Redistribution of cardiac output caused by opening of arteriovenous anastomoses by a combination of azaperone and metomidate

Physiological parameter values for physiologically based pharmacokinetic models in food-producing animals. Part I: Cattle and swine

Physiologically based pharmacokinetic (PBPK) models for chemicals in food animals are a useful tool in estimating chemical tissue residues and withdrawal intervals. Physiological parameters such as organ weights and blood flows are an important component of a PBPK model. The objective of this study was to compile PBPK‐related physiological parameter data in food animals, including cattle and swine. Comprehensive literature searches were performed in PubMed, Google Scholar, ScienceDirect, and ProQuest. Relevant literature was reviewed and tables of relevant parameters such as relative organ weights (% of body weight) and relative blood flows (% of cardiac output) were compiled for different production classes of cattle and swine. The mean and standard deviation of each parameter were calculated to characterize their variability and uncertainty and to allow investigators to conduct population PBPK analysis via Monte Carlo simulations. Regression equations using weight or age were created for parameters having sufficient data. These compiled data provide a comprehensive physiological parameter database for developing PBPK models of chemicals in cattle and swine to support animal‐derived food safety assessment. This work also provides a basis to compile data in other food animal species, including goats, sheep, chickens, and turkeys.

Doppler ultrasound can be used to monitor umbilical arterial blood flow in lightly sedated pigs at multiple gestational ages

Doppler ultrasound was performed under moderate sedation (ketamine and azaperone) for 30min to monitor umbilical arterial (UA) blood flow in one uterine horn of Large White×Landrace gilts (n=23) at Gestational Days (GD) 30, 45, 60 and 90. Gilts were scanned before they were killed to examine relationships between litter size, sex ratio and five UA parameters (peak systolic velocity (PSV), end diastolic velocity (EDV), A/B (PSV to EDV) ratio, fetal heart rate (FHR) and resistance index (RI)). In gilts in which scans were obtained from all fetuses in the scanned horn, relationships between UA parameters, and fetal weight and sex were examined. A subset of gilts were sedated, scanned and recovered (SSR) earlier in gestation (GD30 or GD45) to assess the effects of sedation on later fetal development by comparison with control litters (no previous sedation). Temporal changes were observed in all UA parameters (P≤0.001). At GD60 and GD90, FHR decreased with increasing duration of sedation (P≤0.001). Sex ratio and fetal weight affected UA blood flow, whereas litter size and fetal sex did not. SSR at GD30 and GD45 was associated with decreased fetal weight at GD60 (P≤0.001) and GD90 (P=0.06) respectively, compared with controls. These results suggest maternal sedation during gestation affects fetal development, which should be investigated further. Measuring UA blood flow in growth-restricted porcine fetuses throughout gestation may be feasible.

Azaperone and xylazine: A pharmacological combination to facilitate captive deer management for red brocket deer (Mazama americana)

The care and management of deer in captivity is challenging, especially in the case of red brocket deer (Mazama americana), whose routine management using physical restraint is difficult. Our study evaluated the effects of azaperone and xylazine combination for immobilizing red brocket deer and allow for the standard capture and handling protocols (e.g., biological material, horn cutting, and trimming) to be conducted safely. Six adult, captive, red brocket deer received an intramuscular injection of either 1 mg/kg azaperone and 0.5 mg/kg xylazine (AX0.5) or 1 mg/kg azaperone and 1 mg/kg xylazine (AX1.0). Sedation latency, sternal recumbency, safe handling, and quality of the sedation were evaluated to provide an overview of how the immobilizing drugs affected managing the species in captivity. Additionally, heart rate, respiratory rate, mean arterial pressure, rectal temperature, pH, PaO₂, PaCO₂, SaO₂, HCO₃^-, BE, Na⁺, K⁺ and serum lactate were also measured. The latency period of the animals in the AX0.5 group was greater than that of the animals in the AX1.0 group (7 ± 6.6 min vs. 5 ± 2.0 min), as was the time for them to assume sternal recumbency (12 ± 9.7 min vs. 6 ± 3.1 min). However, the time after the initial dose at which the animals could safely be handled (14 ± 4.5 min vs. 12 ± 5.2 min), and the time until the end of the safe handling period (75 ± 12.3 min vs. 85 ± 6.8 min) were similar for both groups. Animals in both groups showed physiological stability during all evaluations, but hypoxemia was observed in one animal in each group. We conclude that both drug combinations are safe and effective at sedating red brocket deer in captivity and suggest that the procedure be performed with oxygen supplementation to reduce the potential for hypoxia.

