Effect of intrahypothalamic injections of norepinephrine and serotonin on plasma arginine vasotocin and mesotocin in the White Leghorn cockerel

1. Saline (10 microliters), norepinephrine (NE) and Serotonin (5-HT), 500 nmol each, were injected into the anterior third ventricle (A3V; n = 7) or the posterior third ventricle (P3V; n = 11) of ananesthetised, unrestrained White Leghorn cockerels. Plasma arginine vasotocin (AVT) and mesotocin (MT) were measured 20, 60 and 120 min after injection. 2. Injection of NE into both the A3V and P3V had no significant effect on either plasma AVT or plasma MT at any of the sampling times. 3. Administration of 5-HT into the A3V significantly increased plasma MT about two-fold 20 min following injection. At 120 min time, plasma MT returned to normal. 4. In P3V birds, 5-HT had no effect on plasma MT in the first 20 min, but a significant increase in plasma MT occurred 60 to 120 min after injection. The magnitude of the response was lower than in the A3V cockerels. 5. Plasma AVT was not affected by 5-HT administration into the A3V at any of the sampling times, but 5-HT administration into the P3V caused significant rises in plasma AVT at 120 min. 6. Serotonergic, but not noradrenergic, induction of neurohypophysial peptide secretion was demonstrated.     

Arginine vasotocin and mesotocin in the anterior hypothalamus, neurohypophysis, proventriculus and plasma of White Leghorn cockerels, during dehydration

1. The effect of 96 hrs of water deprivation on plasma electrolytes, osmolarity, arginine vasotocin (AVT), mesotocin (MT), and on AVT and MT content in the neurohypophysis, anterior hypothalamic area (AHA) and proventriculus, was studied at 24 hrs intervals, in adult White Leghorn cockerels. 2. Plasma AVT increased three fold during the first 24 hrs but there was no further change during the next 48 hrs. In the last 24 hrs, plasma AVT decreased in about 25%. Plasma MT did not change during the entire period of dehydration. 3. Plasma sodium and osmolarity gradually increased during that time. 4. Neurohypophysial AVT content was depleted by 95% during the period of dehydration while MT content did not change. 5. In the AHA there was no change in AVT levels during dehydration while the levels of MT increased while in the proventriculus there was no change in either AVT or MT levels. 6. For the data collected during the entire experimental period, no correlation was found between plasma osmolarity and plasma AVT, but there was a highly significant negative correlation between plasma osmolarity and neurohypophysial AVT content. 7. It may be suggested that the depletion in AVT content in the neurohypophysis during progressive water deprivation resulted in an insufficient level of AVT in circulation to enable the cockerels to counter the dehydration. This may explain the death of those cockerels which were dehydrated for a further 24 hr period.     

Physiological effects of arginine vasotocin and mesotocin in cockerels

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels.

2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca.

3. Doses of 0.1 and 1.0 mU MT/mu/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone.

4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature.

5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT.

6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects     

Different responses of protein synthesis to refeeding in various muscles of fasted chicks

1. The change in the rate of protein synthesis of different muscles, concentrations of plasma insulin, plasma insulin-like growth factor-I (IGF-I) and other plasma components were investigated after refeeding in fasted chicks. 5.2 g of the complete diet was refed. This was the maximum that could be force-fed with water. 2. The fractional synthesis rates (FSR) of breast (M. pectoralis major) and leg (M. gastrocnemius) muscles were measured after injection of L-[2, 6-(3)H]phenylalanine. Plasma insulin and IGF-I concentration were determined by radioimmunoassay. 3. In the breast muscle, FSR was significantly reduced by 2-d fasting. The FSR had recovered completely after 1 h of refeeding and was maintained until 6 h. The change in FSR after refeeding was associated with the change in ribosomal efficiency (K(RNA); absolute synthesis rate per unit RNA), while no change in ribosomal capacity (C(S); RNA: protein ratio) was observed. 4. In the leg muscle, FSR was decreased by 2-d fasting and increased gradually toward 6 h after refeeding but did not reach the level of the fed control. In contrast to the breast muscle, no significant changes in Cs and K(RNA) in the leg muscle were observed. 5. Plasma glucose concentration increased significantly at 1 h after refeeding but returned to the fasted level after 24 h. Plasma insulin concentration in chicks refed for 1 h was higher than in the fasted group. There was no significant change in plasma IGF-I concentration. 6. These results suggest that the FSR of breast muscle was more sensitive to refeeding than that of leg muscle which may be explained, in part, by differences in sensitivity to the change in circulating plasma insulin concentration after refeeding.     

