonate buffer containing no substrate (control), glucose, amino acids, or VFA at 39 degrees C. After 60 min of incubation, neurohormonal mimics (none; control), carbachol (acetylcholine analog; 10 microM final), or caerulein (cholecystokinin mimic; 100 nM final) were added to the flasks and tissue was incubated for 60 min. Pancreatic tissue concentrations and in vitro release of alpha-amylase and trypsin decreased (P < 0.001) in calves abomasally infused with SH. Carbachol increased (P < 0.10) alpha-amylase and trypsin release in tissue collected from all calves. An effect of caerulein to increase alpha-amylase release (P < 0.10) was only observed with prior exposure to abomasal casein infusion in vivo or with simultaneous incubation with amino acids in vitro. Caerulein increased (P < 0.10) trypsin release in tissue collected from all calves except for those receiving SH + casein. Glucose decreased (P < 0.10) alpha-amylase release from pancreatic tissue collected from calves receiving abomasal control and casein treatments. Amino acids decreased (P < 0.10) alpha-amylase and trypsin release from pancreatic tissue collected from calves receiving the abomasal control treatment. Glucose, amino acids, and VFA decreased (P < 0.10) trypsin release from tissue collected from calves receiving abomasal SH. These data indicate that carbachol can stimulate pancreatic enzyme release in vitro. Caerulein, however, is only effective in stimulating in vitro pancreatic enzyme release in tissue from calves with an increased postruminal protein supply or in tissue incubated with amino acids. The results indicate that postruminal and local nutrients might be important in altering the responsiveness to a neuroendocrine challenge and could be an important regulatory event involved with dietary adaptation in ruminants.     

Relations between body weight, feed intake, daily weight gain, and exocrine pancreatic secretion in chronically catheterized growing pigs

The aim of this investigation was to develop models that would make it possible to correct exocrine pancreatic secretion data for the effect of BW and feed intake in growing pigs. In addition, the significance of exocrine pancreatic secretion for daily weight gain (DWG) was studied. Data were used from 10 pigs (16 to 32 kg BW) surgically fitted with chronic pancreatic catheters. The samples were collected under controlled conditions for two to five experimental days per animal (a total of 39 observations), during 2 h preprandially and during 2 h when feeding (postprandially). The exocrine pancreatic secretion traits included the hourly output of volume, the amount of protein, and trypsin and amylase activities. Multiple linear regressions were used to develop models to describe exocrine pancreatic secretion. The individual pig was the most important source of variation in the model. With increasing BW, 7 out of 10 pigs showed an increase in exocrine pancreatic secretion. However, the slopes of the regression lines differed between animals, which made it impossible to develop general models for the correction of secretion data for the effect of BW. Postprandial exocrine pancreatic secretion was always higher than preprandial secretion, but the amount of feed intake per se did not seem to affect secretion. Exocrine pancreatic secretion and DWG were positively correlated. We concluded that, under the present circumstances, expressing secretion per kilogram BW or kilogram feed intake was not feasible. Expressing secretion per hour was the best way to present the data.     

Pancreatic exocrine secretion in steers infused postruminally with casein and cornstarch

Our objective was to evaluate the effect of postruminal protein infusion on pancreatic exocrine secretions. One Holstein, two crossbred, and five Angus steers (305 +/- 5 kg) with pancreatic pouch-duodenal reentrant cannulas and abomasal infusion catheters were used in a replicated 4 x 4 Latin square. All steers were abomasally infused with 1,050 g/d of raw cornstarch with treatments of 0, 60, 120, or 180 g/d of sodium casein suspended in water to yield 6,000 g/d of infusate daily. Steers were limit-fed (1.5 x NEm; 12 equal portions daily) a 90% corn silage, 10% supplement diet formulated to contain 12.5% CP. Periods consisted of 3 d of adaptation to infusion, 7 d of full infusion, 1 d of collection, and 7 d of rest. Pancreatic juice was collected in 30-min fractions continuously for 6 h. Total juice secreted and the pH of individual fractions were recorded, a 10% subsample was retained to form a composite sample, and remaining fluid was returned to the duodenum. Juice composite samples were stored (-30 degrees C) until analyzed for total protein and activities of alpha-amylase, trypsin, and chymotrypsin. Casein infusion linearly increased alpha-amylase concentration (182 to 271 units/mL; P < 0.02; 17.5 to 24.6 units/mg of protein; P < 0.03) and secretion rate (26,847 to 41,894 units/h; P < 0.01). Total juice secretion (155 g/h), pH of pancreatic juice (8.13), secretion rate of protein (1,536 mg/h), and concentration of protein (10.2 mg/mL) in pancreatic secretions were not affected (P > 0.05) by casein infusion. Similarly, casein infusion did not change 0.05) trypsin and chymotrypsin concentrations (1,379 and 349 units/L or 0.134 and 0.033 units/mg of protein, respectively) or secretion rates (206 and 52 units/h, respectively). Abomasal infusion of protein with starch stimulated a greater pancreatic secretion of alpha-amylase activity into the intestine than infusion of starch alone.     

