Effects of intracerebroventricular corticotropin-releasing hormone and intravenous morphine on cortisol, prolactin and growth hormone secretion in sheep

Effect of Morphine Administration on Social andNon-Social Play Behaviour in Calves

Simple Summary

Play can be used as an indicator of welfare in animals, because animals play more when all their basic needs are met. Opioids have a modulatory effect on social play behaviour in rodents and primates, however little is known regarding the central mechanisms involved in play behaviour in ruminants. In ruminants, we need to know more about what factors influence play behaviour, to determine which elements of play may more accurately be used as indicators of positive welfare. Therefore, the objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. In an arena test, morphine administration increased the performance of social play events but had no effect on locomotor play in calves. Similar to research in rodents and primates, morphine administration appears to increase social but not non-social elements of play in calves, suggesting that increased social play may be more indicative of a positive affective state.

Abstract

The objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. Twelve calves experienced four treatments in a cross over 2 × 2 factorial design: Calves received an intravenous injection of morphine or saline 10 min prior to being tested individually or in pairs in an arena for 20 min. Play behaviour was continuously recorded in the arena test. Lying times were recorded in the home pen. Cortisol concentrations were measured before and after testing. In the arena test, calves given morphine tended to perform more social play events than calves given saline, however, morphine administration had no effect on locomotor play. Calves given morphine spent less time lying than calves given saline during the first 4 h after returning to the home pen. Cortisol concentrations were suppressed in calves given morphine. Administration of morphine appeared to increase social play but had no effect on locomotor play in calves. This study highlights the importance of investigating different aspects of play behaviour in animals as some may be more indicative of a positive affective state than others. More studies investigating the effects of morphine on play are needed to confirm the results found in this study.

Stress and travel sickness in pigs: effects of road transport on plasma concentrations of cortisol, beta-endorphin and lysine vasopressin

Two experiments were made to investigate the effects of road transport on stress hormone responses in pigs. In experiment 1, seven 40-kg pigs, prepared with jugular catheters, were loaded onto a livestock lorry and transported over a 2-day period on routes characterized, by means of an accelerometer, as rough or smooth. Two 100-min journeys, one rough and one smooth, separated by a 100-min rest period, were conducted each day. The experimenters travelled with the animals and blood samples were taken for hormone analysis from each pig at 20-min intervals. On the 3rd day, samples were collected from the pigs when housed in their home pen (control). Plasma concentrations of cortisol increased after loading, remained higher for longer on rough compared with smooth journeys and were higher during both journeys on day 1 compared with day 2. Concentrations of beta-endorphin increased after loading on day 1 but neither beta-endorphin nor lysine vasopressin showed clear changes in secretion pattern during rough or smooth journeys. On day 3 (control), mean concentrations of all three hormones were significantly lower than on days 1 and 2, indicating that the responses observed were not due to a diurnal rhythm. In experiment 2, six 35-kg catheterized pigs were loaded on a lorry (09.30 h) that remained stationary while blood samples were taken at 30-min intervals during the next 8 h (control). Two days later, this procedure was repeated with the vehicle in motion for 8 h. Plasma concentrations of lysine vasopressin during driving increased between 2 and 4·5 h which coincided with behavioural observations indicating that the pigs were travel sick.

Behavioural and hormonal responses of pigs during transport: effect of mixing and duration of journey

Two experiments investigated the welfare of pigs during transport. In experiment 1, 12 groups offour 90-kg pigs were transported to slaughter in a commercial livestock lorry for 1·5 h. Half the animals were transported in their social groups (unmixed condition) and half were transported with groups of previously unfamiliar pigs mixed together (mixed condition). Behaviour was recorded, a general activity index scored and saliva samples taken at different stages of the journey for analysis ofcortisol. Pigs spent most of their time standing in both conditions. The journey was very rough (as revealed by characterization with an accelerometer) and in the unmixed condition the pigs appeared to stand to reduce travel sickness. In contrast, in the mixed condition, this preference for standing seemed to be due to fighting which stressed and exhausted the animals (the general activity index was three times the unmixed condition). Levels of salivary cortisol were higher in the mixed condition at the beginning, middle and end of the journey. In experiment 2, six 35-kg pigs, prepared in advance with jugular vein catheters, were loaded onto a commercial livestock lorry (09.30 h) where they were individually penned. The vehicle remained stationary with the engine off and blood samples were taken at 30-min intervals during the next 8 h (control). Two days later this procedure was repeated while the vehicle was driven for 8 h (on main roads and motorways). Plasma concentrations of cortisol and beta-endorphin increased markedly in both conditions immediately after loading. Cortisol levels were greater (relative to control) at the beginning, in the middle and at the end of the journey. Concentrations of beta-endorphin did not differ between control and experimental conditions except during the final 180 min of the journey when the control levels were higher.

