Conscious Calves Research Articles

Quantitative Electroencephalographic Findings Associated with Nociception Following Surgical Castration in Conscious Calves

Pain suffered by livestock due to routine husbandry is an issue of growing concern, yet there is no validated model of pain available to assess the efficacy of pain-mitigating procedures. This study assessed quantitative EEG parameters in fully conscious calves in response to surgical castration.

Comparison of a small volume of hypertonic saline solution and dextran 40 on hemodynamic alternations in conscious calves

The hemodynamic effects of rapid intravenous (IV) administration of 10% dextran 40 in saline solution (D40) and 7.2% hypertonic saline solution (HSS) in calves were compared. Calves received isotonic saline solution (ISS), HSS or D40 (3 calves/group) and were monitored of blood pressure, and cardiac output (CO) for 180 min. HSS and D40 infusions induced a significant increase in relative plasma volume reaching 134.9+/-2.8 and 125.0+/-1.9%, respectively at the end of fluid infusion. In the HSS group, CO, cardiac index (CI) and stroke volume (SV) remained constant at low levels after 90 minutes despite the maximal values of CO, CI and SV at the end of infusion, reaching 21.0+/-6.3 l/min (p<0.05), 177.8+/-14.2 ml/min/kg (p<0.001) and 0.20+/-0.03 l/beat (at t=10 min, p<0.001), respectively. In contrast, CI and SV in the D40 group showed significant increases to 14.7+/-2.9 l/min and 153.5+/-17.2 ml/min/kg, respectively, at the end of fluid infusion. And those values remained constant at higher levels than those of the before infusions values throughout the experimental periods. Positive effects for hemodynamic alternations of D40 in calf practice were milder and longer than those of HSS. Therefore, the D40 infusion should be explored as a possible treatment for dehydrated calves, since rapid infusion of D40 may be safe and more beneficial for rehydrating more than HSS treatment.

A novel stereotaxic approach to the hypothalamus for the use of push-pull perfusion cannula in Holstein calves

To determine secretory patterns of growth hormone-releasing hormone (GHRH) and somatostatin (SS) and their roles in the regulation of growth hormone (GH) secretion, a method for collecting hypothalamic perfusates, a push-pull perfusion method was developed in calves. With the use of the stereotaxic apparatus for cattle, a cannula was implanted into the hypothalamus of four male calves based upon cerebral ventriculography. Push-pull perfusates were collected at 10 min intervals for 6 h and GHRH and SS concentrations in perfusates and plasma GH concentration were determined by EIAs and RIA, respectively. A cannula was implanted into the hypothalamus based on the image of the third ventricle and maintained for 1 month. GHRH and SS showed pulsatile secretion and the pulses for GHRH and SS were irregular in conscious animals. Neither GHRH nor SS secretion had a clear relationship with GH secretion. In the present study, we thus (1) established a stereotaxic technique for approaching the hypothalamus using cerebral ventriculography for calves, and (2) demonstrated that GHRH and SS secretion were pulsatile but not closely related to GH profile in conscious calves. The technique is useful for the study of the functions of the hypothalamus in the control of pituitary hormones in cattle.

Comparison Between Radioactive Aerosol, Technegas and Krypton for Ventilation Imaging in Healthy Calves

The use of lung scintigraphy in calves necessitates the validation of a ventilation (V•) imaging agent compatible with clinical applications. This study aimed at defining the value of an inhaled radioactive aerosol (99mTc-DTPA) and a ‘pseudogas’ (Technegas) in the assessment of regional V• in healthy conscious calves by comparing99mTc-DTPA and Technegas deposition (D) images to V• (V) images obtained from the steady-state inhalation of the short half-life krypton 81 (81mKr) gas.Images were compared by analysis of radioactivity distribution in computer-generated regions of interest within the right lung and D to V ratio images were generated in order to highlight areas of mismatching between99mTc-DTPA or Technegas and81mKr distributions. Results of this analysis showed that the99mTc-DTPA aerosol droplets were unable to reach the lung parenchyma because of significant particle impaction in the major conducting airways. Better definition of the ventilated lung was obtained when using Technegas because of minimal deposition in conducting airways. Furthermore, the Technegas and81mKr distribution patterns were highly equivalent.