Leucine markedly regulates pancreatic exocrine secretion in goats

Four goats (30.1 ± 1.3 kg) with common bile duct re‐entrant catheter and duodenal catheter were used to evaluate the effects of duodenal leucine infusion on pancreatic exocrine secretion and plasma parameters with two 4 × 4 Latin square design experiments. In the long‐term infusion experiment, goats were fed twice daily [700 g/day, dry matter (DM) basis] at 8:00 and 18:00 hours and were duodenally infused with 0, 3, 6, 9 g/day leucine for 14 days. Pancreatic juice and jugular blood samples were collected over 1‐h intervals for 6 h daily from d 11 to 14 days to encompass a 24‐h day. In the short‐term experiment, goats were infused leucine for 10 h continuously at the same infusion rate with Experiment 1 after feed deprivation for 24 h repeated every 10 days. Pancreatic juice and blood samples were collected at 0, 1, 2, 4, 6, 8 and 10 h of infusion. The results showed that the long‐term leucine infusion did not affect pancreatic juice secretion, protein output, trypsin and lipase secretion and plasma insulin concentration, but linearly increased α‐amylase secretion. No changes in pancreatic protein and lipase secretion were observed in the short‐term infusion. Pancreatic juice and α‐amylase secretion responded quadratically, with the greatest values observed in the 3 and 6 g/day leucine respectively. Trypsin secretion linearly decreased, while plasma insulin concentration increased linearly with increased leucine infusion. The results demonstrated that duodenal leucine infusion dose and time dependently regulated pancreatic enzyme secretion not associated with the change in plasma insulin concentration.     

Differential effects of the endocrine-disrupting compounds bisphenol-A and octylphenol on gonadotropin secretion, in prepubertal ewe lambs

This study examined the effects of long-term exposure to the endocrine-disrupting compounds (EDCs) Bisphenol-A (BPA) and Octylphenol (OP) on gonadotrophin secretion in pre-pubertal female sheep. Four-week-old, female lambs were randomly allocated to four groups (n=6), and twice each week treated with i.m. injections of either corn oil (vehicle controls), diethylstilbestrol (DES; 0.175mg/kg), BPA (3.5mg/kg) or OP (3.5mg/kg). After 5 weeks of treatment, animals were ovariectomized (ovx) and ovary weights recorded. Two weeks later, blood samples were collected from lambs every 15min for 6h, for LH pulse analysis. Animals were then euthanased and adrenal and kidney weight recorded. An age-related increase in tonic LH secretion was noted in Control, BPA- and OP-treated lambs, but was absent in DES-treated lambs. Following ovx, LH secretion increased in all except DES-treated lambs; FSH concentrations increased in all groups. BPA and DES significantly suppressed LH pulse frequency (C: 6.7+/-0.3pulses/6h, DES: 1.5+/-0.8pulses/6h, BPA: 2.3+/-0.8pulses/6h) and amplitude (C: 7.1+/-1.0ng/ml, DES: 1.9+/-0.6ng/ml, BPA: 1.6+/-0.4ng/ml). OP had no effect on LH secretion (Frequency: 5.8+/-0.5pulses/6h, amplitude: 8.0+/-2.0ng/ml). Ovary weight was similar among all groups. Results show that chronic in vivo exposure of prepubertal female lambs to BPA, at levels lower than those reported previously, can have significant effects on LH secretion that are comparable to those seen following exposure to the known xenoestrogen, DES. Exposure to an equal dose of the EDC OP, over the equivalent period of time was without effect on gonadotropin secretion in the prepubertal ewe lamb. These results indicate that exposure of prepubertal female lambs to the EDC BPA can induce significant effects on gonadotropin secretion, the potential long-term effects of exposure and the effects of these changes on reproductive performance and efficacy, therefore, merit further study.     