Effects of a maximum permissible journey time (31 h) on physiological responses of fleeced and shorn sheep to transport, with observations on behaviour during a short (1 h) rest-stop

Concern for the welfare of export lambs during long-distance road transport has prompted much research and a recommended change in procedure. The latter envisages an absolute maximum journey time of 31 h and includes a rest-stop (minimum duration 1 h) for feeding and watering. In the present experiment, the physiological and behavioural responses to this new protocol have been investigated in fleeced and shorn lambs (no. = 10 per group) provided with venous catheters and heart rate monitors. The two groups were loaded on a vehicle into separate adjacent pens and driven for 14 h; then unloaded into a lairage, where their behaviour was recorded. After 1 h they were reloaded and driven for a further 15·5 h, finally arriving at a slaughterhouse where carcass condition was evaluated. Blood samples collected at 30- or 60-min intervals by experimenters travelling with the animals were analysed to determine haematocrit, plasma osmolality, plasma concentrations of glucose, creatinine phosphokinase (CPK), and the stress-responsive hormones, cortisol, prolactin, adrenaline and noradrenaline. The results showed that haematocrit increased after loading although the general trend during transport, as with osmolality, was a decline (P < 0·05). No significant changes in plasma glucose were detected but CPK increased in fleeced lambs after loading (P < 0·05). Cortisol release was stimulated by loading, especially in fleeced sheep (P < 0·001) but returned to home pen values within 6 h; heart rates changed in a similar manner. Transport did not markedly affect prolactin release although concentrations were consistently greater in fleeced sheep (P < 0·001). Noradrenaline, however, tended to be higher in shorn animals (P < 0·05). In lairage, both groups readily consumed hay, and especially concentrates, but the shorn lambs spent more time eating (P < 0·001). None of the shorn sheep, and only a few fleeced animals, drank water. There was no evidence for differences in weight loss between the two groups during the experiment and carcass quality at slaughter was within the normal expected range. The implications of these, and other related studies, for future transport policy are discussed, with particular reference to rest-stop duration and handling procedures.

Behavioral effects of betacarbolines in pigs:. anxiety or aversion?

Betacarbolines are often considered to be anxiogenic and may, therefore, have similar behavioral effects to those of corticotrophin releasing hormone (CRH); however, their actions have been little studied in pigs. This investigation was concerned with the effects of ethyl-beta-carboline-3-carboxylate (BCCE) and noreleagnine (NOR) on operant feeding, cortisol release, and overt behavior in swine, all of which are known to be affected by CRH in this species. Three experiments are described in which BCCE or NOR were given intravenously to prepubertal boars (n = 7). In Experiment 1, 400 microg/kg, but not 100 or 200 microg/kg, BCCE produced a rapid inhibition of ingestive activity whereas NOR (100, 200, or 400 microg/kg) was without effect. In Experiment 2, both BCCE and NOR increased plasma cortisol, but not growth hormone, concentrations. In Experiment 3, a high dose of BCCE (2 mg/kg) produced transient arousal and a sustained increase in respiration rate and plasma cortisol. These results indicate that although the responses of pigs to BCCE and CRH are similar in some respects, there are also marked behavioral differences. The possibility that BCCE has aversive rather than anxiogenic actions in this species is discussed.