Effects of sex and gonadal steroids on arginine vasotocin and mesotocin in the pineal gland and neurohypophysis of White Leghorn fowls

1. Pineal and neurohypophysial arginine vasotocin (AVT) and mesotocin (MT) were measured in White Leghorn hens, cockerels and castrated males treated with either testosterone propionate (TP) or oestradiol benzoate (EB) (n = 10/group). The lighting regimen was 14 h light: 10 h dark, supplied by natural diffused sunlight and incandescent bulbs. 2. Both AVT and MT were detected in the pineal gland of all the chickens. 3. There was no significant effect of either sex or treatments on pineal MT. 4. Females had about 4 times more pineal AVT than males, regardless of their treatment. There was no effect of the treatments on pineal AVT in the males. 5. No sexual difference in neurohypophysial AVT was detected, but the neurohypophysis of the castrated males treated with EB contained less AVT than the neurohypophysis of the intact males. 6. Intact males had about twice as much MT in the neurohypophysis as females. Castrated males treated with either TP or EB had similar concentrations of neurohypophysial MT, which were lower than that of the intact males, but higher than that of the females.     

The effect of arginine vasotocin on blood volume, plasma protein and electrolyte concentrations in the cockerel, Gallus domesticus

The effect of arginine vasotocin (AVT), 0.1 μg/kg body weight, on blood volume, plasma protein and Na+ and K+ concentrations was investigated in New Hampshire cockerels. Significant increases in blood volume were observed 45 and 90 min following AVT. The plasma protein concentration decreased significantly after 4 h. The plasma Na⁺ concentration significantly increased while that of K+ decreased after 1 h. Significant changes in electrolyte concentrations were found up to 4 h following the AVT administration.     

Hypertension in bulls and steers anesthetized with guaifenesin-thiobarbiturate-halothane combination

Eight bulls and steers (research animals) and 18 bulls (surgical patients) were anesthetized with guaifenesin and thiopental or thiamylal and for 90 minutes with halothane. Arterial blood pressure and heart rate were recorded in all animals. Cardiac output, plasma glucose and lactate concentrations, PCV, plasma proteins and plasma thromboxane B2 values were determined before (control) and every 15 minutes during anesthesia in the research animals. Plasma catecholamine concentrations were measured in 3 of the research animals and 3 of the surgical patients. Arterial pressure, heart rate, and plasma thromboxane B2 and catecholamine concentrations were also measured immediately after the trachea was intubated. All animals, except one, were hypertensive during anesthesia. Heart rate during anesthesia was significantly increased, compared with control measurements, and cardiac output was decreased. Plasma glucose and lactate values significantly increased when the animals were restrained on their sides. Plasma glucose concentrations remained increased during anesthesia, but lactate decreased. Packed cell volume and plasma proteins were unchanged by the induction of anesthesia. Plasma norepinephrine concentration was unchanged during anesthesia, and epinephrine concentration was decreased. Endotracheal intubation caused a transient significant increase in arterial pressure, heart rate, and thromboxane B2 and a nonsignificant increase in norepinephrine.     

