Acute changes in blood flow in pigs infused with beta-adrenergic agonists

Previous results indicate that clenbuterol decreases carcass adipose tissue accretion when administered to pigs but does not appear to stimulate the adipose tissue beta-adrenergic receptor. Clenbuterol increases plasma free fatty acid concentration when acutely infused in vivo, suggesting an indirect affect. One possible indirect effect is that clenbuterol could change blood flow to adipose tissue. Blood flow was measured with radiolabeled microspheres in tissues from pigs before and after infusion of a beta-adrenergic agonist for 30 min. High probability levels (up to P less than .2) were used to indicate trends due to extreme variability. Infusion of isoproterenol increased heart rate, plasma free fatty acid concentration and blood flow at many adipose tissue sites and at a few skeletal muscle sites. Infusion of isoproterenol decreased blood pressure. Infusion of clenbuterol increased heart rate and tended to increase blood flow to several skin and adipose tissue sites slightly. The results suggest that increased adipose tissue blood flow may contribute to the accelerated release of free fatty acids when clenbuterol is infused acutely in vivo.     

Lipid mobilization by obese and lean pigs infused with the beta-adrenergic agonist isoproterenol

Generally obese and lean pigs in both the fed and fasted states were anesthetized and then acutely infused with increasing concentrations of the beta-adrenergic agonist isoproterenol. Plasma free fatty acid (FFA), blood glycerol, glucose and lactate, and heart rate were monitored during the infusion period. Data were reduced by estimating the parameters of the generalized logistic function (minimum, maximum, ED50 and slope) and subsequently analyzed to compare the lean and obese genotypes within nutritional state. Lactate data could not be fitted to this function because the upper asymptote was not approached during the experiment. The minimum plasma concentration of FFA tended (P less than .1) to be less in obese than in lean pigs. The maximum, ED50 and slope for the responses of FFA were similar for obese and lean pigs in fed pigs and in fasted pigs. In fed pigs, the minimum glycerol concentration was greater in obese than in lean pigs, and the ED50 for heart rate tended to be lower in lean than in obese pigs. All other estimated parameters for the variables were similar in fed obese and lean pigs. In fasted pigs, the maximum glucose concentration was greater in obese than in lean pigs. All other parameters for the variables were similar in fasted obese and lean pigs. The results suggest that there was no major defect in lipid mobilization in these obese pigs (only a lower minimum FFA concentration was detected) and that an increased maximum blood glucose concentration in the fasting state might contribute to the obesity.     

Effect of exogenous glucagon and free fatty acids on gluconeogenesis in fasting neonatal pigs

Thirty-two pigs (1 d old) were used to determine if exogenous glucagon and(or) free fatty acids (FFA oleic acid) would enhance gluconeogenesis and glucose homeostasis during fasting. Pigs were acquired at birth, fitted with an indwelling arterial cannula (via umbilicus) and fasted 24 h to deplete liver glycogen. A jugular cannula was inserted nonsurgically 8 to 10 h before initiation of a primed-continuous infusion consisting of control (excipient), glucagon (Glu), oleic acid (FFA), or both glucagon and oleic acid (Glu-FFA). Plasma Glu averaged 395 pg/ml preinfusion and was similar across treatments. The concentration increased fivefold (P less than .05) by 80 min for Glu and Glu-FFA pigs and remained constant thereafter (160 min: 2,379, 2,258 pg/ml; 240 min: 2,355, 2,274 pg/ml, respectively). Glucagon infusion did not alter plasma glucose after 240 min of infusion (control, 50 vs Glu, 51 mg/dl); however, Glu-FFA effected an increase (60 mg/dl, P less than .10). In contrast, pigs infused with FFA alone had a lower glucose concentration (40 mg/dl, P less than .10). Rate of glucose synthesis was determined using liver slices, acquired immediately postinfusion, with alanine and lactate as substrate (7.5 mM). The rate of synthesis was not altered by Glu or Glu-FFA infusion (2.91, 2.43 mumol glucose X g-1 X h-1 vs 2.91 for control). In contrast, exogenous FFA reduced synthesis to 1.85 mumol glucose X g-1 X h-1 (P less than .05) with lactate as substrate. It appears that Glu is not the primary factor limiting gluconeogenesis in fasting newborn pigs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of increasing infusion rates of dopamine, dobutamine, epinephrine, and phenylephrine in healthy anesthetized cats