Endogenous monoamine oxidase inhibitory activity and HPA activation in the pig

Previously we have shown that an increase in endogenous monoamine oxidase A inhibitory activity (MAO-AI), measured in human saliva, both precedes and predicts psychological stress-induced activation of the hypothalamic pituitary adrenal (HPA) axis, as determined by the cortisol response. We now report the relationship between endogenous MAO-AI and the cortisol response in the plasma of prepubertal pigs (n=5 or 6) under two experimental paradigms of HPA activation. In the first condition, pigs were physically restrained (snaring) for 15 minutes. Blood samples were taken from indwelling catheters at intervals before and after snaring (a sampling period of about 1 hour), and at the same time intervals on a separate day to provide baseline measures. Both cortisol concentration and percentage MAO-AI were determined in each plasma sample. There was a pronounced cortisol response on the snaring day (cortisol peaked 30 minutes after the start of the snaring). There was also a significant MAO-AI response to snaring which peaked 15 minutes after the start of the stress challenge. In the second experimental paradigm, bacterial endotoxin (LPS: 20microg/pig) was used to induce HPA activation and plasma cortisol and MAO-AI were determined. This time, however, the cortisol response was not preceded by any change in MAO-AI. We conclude that generation of MAO-AI, which is associated with HPA activation induced by psychological stress, is not a component of the pathways involved in immunological stimulation of the HPA axis.

The timing of parturition in the pig is altered by intravenous naloxone

This experiment tested the hypothesis that opioid antagonists could influence the timing of the onset and progress of parturition in the pig. Primiparous pigs (gilts) received a jugular catheter on Days 104 to 106 of pregnancy. At 1400 h on Day 112 the gilts received 10 mg PGF2alpha, i.m. to induce parturition. At 1000 h on Day 113 (i.e., 20 h later) gilts received either saline (n=6), 1 mg/kg, i.v. naltrexone (n=4) or 1 mg/kg, i.v. naloxone (n=5). Blood samples were taken daily from Days 108 to 116. On Day 113, blood samples were taken hourly from 0500 to 0900 h and then every 30 min until 2400 h, or until the birth of the last piglet (BLP) (whichever was sooner) and assayed for progesterone, oxytocin (OT), cortisol and PRL. Additional blood samples for OT and cortisol assay were taken every minute from 0930 to 1100 h on Day 113 and for 30 min during parturition. Naloxone, but not naltrexone, delayed the onset of parturition relative to saline controls (by 14 h 21 min; P<0.05). Duration of parturition and rate of births were not significantly affected by treatment. Mean plasma OT increased in the 4 h following naloxone but not saline treatment, during which time OT plasma pulse amplitude was reduced in naloxone and naltrexone-treated animals relative to saline treated controls. The PRL secretion rose following treatment in saline treated animals, consistent with approaching parturition, but failed to rise in opioid antagonist treated animals. Progesterone concentrations remained elevated in naloxone-treated animals for longer than in the other groups. These data suggest that a rapid change in overall effect of parenteral administration of naloxone to parturient pigs occurs from delaying its onset when administered as in these experiments, to facilitating its progress when given during parturition (earlier experiments). The delay of onset of parturition may be mediated by interference with hypothalamic control of OT or PRL release.

Behavioral and hormonal effects of centrally injected "anxiogenic" neuropeptides in growing pigs

Records of behavior (alertness, posture, oro-nasal responses, activity level, and vocalization pattern) were made in prepubertal pigs (n = 6) during a 60-min period following central injections of equimolar (21 nmol) doses of porcine CRH (pCRH), urocortin (UCN), octadecaneuropeptide (ODN), or saline vehicle (SAL). Blood samples were also collected at 15-min intervals before, during, and after the test, and used to determine plasma cortisol, prolactin, and growth hormone concentrations. The pigs became excited and highly active after pCRH, and to a lesser extent following UCN administration, but were subdued when given ODN or SAL. None of the peptides significantly affected prolactin or growth hormone release, but both UCN, and especially pCRH, increased cortisol concentrations. The emotional responses induced by pCRH and UCN are consistent with observations in rodents, which indicate that centrally administered CRH-like peptides have anxiogenic effects. In contrast, ODN, which inhibits benzodiazepine binding at the GABA(A) receptor and is anxiogenic in rodents, lowered plasma cortisol and had no overt behavioral effects. Hence, at the dose administered, there was no evidence to indicate that ODN acted as an anxiogen in this species.

