Cooling augments alpha 2-adrenoceptor-mediated contractions in rat tail artery

Differential contribution of calcium channels to α1-adrenoceptor-mediated contraction is responsible for diverse responses to cooling between rat tail and iliac arteries

Our previous studies have shown that α₁-adrenoceptors, in addition to α₂-adrenoceptors, are involved in enhanced contraction of cutaneous blood vessels during cooling. The present study aimed to elucidate the mechanism underlying it. In tail and iliac arteries isolated from rats, isometric contraction was measured using a myograph and the phosphorylation level of myosin phosphatase target subunit 1 (MYPT1) was quantified by western blotting. The phenylephrine-induced contraction was enhanced by cooling to 24 °C in tail arteries, but was suppressed in iliac arteries. Endothelium denudation or treatment with iberiotoxin enhanced the phenylephrine-induced contraction in tail arteries at 37 °C; however, neither affected the contraction at 24 °C. The phenylephrine-induced contraction at 37 °C was largely suppressed by nifedipine in iliac arteries, but only slightly in tail arteries. The Rho kinase inhibitor H-1152 largely suppressed the phenylephrine-induced contraction at 24 °C, but only slightly at 37 °C, in both arteries. The phosphorylation level of MYPT1 at Thr855 in tail arteries was increased by the cooling. Taken together, these results suggest the following mechanism in regard to cooling-induced enhancement of α₁-adrenoceptor-mediated contraction in tail arteries: Cooling enhances the contraction of tail arteries via α₁-adrenoceptor stimulation by reducing endothelium-dependent, large-conductance Ca²⁺-activated K⁺ channel-mediated relaxation and by inducing Rho kinase-mediated Ca²⁺ sensitization, although the latter occurs even in iliac arteries. A smaller contribution of voltage-dependent Ca²⁺ channels, which are largely suppressed by cooling, to α₁-adrenoceptor-mediated contraction in tail arteries seems to be more crucially involved in the appearance of the enhanced contractile response to cooling.

Intracellular α(2C)-adrenoceptors: storage depot, stunted development or signaling domain?

G-protein coupled receptors (GPCRs) are generally considered to function as cell surface signaling structures that respond to extracellular mediators, many of which do not readily access the cell's interior. Indeed, most GPCRs are preferentially targeted to the plasma membrane. However, some receptors, including α(2C)-Adrenoceptors, challenge conventional concepts of GPCR activity by being preferentially retained and localized within intracellular organelles. This review will address the issues associated with this unusual GPCR localization and discuss whether it represents a novel sub-cellular niche for GPCR signaling, whether these receptors are being stored for rapid deployment to the cell surface, or whether they represent immature or incomplete receptor systems.

Normothermia is the Key for the Treatment of Internal Thoracic Artery Spasm

BACKGROUND

Free flow of the internal thoracic artery decreases commonly after harvesting because of spasm. Tissue heat loss is inevitable during surgery. The aim of this study was to compare the internal thoracic artery pedicle rewarming method with topical papaverine applications in different thermal conditions.

METHODS

Patients (n = 120) were organized in to 6 equally sized groups. The effects of topical papaverine application at room temperature, topical heated papaverine (at 37 degrees C) application, internal thoracic artery pedicle storage in normothermic conditions, pedicle storage in normothermic conditions combined with topical papaverine application, and pedicle storage in normothermic conditions combined with topical heated papaverine application were investigated. In the control group, no treatment was applied and the pedicle was stored in room temperature conditions. We measured internal thoracic artery free flows at 3 stages: at the initiation of harvesting, after total harvesting, and after antispasmodic treatment. Durations of the stages were recorded. At each stage hemodynamic parameters, tissue and core temperatures were also monitored.

RESULTS

Internal thoracic artery pedicle temperature significantly decreased simultaneously with the free flow after the harvesting procedure. Recovery of the physiologic temperature state, provided by storing the internal thoracic artery pedicle in normothermic conditions, improved the flow and increased the efficiency of topically applied papaverine on the vasospasm of the internal thoracic artery.

CONCLUSION

Topical application of heated papaverine itself does not warm pedicle tissue, but papaverine efficiency increases when the pedicle is stored in normothermic conditions. Preserving internal thoracic artery pedicles in normothermic conditions can be the preferred treatment for spasms.

