Characterization and comparison of the responses of equine digital arteries and veins to endothelin-1

OBJECTIVE: To compare the responses of equine digital arteries (EDAs) and equine digital veins (EDVs) to endothelin-1 (ET-1) and determine the role of the endothelium and type of receptors involved in the modulation and mediation of those responses, respectively. SAMPLE POPULATION: 5 to 9 palmar digital vessels/experiment from 28 healthy horses. PROCEDURE: Rings of dissected vessels were mounted under tension between force transducer wires in organ baths containing Krebs-Henseleit solution at 30 degrees C. Responses of EDAs and EDVs (with intact [+e] or denuded [-e] endothelium) to cumulative concentrations of ET-1 (10(-10) to 3 X 10(-7) M) were compared. For (+e)EDAs and (+e)EDVs precontracted with a thromboxane-mimetic (U44069; 10(-8) M) and (-e)EDAs and (-e)EDVs, responses to an ETB receptor agonist (S6c; 10(-10) to 3 X 10(-7) M) were evaluated. Responses to ET-1 (10(-7) M) in (-e)EDAs and (-e)EDVs were evaluated after incubation with an ETA receptor antagonist (BQ-123; 3 X 10(-7) M), an ETB receptor antagonist (BQ-788; 3 X 10(-7) M), or vehicle solution. RESULTS: Endothelin-1 induced a concentration-dependent contraction of endothelium-intact and -denuded EDAs and EDVs; EDVs were more sensitive. Neither vessel type relaxed in response to S6c, although 2 of the (-e)EDAs contracted mildly. Whereas BQ-123 inhibited the (-e)EDA and (-e)EDV responses to ET-1, BQ-788 had no effect. CONCLUSIONS AND CLINICAL RELEVANCE: Endothelin-1 induced digital vasoconstriction (marked constriction in veins). This action was unaffected by endothelium and mediated predominantly by ETA receptors. These findings suggest ET-1 can induce selective digital venoconstriction.     

Characterisation of the response of equine digital arteries and veins to substance P

Substance P (SP), a potent vasodilator, has been detected in equine digital sensory-motor nerves. The aim of the study was to characterise the functional responses of equine digital blood vessels to exogenous SP. Pre-constricted equine digital arteries (EDA) and veins (EDV) vasodilated in a biphasic, endothelium- and concentration-dependent manner to SP. A nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME; 300 microm) inhibited both phases of the relaxation response curve of EDAs to SP by >70%. In EDVs, the first relaxant phase to SP was largely L-NAME-resistant, whereas the second phase was inhibited by 60%. Both L-NAME and a cyclo-oxygenase inhibitor (ibuprofen; 10 microm) were required to inhibit EDV relaxation to SP by > or =80%. Experiments determining the receptor mediated responses to physiological concentrations of SP (1 nm) revealed that the relaxant responses of both EDA and EDV were inhibited by a neurokinin-1 (NK1) receptor antagonist (CP-96 345; 10 nm). In conclusion, SP is an endothelium-dependent vasodilator of both EDA and EDV. NO is the predominant pathway activated in EDA, whereas both prostacyclin and NO pathways are involved in EDVs. NK1 receptors appear to mediate responses to low concentrations of SP.     