Effects of oestrogen supplementation and space restriction on PGF2alpha-induced nest-building in pseudopregnant gilts

This study examined the role of oestrogen supplementation on PGF2alpha-induced nest-building in pseudopregnant gilts. Oestradiol valerate (5 mg/day) injections were given on Days 11-15 of the oestrous cycle to induce pseudopregnancy. A further series of injections of either oestradiol valerate (5 mg/day) or vehicle were given on days 44-46 of pseudopregnancy to reflect more closely the hormone profile seen in pregnancy. Nest-building was induced by a single intramuscular injection of 15 mg of PGF2alpha (Lutalyse) on Day 47 of pseudopregnancy. The gilts were housed in pens (2.8 x 1.7 m) containing straw in experiment 1 or chronically confined in crates (0.6 x 1.7 m) that did not contain straw on days 44-48 of pseudopregnancy for experiment 2. Oestrogen supplemented gilts had significantly higher concentrations of circulating 17beta-oestradiol on day 47 of pseudopregnancy but there were no significant differences between treatments for circulating levels of prolactin, progesterone, cortisol or oxytocin, or for any behavioural measure in either experiment. These results indicate that there is no direct effect of supplementing already pseudopregnant gilts with oestradiol valerate on PGF2alpha-induced nest-building. The results also show that the pre-partum environment has a pronounced effect on nest-building behaviours and that non-pregnant pigs might be a useful model for pre-partum nest-building in this species.

Studies of endotoxin-dependent fever in pre-pubertal pigs following acute activation of the pituitary-adrenocortical axis: towards a new hypothesis of fever regulation

The possibility that adrenocortical activation might alter the pyretic effects of bacterial lipopolysaccharide endotoxin in growing pigs was investigated. In a series of four experiments, animals received increasing doses of porcine adrenocorticotrophic hormone ACTH (1.5, 4.5, 13.5 IU kg-1) or CRH (7 microg kg-1), all of which markedly affected cortisol release. Unexpectedly, these treatments tended to increase body temperature during the early and middle stages of the febrile response, although they did appear to induce an earlier deferscence. These results suggest that acute stress may not modify fever induced by immunological challenge, although a different situation could obtain during chronic stress. Furthermore, a hypothesis of fever regulation is proposed which attempts to reconcile the present findings with those from previous studies in swine.

Travel Sickness and Meat Quality in Pigs

An experiment was conducted to investigate the incidence of travel sickness in pigs, specific hormone concentrations at exsanguination and subsequent meat quality. Fifty, 80kg slaughter pigs were transported on a lorry for 4.5h. During the journey, behavioural observations of the individually marked pigs were made by scanning every 8min to establish whether the pigs exhibited certain symptoms of travel sickness (foaming at the mouth and chomping) and incidences of retching and vomiting were noted as they occurred. Upon arrival at the slaughterhouse, pigs were unloaded, slaughtered immediately and a blood sample was taken at exsanguination for analysis of plasma Cortisol, beta-endorphin and lysine vasopressin concentrations. On the day following slaughter, the chilled carcase of each pig was assessed for meat quality (using pH, Fibre Optic Probe, and Tecpro Pork Quality Meter measurements) in the longissimus dorsi, semimembranosus and adductor muscles to determine the incidence of PSE (pale, soft, exudative) or DFD (dark, firm, dry) meat quality. Twenty-six per cent of the pigs (a total of 13 individuals) vomited or retched during the journey. There was no relationship between the incidence of travel sickness and either the concentrations of the hormones analysed at exsanguination or subsequent meat quality. Correlations revealed no significant relationship between concentrations of the hormones and meat quality measurements.

Pulsatile luteinizing hormone secretion in the ovariectomized, thyroidectomized red deer hind following treatment with dopaminergic and opioidergic agonists and antagonists

Two experiments were conducted to determine whether dopaminergic or opioidergic pathways are modulated by thyroid gland secretions for seasonal suppression of LH secretion in red deer hinds. Ovariectomized (n = 5) or ovariectomized and thyroidectomized (n = 4) hinds, treated with estradiol implants, received the dopamine agonist bromocriptine or the antagonist sulpiride during pulse bleeds in July (breeding season) and October (nonbreeding season). Comparison of July and October mean plasma LH concentration (3.5 +/- 1.3, 0.7 +/- 0.1 ng/ml, respectively), pulse frequency (1.9 +/- 0.4, 0.7 +/- 0.2 pulses/4 h), and pulse amplitude (1.3 +/- 0.5, 0.7 +/- 0. 02 ng/ml) showed lower (p < 0.05) levels in October, and these levels were not significantly affected by thyroidectomy or drug treatment. In the absence of estradiol implants, the hinds received bromocriptine or morphine during the breeding season (July) and their antagonists, sulpiride or naloxone, respectively, in the nonbreeding season (November). In euthyroid hinds there was a seasonal decrease (p < 0.05) in mean plasma LH concentration, pulse frequency, and pulse amplitude, which did not occur in thyroidectomized hinds. There were no effects of drug treatment on LH concentration except for a small increase following sulpiride in November. Plasma prolactin concentration was significantly increased by antagonists and decreased by agonists on most occasions. We conclude that in red deer hinds, seasonal regulation of LH secretion does not involve dopamine or endogenous opioids and the thyroid gland is required specifically for LH suppression in the absence of estradiol.