Effect of propofol and remifentanil on cerebral perfusion and oxygenation in pigs: a systematic review

The objective of this review is to evaluate the existing literature with regard to the influence of propofol and remifentanil total intravenous anaesthesia (TIVA) on cerebral perfusion and oxygenation in healthy pigs. Anaesthesia has influence on cerebral haemodynamics and it is important not only in human but also in veterinary anaesthesia to preserve optimal regulation of cerebral haemodynamics. Propofol and remifentanil are widely used in neuroanaesthesia and are increasingly used in experimental animal studies. In translational models, the pig has advantages compared to small laboratory animals because of brain anatomy, metabolism, neurophysiological maturation, and cerebral haemodynamics. However, reported effects of propofol and remifentanil on cerebral perfusion and oxygenation in pigs have not been reviewed. An electronic search identified 99 articles in English. Title and abstract screening selected 29 articles for full-text evaluation of which 19 were excluded with reasons. Of the 10 peer-reviewed articles included for review, only three had propofol or remifentanil anaesthesia as the primary study objective and only two directly investigated the effect of anaesthesia on cerebral perfusion and oxygenation (CPO). The evidence evaluated in this systematic review is limited, not focused on propofol and remifentanil and possibly influenced by factors of potential importance for CPO assessment. In one study of healthy pigs, CPO measures were within normal ranges following propofol-remifentanil anaesthesia, and addition of a single remifentanil bolus did not affect regional cerebral oxygen saturation (rSO2). Even though the pool of evidence suggests that propofol and remifentanil alone or in combination have limited effects on CPO in healthy pigs, confirmative evidence is lacking.

Laparoscopy guided Doppler ultrasound measurement of fetal blood flow indices during early to mid-gestation in pigs

The objectives of this study were to obtain relevant blood flow indices of umbilical arteries (UmA) of porcine fetuses using a laparoscopic ultrasound probe and to relate these data with fetal size at early to mid gestation. Fetal parameters and flow indices, i.e., fetal length and area, fetal heart rate (FHR), systolic pulse duration (T1), interpulse duration (T2), T2/T1 ratio, peak systolic velocity (PSV), time averaged velocity (TAV), resistance index (RI) and pulsatility index (PI), were measured in 182 fetuses of 26 pregnant Landrace gilts on pregnancy day (PD) 36 (122 fetuses from 17 gilts), PD42 (19 fetuses from 3 gilts) and PD51 (42 fetuses from 6 gilts). Fetal heart rate was higher on PD36 than on PD42 (P<0.05). No differences (P>0.05) were obtained concerning systolic pulse duration, flow velocities and RI. On PD42, the PI was lower (P<0.05), while the interpulse duration (P=0.06) and T2/T1 ratio tended (P=0.08) to be higher on PD42 compared with PD36 and to PD51. To find differences in UmA blood flow parameters concerning fetal size, i.e., fetal length, fetuses were retrospectively grouped as follows: small (lower 25%), medium (mean 50%) and large (upper 25%), respectively. Although, fetuses differed in size (P<0.001) within and between days of pregnancy, FHR, PSV, TAV, RI and PI did not differ (P>0.05) among the size classes. Only systolic pulse duration tended to be longer (P=0.05) in large compared with small fetuses on PD36, and interpulse duration was lower in large fetuses on PD36 in comparison with PD51 (P<0.05). Though there was no link between fetal blood flow indices and fetal intrauterine growth retardation (IUGR), with further studies based on these flow indices, it might be possible to evaluate nutrient- or stress-related influences on fetal growth and development, particularly in the case of IUGR.