Local regulation of skin blood flow during cooling involving presynaptic P2 purinoceptors in rats

1. This study investigated a local effect of cooling on the plantar skin blood flow (PSBF) of tetrodotoxin-treated rats by laser-Doppler flowmetry. 2. When the air temperature around the left foot was locally cooled from 25 to 10 degrees C, the PSBF of the left foot decreased. 3. The response was inhibited by the alpha-adrenoceptor antagonist phentolamine, the alpha1-adrenoceptor antagonist bunazosin, the alpha2-adrenoceptor antagonist RS79948, and bretylium and guanethidine that inhibit noradrenaline release from sympathetic nerves. Adrenalectomy of the rats did not affect the cooling-induced response. 4. The P2 purinoceptor antagonists suramin and PPADS also significantly suppressed the cooling-induced reduction of PSBF. However, the inhibitory effect of PPADS on the cooling-induced response was abolished after the treatment with phentolamine. Intra-arterial injections of ATPgammaS, a stable P2 purinoceptor agonist, at 25 degrees C caused a transient decrease in PSBF in a dose-dependent manner, which was significantly inhibited by phentolamine and guanethidine. 5. These results suggest a novel mechanism for local cooling-induced reduction of skin blood flow in vivo; moderate cooling of the skin induces the release of ATP, which stimulates presynaptic P2 purinoceptors on sympathetic nerve terminals and facilitates the release of noradrenaline, thereby causing contractions of skin blood vessels via the activation of alpha1-and alpha2-adrenoceptors.

Sympathetic, sensory, and nonneuronal contributions to the cutaneous vasoconstrictor response to local cooling

Previous work indicates that sympathetic nerves participate in the vascular responses to direct cooling of the skin in humans. We evaluated this hypothesis further in a four-part series by measuring changes in cutaneous vascular conductance (CVC) from forearm skin locally cooled from 34 to 29 degrees C for 30 min. In part 1, bretylium tosylate reversed the initial vasoconstriction (-14 +/- 6.6% control CVC, first 5 min) to one of vasodilation (+19.7 +/- 7.7%) but did not affect the response at 30 min (-30.6 +/- 9% control, -38.9 +/- 6.9% bretylium; both P < 0.05, P > 0.05 between treatments). In part 2, yohimbine and propranolol (YP) also reversed the initial vasoconstriction (-14.3 +/- 4.2% control) to vasodilation (+26.3 +/- 12.1% YP), without a significant effect on the 30-min response (-26.7 +/- 6.1% YP, -43.2 +/- 6.5% control; both P < 0.05, P > 0.05 between sites). In part 3, the NPY Y1 receptor antagonist BIBP 3226 had no significant effect on either phase of vasoconstriction (P > 0.05 between sites both times). In part 4, sensory nerve blockade by anesthetic cream (Emla) also reversed the initial vasoconstriction (-20.1 +/- 6.4% control) to one of vasodilation (+213.4 +/- 87.0% Emla), whereas the final levels did not differ significantly (-37.7 +/- 10.1% control, -37.2 +/- 8.7% Emla; both P < 0.05, P > 0.05 between treatments). These results indicate that local cooling causes cold-sensitive afferents to activate sympathetic nerves to release norepinephrine, leading to a local cutaneous vasoconstriction that masks a nonneurogenic vasodilation. Later, a vasoconstriction develops with or without functional sensory or sympathetic nerves.

Silent alpha(2C)-adrenergic receptors enable cold-induced vasoconstriction in cutaneous arteries