Heart Rate and Stress Hormone Responses of Sheep to Road Transport Following Two Different Loading Procedures

This study was designed to investigate the physiological responses induced in sheep (n = 18) by two different loading techniques followed by a short road journey. All animals were prepared with venous catheters, to minimize the disturbing effects of blood sampling, and nine sheep were fitted with heart rate monitors. The animals were loaded onto a transport vehicle in groups of three, alternately using a conventional tailgate ramp or a crate raised with a hydraulic lift. When all of the sheep were loaded, they were taken on a journey lasting 195min. Blood samples were collected in the home pen, directly after loading, and at 15min intervals during the journey. Measurements were made of plasma concentrations of Cortisol, prolactin and catecholamines (adrenaline and noradrenaline). The results indicated that heart rate increased during loading, regardless of the method used. No changes in concentrations of Cortisol or the catecholamines were detected, although a small increase in prolactin was noted when animals were loaded using the ramp. During transport, all sheep exhibited increases in plasma Cortisol concentrations which were greatest during the first 2h of the journey. The results suggest that, under the conditions employed in this experiment, the effects of the two loading procedures were similar and that transport appeared to be more stressful than loading.

Effects of transport and indomethacin on telemetered body temperature and release of cortisol and prolactin in pre-pubertal pigs

Previous research indicates that acute physical stress (restraint) raises core temperature in growing pigs via a prostaglandin-dependent mechanism. This study investigated whether transport stress affects body temperature in pigs and whether any such changes might involve endogenous prostaglandins. Pre-pubertal boars (n = 7) were implanted with venous catheters and biotelemetry devices for the measurement of core temperature. They were transported for two hours, with and without indomethacin (IND) pre-treatment, and blood samples were taken at 15 minute intervals for the determination of plasma cortisol and prolactin concentrations. The results indicated that, contrary to predictions, body temperature tended to fall during transport and that the effect was exaggerated by IND. By contrast, cortisol concentrations increased during transport and were unaffected by IND whereas the tendency for transport to stimulate prolactin release was reversed by IND.

Comparison of the antipyretic actions of indomethacin and L-745,337, a selective cyclooxygenase-2 inhibitor, in endotoxin-treated prepubertal pigs

1. The growing pig provides a useful, nonrodent model for studying mechanisms involved in the febrile response. 2. Indomethacin (IND) has previously been shown to prevent lipopolysaccharide (LPS) fever in prepubertal pigs. 3. This study compared the abilities of IND and L-745,337, a novel cyclooxygenase-2 (cox-2) inhibitor, to counteract the effects a low dose of LPS (20 micrograms/pig IV) on deep body temperature. Effects of IND and L-745,337 on core temperature and plasma cortisol concentrations were also examined in nonfebrile animals. 4. L-745,337 (0.3 mg/kg IV) did not alter the response to LPS, whereas both IND and L-745,337 (1.7 mg/kg) reduced the febrile effects of LPS given 60 min earlier. 5. Neither IND, nor L-745,337 (1.7 mg/kg IV) affected core temperature in nonfebrile animals whereas IND, but not L-745,337, stimulated cortisol release. 6. The results suggest that prostaglandin modulates the febrile effects of LPS in swine and that inhibition of inducible cyclooxygenase (Cox-2) suppresses fever without producing the stressful side-effects that accompany constitutive cyclooxygenase (Cox-1) inhibition, as exemplified by IND (a mixed Cox-1/Cox-2 antagonist).