Characterization of vasodilatory adenosine receptors in equine digital veins

Isolated equine digital veins (EDVs) which had been denuded of their endothelium were used to study adenosine receptors causing vasodilation. When the blood vessel wall tension was raised with the thromboxanemimetic, U44069 (30 n m ), the order of vasodilator potency of adenosine receptor agonists was: 5'-N-ethylcarboxamidoadenosine (NECA) > 2- p -(2-carboxyethyl)phenyl amino-5'-N-ethylcarboxamido-adenosine (CGS 21680) > 5'-N-methylcarboxamido-adenosine (MECA) > > N⁶-cyclohexyladenosine (CHA) > N⁶-cyclopentyladenosine (CPA) > N⁶–2-(4-Aminophenyl)ethyladenosine (APNEA) > adenosine. Removal of the endothelium had no significant effect on the responses to NECA. The adenosine receptor antagonists, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; A₁-selective) and xanthine amine cogener (XAC; non-selective antagonist) inhibited responses to NECA and CHA in a competitive manner and XAC proved to be 8–25 times more potent than DPCPX against both agonists. These data support the presence of A₂ adenosine receptors in EDVs, located on the vascular smooth muscle cells, which are most likely to be of the A_2A-adenosine receptor subtype. A direct comparison between the potency and efficacy of NECA and adenosine as vasodilators of EDV and equine digital arteries was made and both agonists proved to be significantly more potent and efficacious as vasodilators of EDVs. These data suggest that adenosine may be an important local mediator regulating blood flow through the digital circulation and that its generation under hypoxic conditions would lead to selective venodilation.     

A comparative study between responses of isolated bovine and equine digital arteries to vasoactive mediators

Hemodynamic perturbations, partly resulting from abnormal vasoconstriction of digital vessels, have been implicated in the pathogenesis of bovine and equine laminitis. This study compared the responsiveness of isolated bovine (BDA) and equine (EDA) digital arteries to pharmacological agents that stimulate receptor systems involved in the regulation of normal vessel tone. The role of the endothelium and the short‐ and longer‐term effects of an experimentally induced endothelial damage were also evaluated. Species‐related differences were found in the vessel reactivity to all of the receptor agonists tested. In intact BDA, as compared to intact EDA, norepinephrine was a more effective vasoconstrictor, 5‐hydroxytryptamine a more effective but less potent vasoconstrictor, isoproterenol a less effective vasodilator and carbamylcholine a less potent vasodilator. In BDA, but not in EDA, the contractile responses to norepinephrine and 5‐hydroxytryptamine were enhanced immediately after endothelium removal. However, the contractile reactivity of denuded BDA returned to basal values following overnight incubation. The differences suggest species specificity for the pathophysiology of digital vasomotor tone and function in horses and cattle.     

The distribution of nerve fibres immunoreactive for vasoactive intestinal peptide, calcitonin gene-related peptide, substance P and dopamine beta-hydroxylase in the normal equine larynx

The autonomic innervation of the mammalian respiratory system is complex, and involves a wide variety of peptide and non-peptide neurotransmitters which will have an important role in normal laryngeal function and the response to disease. This innervation has been partially described in the horse airway and lung, but there is no information on the equine larynx. This paper describes the expression and distribution of nerve fibres immunoreactive for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP) and the adrenergic enzymatic marker dopamine beta-hydroxylase (DBetaH) in the mucosa of the equine larynx. The overall relative density of nerve fibres immunoreactive for the different antigens was VIP>CGRP>SP>DBetaH. There were differences in the distribution of nerve fibre types, although each antigen was found in nerve fibres adjacent to blood vessels and mucous glands. VIP -like immunoreactivity (VIP -Li) was particularly extensive in association with mucous glands. SP - and CGRP -like immunoreactivity (SP -Li, CGRP -Li) were also seen close to the epithelium, with occasional nerve fibres coursing beneath and between the epithelial cells. Fragments of SP -Li and CGRP -Li fibres were also present in large nerve fibre bundles and ganglionic cell clusters, but not in the neurons themselves. The density of nerve fibres immunoreactive for DBetaH was very low and restricted to blood vessels and mucous glands. There was marked variation in the density of nerve fibres at the different sites, with the greatest density, particularly for VIP, over the arytenoid cartilage. Immunoreactive nerve fibres were less plentiful over the epiglottis, and the density of all types of nerve fibres was low over the cricoid cartilage. Overall VIP -Li nerve fibres were the most plentiful.     