Cold constricts cutaneous blood vessels by increasing the reactivity of smooth muscle alpha(2)-adrenergic receptors (alpha(2)-ARs). Experiments were performed to determine the role of alpha(2)-AR subtypes (alpha(2A)-, alpha(2B)-, alpha(2C)-ARs) in this response. Stimulation of alpha(1)-ARs by phenylephrine or alpha(2)-ARs by UK-14,304 caused constriction of isolated mouse tail arteries mounted in a pressurized myograph system. Compared with proximal arteries, distal arteries were more responsive to alpha(2)-AR activation but less responsive to activation of alpha(1)-ARs. Cold augmented constriction to alpha(2)-AR activation in distal arteries but did not affect the response to alpha(1)-AR stimulation or the level of myogenic tone. Western blot analysis demonstrated expression of alpha(2A)- and alpha(2C)-ARs in tail arteries: expression of alpha(2C)-ARs decreased in distal compared with proximal arteries, whereas expression of the glycosylated form of the alpha(2A)-AR increased in distal arteries. At 37 degrees C, alpha(2)-AR-induced vasoconstriction in distal arteries was inhibited by selective blockade of alpha(2A)-ARs (BRL-44408) but not by selective inhibition of alpha(2B)-ARs (ARC-239) or alpha(2C)-ARs (MK-912). In contrast, during cold exposure (28 degrees C), the augmented response to UK-14,304 was inhibited by the alpha(2C)-AR antagonist MK-912, which selectively abolished cold-induced amplification of the response. These experiments indicate that cold-induced amplification of alpha(2)-ARs is mediated by alpha(2C)-ARs that are normally silent in these cutaneous arteries. Blockade of alpha(2C)-ARs may prove an effective treatment for Raynaud's Phenomenon.

The role of alpha 2-adrenoceptors in the vasculature of the rat tail

1. The effects of alpha 2-adrenoceptor agonists and antagonists on rat tail skin temperature (tts), an indicator of local cutaneous blood flow, were studied in conscious and anaesthetized rats and in the isolated, Krebs perfused, vascular bed of the rat tail. 2. In conscious rats, at an ambient temperature of 18.5-20 degrees C, tts was 21.0 +/- 0.2 degrees C and core (rectal) temperature (tc) was 38.2 +/- 0.04 degrees C (n = 126). The alpha 2-adrenoceptor antagonist, delequamine (RS-15385-197; 1 mg kg-1, s.c., n = 6), produced a rapid elevation in tts to 29.1 +/- 0.7 degrees C (P < 0.001 vs. saline-treated control group), attained 10 min after injection. tc fell slightly, by 1.0 +/- 0.1 degrees C. The tts response was dose-related over the dose-range tested (0.01-1 mg kg-1, s.c.), with an ED50 of 17 micrograms kg-1, s.c. (n = 6 per dose). 3. The maximum increases in tts in response to a dose of 1 mg kg-1, s.c. of alpha 2-adrenoceptor antagonists were as follows (n = 6 per drug): delequamine (+9.6 +/- 0.8 degrees C) > yohimbine (+9.0 +/- 1.0 degrees C) > WY-26703 (+7.9 +/- 1.3 degrees C) > piperoxan (+5.6 +/- 1.7 degrees C) > idazoxan (+4.6 +/- 1.3 degrees C) > imiloxan (+4.1 +/- 1.3 degrees C) > SKF 104078 (+2.0 +/- 1.9 degrees C) > BDF-6143 (+1.3 +/- 0.8 degrees C). 4. Prazosin (0.3 mg kg-1, s.c.), hydralazine (10 mg kg-1, s.c.) and nifedipine (3 mg kg-1, s.c.) did not increase tts, whereas propranolol (10 mg kg-1, s.c.) evoked a small increase in tts (+2.9 +/- 1.0 degrees C). Pentolinium (2-10 mg kg-1, s.c.) elicited a dose-related increase in tts, which was elevated by 4.4 +/- 1.3 degrees C after a dose of 10 mg kg-1; tc was reduced in a dose-related manner. Drug vehicles (1 ml kg-1, s.c.) had no effect on tts or tc. 5. In anaesthetized rats, idazoxan (300 microg, i.v.) produced a rapid increase in tts which was detectable 2 min after beginning the injection, reaching a peak after 7 min. When the same dose was administered i.c.v., tts also rose, but more slowly. The peak response (+ 3.6 +/- 0.70C, n = 5) was significantly smaller than when idazoxan was administered intravenously (+ 6.3 +/- 1.2 C, n = 5), which suggests that the increase in tts following systemic administration of M2-adrenoceptor antagonists is not due to a central effect. The change in tts was not secondary to changes in blood pressure.6. In the isolated, Krebs perfused, tail vascular bed of the rat, at an ambient temperature of 20-21C,under constant flow conditions (3.5-4.0 ml min-1; n = 4), baseline perfusion pressure was 57 +/- 4 mmHg.5-Hydroxytryptamine (5-HT; 70-150 nM) increased perfusion pressure by 56+/- 9 mmHg. The alpha2-adrenoceptor agonist, UK-14,304 (10 nmol), elicited a further increase in perfusion pressure by27.5 +/- 15 mmHg but had no effect in the absence of 5-HT; this response to UK-14,304 was abolished by rauwolscine (1 microM).7. Under constant pressure conditions (-100 mmHg; n = 9), baseline mean perfusion flow was 2.1 +/- 0.2 ml min-1, and mean tail skin temperature was 31.6 +/- 0.6C. 5-HT (119 +/- 28 nM) decreased tts.by 3.3 +/- 2.0 C and reduced flow by 1.2 +/- 0.3 ml min-1. UK-14,304 (10 nmol) further reduced tts by 3.0 +/- 0.3 C without significant effect on flow; this effect was also abolished by 1 microM rauwolscine.8. We conclude that post-junctional M2-adrenoceptors in the vasculature of the rat tail have a major vasoconstrictor role, controlling both the flow and distribution of blood within the tail and thereby thermoregulatory heat loss from its surface.