The effect of bovine somatotropin and diet on somatotropin binding sites in hepatic tissue of lactating dairy cows

In the lactating cow, galactopoiesis is stimulated by treatment with recombinant bovine somatotropin (bST) and by an improved plane of nutrition. The present study determined the interaction between these variables and examined whether a positive galactopoietic effect was accompanied by a change in hepatic binding sites for bST. Lactating dairy cows received one of three diets with increasing nutrient density; diet 1, 150 g/kg of dry matter (DM) of crude protein (CP) and 10.5 MJ/kg of DM of metabolizable energy; diet 2, 170 g/kg of DM of CP and 11.3 MJ/kg of DM of metabolizable energy; and diet 3, 190 g/kg of DM of CP and 12.1 MJ/kg of DM of metabolizable energy. At 90 d after calving, half of the cows in each dietary group were treated with bST every 14 d for the rest of the lactation. Both nutrient density and administration of bST increased milk yield significantly in mid and late lactation; there was no significant treatment by diet interaction. Treatment with bST significantly increased plasma concentrations of insulin-like growth factor (IGF)-I compared with IGF-I concentrations in controls in both mid and late lactation. Comparisons within diet revealed that concentrations of IGF-I were significantly higher in cows fed diet 3 than in cows fed diets 1 and 2 at both stages of lactation. Increases in plasma insulin were confined to cows in late lactation, and no changes were observed for nonesterified fatty acids. Liver biopsies showed that concentrations of hepatic binding sites for bST were not affected significantly by bST treatment but were increased in midlactation for cows fed diet 3. Concentration of hepatic binding sites per unit weight of tissue were greater for cows in midlactation than for cows in late lactation. In summary, exogenous bST treatment and increased nutrient density were associated with elevated plasma IGF-I concentrations and increased milk yield; however, only nutrient density in midlactation increased the number of hepatic binding sites for bST. Exogenous bST treatment had relatively little effect on the concentration of hepatic bST receptors compared with nutrient density.

Restricting maternal space during parturition in the pig. Effects on oxytocin, vasopressin and cortisol secretion following vagino-cervical stimulation and administration of naloxone

This experiment studied the effects on endocrine and birth parameters of parturient pigs produced by restricting maternal freedom of movement without otherwise altering environment. Six primiparous pigs (gilts) were each given a jugular catheter under anaesthesia 7 days before parturition and commenced birth in a strawed pen, 2.0 m x 1.5 m in size. Continuous automated blood sampling (3 ml min-1) from unrestrained gilts began following the birth of the first piglet (stage 1) and continued for 2 h. After at least 30 min of blood collection, maternal space was reduced to 2.0 m x 0.55 m by placing rails across the pen (stage 2). The scope for movement in stage 2 was similar to that offered by a farrowing crate. After at least 25 min each gilt was given the opioid antagonist naloxone (1 mg kg-1 i.v.: stage 3). At each stage, vagino-cervical stimulation (VCS) was applied to mimic foetal ejection. Non-cervically stimulated oxytocin (OT) secretion between stages 1 and 2 was unchanged (P > 0.05) but increased significantly relative to both stages 1 and 2 following naloxone treatment for 15-20 min (P < 0.05, paired t-tests on log10 data). Following VCS in all stages plasma OT rose (P < 0.05) for 1-2 min in a similar way to that seen previously following foetal ejection, the increases being proportionally similar irrespective of stage or baseline secretion. Cortisol secretion did not increase as a consequence of space restriction (mean +/- SEM concentrations were 28.6 +/- 8.51 pmol l-1 and 32.3 +/- 11.8 pmol l-1 in stages 1 and 2, respectively). In addition, VCS did not significantly affect cortisol output. Lysine vasopressin concentrations were not affected as a consequence of either stage or VCS. Parturition was not interrupted following space restriction of gilts. These data suggest that reducing maternal space allowance during parturition is not stressful when the process does not involve the movement of animals to novel surroundings.

Hormonal and physiological effects of a 15 hour road journey in sheep: comparison with the responses to loading, handling and penning in the absence of transport

A controlled study was carried out to investigate the physiological effects of road transport on sheep. Animals (n = 10; body weight 38.9 +/- 1.3 kg), previously with catheters in their jugular veins, were rounded up and loaded onto a vehicle where they were held in a communal pen with eight other lambs. Blood samples were taken at 30 min intervals during the next 15 h while the vehicle remained stationary or was driven a distance of 548 miles (876 km). Measurements were made of plasma concentrations of cortisol, prolactin, creatine phosphokinase and lactase dehydrogenase isozymes and also of plasma osmolality, haematocrit and body weight; heart rate was also recorded in one animal. Loading and the start of driving produced large increases in cortisol and prolactin concentrations. Heart rate also increased whereas osmolality and haematocrit decreased. The major changes in hormone release occurred in the first 3 h period while, during the remaining 12 h, the stimulatory effect of transport was present but small. Body weight loss was similar under both stationary and driven conditions.