Regulation of pancreatic exocrine secretion in goats: differential effects of short‐ and long‐term duodenal phenylalanine treatment

Four yearling goats (31.2 ± 2.5 kg), surgically fitted with common bile duct reentrant and duodenal catheter, were used in two 4 × 4 Latin square design experiments to investigate the effects of duodenal infusion of phenylalanine for different times on pancreatic exocrine secretion (PES). In experiment 1 (the long‐term experiment), goats were duodenally infused with 0, 2, 4 or 8 g/day phenylalanine for 14 day. Pancreatic juice and jugular blood samples were collected over 1‐h intervals for 6 h daily from day 11 to day 14 to encompass a 24‐h day. In experiment 2 (the short‐term experiment), goats were infused with phenylalanine for 10 h continuously at the same infusion rate as experiment 1 after feed deprivation for 24 h repeated every 10 day. Pancreatic juice and blood samples were collected at 0, 1, 2, 4, 6, 8 and 10 h of infusion. The volume and pH of pancreatic juice were measured, and a 5% subsample was composited and frozen until analysis of enzyme activities. Plasma was frozen until analysis of insulin and cholecystokinin (CCK). In experiment 1, pancreatic juice, α‐amylase secretion and plasma CCK concentration responded quadratically (p < 0.05), with the top value observed at the 2 g/day phenylalanine. Trypsin secretion had a quadratic response (p < 0.05), with secretion increasing up to 4 g/day phenylalanine and decreasing thereafter. Phenylalanine linearly decreased pancreatic protein and lipase secretion (p < 0.05). The results of correlation analysis showed significant correlations (p < 0.05) between plasma CCK concentration and secretion of α‐amylase and trypsin. However, the short‐term phenylalanine infusion did not influence (p > 0.05) pancreatic juice, protein, α‐amylase, lipase, trypsin secretion and plasma CCK concentration. These results indicate PES of ruminants is stimulated by phenylalanine and is potentially mediated by CCK in the long‐term duodenal infusion treatment, but is not influenced by phenylalanine in the short‐term duodenal infusion treatment.     

Collection of pancreatic exocrine secretions by formation of a duodenal pouch in cattle.

Collection of exocrine pancreatic secretions from cattle by use of a single-unit cannula was performed. The major advantage of the cannula was simple technical management. A small pouch of the duodenum into which the major pancreatic duct drains was formed. Continuity of the duodenum was reestablished by end-to-end anastomosis. A side arm of the cannula was inserted into the pouch to collect exocrine secretions, and the main portion of the cannula was placed cranial to the anastomosis to return pancreatic secretions to the small intestine between collection periods. The accessory pancreatic duct was ligated in 2 of 4 cattle to evaluate possible secretory contribution from this source. All cattle remained healthy after cannulation, and cattle gained approximately 100 kg of body weight in the 5 months after surgery. The mean secretory rate for exocrine pancreatic secretion in cattle was 106 +/- 6.8 ml/h. There was no effect of feeding on the pattern of secretion nor were there significant differences between cattle. A fistula formed between the pouch and duodenum approximately 120 days after surgery in the first 2 cattle used. Development of fistulas was prevented for 300 days in subsequently prepared cattle by use of surgical mesh around the cannulas, leading to functional cannulation sites. Preparation of a duodenal pouch appeared useful for long-term studies of pancreatic exocrine secretion in cattle.     