OBJECTIVE: To determine the cardiopulmonary effects of increasing doses of dopamine, dobutamine, epinephrine, and phenylephrine and measure plasma concentrations of norepinephrine, epinephrine, and dopamine in cats anesthetized with isoflurane. ANIMALS: 6 healthy adult cats. PROCEDURES: Each cat was anesthetized with isoflurane (1.5 X minimum alveolar concentration) on 4 occasions. Cardiopulmonary measurements were obtained after a 30-minute stabilization period; 20 minutes after the start of each infusion dose; and 30, 60, and 90 minutes after the infusion was discontinued. Cats received 5 progressively increasing infusions of epinephrine or phenylephrine (0.125, 0.25, 0.5, 1, and 2 microg/kg/min) or dobutamine or dopamine (2.5, 5, 10, 15, and 20 microg/kg/min). The order of treatment was randomly allocated. Results-All 4 treatments increased oxygen delivery. Heart rate (HR) increased during administration of all drugs except phenylephrine, and mean arterial pressure increased during administration of all drugs except dobutamine. A progressive metabolic acidosis was detected, but whole-blood lactate concentration only increased during administration of epinephrine and dobutamine. Systemic vascular resistance index increased during administration of phenylephrine, decreased during administration of dobutamine, and remained unchanged during administration of dopamine and epinephrine. A positive inotropic effect was detected with all treatments. CONCLUSIONS AND CLINICAL RELEVANCE: During anesthesia in cats, administration of dopamine, dobutamine, and epinephrine may be useful for increasing cardiac output, with dopamine having the most useful effects. Administration of phenylephrine increased cardiac and systemic vascular resistance indexes with minimal effect on HR and may be useful for increasing mean arterial pressure without increasing HR.     

Catecholamine and cortisol responses of horses to incremental exertion

The responses of the plasma concentrations of catecholamines and cortisol in horses to varied relative intensities of exertion were examined. The plasma concentrations of cortisol, epinephrine and norepinephrine increased significantly (p<0.05) with exertion. The plasma cortisol concentrations at relative work intensities of 48.3%±1.4%, 82.3%±2.0% and 99.6%±0.4% of VO_2max were 114%, 124%, and 126%, respectively, of those at rest, whereas the plasma epinephrine concentrations were 239%, 772% and 3483%, and the norepinephrine concentrations were 138%, 255%, and 1121% of the values at rest. There was a significant (p<0.0001) relationship between the plasma epinephrine and norepinephrine concentrations. The blood lactate concentration and the plasma epinephrine and norepinephrine concentrations were significantly (p<0.0001) related, as were the relative work intensity (%VO_2max) and the plasma epinephrine and norepinephrine concentrations. The relationships between the plasma cortisol concentration and work intensity or blood lactate concentration were not significant (p>0.05). This study demonstrates a relationship between relative work intensity and indicators of adrenal medullary and sympathetic activity during brief exertion in horses.     

Influence of catecholamines, prostaglandins and thyroid hormones on growth hormone secretion by chicken pituitary cells in vitro

In young chickens plasma concentrations of growth hormone (GH) are depressed by prostaglandins (PG) E1 and E2, epinephrine, norepinephrine, alpha 2 and beta agonists or thyroid hormones. A primary culture of chicken adenohypophyseal cells was used to examine the direct effects of these agents at the level of the pituitary as evaluated by GH release in the presence and absence of growth hormone releasing factor (GRF). Following collagenase dispersion and culture (preincubation, 48 hr) cells were exposed (incubation, 2 hr) to test agents, except for thyroid hormones which were added during the preincubation, and incubation period. Growth hormone release was increased (P less than .05) in the presence of PGE1 (10(-8)M by 34%; 10(-7)M by 54%), PGE2 (10(-8)M by 29%; 10(-7)M by 29%), PGF2 alpha (10(-8)M by 28%), and the beta agonist isoproterenol (10(-7)M by 46%). Basal GH release from chicken pituitary cells was not affected by dopamine, norepinephrine, epinephrine, thyroxine (T4), triiodothyronine (T3), or alpha adrenergic agonists. Growth hormone releasing factor stimulated GH release was not affected by the presence of prostaglandins E1, E2 or F2 alpha in the incubation media. However, GRF stimulated GH release was reduced by high doses of catecholamines: dopamine (10(-6)M by 34%), norepinephrine (10(-6)M by 74%), epinephrine (10(-8)M by 47%; 10(-7)M by 41%; 10(-6)M by 89%), and by the alpha 1 adrenergic agonist, phenylephrine (10(-7)M by 52%), the alpha 2 agonist, clonidine (10(-8)M by 34%; 10(-7)M by 83%) and the beta agonist, isoproterenol (10(-7)M by 64%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of growth hormone-releasing factor infusion on somatotropin, prolactin, thyroxine, insulin, insulin-like growth factor I and blood metabolites in control and somatostatin-immunized growing pigs.