Vasodilatory effect of pentoxifylline in isolated equine digital veins

The direct vasodilatory action of pentoxifylline (1-(5-oxohexyl)-3,7-dimethylxanthine) and its signalling pathway was evaluated in equine digital veins. Cumulative concentration-response curves to pentoxifylline (1 nM to 300 μM) were recorded in phenylephrine-precontracted equine digital vein rings under different experimental conditions. Relaxation to pentoxifylline was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (a non-xanthine adenosine receptor antagonist; 3 μM). Nitric oxide synthase (NOS), soluble guanylate cyclase and cyclooxygenase (COX) inhibitors (Nω-nitro-L-arginine methyl ester (100 μM), ODQ (30 μM) and indomethacin (10 μM), respectively) significantly reduced the maximum relaxation induced by pentoxifylline. Moreover, pentoxifylline-induced relaxation was strongly reduced by Rp-8-Br-PET-cyclic guanosine monophosphate-S (a protein kinase G inhibitor; 3 μM), but remained unaffected by H-89 (a protein kinase A inhibitor; 2 μM). Pentoxifylline-induced relaxation was associated with a 3.4-fold increase in tissue cGMP content. To investigate whether pentoxifylline can affect cAMP- and cGMP-mediated relaxations, curves to forskolin, to sodium nitroprusside (SNP) and 8-bromo-cGMP were also recorded in endothelium-denuded equine digital vein rings pretreated with pentoxifylline (10 and 100 μM). Pentoxifylline only potentiated the SNP-mediated relaxation at the highest concentration (100 μM). Thus, pentoxifylline relaxed equine digital veins via endothelium-dependent and endothelium-independent components. The effect was mediated through both the NOS and COX pathways and could also result from inhibition of cGMP specific-phosphodiesterase activity at the highest concentrations used.     

Pharmacological characterization of alpha1-adrenoceptors in equine digital veins

Alpha-adrenoceptors mediate contractile responses in equine digital veins (EDVs) and arteries. Vascular smooth muscle alpha(1)-adrenoceptor subtypes have been implicated in a number of conditions, such as acute equine laminitis, and are therapeutic targets for the treatment of this condition. Digital veins, rather than arteries, were investigated in the present study because they have been specifically implicated in the pathophysiology of acute laminitis. The order of potency of a series of alpha(1)-adrenoceptor-selective agonists and antagonists was determined in isolated rings of EDVs under conditions of isometric tension. A61603 was the most potent agonist, with a higher potency (76-fold greater) than phenylephrine (PHE), suggesting the presence of the alpha(1A)-adrenoceptor subtype. Prazosin (30 nm) caused competitive inhibition of the responses to A61603 and PHE, with pK(b) values of 8.05 +/- 0.28 and 8.20 +/- 0.27, respectively. In addition, the alpha(1A)-adrenoceptor antagonist, WB4101 (10 nm), also caused competitive inhibition of the responses to the two agonists, with pK(b) values of 8.37 +/- 0.16 and 8.54 +/- 0.23, respectively, confirming the presence of the alpha(1A)-adrenoceptor subtype in EDVs. The selective alpha(1D)-adrenoceptor antagonist, BMY7378 (100 nm) did not cause a significant change in the response to the agonists, giving lower pK(b) values (6.97 +/- 0.27 and 6.88 +/- 0.17 vs. A61603 and PHE, respectively). Chloroethylclonidine dihydrochloride (45 microm, 30 min), used to produce selective inactivation of alpha(1B)-adrenoceptors, caused noncompetitive inhibition of the response to PHE, but was without effect on the response to A61603. These findings indicate that EDVs possess at least two different alpha(1)-adrenoceptor populations, which are predominantly of the alpha(1A) and alpha(1B) subtypes. These data may assist in the development of more selective antagonists for therapeutic use in horses.     

Innervation pattern of substance P- and calcitonin gene-related peptide-immunoreactive nerves of the cerebral arteries in the quail

The pattern of cerebrovascular substance P (SP)- and calcitonin gene-related peptide (CGRP)-immunoreactive (IR) innervation was investigated in the quail. SP- and CGRP-IR nerves were relatively a few in the rostral part of the anterior circulation, and very scanty or lacking in its caudal part and the whole of the posterior circulation. A significant finding was that the anterior circulation in the majority of individuals is furnished with a varying proportion of SP-IR nerves with or without CGRP immunoreactivity. There was a good correlation in the expression of CGRP immunoreactivity between SP-IR cells in the ophthalmic division of the trigeminal ganglion and SP-IR nerves supplying the major cerebral arteries. In the quail, SP- and CGRP-IR fiber bundles are usually present in the internal ethmoidal artery (IEA). From these and other findings, it is most probable that cerebral perivascular SP- and CGRP-IR nerves are mainly derived from the same categories of neurons in the primary sensory ganglion via the IEA. The close association of varicose SP-IR axons to the nerve cells in the pial arteries suggests that these intrinsic neurons may play some vasocontrolling roles through the modulatory effect of their pericellular SP-IR axons.     