Growth hormone secretion and pancreatic function following somatostatin infusion in ducks (Anas platyrhynchos)

The intravenous infusion of somatostatin (800 ng/kg min) reduced the concentration of growth hormone (GH) in the plasma of 4 to 5, 6 to 7 and 8 to 9 week-old ducklings, but not in adult ducks. The inhibition of GH secretion was not due to accompanying changes in pancreatic function, since the infusion of a lower dose of somatostatin (200 ng/kg min) increased glucagon release and decreased plasma free fatty acids (FFA), as observed with the higher dose, but had no effect on GH concentrations. The withdrawal of somatostatin inhibition resulted in rebound GH secretion in immature birds, the magnitude of which was directly related to the pre-treatment level. Following somatostatin infusion (800 ng/kg min) no modification in GH concentration was observed in adult ducks. These results demonstrate that basal GH release in young birds is not autonomous and is suppressible by somatostatin. The data provide further evidence for age-related changes in the control of avian GH and insulin release and for the independence of the effects of somatostatin on the pituitary and pancreas glands.     

Effects of xylazine on the stress response to transport in male goats.

A 20-min van journey increased plasma cortisol concentrations to 15-25 ng/ml in male goats, blood glucose concentrations were not affected, but respiratory rates and heart rates were increased, the latter by 40 beats per min. A 2-h van journey increased plasma cortisol to greater than 25 ng/ml and blood glucose to greater than 5 mmol/l. Respiratory rates were increased to greater than 40 breaths per min and heart rates by greater than 100 beats per min. Xylazine alone (0.01 mg/kg) suppressed resting plasma cortisol concentrations, increased blood glucose concentrations to 4.5 +/- 0.8 mmol/l and suppressed respiratory rates by 5-10 breaths per min and heart rates by 20 beats per min. Cortisol concentrations were suppressed by xylazine treatment if given before a 20-min van journey, and for approximately 60 min if given 20 min after the start of a 2-h journey. When combined with transport, xylazine caused an additive effect on glucose concentrations, but suppressed respiratory and heart rates. However, for the latter criteria the timing of suppression was different depending on the time of onset and duration of the stressor. Injection of 50 micrograms ovine corticotrophin releasing factor (CRF) caused an immediate elevation of cortisol concentrations (but not glucose) which lasted for at least 6 h compared with the return to baseline within 60 min after either length of journey. Xylazine pretreatment did not alter the cortisol response to CRF, suggesting that xylazine must act centrally above pituitary level when blocking the cortisol response to transport. It is proposed that under resting conditions the hypothalamus is under alpha 2-adrenergic suppression. Stimulation of cortisol secretion in response to a stressor can be inhibited by an alpha 2-adrenergic agonist.     

Effects of estradiol-17 beta, naloxone and gonadotropin releasing hormone on postpartum secretion of luteinizing hormone in fall-lambing ewes

The interaction among exogenous estradiol-17 beta, naloxone and gonadotropin releasing hormone (GnRH) in the control of luteinizing hormone (LH) secretion was studied in intact postpartum ewes nursing their offspring. One-half of 30 fall-lambing ewes were implanted subcutaneously with an estradiol-17 beta containing Silastic capsule between postpartum d 1 and 12 which doubled their serum concentrations of estradiol (16.0 +/- .1 vs 8.4 +/- .1 pg/ml). Blood samples were collected from implanted and non-implanted ewes at 15-min intervals for 5 h on d 3, 8, 13, 20 and 28 postpartum. Pre-injection samples were collected for 1 h, and ewes were injected with saline, naloxone (NAL;1 mg/kg) or GnRH (100 micrograms/ewe). When averaged across all days and implant groups, serum LH in the three post-NAL samples was higher (P less than .05) than in the three pre-NAL samples (3.6 +/- 1.2 vs .6 +/- .2 ng/ml). Post-GnRH concentrations of serum LH were lower (P less than .05) in estradiol-implanted ewes than in non-implanted ewes on d 8 and 13, but there were no differences in any LH characteristics on d 20 and 28 after implant removal on d 12. In non-implanted ewes, serum LH responses to GnRH increased (P less than .05) eightfold from d 3 (3.8 +/- 1.4 ng/ml) to d 8 (31.6 +/- 1.4 ng/ml), remained elevated through d 20, but declined by d 28 (10.8 +/- 1.4 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary adenylate cyclase-activating polypeptide induces secretion of growth hormone in cattle.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hypothalamic neuropeptide that stimulates release of growth hormone (GH) from cultured bovine anterior pituitary gland cells, but the role of PACAP on the regulation of in vivo secretion of GH in cattle is not known. To test the hypothesis that PACAP induces secretion of GH in cattle, meal-fed Holstein steers were injected with incremental doses of PACAP (0, 0.1, 0.3, 1, 3, and 10 microg/kg BW) before feeding and concentrations of GH in serum were quantified. Compared with saline, injection of 3 and 10 microg PACAP/kg BW increased peak concentrations of GH in serum from 11.2 ng/ml to 23.7 and 21.8 ng/ml, respectively (P < 0.01). Peak concentrations of GH in serum were similar in steers injected with 3 or 10 microg PACAP/kg BW. Meal-fed Holstein steers were then injected with 3 microg/PACAP/kg BW either 1 hr before feeding or 1 hr after feeding to determine if PACAP-induced secretion of GH was suppressed after feeding. Feeding suppressed basal concentrations of GH in serum. Injection of PACAP before feeding induced greater peak concentrations of GH in serum (19.2 +/- 2.6 vs. 11.7 +/- 2.6 ng/ml) and area under the response curve (391 +/- 47 vs. 255 +/- 52 ng. ml(-1) min) than injection of PACAP after feeding, suggesting somatotropes become refractory to PACAP after feeding similar to that observed by us and others with growth hormone-releasing hormone (GHRH). We concluded that PACAP induces secretion of GH and could play a role in regulating endogenous secretion of GH in cattle, perhaps in concert with GHRH.     