Effect of temperature on muscarinic cholinoceptor-mediated phosphoinositide metabolism and tension generation in bovine tracheal smooth muscle

The effect of decreased temperature on phosphoinositide metabolism was studied in flurbiprofen pretreated bovine tracheal smooth muscle (BTSM) by investigating the consequences of cooling on muscarinic-cholinoceptor-mediated [3H]inositol phosphate ([3H]InsP) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) accumulation, basal phosphoinositidase C (PIC) activity and airways smooth muscle (ASM) tone. Cooling of [3H]Ins labelled BTSM slices from 37 degrees C to 27 degrees C for 20 min prior to the addition of agonist caused a substantial (73.0 +/- 2.5%) inhibition of carbachol (100 microM, 30 min)-stimulated [3H]InsP accumulation compared to values measured at 37 degrees C. The degree of inhibition of [3H]InsP accumulation was similar at all agonist time points (2-30 min) studied. In parallel experiments, cooling of unlabelled BTSM slices from 37 degrees C to 27 degrees C resulted in a 34% reduction in basal Ins(1,4,5)P3 mass (37 degrees C, 13.1 +/- 0.6 pmol mg-1 protein; 27 degrees C, 8.9 +/- 0.9 pmol mg-1 protein; P < 0.02) and markedly attenuated carbachol (100 microM)-stimulated increases in Ins(1,4,5)P3 accumulation. Basal PIC activity in the soluble fraction of BTSM homogenates, measured using a [3H]phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) /deoxycholate assay system, was also significantly lower at 27 degrees C compared to 37 degrees C (initial velocities of PtdIns(4,5)P2 hydrolysis of 853 +/- 167 (37 degrees C) and 418 +/- 119 (27 degrees C) pmol min-1 ml-1 (1/400 diluted) BTSM cytosol; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Chloroethylclonidine irreversibly activates postjunctional alpha 2-adrenoceptors in the dog saphenous vein

This study was aimed at analysing the contractile response of the dog saphenous vein to chloroethylclonidine. At 37 degrees C, chloroethylclonidine (0.1-100 mumol.l-1) caused a long-lasting contraction in both proximal and distal segments of the dog saphenous vein, reaching 77.6 and 52.6% of the maximal response to phenylephrine, respectively. At 18 degrees C, and in both segments, the maximal response to chloroethylclonidine was markedly reduced, whereas that to phenylephrine was not changed and that to UK-14,304 was enhanced. The response to chloroethylclonidine was unaffected by pretreatment with cocaine. Warming to 37 degrees C caused contraction of strips which at 18 degrees C had remained unresponsive to chloroethylclonidine, even if these strips were repeatedly washed before warming. At 18 degrees C, chloroethylclonidine (100 mumol.l-1) did not alter the responses to UK-14,304 and phenylephrine. At 37 degrees C, the contractile response to chloroethylclonidine was antagonized by yohimbine, rauwolscine and prazosin, with the potency rank yohimbine = rauwolscine > prazosin. Phenoxybenzamine (30 nmol.l-1) displaced the concentration-response curve to chloroethylclonidine to the right and depressed its maximum. After phenoxybenzamine, yohimbine continued to be more effective than prazosin, which remained very potent.(ABSTRACT TRUNCATED AT 250 WORDS)