In vitro responses of equine digital vessels to dopamine and fenoldopam.

The in vitro responses of isolated vascular preparations of digital arteries and veins obtained from healthy anaesthetised horses were determined for dopamine and fenoldopam. The digital vessels were harvested, cut into 4 mm vascular segments, suspended in tissue baths and attached to force-displacement transducers. Dose-response studies between 10(-8) and 10(-4)M concentrations were performed for all drugs. The change in tension of each vascular ring was measured in grams of force. The reactivity between palmar and plantar digital vessels and baseline vascular responses were determined for dopamine. The vascular responses of dopamine were compared to in vitro data for other known vasoconstrictor agents. The mechanism of vasoconstriction induced by dopamine was further defined using prazosin, a specific competitive alpha-1 adrenoceptor antagonist. The vasodilating ability of fenoldopam, a dopamine-1 (DA-1) receptor agonist, was also determined using noradrenaline- preconstricted vascular segments from palmar digital vessels. The effective concentration to produce 50 per cent of the maximal response (EC50) and the maximal contraction in grams of force per milligram of the vascular ring (g/mg) were calculated. There were no differences in the reactivity between the palmar and plantar digital vessels. Dopamine produced intense constriction in arteries and veins but only at very high molar concentrations. Prazosin decreased significantly the sensitivity of the veins to dopamine (increased the mean EC50 values) but not the arteries. Prazosin had no effect on the maximal contractions of the vessels. Fenoldopam produced very little relaxation of either the arteries or veins. These results suggest that dopamine produces constriction in equine digital arteries and veins and that the constriction is only partially mediated by alpha-1 adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hemodynamic responses of the equine digit to intravenous and digital arterial infusion of dopamine

In 6 adult horses anesthetized with pentobarbital, the hemodynamic responses of the equine digit to infusion of dopamine were evaluated by use of an isolated extra corporeal pump perfused digital preparation. Digital blood flow was maintained at a constant rate that was independent of systemic hemodynamic changes. Three sequential experiments were performed on each horse. In the first experiment (n = 6), dopamine was infused IV at rates of 1.0, 2.5, and 5.0 micrograms/kg/min. For the second experiment (n = 5), dopamine (400 micrograms/ml) was infused into the digital artery at the rates of 0.07, 0.7, and 1.2 ml/min. The third experiment (n = 5) consisted of a 5-minute intra-arterial infusion of phentolamine followed by the intra-arterial infusion of dopamine while continuing the infusion of phentolamine. Digital venous, arterial, and capillary pressures, total digital vascular resistance, and precapillary to postcapillary resistance ratios were determined in each experiment. Systemic infusion of dopamine did not induce changes in the hemodynamics of the digital vasculature. Digital arterial infusion of dopamine alone resulted in a dose-dependent increase in arterial pressure, total digital vascular resistance, and an increase in the precapillary to postcapillary resistance ratio. Phentolamine attenuated the vasoconstrictive response elicited by intra-arterial infusion of dopamine.     