The aim of this study was to characterize the effects of prolonged infusion of growth hormone-releasing factor (1-29)NH2 (GRF) on plasma concentrations of hormones and metabolites when administered to control pigs and pigs immunized against somatostatin (SRIF). In the first experiment, eight purebred Yorkshire boars averaging 113 +/- 2 kg BW were immunized against SRIF conjugated to bovine serum albumin (BSA) (n = 4) or BSA alone (n = 4). Somatotropin (ST) response to four rates of GRF infusion (0, 1.66, 5 and 15 ng/min/kg BW) for 6 hr was evaluated using a double balanced 4 x 4 Latin square design. During the 4 hr before infusion, SRIF-immunized animals tended (P = 0.06) to have a higher ST release (613 vs 316 ng.min/ml, SE = 232) than controls. During infusion, GRF elicited a dose-dependent increase in ST release in both squares; the ST response was not better in SRIF-immunized animals than in controls (P greater than 0.05) (1435 vs 880 ng.min/ml; SE = 597). In the second experiment, ten purebred Yorkshire boars (5 controls and 5 SRIF-immunized animals) averaging 69 +/- 2 kg BW were continuously infused with GRF at the rate of 15 ng/min/kg BW for six consecutive d. Under GRF infusion, ST concentrations increased (P less than 0.05) from 805 to 4768 ng.min/ml (SE = 507) from day 1 to day 6 in both SRIF-immunized and control animals. Prolactin levels increased (P less than 0.05) with GRF infusion; pattern of increase was different (P less than .01) overtime in control and SRIF-immunized animals. Thyroxine levels increased from 2.53 to 3.45 micrograms/dl (SE = 0.16) after six d of infusion. Insulin-like growth factor I was higher (P less than 0.05) before (139 vs 90 ng/ml; SE = 11) and during (222 vs 185 ng/ml; SE = 11) GRF infusion in SRIF-immunized animals. A transient increase (P less than 0.05) in glucose and insulin was observed in both groups. Immunization against SRIF had no effect on blood metabolites; however, GRF infusion increased free fatty acids from 157 to 204 microEq/l (SE = 11) and decreased blood urea nitrogen from 4.1 to 3.5 mmol/l (SE = 0.2) from day 1 to day 6, respectively. In summary, active immunization against SRIF in growing pigs increased ST and IGF-I concentrations. Infusion of GRF continuously raised ST levels with days of infusion without any sign of decrease responsiveness.     

Responses of calves to treadmill exercise during beta-adrenergic agonist administration.

Calves perorally administered the beta-adrenergic agonist (beta-A) clenbuterol for 28 d were studied before, during, and after a 12-min treadmill exercise. During exercise on d 1 of clenbuterol administration, respiratory rate, respiratory minute volume, and heart rate and blood glucose, lactate, and insulin concentrations increased more in beta-A-treated calves than in controls. Oxygen extraction rate and growth hormone concentrations were lower in clenbuterol-treated calves, whereas oxygen consumption, carbon dioxide production, and blood cortisol concentration increased similarly in the absence and presence of the beta-A. After 2 wk of daily clenbuterol administration, respiratory rate and respiratory minute volume during exercise were still higher and oxygen extraction was still lower, whereas all other measures were similar to those in controls. The increased heart rate in response to isoproterenol after 3 wk of clenbuterol administration was reduced markedly in resting but only slightly in exercising animals, whereas heart rate reduction by propranolol during exercise was similar to that in controls. Seven days after withdrawal of clenbuterol, newly administered clenbuterol evoked the same effects as on d 1. In conclusion, there were marked reactions to the first clenbuterol treatment that were in part enhanced during treadmill exercise. After 2 wk of beta-A administration, animals responded much less to the beta-A and changes were not different from those in controls. Resensitization to the beta-A was observed 7 d after its withdrawal.     