Orexin-B modulates luteinizing hormone and growth hormone secretion from porcine pituitary cells in culture

To test the hypothesis that orexin-B acts directly on the anterior pituitary to regulate LH and growth hormone (GH) secretion, anterior pituitary cells from prepuberal gilts were studied in primary culture. On day 4 of culture, 10(5) cells/well were challenged with 0.1, 10 or 1000 nM GnRH; 10, 100 or 1000 nM [Ala15]-hGRF-(1-29)NH2 or 0.1, 1, 10 or 100 nM, orexin-B individually or in combinations with 0.1 and 1000 nM GnRH or 10 and 1000 nM GRF. Secreted LH and GH were measured at 4 h after treatment. Basal LH and GH secretion (control; n = 6 pigs) was 183 +/- 18 and 108 +/- 4.8 ng/well, respectively. Relative to control at 4 h, all doses of GnRH and GRF increased (P < 0.0001) LH and GH secretion, respectively. All doses of orexin-B increased (P < 0.01) LH secretion, except for the 0.1 nM dose. Basal GH secretion was unaffected by orexin-B. Addition of 1, 10 or 100 nM orexin-B in combinations with 0.1 nM GnRH increased (P < 0.001) LH secretion compared to GnRH alone. Only 0.1 nM (P = 0.06) and 100 nM (P < 0.001) orexin-B in combinations with 1000 nM GnRH increased LH secretion compared to GnRH alone. All doses of orexin-B in combination with 1000 nM GRF suppressed (P < 0.0001) GH secretion compare to GRF alone, while only 0.1 nM orexin-B in combination with 10 nM GRF suppressed (P < 0.01) GH secretion compared to GRF. These results indicate that orexin may directly modulate LH and GH secretion at the level of the pituitary gland.     

Lamprey GnRH‐III Releases Luteinizing Hormone but not Follicle Stimulating Hormone in Pigs