Evaluation of beta3-adrenoceptor-mediated relaxation in intact and endotoxin-treated equine digital veins

OBJECTIVE: To investigate the functional expression of beta3-adrenoceptors (beta3-ARs) in equine digital veins (EDVs) and to examine whether beta3-AR relaxation was altered in EDVs incubated with endotoxin. SAMPLE POPULATION: Forelimbs obtained from 30 horses. PROCEDURE: Forelimbs were obtained from horses in an abattoir. Equine digital veins were carefully removed from distal portions of the forelimbs. Rings of dissected EDVs were mounted in 5-mL organ baths to record isometric tension in the presence of various beta3-AR agonists (SR 58611A, ZD 2079, and ZM 215001). RESULTS: In intact EDVs, isoprenaline, SR 58611A, ZD 2079, and ZM 215001 induced concentration-dependent relaxation. Isoprenaline and SR 58611A-induced relaxations were reduced or unaffected by nadolol, respectively. In intact EDVs, SR 58611A-induced relaxation was significantly reduced in the presence of 2 microM ZM 215001 (used as a beta3-AR antagonist). In endothelium-denuded EDVs or intact EDVs in the presence of a nitric oxide synthase inhibitor, isoprenaline and SR 58611A-induced relaxations were significantly decreased. The endothelium-independent relaxation to SR 58611A was significantly inhibited in the presence of ZM 215001. In endotoxin-treated EDV, isoprenaline- and SR 58611A-induced relaxations were significantly reduced. In these conditions, cycloheximide (a protein synthesis inhibitor) and ibuprofen (a cyclooxygenase inhibitor) restored the relaxant response to SR 58611A. CONCLUSIONS AND CLINICAL RELEVANCE: Beta3-adrenoceptors are functionally expressed in EDVs. Incubation in the presence of endotoxin, used as an in vitro model of laminitis, induced an alteration of beta-AR-mediated relaxations in EDVs, which could be the consequence of cyclooxygenase induction and subsequent prostanoid production.     

Calbindin D-28k, parvalbumin and calcitonin gene-related peptide immunoreactivity in the canine spinal cord

This study was conducted as a comparative analysis of the immunohistochemical localization of calbindin D-28k, parvalbumin and the calcitonin gene-related peptide (CGRP) in the cervical through the sacral spinal cord of mongrel dogs, to reveal any distinct patterns of distribution and possible involvement in spinal processing. In laminae I and II of the substantia gelatinosa, both calbindin D-28k and CGRP showed strong immunoreactivity, with calbindin D-28k being positive in both cells and fibres, while CGRP was positive in fibres only. Parvalbumin and CGRP immunoreactive cells were widely distributed in various nuclei and lower motor neurones in the ventromedial horn. In addition, the lower motor neurones expressed CGRP as well as parvalbumin, but not calbindin D-28k. These results are generally consistent with previous reports, and the co-localization of parvalbumin and CGRP may explain the functional improvement of lower motor neuron disease.     

In vitro pharmacologic effect of two endothelin-1 antagonists on equine colonic arteries and veins

OBJECTIVE: To evaluate the effectiveness of 2 potential endothelin (ET)-1 antagonists in blocking the contractile responses of equine colonic vessels to increasing concentrations of ET-1. SAMPLE POPULATION: Mesenteric vessels from 6 clinically healthy horses. PROCEDURE: Colonic vessels (arterial and venous rings) were placed in organ baths with oxygenated Tyrode solution at 37 C. Each was attached to a force transducer interfaced with a polygraph, and 2 g of tension was applied and equilibrated for 45 minutes. Then, B-1 (PD 142893) and B-2 (PD 145065) ET-1 antagonists were tested. One ring from each vessel type was used as a control for determining concentration-response relationships of ET-1 (10(-10) to 10(-6)M). Three rings of each vessel type were incubated with 3 concentrations of each antagonist (10(-7), 10(-6), and 10(-5) M) for 30 minutes before ET induced contractions were determined. The maximum contractile response and pA2 values were determined. RESULTS: Vessels contracted in a concentration-dependent manner to ET-1. Arteries responded slowly but reached greater contractions. Veins responded immediately with sustained contractions. Both antagonists inhibited contractions in a concentration-dependent manner with significant differences at 10(-6) and 10(-5)M for arteries and 10(-5) M for veins. Complete blockade of contractions was observed with B-2 (10(-5)M). The pA2 values for B-1 were 8.26 and 6.82 for arteries and veins, respectively, whereas they were 8.25 and 7.21 for B-2. CONCLUSION AND CLINICAL RELEVANCE: Both antagonists effectively blocked ET-1-induced contractions of equine colonic vessels. Because B-2 is water soluble and caused complete blockade at 10(-5) M, it appears to be the preferred antagonist.     