MEASUREMENT OF CARDIAC OUTPUT IN NORMAL CALVES

The calf has been used extensively as a model for in vivo testing of various total artificial hearts (TAHs) and ventricular assist devices (VADs). However, the physiologic range of resting and exercise cardiac output in 80 to 150 kg calves is not well documented. Such information would allow researchers to appreciate the constraints of the animal model used and of the devices being tested. Three calves under sedation were instrumented with an Edwards Vigilence® Continuous Cardiac Output (CCO) [Edwards Critical Care, Irvine CA] catheter connected to the CCO monitor while in their stanchion. Upon reversal of the sedative, the calves were allowed to return to a normal alert state indicated by behavioral signs such as eating, drinking, and eructating. Cardiac output (CO) measurements were taken every hour for a 24-hour period, as the animal was standing or lying down. The body surface area (BSA) was calculated from the empirical formula: BSA (m2)=0.105 x Weight (kg)0.667. CO was collected and cardiac index (CI) was calculated by normalizing CO with BSA. The results were as follows:TableThere was no difference in CO in relation to whether the calf was standing or lying down, possibly due to the stanchion limiting the animal's mobility in either position. This study provides information regarding the physiologic values of CO in conscious calves at rest. Further experiments are under way to expand the limited sample size of the present study and to investigate the CO ranges under various states of physical exertion (standardized treadmill test).

The Role of Nitric Oxide in Mediating Pancreatic Endocrine Responses to Insulin‐Induced Hypoglycaemia in the Conscious Calf

The role of nitric oxide (NO) in mediating pancreatic endocrine responses to moderate hypoglycaemia has been investigated in conscious unrestrained calves. The synthesis of endogenous NO was inhibited by the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mg kg-1 I.A.), while sodium nitroprusside was infused continuously (2-4 microg min-1 kg-1 I.V.) to mimic the tonic production of NO. This effectively abolished the rise in plasma pancreatic polypeptide (PP) concentration during moderate hypoglycaemia (0.7 nmol kg-1 insulin I.V.) and significantly reduced the response to more intense hypoglycaemia (2.0 nmol kg-1 insulin I. V.). In contrast, the glucagon response was not significantly affected in either group, although consistently higher plasma glucagon values were obtained in response to the higher dose of insulin following the administration of L-NAME. It is concluded that, in the absence of L-NAME, production of NO contributes to the PP response, but not the glucagon response to hypoglycaemia in this species under physiological conditions.

Exogenous CCK and gastrin stimulate pancreatic exocrine secretion via CCK-A but also via CCK-B/gastrin receptors in the calf.

A predominance of the pancreatic cholecystokinin (CCK) receptor of the B/gastrin subtype (CCK-B/G) was reported in calves older than 1 month. Specific CCK-A and CCK-B/G receptor antagonists (SR 27897 and PD 135158, respectively) were used to identify the CCK receptor subtype involved in exogenous CCK- and gastrin-induced exocrine pancreatic responses. Conscious calves (2 months old) with catheterized pancreas, jugular vein and duodenum were used; the pancreatic juice was continuously reinfused. CCK (30 pmol kg-1 min-1, 40 min) evoked an increase in pancreatic juice flow and enzyme secretion, while the same dose of gastrin increased enzyme secretion alone. CCK-induced pancreatic secretion was abolished by SR 27897 (15 nmol kg-1 min-1, 55 min) and reduced by PD 135158 (0.15 nmol kg-1 min-1, 55 min). Gastrin-induced enzyme secretion was reduced by PD 135158 (50% to 90%) and to a lesser extent by SR 27897 (50% to 60%). These results demonstrate that CCK and gastrin in the physiological range stimulate pancreatic exocrine secretion in calves and that these effects are partly mediated by CCK-B/G receptors. Although CCK-A receptors are not predominantly expressed, they seem to play a major role in the response of pancreatic exocrine secretion to CCK.