Interspecies scaling in pharmacokinetics: a novel whole-body physiologically based modeling framework to discover drug biodistribution mechanisms in vivo

Drug approval processes require extensive testing and have recently put more emphasis on understanding mechanistic drug action in the body including toxicity and safety.1 Consequently, there is an urgent need in the pharmaceutical industry to develop mechanistic pharmacokinetic (PK) models able to both expedite knowledge gain from experimental trials and, simultaneously, address safety concerns. We previously developed a first principles based whole-body PK model, which incorporated physiological dimensions and drug mass transport. In this follow-up article, we demonstrate how the first principles model in combination with novel physiological scaling laws yields more reliable interspecies and intraspecies extrapolation of drug biodistribution. We show how experimental dose-response data in rats for immunosuppressant cyclosporin are sufficient for predicting the biodistribution of this drug in pigs, monkeys, and humans. The predicted drug concentrations extrapolated by interspecies scaling laws match well with the experimental measurements. These promising results demonstrate that the whole-body PK modeling approach not only elucidates drug mechanisms from a biochemical standpoint, but offers better scaling precision. Better models can substantially accelerate the introduction of drug leads to clinical trials and eventually to the market by offering more understanding of the drug mechanisms, aiding in therapy design, and serving as an accurate dosing tool.

Possible role of alpha-adrenoceptor subtypes in acute migraine therapy

Even though the underlying mechanisms for the pathophysiology of migraine attacks are not completely understood, little doubt exists that the headache phase is explained by dilatation of cranial, extracerebral blood vessels. In this context, experimental models predictive for anti-migraine activity have shown that both triptans and ergot alkaloids, which abort migraine headache, produce vasoconstriction within the carotid circulation of different species. In contrast to the well-established role of serotonin (5-hydroxytryptamine; 5-HT) 5-HT1B receptors in the common carotid vascular bed, the role of alpha-adrenoceptors and their subtypes has been examined only relatively recently. Using experimental animal models and alpha1- and alpha2-adrenoceptor agonists (phenylephrine and BHT933, respectively) and antagonists (prazosin and rauwolscine, respectively), it was shown that activation of either receptor produces a cranioselective vasoconstriction. Subsequently, investigations employing relatively selective antagonists at alpha1- (alpha1A, alpha1B, alpha1D) and alpha2- (alpha2A, alpha2B, alpha2C) adrenoceptor subtypes revealed that specific receptors mediate the carotid haemodynamic responses in these animals. From these observations, together with the potential limited role of alpha1B- and alpha2C-adrenoceptors in the regulation of systemic haemodynamic responses, it is suggested that selective agonists at these receptors may provide a promising novel avenue for the development of acute anti-migraine drugs.

A61603-induced vasoconstriction in porcine carotid vasculature: involvement of a non-adrenergic mechanism

It has recently been shown that the pharmacological profile of alpha(1)-adrenoceptors mediating constriction of porcine carotid arteriovenous anastomoses resembles that of alpha(1A)- and alpha(1B)-adrenoceptor subtypes. In an attempt to verify the involvement of alpha(1A)-adrenoceptors, we used the potent alpha(1A)-adrenoceptor agonist N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydro-naphthalen-1-yl]methane sulphonamide (A61603) and found that intracarotid (i.c.) administration of A61603 (0.3-10 microg kg(-1)) dose-dependently decreased porcine carotid blood flow and vascular conductance. This decrease was exclusively due to a constriction of carotid arteriovenous anastomoses; the capillary blood flow and conductance remained unchanged. Surprisingly, the responses to A61603 were little modified by prior i.v. treatment with 5-methylurapidil (1000 microg kg(-1)), prazosin (100 microg kg(-1)) or a combination of prazosin and rauwolscine (100 and 300 microg kg(-1), respectively). The 5-HT(1B/1D) receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'(5-methyl-1,2,4-oxadiazol-3-yl)[1,1,-biphenyl]-4-carboxamide hydrochloride monohydrate (GR127935; 500 microg kg(-1)) and ketanserin (500 microg kg(-1)) also failed to modify carotid vascular responses to A61603, but, interestingly, methiothepin (3000 microg kg(-1)) proved to be an effective antagonist. Taken together, the present results show that A61603 is a relatively poor agonist at the alpha(1A)-adrenoceptor in anaesthetised pigs and that the carotid vasoconstriction produced by A61603 is mediated by a novel non-adrenergic mechanism.