The effect of exogenous administration of lamprey GnRH‐III (IGnRH‐III) on gonadotropin secretion was evaluated in pigs. Six crossbred barrows (82.4 ± 3.5 kg body weight) were assigned randomly to a replicated 3 × 3 Latin square design to evaluate the effect of 0.1, 1.0 or 10.0 μg/kg body weight of exogenous IGnRH‐III on LH and FSH secretion. To facilitate blood collection and infusion of IGnRH‐III, barrows were catheterized in the jugular vein 1 day before initiation of experiments. Blood samples were taken at 10‐min intervals for 6 h, starting 2 h before treatments were applied. Relative concentrations of LH and FSH were calculated by obtaining the ratio of the average concentration of each hormone 2 h after infusion divided by the average concentration during the 2 h before infusion. Relative concentrations of FSH after IGnRH‐III infusion did not influence mean concentration of FSH at any of the doses; yet 10.0 μg/kg body weight had a significant effect on LH secretion (p < 0.01). Relative concentrations of LH averaged 1.2, 1.0 and 3.0 ng/ml (for doses of 0.1, 1.0 and 10.0 μg/kg body weight of IGnRH‐III respectively). Only a dose of 10 μg/kg body weight elicited a significant LH increase that was associated with exogenous IGnRH‐III infusion. We conclude that IGnRH‐III is a weak GnRH agonist and at high doses, IGnRH‐III has the ability to release LH but not FSH in barrows.     

The response of bile secretion and ubiquinone Q10 to hyperglycaemia in sheep

The aim of these investigations was to establish the secretion of ubiquinone Q10 (UQ10) in bile of sheep under glucose-induced cholestasis. Experiments were performed on 9 cannulated sheep divided into three groups: I-infused with sodium taurocholate, II-with Na-taurocholate plus glucose, III-with Na-taurocholate and glucose plus propranolol, phentolamine and atropine. Infusion of glucose increased plasma glucose concentration from 3.89 +/- 0.593 mM/l to 12.69 +/- 0.852 mM/l in 90 min and produced elevation of plasma insulin from 124.68 +/- 1.984 to 839.54 +/- 29.212 pM/l. Employment of blocking agents reduced insulin release to maximum 685.71 +/- 50.087 pM/l in 90 min. Under infusion of Na-taurocholate, bile flow averaged 14.016 +/- 0.706 microl/min/kg b wt. In the second group, bile flow decreased to 7.08 +/- 0.59 microl/min/kg b wt. in 90 min, and reached 11.25 +/- 0.25 microl/min/kg b wt in 240 min. Addition of the blocking agents in the third group, resulted in a significant (p < 0.05) decrease in bile flow to 3.733 +/- 0.680 microl/min/kg b wt in 105 min. This reduction of bile flow occurred with significant (p < 0.05) reduction of bile acids secretion that averaged 0.032 +/- 0.087 mM/min/kg in the first hour after glucose infusion and was maintained to the end of the experiment. Marked (p < 0.05) increase in UQ10 secretion was observed in both experimental groups. Maximum values of UQ10 secretion were obtained during the second hour of the experiment and averaged 0.449 +/- 0.196ng/min/kg b wt in the second, and 0.338 +/- 0.184ng/min/kg b wt in the third group of animals. Because at the end of the experiment UQ10 secretion gradually decreased we have concluded that free radicals generated during cholestasis lead to reduction of endogenous antioxidant capacity.     

Does cortisol inhibit vasopressin secretion in sheep?

Glucocorticoids inhibit the plasma vasopressin responses to hemorrhage and hypoxia in dogs. Attempts to demonstrate glucocorticoid inhibition of vasopressin secretion in fetal sheep have been unsuccessful, suggesting the possibility that there is an influence of development on the expression of this interaction, or that the interaction cannot be demonstrated in all mammalian species. This study was designed to investigate these two possibilities. Adult ewes chronically prepared with carotid arterial loops, were subjected to 5 hr infusions of cortisol at a rate of 6 ug/kg min or vehicle (5% ethanol in saline). The infusion of cortisol increased plasma cortisol concentration from 26 +/- 3 to 46 +/- 8 ng/ml, while vehicle infusion was associated with a decrease in plasma cortisol concentration from 23 +/- 4 to 15 +/- 3 ng/ml. One hr after the end of the cortisol or vehicle infusions, vasopressin secretion was stimulated by arterial hypotension produced by 10 min infusions of sodium nitroprusside (20 ug/kg min). Nitroprusside decreased arterial blood pressure equally in both groups. Plasma vasopressin concentrations were increased to peak concentrations of 92 +/- 33 and 116 +/- 20 pg/ml in the vehicle- and cortisol-infused groups, responses which were not significantly different as tested by ANOVA. We conclude that increases in plasma cortisol concentration, equal to those observed during responses to stressors, do not inhibit vasopressin secretion in this species.