Effects of intraduodenal administration of tarazepide on pancreatic secretion and duodenal EMG in neonatal calves

The influence of CCK-A receptor antagonism on pancreatic exocrine secretion and duodenal EMG, and the mechanism(s) involved in CCK-induced pancreatic secretion were studied in conscious calves. Seven 1-week-old calves were fitted with a pancreatic duct catheter, duodenal cannula and duodenal electrodes. Pancreatic exocrine secretion and duodenal EMG were studied following intraduodenal CCK-A receptor antagonist (Tarazepide), intravenous atropine, and intravenous or intraduodenal CCK-8 administrations. Tarazepide decreased duodenal electric activity, reduced interdigestive pancreatic secretion, especially protein; reduced cephalic and early postprandial (milk) induced secretion of bicarbonate and protein. Pancreatic protein secretion to intravenous CCK-8 was little affected by atropine, but was significantly reduced by Tarazepide±atropine; in contrast, protein secretion to intraduodenal CCK-8 was abolished by Tarazepide or atropine. We conclude that pre- and especially early postprandial pancreatic secretion are partly controlled via CCK-A (mainly mucosal) mediated mechanisms.

Regulation of adrenal function in the conscious calf.

Regulation of adrenal function in the conscious calf.

Cardiovascular and pancreatic endocrine responses to glucagon-like peptide-1(7-36) amide in the conscious calf.

Intravenous infusions of glucagon-like peptide-1(7-36) amide (GLP-1; 35 pmol min-1 kg-1 for 10 min) produced a significant rise in mean heart rate, without significant change in mean aortic blood pressure, together with a significant rise in mean arterial plasma insulin, but not in plasma pancreatic glucagon or pancreatic polypeptide concentration, in conscious calves given exogenous glucose (30-60 micromol min-1 kg-1 i.v.). The insulinotropic effect was eliminated in the presence of exogenous amino acids (0.03 mmol min-1 kg-1 i.v.). It was not affected predictably by blocking the synthesis of nitric oxide or by the simultaneous administration of the established incretin factor gastrin-releasing peptide (GRP). Whereas GLP-1 produced a statistically significant rise in plasma insulin concentration in these animals, it was much less effective than GRP in this respect, when given by continuous i.v. infusion.

Pancreatic endocrine responses to the peptides VIP and PACAP in the conscious calf.

Pancreatic endocrine responses to vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP) and acetylcholine have been investigated in conscious calves, while continuously monitoring aortic blood pressure and heart rate, in order to assess the effects of these neuropeptides under normal physiological conditions. VIP was found to modulate the release of pancreatic polypeptide (PP) in response to acetylcholine at a dose which had no significant effect on the release of either pancreatic glucagon or insulin. PACAP stimulated the release of insulin and the effect was potentiated during infusions of exogenous glucose. PACAP, when infused together with acetylcholine, also stimulated the release of pancreatic glucagon in the absence of exogenous glucose but not in its presence. Release of PP was stimulated during infusions of PACAP, whether or not exogenous glucose was given, and this effect was found to be additive with that of acetylcholine.

Role of adrenoceptors in the hypertensive response to feeding in the conscious calf.

Ingestion of milk during suckling causes hypertension and tachycardia in young, unweaned animals of many species, but these responses are most pronounced in the calf. The present study was undertaken to assess the extent to which this phenomenon depends on activation of adrenoceptors in these animals. Mean basal heart rate was 100 +/- 8 beats/min and mean basal aortic blood pressure was 92 +/- 5 mmHg. The rise in heart rate during feeding was almost completely suppressed after propranolol (2-4 mg/kg iv), which also significantly reduced the rise in blood pressure from 67 +/- 4 to 44 +/- 3 mmHg (P < 0.005). Additional pretreatment with phentolamine (1.0 mg/kg and < or =0.1 mg x min(-1) x kg(-1) iv) virtually eliminated the rise in blood pressure during feeding; it rose by only 8 +/- 4 mmHg (P < 0.001). Section of both splanchnic nerves also significantly reduced the rise in blood pressure during feeding, especially after pretreatment with propranolol. Neither section of the splanchnic nerves nor the administration of the blocking agents significantly affected the rises in plasma insulin and pancreatic polypeptide that occurred after feeding. There was no detectable rise in plasma neuropeptide Y concentration in response to feeding. The hypertensive response to direct electrical stimulation of the peripheral end of a splanchnic nerve and to intra-arterial injections of norepinephrine were completely abolished after combined pretreatment with atropine, propranolol, and phentolamine after the ipsilateral adrenal vein had been tied off. It is concluded that the cardiovascular changes that occur during feeding in these animals are attributable very largely, if not entirely, to activation of adrenoceptors.