Evaluation of plasma catecholamine and serum cortisol concentrations in horses with colic

OBJECTIVE: To evaluate plasma epinephrine and norepinephrine concentrations and serum cortisol concentration in horses with colic and assess the relationship of these variables with clinical signs, routinely measured clinicopathologic variables, and outcome in affected horses. DESIGN: Prospective observational study. ANIMALS: 35 horses with colic. PROCEDURE: Blood samples were collected within 30 minutes of arrival at the veterinary hospital from horses referred because of colic. Plasma and serum samples were analyzed for cortisol, epinephrine, norepinephrine, lactate, and electrolyte concentrations and acid-base variables. Heart rate at admission and outcome (survival or nonsurvival) were recorded. Univariate logistic regression was used to calculate crude (unadjusted) odds ratios and 95% confidence intervals. RESULTS: Of the 35 horses with colic, 26 survived. Higher plasma epinephrine, plasma lactate, and serum cortisol concentrations were significantly associated with increased risk of nonsurvival, but plasma norepinephrine concentration was not associated with outcome. Plasma epinephrine concentration was significantly correlated with heart rate (r = 0.68), plasma lactate concentration (r = 0.87), blood pH (r = -0.83), anion gap (r = 0.74), and base excess (r = -0.81). CONCLUSIONS AND CLINICAL RELEVANCE: The risk of death appears to be greater in colic-affected horses with high circulating concentrations of epinephrine and cortisol. The correlation of epinephrine with other biochemical markers of illness severity and with heart rate indicates that the degree of sympathetic activation in horses with colic can be inferred from routinely measured variables.     

The influence of restraint immobilization stress on the concentration qf bioamines and cortisol in plasma of Pietrain and Duroc pigs

Forty-five Duroc (recognized as not susceptible to stress) and 34 Pietrain (susceptible to stress) pigs were subjected to immobilization stress in a prone position for 5, 15, 30 and 60 min. Plasma concentrations of epinephrine (E), norepinephrine (NE), dopamine (DA) and cortisol (C) were determined in response to restraint stress. The concentrations of E, NE and DA were different between the two strains of pigs (some significant interactions); the highest response was seen after 5 min of stress. The concentration of plasma C increased with duration of stress and there was a significant interaction between strain of animals and the time of stress. Our data substantiate the use of E, NE, DA and C as indicators of stress in swine as early as 5 min after exposure to the stressor. It is also shown that stress-susceptible Pietrain pigs had higher plasma concentrations of E, NE and DA than Duroc pigs.     

Effects of dietary clenbuterol on metabolism of the hindquarters in steers

The objective of this study was to measure acute (d 1) and chronic (d 9) effects of dietary clenbuterol on heart rate, blood flow, oxygen uptake, and net uptake/release of metabolites in the hindquarters of growing steers. The design was a single reversal with two 9-d periods of control or 8 mg clenbuterol/d with 5 d between periods. Within 2 h of initial consumption of 2 mg clenbuterol (d 1), heart rate and blood flow doubled and arterial plasma concentrations of glucose, L-lactate and nonesterified fatty acid (NEFA) increased, whereas alpha-NH2 N and NH3 concentrations decreased, demonstrating an acute response. Uptake of oxygen increased and net uptake of alpha-NH2 N decreased. Net release of both L-lactate and NEFA increased. On d 9, there were no acute responses to clenbuterol consumption; however, heart rate, blood flow, and NEFA concentration remained chronically elevated, and plasma concentrations of acetate and propionate decreased compared with control feeding. Net uptake of alpha-NH2 N, oxygen and release of L-lactate by the hindquarters chronically increased on d 9 of clenbuterol feeding. Changes in both blood flow and arteriovenous (AV) concentration difference contributed to changes in uptake/release. The chronic metabolic changes and oxygen uptake were consistent with increased N retention in the hindquarters through increased protein synthesis, decreased use of acetate and increased reliance on NEFA for cellular energy. In conclusion, the data show that the perturbation of homeostatic regulation by dietary clenbuterol on d 1 evolved to establishment of homeorhetic regulation by d 9 that is consistent with increased skeletal protein accretion in growing steers.     