Adrenocortical and heterophil/lymphocyte responses to challenge in hens showing short or long tonic immobility reactions

1. Adult White Leghorn hens showing short or long tonic immobility reactions were classified as low-fear (LF) or high-fear (HF) responders, respectively. Following cannulation, their adrenocortical responsiveness to ACTH administration and the effects of chronic frustration induced by thwarting of feeding on plasma corticosterone concentrations and heterophil/lymphocyte (H/L) ratios were measured at regular intervals. 2. ACTH injection elicited significant and similar mean increases in circulating corticosterone concentrations in both the LF and HF groups. 3. Absolute H/L ratios were higher in HF than in LF hens after cannulation, although both groups showed similar proportional increases from pre-operation ratios. 4. Plasma corticosterone concentrations and H/L ratios were significantly increased at 20 h and 44 h respectively after the frustration of feeding regime began. Thus, adrenocortical activation preceded increases in H/L ratios but, whereas the elevated plasma corticosterone concentrations found after 20 h remained virtually constant thereafter, H/L ratios rose progressively throughout the 68 h frustration period. 5. There were no significant differences between groups in their plasma corticosterone and H/L responses to frustration. However, a consistent trend towards greater adrenocortical activation was observed in the HF than in the LF hens.     

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.     

Comparison of arterial and central venous cannulations using ultrasound guidance in pigs

OBJECTIVE: To evaluate the feasibility of ultrasound guided vascular access in pigs by comparing central venous and arterial cannulation techniques. ANIMALS: Twenty-two healthy female Pietrain pigs, 14-18 weeks old and weighing 51.1 +/- 4.3 kg (mean +/- SD). STUDY DESIGN: Comparative animal trial. MATERIALS AND METHODS: After induction of general anaesthesia, cannulation of the external jugular vein and internal carotid artery was attempted using real-time ultrasound guidance. The quality of the ultrasound picture was assessed on an analogue scale from 1 (excellent) to 5 (insufficient). Vessel size, cannulation success rate, number of puncture attempts and time from first puncture attempt until insertion of the Seldinger wire were recorded. RESULTS: Cannulation was successful in all but one animal in which a cut-down technique was performed. The arteries were significantly smaller than the veins (p < 0.001) resulting in a significantly prolonged cannulation time (p = 0.032) for insertion of arterial catheters without differences in success rate. In 89% of attempted cannulations, the Seldinger wire was inserted within 5 minutes. CONCLUSIONS AND CLINICAL RELEVANCE: In anaesthetized pigs undergoing instrumentation for biomedical research, ultrasound-guided vascular access is a simple and rapid alternative to surgical cut-down. In veterinary anaesthesia, the technique might be useful in sedated or anesthetized pigs in which arterial or central venous access is required.     

Effects of anesthesia, surgery, and intravenous administration of fluids on plasma antidiuretic hormone concentrations in healthy dogs

OBJECTIVE: To evaluate effects of anesthesia, surgery, and intravenous administration of fluids on plasma concentrations of antidiuretic hormone (ADH), concentration of total solids (TS), PCV, arterial blood pressure (BP), plasma osmolality, and urine output in healthy dogs. ANIMALS: 22 healthy Beagles. PROCEDURE: 11 dogs did not receive fluids, and 11 received 20 ml of lactated Ringer's solution/kg of body weight/h. Plasma ADH adn TS concentrations, PCV, osmolality, and arterial BP were measured before anesthesia (T0) and after administration of preanesthetic agents (T1), induction of anesthesia (T2), and 1 and 2 hours of surgery (T3 and T4, respectively). Urine output was measured at T3 and T4. RESULTS: ADH concentrations increased at T1, T3, and T4, compared with concentrations at T0. Concentration of TS and PCV decreased at all times after administration of preanesthetic drugs. Plasma ADH concentration was less at T3 in dogs that received fluids, compared with those that did not. Blood pressure did not differ between groups, and osmolality did not increase > 1% from To value at any time. At T4, rate of urine production was less in dogs that did not receive fluids, compared with those that did. CONCLUSIONS AND CLINICAL RELEVANCE: Plasma ADH concentration increased and PCV and TS concentration decreased in response to anesthesia and surgery. Intravenous administration of fluids resulted in increased urine output but had no effect on ADH concentration or arterial BP. The causes and effects of increased plasma ADH concentrations may affect efficacious administration of fluids during the perioperative period in dogs.     