降钙素基因相关肽在鸭腔上囊胚胎及胚后发育过程中的表达

应用免疫组织化学技术研究降钙素基因相关肽在鸭腔上囊胚胎及胚后发育过程中的表达特征.结果显示,降钙素基因相关肽强阳性细胞出现于20 d胚龄至胚后14周龄的滤泡间上皮,20 d胚龄至胚后17周龄的小结相关上皮,新生雏至胚后14周龄的滤泡皮质,24 d胚龄至胚后14周龄的滤泡髓质,20 d胚龄至胚后14周龄的肌层和小动脉平滑肌.结果说明,降钙素基因相关肽表达于鸭腔上囊的不同部位及不同发育阶段;在腔上囊退化期,降钙素基因相关肽的表达表现出明显的变化特征,这可能是导致腔上囊退化的原因之一;滤泡间上皮与小结相关上皮在神经肽表达方面存在差异.     

Characterization of the in vitro responses of equine cecal longitudinal smooth muscle to endothelin-1

OBJECTIVE: To characterize the in vitro response of equine cecal longitudinal smooth muscle (CLSM) to endothelin (ET)-1 and assess the role of ETA and ETB receptors in those ET-1-induced responses. ANIMALS: 36 horses without gastrointestinal tract disease. PROCEDURE: To determine cumulative concentration-response relationships, CLSM strips were suspended in tissue baths containing graded concentrations of ET-1 (10(-9) to 10(-6)M) with or without BQ-123 (ETA receptor antagonist); with or without IRL-1038 (ETB receptor antagonist); or with both antagonists at concentrations of 10(-9), 10(-7), and 10(-5)M. To determine the percentage change in baseline tension of CLSM, the areas under the curve during the 3-minute periods before and after addition of each dose were compared. Also, the effects of ET-1 and a combination of selective ETA and ETB receptor antagonists on electrically evoked contractions were studied. RESULTS: ET-1 caused sustained increases in CLSM tension in a concentration-dependent manner. Contractile responses to ET-1 were not significantly inhibited by either BQ-123 or IRL-1038 alone at any concentration; however, responses were significantly inhibited by exposure to the antagonists together at a concentration of 10(-5)M. Electrical field stimulation did not change the spontaneous contractile activity of CLSM and did not significantly alter the tissue response to ET-1, BQ-123, or IRL-1038. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that ET-1 has a contractile effect on equine CLSM that is mediated via ETA and ETB receptors. In vitro spontaneous contractions of equine CLSM apparently originate in the smooth muscle and not the enteric nervous system.     

Contractile responses of isolated equine digital arteries under hypoxic or hyperoxic conditions in vitro: role of reactive oxygen species and Rho kinase

The underlying pathophysiological triggers for equine acute laminitis are unknown, although digital vasoconstriction, ischaemia, hypoxia and reperfusion injury may be involved. The contractile responses of isolated equine digital arteries (EDAs), harvested from the hindlimbs of normal horses postmortem at an abattoir, were studied acutely (up to 3 h) under hyperoxic (95% oxygen, 5% CO₂) and hypoxic (95% nitrogen, 5% CO₂) conditions in organ baths. Phenylephrine (PHE; 10^?6 m ), 5‐hydroxytryptamine (5‐HT; 10^?7 m ) and high potassium (K⁺; 118 mm ) caused contraction in EDAs which was significantly (P < 0.0001) enhanced under hypoxic conditions. In contrast, contraction stimulated by 9,11‐dideoxy‐9α,11α‐epoxymethanoprostaglandin F_2α (U44069; 3 × 10^?8 m ) was not significantly enhanced by hypoxia (P = 0.75). Hypoxia‐enhanced contraction in response to K⁺ was greater (P < 0.03) in vessels with a functional endothelium than in vessels in which the endothelium was removed by rubbing. Fasudil (10^?6 to 10^?5 m ), a Rho kinase inhibitor, and apocynin (10^?3 to 3 × 10^?3 m ), an NADPH oxidase inhibitor, significantly (P ≤ 0.05) inhibited hypoxia‐enhanced contraction in response to PHE and 5‐HT. In conclusion, hypoxia‐enhanced contraction occurred in EDAs. This appears to be partially mediated by reactive oxygen species produced by NAPDH oxidase, which activate Rho kinase to increase calcium sensitisation and enhance smooth muscle contraction.     