Effect of beta-adrenergic agonists on lipolysis and lipogenesis by porcine adipose tissue in vitro

The effects of the beta-adrenergic agonists isoproterenol, cimaterol, ractopamine and clenbuterol on lipolysis (release of glycerol and free fatty acids) and lipogenesis (incorporation of 14C into fatty acids from [14C]glucose) was examined in porcine adipose tissue explants in vitro. Lipolysis was stimulated by isoproterenol, cimaterol or ractopamine but not by clenbuterol. Insulin reduced the lipolytic effects of the beta-adrenergic agonists (isoproterenol, cimaterol and ractopamine). Lipogenesis was inhibited by all beta-adrenergic agonists tested (isoproterenol, cimaterol, ractopamine and clenbuterol). The antilipogenic effect of the beta-adrenergic agonists was reduced by the presence of insulin in the incubation. Although effects of the different beta-adrenergic agonists varied, all had some direct effects that could be expected to reduce adipose accretion. Effects of beta-adrenergic agonists in the pig are due in part to direct effects on adipose tissue.     

Fasting plasma hormones and metabolites in feral and domestic newborn pigs

Newborn Yorkshire and Ossabaw (feral) pigs were examined under thermoneutral conditions to determine whether survival rate during fasting differs between these breeds and whether any blood-borne factors are associated with improved survival. Newborn pigs were removed from the sow before suckling. Body composition was determined on 10 newborn Ossabaw and 12 newborn Yorkshire pigs. Another group of animals (eight Ossabaw, 12 Yorkshire) was fasted for 72 hr, with blood samples drawn at birth and 12 and 24 hr into fasting. Glucose, free fatty acid (FFA), growth hormone (GH), insulin, thyroxine (T4), triiodothyronine (T3), cortisol and glucagon concentrations were measured in plasma of fasted pigs. Concentrations of carcass lipid, dry matter and ash were higher in newborn Ossabaw pigs than in newborn Yorkshire pigs. Survival through 72 hr of fasting was lower among Yorkshire pigs. Yorkshire and Ossabaw pigs had similar concentrations of metabolites and hormones at birth, with the exceptions of lower plasma GH and higher T3 concentrations in Ossabaw pigs. Higher plasma T3 concentrations would indicate a greater potential for fatty acid oxidation. During fasting, Ossabaw pigs had lower plasma GH and T4 concentrations and higher glucagon and FFA concentrations. Increased survival among newborn Ossabaw pigs may have been due to increased availability of FFA during fasting, and to a greater potential for gluconeogenesis through increased oxidation of fatty acids and higher plasma glucagon concentrations. This would suggest that maternal treatments that would increase storage of fat and(or) increase the capacity for oxidation of fat in utero would improve survival of newborn pigs.     

Comparison of plasma free-fatty-acid and blood-glycerol concentrations with measurement of lipolysis in porcine adipose tissue in vitro

Rates of adipose tissue lipid metabolism in vitro are often measured to evaluate the function in vivo of metabolic pathways and thus appraise the accretion or loss of depot fat. This study directly addressed the comparison of degradative metabolism in vitro and in vivo. The concentrations of plasma free-fatty-acids and blood-glycerol as putative representatives of lipolysis in vivo and the lipolytic rate in adipose tissue in vitro obtained at the time of blood sampling were both measured in the same pig. Concentrations of plasma free-fatty-acids and blood-glycerol were increased or decreased by infusion of the norepinephrine analog, isoproterenol or by infusion of the adrenergic antagonist, propranolol, respectively. Although lipolytic rates and sensitivity to isoproterenol in vitro changed during some acute hormonal manipulations of the pig, the modulation in vitro was usually small relative to the large changes observed in plasma free-fatty-acid and blood-glycerol concentrations. Some of the subtle changes in vitro may reflect biological responses to hormone infusion, e.g., desensitization of the response to adrenergic agonists, but the magnitude of rate changes in vitro negates prediction of the rates in vivo from rates in vitro. Extrapolation of lipolytic rates in vitro and several adipose tissue anabolic rates obtained from the literature indicate the improbability for prediction of rates and degree of fat accretion in pigs from metabolic rates in vitro.     