Pharmacologic and pharmacokinetic properties of methocarbamol in the horse

The hemodynamic, respiratory, and behavioral effects, as well as the pharmacokinetic properties of methocarbamol, were determined in horses. Heart rate, cardiac output, arterial and venous blood pressures, respiratory rate, and arterial blood gases did not change after IV methocarbamol (4.4, 8.8, 17.6 mg/kg) administration. There were no signs of behavior modification or ataxia observed. Analysis of plasma concentration time data indicated that the disposition of methocarbamol may be dose-dependent. Clearance and steady-state volume of distribution decreased as the dose increased. Plasma concentrations of guaifenesin, a metabolite of methocarbamol, were never greater than 0.5% of the plasma concentration of methocarbamol.     

Assessment of zinc and copper status in weaned piglets in relation to dietary zinc and copper supply

The aim of the study was to determine the effect of weaning and the effect of increasing dietary zinc concentrations on the zinc and copper status of weaned piglets (study 1) and to study the effect of high concentrations of dietary zinc and/or copper on zinc and copper status of weaned piglets (study 2). Study 1 included 54 piglets (six litters of nine piglets). One piglet from every litter was killed 1 day before weaning. The remaining 48 piglets were allocated at weaning (28 days) to four dietary zinc treatments (100, 250, 1000 or 2500 ppm) and subsequently killed 1-2, 5-6 or 14-15 days after weaning. Study 2 included 48 piglets (six litters of eight piglets) allocated to four dietary treatments, consisting of low or high dietary zinc (100 or 2500 ppm) in combination with low or high dietary copper (20 or 175 ppm). All piglets in study 2 were killed 5-7 days after weaning. In both studies, the trace mineral status was assessed by zinc and copper concentrations and alkaline phosphatase (AP) activity in plasma and mucosal tissue. In study 2, lymphocyte metallothionein (MT) mRNA and intestinal mucosa MT mRNA concentrations were included as zinc status markers. The results showed that the zinc status, measured as zinc in plasma and mucosa, was not affected by weaning of the piglets. Plasma copper concentrations decreased during the first 2 weeks after weaning. High dietary copper concentrations did not affect the concentration of copper in plasma, but increased the concentration of copper in mucosa and the concentration of zinc in plasma. The dietary zinc treatments increased the zinc concentration in plasma as well as the zinc and MT mRNA concentration in mucosa. Lymphocyte MT mRNA concentrations did not reflect the differences in dietary zinc supplementation.     

Exercise-induced alterations in plasma concentrations of ghrelin, adiponectin, leptin, glucose, insulin, and cortisol in horses

Six Standardbred (STB) mares (11+/-2 years, 521+/-77 kg; means+/-SD) performed an exercise trial (EX) where they underwent an incremental exercise test (GXT) as well as a parallel control trial (CON) to test the hypothesis that short-term, high intensity exercise would alter plasma concentrations of glucose, leptin, adiponectin, ghrelin, insulin and cortisol. Plasma samples were taken before (0 min), during (last 10s at 6, 8m/s, and the velocity eliciting VO(2max)), and after exercise (2, 10, 30, 60 min; 12 and 24h post-GXT). A second set of blood samples was collected before and after an afternoon meal given at 1515 h (at 1500, 1514, 1530, and 1545 h). Data were analyzed using ANOVA for repeated measures and Tukey's test. During the GXT, there were no changes (P>0.05) in the plasma concentrations of glucose, leptin, adiponectin or ghrelin. However, there was a 29% increase (P<0.05) in mean plasma cortisol concentration and a 35% decrease (P<0.05) in mean plasma insulin concentration. Substantial increases (P<0.05) in the mean plasma concentrations of glucose and cortisol of 36% and 102%, respectively, were seen in the EX trial during the first 60 min post-GXT. Plasma leptin concentration, measured at the 24h post-GXT time point, was 20% lower (P<0.05) during the EX trial compared with the parallel time point in the standing control (CON) trial. Plasma ghrelin concentration was 37% lower (P<0.05) in the EX trial compared with CON before and after the afternoon meal, but was 43% higher (P<0.05) 12h post-GXT. There were no differences between EX and CON for plasma concentrations of insulin or adiponectin during recovery. It was concluded that short-term high intensity exercise alters plasma leptin and ghrelin concentrations in STB mares post-exercise, which may signal the exercised animals to alter energy intake.     