Effect of M 3 muscarinic antagonist (4-DAMP) administration on non-stimulated and cholecy stokinin-8-stimulated secretion of pancreatic juice and duodenal motility in conscious calves

Effect of M 3 muscarinic antagonist (4-DAMP) administration on non-stimulated and cholecy stokinin-8-stimulated secretion of pancreatic juice and duodenal motility in conscious calves

Electrophysiologic evaluation of the phrenic nerve-diaphragm pathway in an intact, conscious calf model

SUMMARY Owing to technical and ethical limitations, a substantial part of the knowledge about the pathophysiologic mechanism of the human diaphragm has been obtained from studies in which phrenic nerve activation was usually carried out by direct surgical exposure of the nerves in the neck of deeply anesthetized, mechanically ventilated animals. Novel information has been gleaned from such studies, but the restrictive conditions under which it was collected preclude reliable extrapolation. We, therefore, addressed the question of whether accurate electrophysiologic evaluation of the phrenic nerve-diaphragm pathway can be performed in intact, nonanesthetized calves. Transjugular phrenic activation was well tolerated, safe, specific, and able to achieve constant symmetric and supramaximal phrenic stimulations during prolonged periods. Eighteen noninvasive cutaneous and esophageal reception circuits were tested for their ability to record the diaphragmatic evoked potential. In addition, they were compared for specificity and reproducibility of the recorded potentials during prolonged periods of tidal or stimulated respiration. The best diaphragmatic potential was recorded from surface electrodes attached to the skin of the ninth and tenth intercostal spaces, using a xyphoidian reference. We describe a method that allows easy, longterm, and reliable electrophysiologic evaluation of the phrenic nerve-diaphragm pathway in intact, conscious calves. It is hoped that such a model will produce relevant novel information regarding pathophysiology of the diaphragm.

Critical appraisal of pressure-frequency relation for estimation of diaphragm function in conscious calves

Summary A method yielding functional diaphragmatic variables in conscious animals is crucially needed to determine whether concepts and conclusions drawn from deeply anesthetized, highly instrumented clinically normal animals can be extrapolated to patients. Transdiaphragmatic pressure (Pdi) was, therefore, measured in 20 conscious calves during supramaximal transvenous bilateral stimulations of the phrenic nerves (pulse duration, 0.2 milliseconds; pulse frequency, 1, 10, 20, 30, 40, 70, and 100 Hz). Constancy of phrenic activation and precontraction length and geometry was ensured by respectively monitoring the amplitudes of right and left mass action potentials and triggering each activation train at end-expiratory lung volume against an occluded airway. Repeated phrenic activation and pressure recording procedures were well tolerated, safe, specific, and able to achieve constant and symmetric diaphragmatic tetanic contractions for prolonged periods. The Pdi increased with frequency of stimulation, so that, at 10, 20, 40, and 70 Hz, the mean ± sd generated Pdi was 33 ± 5, 65 ± 8, 82 ± 6, and 94 ± 6% of Pdi at 100 Hz, respectively. The general shape of the Pdi-frequency relation and the absolute values of the generated Pdi were reproducible at 10-hour intervals despite CO2- or resistor-induced substantial changes in breathing pattern. It is concluded that this experimental model provides a reliable assessment of diaphragm function in conscious animals and can be used to study diaphragmatic contractility.

Pancreatic endocrine responses to substance P and calcitonin gene-related peptide in conscious calves.

Both substance P (SP) and calcitonin gene-related peptide (CGRP; 0.13 micrograms.min-1.kg-1 for 10 min) produced a significant rise in arterial plasma pancreatic polypeptide (PP) concentration, and additive responses were obtained when both peptides were infused simultaneously and/or with acetylcholine (0.7 micrograms.min-1.kg-1 ia). The PP response to SP was abolished by intravenous infusions of glucose, whereas those to CGRP and acetylcholine were not significantly affected. Neither SP nor CGRP had any effect on plasma insulin concentration, either in the presence or absence of exogenous glucose, whether infused singly or together, or in the presence of acetylcholine. SP, but not CGRP, produced a small but statistically significant rise in mean plasma glucagon concentration when infused together with acetylcholine. These results suggest that SP and CGRP may modulate the secretion of PP and glucagon in the normal conscious calf but not that of insulin. It is also possible that SP modulates secretion of pancreatic glucagon in these animals.