Stress Hormone Responses of Sheep to Food and Water Deprivation at High and Low Ambient Temperatures

The effects of food and/or water deprivation at different ambient temperatures (7 or 35 °C) on stress hormone release in sheep (n = 8), were studied to provide background data for research into the effects of road transport. Blood samples were taken from catheterized animals at the start and, at 6h intervals, during 48h tests in an environmental chamber. Cortisol release was unaffected by temperature or deprivation state but was stimulated by introduction to the chamber. Prolactin secretion showed a similar tendency and levels of this hormone were generally higher in the first test, whichever chamber was used. Heat exposure also had a prolonged stimulatory effect on prolactin release, especially in the first test. Growth hormone concentrations were rather variable but tended to be greatest when the animals were deprived of food. Measurements of plasma osmolality indicated that sheep remained in water balance, even when water was withheld for 48h, unless they had access to food. The results suggest that under laboratory conditions, and over a wide thermal range, withholding food and water for 48h does not induce Cortisol or prolactin release in sheep. However, exposure to novel situations seems to have a stimulatory effect.

Effects of centrally administered prostaglandin EP receptor agonists on febrile and adrenocortical responses in the prepubertal pig

Febrile and adrenocortical responses to central (lateral ventricle) injections of prostaglandin E2 (PGE2) and E-series prostanoid receptor agonists (EP1, EP2, EP3, subtypes) were investigated in prepubertal pigs. In Experiment 1, administration of PGE2, (1.4, 5.6 nmol) produced dose-related increases in core temperature and plasma cortisol concentrations. In Experiment 2, approximately equimolar (1.2 to 1.4 nmol) amounts of EP1, EP2, and EP2/EP3 agonists were compared. The EP2 and EP2/EP3 prostanoids raised core temperature, whereas the increase induced by the EP1 agonist was not significant. Similarly, although all of the agonists appeared to stimulate cortisol release, these results were also not significant. In Experiment 3, pigs treated with an EP3 agonist (1.3 nmol) showed marked febrile and adrenocortical responses. The results of these experiments are compared with data from the rat using the same agonists and route of administration. The findings are also discussed in relation to the distribution of receptor populations in vascular and synaptosomal compartments of the porcine brain.

Restraint, but not frustration, induces prostaglandin-mediated hyperthermia in pigs

Three experiments were carried out to investigate stress hyperthermia in prepubertal pigs. Experiment 1 examined the effect of frustrative nonreward (psychological stress) on deep body temperature in animals (n = 7) trained to make operant responses for food following a 17.5-h period of deprivation. There was no change in body temperature when the feeders were switched off whereas there was a small increase (NS) during normal operant feeding that might be attributable to physical exertion. In Experiment 2, the effects of 15-min physical restraint (snaring) were examined in the same group of animals. This procedure induced a significant (p < 0.01) rise in core temperature that was completely abolished by prior administration of a cyclooxygenase inhibitor (indomethacin, 2 mg/kg given intravenously). The final experiment investigated the effects of snaring on plasma cortisol concentrations. Blood samples were taken from indwelling catheters in pigs (n = 5) subjected to 15-min restraint with, or without, indomethacin pretreatment. Snaring produced a significant (p < 0.001) increase in cortisol release that was not affected by the administration of indomethacin. These results suggest that snaring, a physical stress that may also have energy expenditure components, induces a prostaglandin-mediated hyperthermic response in the growing pig.

Hyperthermic and endocrine effects of intravenous prostaglandin administration in the pig

Experimentally induced fever is accompanied by a variety of hormonal changes, and there is evidence to suggest that some of these responses may be mediated by prostaglandins. However, little is known about the endocrine effects of peripherally administered prostaglandins, especially in domesticated species. In this study, the effects of intravenous prostaglandin E2 (PGE2; 20 micrograms/kg) on deep body temperature and plasma concentrations of cortisol, lysine vasopressin (LVP), and growth hormone were investigated in prepubertal pigs (n = 6) prepared with venous catheters and sampled at 10-min intervals for 3 hr. PGE2-induced hyperthermia, which lasted for the duration of the study, was accompanied by a 70-min increase in cortisol and LVP concentrations. Moreover, this hyperthermic response was checked when LVP levels were high. These results indicate that a fever-inducing intravenous injection of PGE2 produced a marked anterior and posterior pituitary hormone response in growing pigs. Also, the transient increase in LVP may be correlated with a central action of the hormone, limiting the extent of the fever. In addition, because the majority of the animals exhibited mild hyperthermia (0.5 degrees C) under control conditions, the results suggest that, in a given population of pigs, there may be some animals that exhibit stress-induced hyperthermia.