Some responses of the immature fowl to the withdrawal of a stressor

1. Light Sussex chicks were treated with corticotrophin (30 IU/kg) five times a week from hatching to 3 weeks of age. Their responses to the cessation of treatment were determined over the subsequent 2 weeks. 2. Growth rate was impaired by the treatment but had returned to normal after 7 d. 3. Adrenal mass was not affected by treatment but hypertrophy was evident after 14 d of recovery. Relative adrenal weight was greater in the treated group throughout the recovery period. 4. Adrenal cholesterol stores were depleted at the end of treatment, were repleted after 7 d but significantly depleted again at 14 d. 5. Plasma glucose concentration was not affected by treatment but birds were hyperglycaemic 7 and 14 d after treatment had ceased. 6. Plasma free fatty acid (FFA) concentrations were not affected at any time. 7. Plasma corticosterone concentration was not affected by the treatment but 7 d later it was greater in the treated birds. 8. Significant correlations between plasma glucose, FFA and corticosterone were found.     

Comparative pharmacokinetics of chlortetracycline in milk-fed versus conventionally fed calves

Plasma and tissue concentration and pharmacokinetics of chlortetracycline (CTC) was determined in milk-fed and conventionally fed Holstein calves. A two-compartment open model was used after a single intravenous dose (11 mgn CTC/kg body weight). There were no significant differences between dietary treatments. The drug was rapidly distributed from plasma into the peripheral compartment but was slowly eliminated, with detectable concentration of CTC continuing for 72 h after dosing. A single-compartment model was used after a single oral dose (22 mg CTC/kg body weight). All but four of the kinetic parameters were significantly different for the two dietary treatments. Milk-fed calves had a larger area under the plasma level curve, a larger fraction of the dose absorbed, a smaller volume of distribution and a smaller overall body clearance rate. Estimated recovery of CTC in the urine of the milk-fed calves was greater, regardless of route of administration. The concentration of CTC in tissues following an oral dose was greatest in kidney, followed by liver, heart, skeletal muscle, spleen and brain. Tissue depletion of CTC closely paralleled the decline in plasma concentration.     

Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes

Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2 % halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, ß-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after premedication, immediately after induction, every 20 min during anaesthesia, and at 20 and 120 min after disconnection. Induction was rapid, excitement-free and good muscle relaxation was observed. There were no changes in heart and respiratory rates. Decrease in temperature, hyperoxia and respiratory acidosis developed during anaes-thesia and slight hypotension was observed (minimum value 76 ± 10 mm Hg at 40 mins). No changes were observed in dynorphin, ß-endorphin, ACTH, catecholamines and glucose. Plasma cortisol concentration increased from 220 ± 17 basal to 354 ± 22 nmol/L at 120 min during anaesthesia; plasma AVP concentration increased from 3 ± 1 basal to 346 ± 64 pmol/L at 100 min during anaesthesia and plasma lactate concentration increased from 1.22 ± 0.08 basal to 1.76 ± 0.13 mmol/L at 80 min during anaesthesia. Recovery was rapid and uneventful with ponies taking 46 ± 6 min to stand. When midazolam/ketamine was compared with thiopentone or detomidine/ketamine for induction before halothane anaesthesia using an otherwise similar protocol in the same ponies, it caused slightly more respiratory depression, but less hypotension. Additionally, midazolam reduced the hormonal stress response commonly observed during halothane anaesthesia and appears to have a good potential for use in horses.     