Muscarinic involvement in vascular and adrenal medullary responses to splanchnic nerve stimulation in conscious calves.

Stimulation of the peripheral end of the right splanchnic nerve (4 Hz for 10 min) in the presence of hexamethonium caused a small but significant rise in mean aortic blood pressure which was subsequently abolished by atropine. There were also small but significant increases in the outputs of catecholamines, [Met5]-enkephalins and corticotrophin releasing factor (CRF) from the right adrenal gland. The catecholamine response was roughly halved after atropine while the outputs of enkephalins and CRF were unaffected. It is concluded that splanchnic sympathetic postganglionic neurones supplying the vasculature are completely blocked by cholinergic blockade whereas adrenal medullary responses persist in an attenuated form.

Effects of substance P on adrenal responses to acetylcholine in conscious calves.

The effect of intra-aortic infusions of substance P (SP; 10 or 20 pmol.min-1.kg-1) on adrenal responses to acetylcholine (4.5 nmol.min-1.kg-1 ia) have been investigated in functionally hypophysectomized calves given exogenous adrenocorticotropic hormone (0.7 pmol.min-1.kg-1). At the lower dose, SP had no effect on cortisol output. In contrast, SP inhibited the output of both catecholamines and enkephalins in response to acetylcholine, without affecting the output of corticotropin-releasing factor (CRF). Increasing the dose of SP to 20 pmol.min-1.kg-1 ia significantly reduced the outputs of both cortisol and CRF (P < 0.025 and 0.01 respectively). It is concluded that SP is capable of modulating both adrenal cortical and medullary responses to acetylcholine and that the latter are more sensitive to this influence than the former.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates exocrine pancreas in conscious preruminating calves

The effects of new hypothalamic peptides, PACAP-27 and PACAP-38, and secretin and VIP on the interdigestive pancreatic secretion and duodenal myoelectric activity during the asecretory phase of the pancreatic interdigestive cycle, compared with the milk ingestion phase, were examined in five calves. Peptides were infused for 5 min into the external jugular vein (0, 3, 10, 30 and 100 pmol/kg body wt during the asecretory phase of the pancreatic interdigestive cycle, and the pancreatic secretory response was compared with that obtained during milk ingestion. Intravenous infusion of PACAP-27 caused dose-related stimulation of pancreatic juice flow and bicarbonate and protein output; this effect was identical to infusion of secretin. The effect of PACAP-38 was less pronounced, and that of VIP was the weakest. Pancreatic juice volume and bicarbonate responses during milk ingestion were similar to responses obtained with the highest doses of hypothalamic peptides and secretin, whereas postprandial protein secretion was much greater than the secretion stimulated with peptides. It was concluded that PACAP from the VIP/secretin family may stimulate pancreatic exocrine secretion in conscious calves and a part of the pancreatic response to food intake can be mediated by PACAP.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates exocrine pancreas in conscious preruminating calves

The effects of new hypothalamic peptides, PACAP-27 and PACAP-38, and secretin and VIP on the interdigestive pancreatic secretion and duodenal myoelectric activity during the asecretory phase of the pancreatic interdigestive cycle, compared with the milk ingestion phase, were examined in five calves. Peptides were infused for 5 min into the external jugular vein (0, 3, 10, 30 and 100 pmol/kg body wt during the asecretory phase of the pancreatic interdigestive cycle, and the pancreatic secretory response was compared with that obtained during milk ingestion. Intravenous infusion of PACAP-27 caused dose-related stimulation of pancreatic juice flow and bicarbonate and protein output; this effect was identical to infusion of secretin. The effect of PACAP-38 was less pronounced, and that of VIP was the weakest. Pancreatic juice volume and bicarbonate responses during milk ingestion were similar to responses obtained with the highest doses of hypothalamic peptides and secretin, whereas postprandial protein secretion was much greater than the secretion stimulated with peptides. It was concluded that PACAP from the VIP/secretin family may stimulate pancreatic exocrine secretion in conscious calves and a part of the pancreatic response to food intake can be mediated by PACAP.