Acute stress hyperglycemia in cats is associated with struggling and increased concentrations of lactate and norepinephrine

We characterized the changes in blood glucose concentrations in healthy cats exposed to a short stressor and determined the associations between glucose concentrations, behavioral indicators of stress, and blood variables implicated in stress hyperglycemia (plasma glucose, lactate, insulin, glucagon, cortisol, epinephrine, and norepinephrine concentrations). Twenty healthy adult cats with normal glucose tolerance had a 5-minute spray bath. Struggling and vocalization were the most frequent behavioral responses. There was a strong relationship between struggling and concentrations of glucose and lactate. Glucose and lactate concentrations increased rapidly and significantly in all cats in response to bathing, with peak concentrations occurring at the end of the bath (glucose baseline 83 mg/dL, mean peak 162 mg/dL; lactate baseline 6.3 mg/dL, mean peak 64.0 mg/dL). Glucose response resolved within 90 minutes in 12 of the 20 cats. Changes in mean glucose concentrations were strongly correlated with changes in mean lactate (r = .84; P < .001) and mean norepinephrine concentrations (r = .81; P < .001). There was no significant correlation between changes in mean glucose concentrations and changes in mean insulin, glucagon, cortisol, or epinephrine concentrations. Struggling and lactate concentrations were predictive of hyperglycemia. Gluconeogenesis stimulated by lactate release is the likely mechanism for hyperglycemia in healthy cats in this model of acute stress. Careful handling techniques that minimize struggling associated with blood collection may reduce the incidence of stress hyperglycemia in cats.     

Adenosine deaminase and porcine meat quality. I. Effect of dipyridamole on plasma free fatty acids, glucose, lactate and c-AMP in pigs representing high and low red cell adenosine deaminase activity

The effect of dipyridamole--an adenosine uptake inhibitor--on the plasma concentration of free fatty acids (FFA), glucose, lactate and cyclic adenosine monophosphate (cAMP) has been examined in 2 groups of Landrace pigs representing low (Ada 0) and high (Ada A) red cell adenosine deaminase (Ada) activity. Pigs fitted with a jugular vein catheter were given dipyridamole (0.16 mg/kg/min) over a period of 30 min. The infusions were performed 22 h after the last meal at a time where pigs were found to show steady increase and decline in rates of lipolysis and glycogenolysis, respectively. The results showed that lipid mobilization as identified by the plasma FFA concentration was markedly depressed. During the infusion of dipyridamole similar degree of inhibition was seen in Ada 0 and Ada A pigs, however, in the period following the infusion, a significantly stronger suppression persisted in the Ada 0 pigs. Both the blood glucose and lactate level rose distinctly as a result of the dipyridamole treatment. This stimulation of the glycolysis rate was significantly more expressed in Ada 0 pigs compared to that of the Ada A pigs. When theophylline, an antagonist of adenosine, was given together with dipyridamole, the rise in the lactate level was considerably diminished. Dipyridamole also produced a distinct rise in the plasma cAMP levels.     

Effects of glucose and amino acids on ghrelin secretion in sheep

Two experiments were conducted to elucidate the effects of post‐ruminal administration of starch and casein (Exp. 1), plasma amino acids concentrations (Exp. 2), and plasma glucose and insulin concentrations (Exp. 2) on plasma ghrelin concentrations in sheep. In Exp. 1, plasma ghrelin concentrations were determined by four infusion treatments (water, cornstarch, casein and cornstarch plus casein) in four wethers. Abomasal infusion of casein increased plasma α‐amino N (AAN) concentrations. Infusion of starch or casein alone did not affect plasma ghrelin concentrations, but starch plus casein infusion increased plasma levels of ghrelin, glucose and AAN. In Exp 2, we investigated the effects of saline or amino acids on ghrelin secretion in four wethers. Two hours after the initiation of saline or amino acid infusion into the jugular vein, glucose was also continuously infused to investigate the effects of blood glucose and insulin by hyper‐glycemic clump on plasma ghrelin concentrations. Infusion of amino acids alone raised plasma levels of ghrelin, but the higher plasma glucose and insulin concentrations had no effect on plasma ghrelin concentrations. These results suggest that high plasma levels of amino acids can stimulate ghrelin secretion, but glucose and insulin do not affect ghrelin secretion in sheep.     