Propionate is not an important regulator of plasma leptin concentration in dairy cattle

Propionate was recently shown to increase leptin synthesis in rodents. To determine if a similar effect occurs in ruminants, propionate was administered to lactating dairy cows. In experiment 1, 31 cows were given an intrajugular Na propionate bolus (1,040 micromol/kg body weight), increasing plasma propionate from 160 to 5,680 microM and plasma insulin from 6.8 to 77.8 microIU/mL. Plasma leptin concentration decreased from 2.11 ng/mL before bolus to 1.99 ng/mL after dosing (P<0.05) with no differences in leptin concentrations at 20, 50, and 100 min post-bolus (P>0.10). In experiment 2, 12 cows were used in a duplicated 6 x 6 Latin square experiment to assess the dose-response effect of ruminal propionate infusion on plasma leptin concentration. Sodium propionate was infused at rates of 0, 260, 520, 780, 1040, or 1,300 mmol/h, while total short-chain fatty acid infusion rate was held constant at 1,300 mmol/h by addition of Na acetate to the infusate. Coccygeal blood was sampled following 18 h of infusion. Increasing the rate of propionate infusion linearly increased plasma propionate concentration from 180 to 330 microM (P<0.001) and plasma insulin concentration from 6.7 to 9.1 microIU/mL (P<0.05). There was a quadratic response in plasma leptin concentration (P=0.04) with a maximum at 780 mmol/h propionate, but leptin concentrations increased by no more than 8% relative to the 0 mmol/h propionate infusion. Leptin concentrations were correlated with insulin concentrations but not with propionate concentrations in plasma. Propionate is not a physiological regulator of leptin secretion in lactating dairy cows.     

Distribution of immunoreactive vasotocin and mesotocin in the chicken gastrointestinal tract

Immunoreactive arginine vasotocin (AVT) and mesotocin (MT) were measured in heart, breast muscle, adrenals, testes, and different parts of the gastrointestinal tract in adult male chickens. Neither of the peptides were detected in liver, testis, heart and breast muscle. The amounts of AVT and MT in the adrenals were 167 +/- 25 and 669 +/- 198 pg/gland, respectively. Considerable amounts of immunoreactive peptides were found in the gastrointestinal tract with the highest concentration in the proventriculus (4.18 +/- 0.31 ng AVT and 16.58 +/- 0.86 ng MT per organ). Dose-response curves of duodenal and proventriculus extracts were parallel with synthetic AVT and MT standards.     

Anesthesia of horses with a combination of detomidine, zolazepam, tiletamine, and isoflurane immediately after strenuous treadmill exercise.

OBJECTIVES: To evaluate effects of strenuous exercise in adult horses immediately before anesthesia and to determine whether prior exercise affects anesthesia induction, recovery, or both. ANIMALS: 6 healthy Thoroughbreds in good condition and trained to run on a treadmill, each horse serving as its own control. PROCEDURE: Horses ran on a treadmill until fatigued, then were sedated immediately with detomidine hydrochloride and anesthetized with a zolazepam hydrochloride-tiletamine combination. Anesthesia was maintained with isoflurane in oxygen for another 90 minutes. Blood samples were taken before, during, and after exercise and during anesthesia. RESULTS: During exercise, changes in heart rate, core body temperature, plasma lactate concentration, arterial pH, and PaCO2 were significant. Plasma ionized calcium concentration was lower after exercise, compared with baseline values, and remained lower at 30 minutes of isoflurane anesthesia. Compared with baseline values, plasma chloride concentration decreased significantly during anesthesia after exercise. Cardiac output during anesthesia was significantly lower than that during preexercise, but significant differences between experimental and control periods were not observed. Arterial blood pressure during anesthesia was significantly lower than that during preexercise and initially was maintained better during isoflurane anesthesia after exercise. Cardiac output and blood pressure values were clinically acceptable throughout anesthesia. CONCLUSION: Administration of detomidine hydrochloride followed by zolazepam hydrochloride-tiletamine appeared to be safe and effective for sedation and anesthesia of horses that had just completed strenuous exercise. CLINICAL RELEVANCE: Anesthetic given in accordance with this protocol can be used to anesthetize horses that are injured during athletic competition to assess injuries, facilitate first aid, and possibly allow salvage of injured horses.