Effects of Rho-kinase and Src protein tyrosine kinase inhibition on agonist-induced vasoconstriction of arteries and veins of the equine laminar dermis

OBJECTIVE: To determine the effects of inhibition of Rho-kinase or Src-family protein tyrosine kinases (srcPTK) on agonist-induced contractile responses in equine laminar arteries and veins. SAMPLE POPULATION: Laminar arteries and veins obtained from 13 adult mixed-breed horses. PROCEDURES: Laminar vessels were mounted on myographs and exposed to phenylephrine (PE), 5-hydroxytryptamine (5-HT), prostaglandin F(2) (PGF(2)), and endothelin-1 (ET-1) with or without the Rho-kinase inhibitor Y-27632 (10 microM), srcPTK inhibitor PP2 (10 microM), or a negative control analogue for PP2 (PP3; 10 microM). RESULTS: Responses to PE were reduced by use of Y-27632 in laminar vessels (approx inhibition, 55%). However, Y-27632 reduced responses to 5-HT to a greater degree in veins than in arteries (approx inhibition of 55% and 35%, respectively). The Y-27632 also reduced responses of laminar veins to ET-1 by approximately 40% but had no effect on maximum responses of laminar arteries to ET-1, although a rightward shift in the concentration response curve was evident. Addition of PP2 reduced responses to PE, 5-HT, and PGF(2) in laminar veins by approximately 40%, 60%, and 65%, respectively, compared with responses after the addition of PP3; PP2 had no effect on responses to ET-1. In laminar arteries, PP2 reduced 5-HT-induced contractions by approximately 50% but did not affect responses to PE or ET-1. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the study were consistent with activation of Rho-kinase being important during agonist-induced constriction in laminar vessels, activation of srcPTK being an agonist-dependent event, and more prominent roles for Rhokinase and srcPTK in veins than in arteries.     

In vitro reactivity of digital arteries and veins to vasoconstrictive mediators in healthy horses and in horses with early laminitis

The in vitro reactivity of vasoconstrictive mediators that are implicated in acute laminitis was determined in palmar and plantar digital arteries and veins obtained from healthy horses and in palmar digital vessels of horses with early laminitis (Obel grade I). To obtain baseline reactivity data, 3 experiments were conducted, using healthy horses: (1) the reactivity of palmar and plantar digital arteries and veins to angiotensin II, norepinephrine, and 5-hydroxytryptamine (serotonin) were compared; (2) the direct effects of bacterial endotoxin on vascular reactivity were assessed; and (3) the reactivity of palmar digital arteries and veins to angiotensin II, norepinephrine, prostaglandin F2 alpha (PGF2 alpha), serotonin, and a thromboxane-endoperoxide analog (U46619) were determined. The vascular reactivity of these same 5 vasoconstrictors then was determined in horses with early laminitis and was compared with data from healthy (control) horses. Obel grade-I laminitis was experimentally induced in horses, using carbohydrate overload. Dose responses were conducted for each agent at concentrations between 10(-8)M and 10(-4)M. The potency of a drug was defined as the mean effective concentration necessary to induce 50% of maximal contraction (EC50). There were no differences in EC50 concentrations and in maximal contractions between forelimb and hind limb arteries and veins for angiotensin II, norepinephrine, and serotonin. Incubation with endotoxin had no effect on the reactivity of arteries and veins to angiotensin II, norepinephrine, and serotonin.(ABSTRACT TRUNCATED AT 250 WORDS)