Alpha1-adrenoceptor subtypes mediating vasoconstriction in the carotid circulation of anaesthetized pigs: possible avenues for antimigraine drug development

It has recently been shown that the alpha-adrenoceptors mediating vasoconstriction of porcine carotid arteriovenous anastomoses resemble both alpha1- and alpha2-adrenoceptors, but no attempt was made to identify the specific subtypes (alpha1A, alpha1B and alpha1D) involved. Therefore, the present study was designed to elucidate the specific subtype(s) of alpha1-adrenoceptors involved in the above response, using the alpha1-adrenoceptor agonist phenylephrine and alpha1-adrenoceptor antagonists 5-methylurapidil (alpha1A), L-765 314 (alpha1B) and BMY 7378 (alpha1D). Ten-minute intracarotid infusions of phenylephrine (1, 3 and 10 microgkg-1.min-1) induced a dose-dependent decrease in total carotid and arteriovenous anastomotic conductance, accompanied by a small tachycardia. These carotid vascular effects were abolished by L-765 314 (1000 microgkg-1; i.v.), while these responses were only attenuated by 5-methylurapidil (1000 microgkg-1; i.v.), and BMY 7378 (1000 microgkg-1; i.v.). Furthermore, intravenous bolus injections of phenylephrine (3 and 10 microgkg-1) produced a dose-dependent vasopressor response, which was only affected by 1000 microgkg-1 of 5-methylurapidil, while the other antagonists were ineffective. These results, coupled to the binding affinities of the above antagonists at the different alpha1-adrenoceptors, suggest that both alpha1A- and alpha1B-adrenoceptors mediate constriction of carotid arteriovenous anastomoses in anaesthetized pigs. In view of the less ubiquitous nature of alpha1B- compared to alpha1A-adrenoceptors, the development of potent and selective alpha1B-adrenoceptor agonists may prove to be important for the treatment of migraine.

Pharmacological evidence that alpha1-and alpha2-adrenoceptors mediate vasoconstriction of carotid arteriovenous anastomoses in anaesthetized pigs

Vasoconstriction of carotid arteriovenous anastomoses may be involved in the therapeutic action of acutely acting anti-migraine agents, including the triptans and ergot alkaloids. While 5-HT1B/1D receptors mediate the effect of triptans, ergotamine and dihydroergotamine also interact with alpha-adrenoceptors. In the present study, we investigated the potential role of alpha1- and alpha2-adrenoceptors in mediating vasoconstriction of carotid arteriovenous anastomoses in anaesthetized pigs. Ten minute intracarotid infusions of phenylephrine (1, 3 and 10 microg kg(-1) min(-1)) or BHT 933 (3, 10 and 30 microg kg(-1) min(-1)) produced dose-dependent decreases in total carotid and arteriovenous anastomotic conductances; no changes were observed in the capillary fraction. The carotid vascular effects of phenylephrine and BHT 933 were selectively abolished by prazosin (100 microg kg(-1), i.v.) and rauwolscine (300 microg kg(-1), i.v.), respectively. The responses to phenylephrine and BHT 933 were not affected by the selective 5-HT1B/1D receptor antagonist GR127935 (500 microg kg(-1), i.v.). These results show that both alpha1- and alpha2-adrenoceptors can mediate vasoconstriction of carotid arteriovenous anastomoses in anaesthetized pigs. Since vasoconstrictor activity in this in vivo model is predictive of anti-migraine activity, an agonist activity at particularly the alpha2-adrenoceptor subtypes, in view of their less ubiquitous nature, could provide migraine abortive potential. Thus, the present results may aid further understanding of the mode of action of some current anti-migraine agents and may eventually be helpful in the development of future treatment in migraine.