Subclinical ammonia toxicity in steers: effects on blood metabolite and regulatory hormone concentrations

The effects of subclinical NH3 toxicity on circulating and regulatory hormone concentrations were investigated in seven Hereford steers. Ammonium chloride (NH4Cl) was infused via a right jugular vein catheter at a rate of 12 mumol NH4Cl.kg BW-1.min-1 for 240 min. This was preceded (PRE) and followed (POST) by saline infusions of 120 and 180 min, respectively. Blood samples were taken at 20-min intervals via a left jugular vein catheter. Metabolite and hormone concentrations during NH4Cl and POST periods were compared to PRE values using the Student's t-test procedure. Plasma NH3 was elevated rapidly (P less than .001) and peaked at 503 micrograms/dl 220 min into NH4Cl infusion. Plasma urea-N and glucose increased (P less than .001) 39 and 12%, respectively, during NH4Cl infusion and remained elevated 180 min POST. Whole blood L-lactate concentrations peaked (P less than .05) at 18% above PRE between 160 and 240 min into the NH4Cl infusion and gradually returned to PRE values, whereas pyruvate levels were not altered (P greater than .10). Plasma nonesterified fatty acids peaked (P less than .001) at 94% above PRE levels 40 min into NH4Cl infusion, thereafter declining to PRE concentrations. Whole blood acetoacetate and beta-hydroxybutyrate concentrations were not altered (P greater than .10) by NH4Cl administration. Plasma insulin concentration decreased (P less than .05) 26 to 46% during NH4Cl infusion and increased (P less than .05) 89 to 122% during POST. Plasma glucagon levels were not altered by NH4Cl infusion, so molar insulin:glucagon ratio changes resembled those of insulin. Plasma epinephrine, norepinephrine and dopamine did not vary (P greater than .10) with treatment. These results support the hypothesis that the hyperglycemia observed during hyperammonemia may result from an under-utilization of glucose by insulin-sensitive tissues.     

Endocrine response to lactate infusion during pentobarbitone anaesthesia

Lactic acid was infused iv in 6 Welsh ponies during pentobarbitone anaesthesia to investigate whether lactate triggers the pituitary-adrenal response to anaesthesia. Ponies were premedicated with acepromazine and anaesthesia was induced with pentobarbitone iv and maintained with pentobarbitone/oxygen for 2 h. Immediately after induction, 3% L(+) lactic acid infusion was started and adjusted to maintain plasma lactate concentration between 2 and 2.5 mmol/l. Cardiorespiratory function, temperature. PCV, plasma glucose, lactate, βendorphin, ACTH, cortisol and catecholamine concentrations were measured before, during and after anaesthesia. Hypothermia, reduced PCV, slight hypotension (minimum value 84 ± 6 mmHg 20 min after induction of anaesthesia), hyperoxia and marked bradypnoea developed during anaesthesia. No acidaemia occurred. Plasma glucose concentration increased at the end of anaesthesia. There were no changes in plasma ACTH, cortisol and catecholamine concentrations, but plasma & endorphin increased after induction until the end of anaesthesia. There was a correlation between plasma lactate and β-endorphin concentrations (P<0.001, r=0.63), which may suggest that lactate stimulates βendorphin release. Beta-endorphin was apparently secreted independently from ACTH and appears to be a sensitive marker of a stress response.     

Effect of somatotropin on nonesterified fatty acid and glycerol metabolism in growing pigs.

Eight crossbred barrows (71 kg initial BW) were allocated to two treatments involving daily i.m. injections of either excipient (control) or recombinantly derived porcine somatotropin (120 micrograms/kg of BW). On d 8 of treatment, beginning 15 h after injection, glycerol and nonesterified fatty acid (NEFA) kinetics were determined using a primed, continuous infusion of [2-3H]glycerol and [9,10(n)-3H]oleic acid. Kinetics were examined under both basal conditions and during a hyperinsulinemic/euglycemic clamp. Plasma concentrations of NEFA and glycerol and their respective entry rates were highly correlated. Insulin had no effect on plasma glycerol or glycerol entry rate, probably due to the very low rates that were observed in both the control and somatotropin-treated pigs. However, both plasma NEFA and oleic acid entry rate were reduced during hyperinsulinemia. Although indices of fat mobilization tended to be higher in pigs treated with somatotropin, the magnitude of the increases were small and would be sufficient to account for only a minor fraction of the decreased lipid accretion observed in somatotropin-treated pigs.