Increased body temperature, cortisol secretion, and hypothalamic expression of c-fos, corticotrophin releasing hormone and interleukin-1 beta mRNAs, following central administration of interleukin-1 beta in the sheep

There is evidence to indicate that cytokines of the interleukin series act within the brain to influence physiological responses to pathological states or stressful events. This investigation examined the effects of intracerebroventricular (lateral ventricle) injection of human recombinant interleukin-1 beta (IL-1 beta) on body temperature, hormone (catecholamine, cortisol, prolactin, growth hormone) release and hypothalamic expression of c-fos, corticotrophin-releasing hormone (CRH), vasopressin (AVP) and IL-1 beta mRNAs in the sheep. A preliminary study showed that central administration of 10 micrograms IL-1 beta significantly (P < 0.05) increased body temperature (by 1.2 degrees C) over a 140 min period but did not affect catecholamine secretion. A second experiment using graded doses (100 ng, 1 microgram, 10 micrograms) of IL-1 beta indicated that only the highest dose significantly (P < 0.01) increased cortisol concentrations and that none of the treatments altered the secretion of prolactin or growth hormone. In a third study, changes in gene expression in the hypothalamus were examined using in situ hybridization histochemistry following treatment with 10 micrograms IL-1 beta. The results showed that IL-1 beta increased c-fos mRNA in the paraventricular (PVN, P < 0.05) and supraoptic (SON, P < 0.05) nuclei, CRH mRNA in the PVN (P < 0.01) and IL-1 beta mRNA in the PVN (P < 0.05). There was, however, no change in AVP mRNA in either the PVN or the SON.

The CCKA receptor antagonist devazepide inhibits the effect of apomorphine on vasopressin release in pigs

1. A transient increase in plasma vasopressin concentrations represents a physiological correlate of nausea in animals that vomit. 2. The CCKA receptor antagonist devazepide has previously been shown to inhibit vasopressin release induced in pigs by intravenous (i.v.) CCK. 3. This study investigated whether devazepide (70 micrograms/kg i.v.) would affect vasopressin secretion induced in pigs (n = 6) by the emetic drug apomorphine (25 micrograms/kg i.v.). 4. Apomorphine stimulated vasopressin release in the 30 min period following injection; this effect was prevented by prior administration of devazepide. 5. The results suggest that CCKA receptor antagonists may have the ability to prevent nausea and/or emesis.

Differential stressor effects on the concentrations of cortisol, prolactin and catecholamines in the blood of sheep

Adult wether sheep (n = 8) were subjected to 60 minutes of psychological (isolation) or physical (transport simulation/standing in water) stress, or a control handling procedure in the home pen. Blood samples were taken before and during these treatments and the plasma concentrations of cortisol, prolactin, noradrenaline and adrenaline determined. All the stressors significantly increased plasma cortisol concentrations (P < 0.001) whereas only transport simulation increased prolactin secretion (P < 0.005). Noradrenaline concentrations showed little change in response to the various treatments, with the exception of isolation which produced a small non-significant increase (P < 0.08). All the stress procedures stimulated adrenaline release within the first 10 minutes but the most marked effects were seen after transport simulation and isolation, both of which induced a significant increase throughout the treatment period (P < 0.01).

Central effects of naloxone and selected opioid agonists on cortisol and prolactin secretion in non-stressed sheep

1. Intravenous morphine decreases cortisol and increases prolactin concentrations in male sheep whereas naloxone has the opposite effect. 2. In this investigation, the effects of intracerebroventricular injections of naloxone, morphine (mu agonist), dynorphin (kappa agonist) and DADLE (delta/mu agonist) on cortisol and prolactin release were investigated. 3. None of the drugs affected cortisol secretion. 4. Naloxone transiently decreased prolactin levels (P < 0.05). 5. All the opioids tended to enhance prolactin secretion and the highest dose (300 micrograms) of DADLE produced a significant (P < 0.007) sustained increase. 6. These results are consistent with the view that exogenous and endogenous opioids affect the pituitary to influence cortisol release in sheep but act also at the hypothalamic level to influence prolactin secretion.