The effect of nitric oxide donors on haemodynamics and blood flow distribution in the porcine carotid circulation

1. The role of nitric (NO) in the regulation of capillary and arteriovenous anastomotic blood flow was evaluated in the carotid circulation of the pig. For this purpose, the effect of intracarotid (i.c.) infusions of saline and two NO donors, nitroprusside sodium (NPR) and S-nitroso-N-acetylpenicillamine (SNAP) in concentrations of 3-100 micrograms min-1 was studied on systemic haemodynamics and carotid blood flow and its distribution in anaesthetized pigs with low arteriovenous anastomotic blood flow, by use of the radioactive microsphere method. 2. Apart from heart rate, which increased after both NPR and SNAP, no major changes in systemic haemodynamic variables were observed. In contrast to saline, both NPR and SNAP increased common carotid blood flow, vascular conductance and vascular pulsations dose-dependently. 3. The distribution of the carotid artery blood flow over capillary and arteriovenous anastomotic fraction remained stable after saline infusions. Both NPR and SNAP enhanced total capillary blood flow and conductance. In contrast to NPR, arteriovenous anastomotic blood flow and conductance were increased by SNAP. 4. At the tissue level, capillary blood flow increases following NPR or SNAP were reflected by an increase in both extracerebral and dural blood flow without changes in total brain blood flow. 5. These results indicate that both NO donors cause arteriolar dilatation together with enhanced vascular pulsations in the carotid circulation of the pig. Probably by way of a 'steal' phenomenon, this pronounced arteriolar dilatation limits the effect of NO donors on arteriovenous anastomoses. 6. The results of the present investigation support the contention that dilatation of intra- and extra cranial arteries and arteriovenous anastomoses leads to increased vascular pulsations, which (rather than increased blood flow) could, at least in part, be responsible for the headache caused by nitro vasodilators.

Nitrogen microbubbles induce a disappearance of single platelets (aggregation) with porcine platelets: a comparative study of the effects of anticoagulants and blood collection methods

The pathogenesis of decompression illness (DCI) is uncertain. DCI involves all parts of the organism where gas bubbles are produced. They have both primary and secondary effects and have been classified as an agonist aggregating human platelets. In vitro effects of N2 bubbles on porcine platelets were investigated. Comparative studies using two different anticoagulants and three different sampling methods were performed. A disappearance of single platelets interpreted as platelet aggregation was observed in the presence of N2 bubbles in all studied groups. Aggregatory responses were more profound with platelets in heparinized plasma than in citrated plasma. In citrated plasma the aggregatory responses were more profound when blood was obtained from nonanaesthetized (awake) animals than from slaugtherhouse animals. Adrenaline (1 microM) had an inhibitory effect on N2 bubble induced platelet aggregation in vitro. The pig could be useful to investigate possible gas bubble effects in vivo.

Cardiovascular profile of the new dihydropyridine derivative S12968

The cardiovascular profile of S12968 was evaluated in anaesthetized pigs, using cumulative 15-min i.v. infusions of 1.25, 2.5, 5, 10 and 20 micrograms.kg-1.min-1 (n = 7) or equal volumes of its solvent (n = 7). S12968 decreased mean arterial blood pressure from 94 +/- 4 to 66 +/- 3 mm Hg (P less than 0.05) and cardiac output from 2.7 +/- 0.2 to 2.2 +/- 0.2 l.min-1 (P less than 0.05), had no effect on heart rate and left ventricular end-diastolic pressure, but decreased maxLVdP/dt (maximal rate of rise in left ventricular pressure) by up to 35 +/- 3% (P less than 0.05). With doses higher than 10 micrograms.kg-1.min-1 transmural left ventricular blood flow increased by up to 49 +/- 22% (P less than 0.05), favouring the subepicardium over the subendocardium. Myocardial oxygen consumption decreased by 22 +/- 7 and 32 +/- 8% (P less than 0.05) during infusion of 10 and 20 micrograms.kg-1.min-1, respectively. Heart rate, left ventricular end-diastolic pressure and arterial blood pressure were not affected, but maxLVdP/dt (partially) and cardiac output returned to pre-drug values a during a 60-min post-infusion period. In conclusion, S12968 exhibited a negative inotropic effect at low doses. However, with higher doses and after discontinuation of the infusion, vasodilatation occurred, while the negative inotropy disappeared. It is possible that an active metabolite, acting preferentially on the vasculature, was responsible for the vasodilatation.