Alpha 1- and alpha 2-adrenergic response in human isolated skin arteries during cooling

Paradoxical effects of acidosis on the noradrenaline-induced and neurogenic constriction of the rat tail artery at low temperatures

Although vasodilatation evoked by acidosis at normal body temperature is well known, the reports regarding effect of acidosis on the reactivity of the isolated arteries at low temperatures are nonexistent. This study tested the hypothesis that the inhibitory effect of acidosis on the neurogenic vasoconstriction may be increased by cooling. Using wire myography, we recorded the neurogenic contraction of the rat tail artery segments to the electrical field stimulation in the absence and in the presence of 0.03-10.0 µmol/L noradrenaline. The experiments were conducted at 37 °C or 25 °C and pH 7.4 or 6.6 which was decreased by means of CO₂. Noradrenaline at concentration of 0.03-0.1 µmol/L significantly potentiated the neurogenic vasoconstriction at 25 °C, and the potentiation was not inhibited by acidosis. Contrary to our hypothesis, acidosis at a low temperature did not affect the noradrenaline-induced tone and significantly increased the neurogenic contraction of the artery segments in the absence and presence of noradrenaline. These effects of acidosis were partly dependent on the endothelium and L-type Ca²⁺ channels activation. The phenomenon described for the first time might be of importance for the reduction in the heat loss by virtue of decrease in the subcutaneous blood flow at low ambient temperatures.

Altered pharmacological effects of adrenergic agonists during hypothermia

Rewarming from accidental hypothermia is often complicated by hypothermia-induced cardiac dysfunction, calling for immediate pharmacologic intervention. Studies show that although cardiac pharmacologic support is applied when rewarming these patients, a lack of updated treatment recommendations exist. Mainly due to lack of clinical and experimental data, neither of the international guidelines includes information about pharmacologic cardiac support at temperatures below 30 °C. However, core temperature of accidental hypothermia patients is often reduced below 30 °C. Few human studies exploring effects of adrenergic drugs during hypothermia have been published, and therefore prevailing information is collected from pre-clinical studies. The most prominent finding in these studies is an apparent depressive effect of adrenaline on cardiac function when used in doses which elevate cardiac output during normothermia. Also noradrenaline and isoprenaline largely lacked positive cardiac effects during hypothermia, while dopamine is a more promising drug for supporting cardiac function during rewarming. Data and information from these studies are in support of the prevailing notion; not to use adrenergic drugs at core temperatures below 30 °C.

The physiologic responses to epinephrine during cooling and after rewarming in vivo

Introduction

The purpose of our study was to determine whether hypothermia has any effects on physiological hemodynamic responses to epinephrine (Epi), and whether rewarming reverses these effects.

Methods

Sprague-Dawley rats were instrumented to measure mean arterial pressure (MAP), and left ventricular (LV) pressure-volume changes were recorded by using a Millar pressure-volume conductance catheter. Core temperature was reduced from 37°C to 28°C and returned to 37°C by using both internal and external heat exchangers. Two groups of rats were infused with either saline (n = 7), or Epi 0.125 μg/min continuously (n = 7). At 33°C, 30°C, and 28°C, the Epi infusion was temporarily increased from 0.125 to 1.25 μg/min.

Results

Before cooling, Epi infusion in both groups resulted in a significant, dose-dependent increase in heart rate (HR), stroke volume (SV), cardiac output (CO), LV dP/dt_max (maximum derivative of systolic pressure over time), but only Epi infusion at 1.25 μg/min caused elevation of MAP. During cooling to 30°C, Epi infusion at 0.125 μg/min caused a significant elevation of central hemodynamic variables, whereas MAP remained unchanged. In contrast, Epi infusions at 1.25 μg/min caused a significant elevation of MAP during cooling to 28°C but no increases in central hemodynamics. After rewarming, all hemodynamic variables returned to baseline in both groups, but only the saline-treated animals displayed the prehypothermic hemodynamic dose responses to Epi infusions.

Conclusions

This study shows that hypothermia causes a change in the physiological hemodynamic response to Epi, which is not reversed by rewarming.

Response of Rabbit Ear and Femoral Arteries to 5-Hydroxytryptamine During Cooling

The effects of cooling on the response of cutaneous and non-cutaneous arteries to 5-hydroxytryptamine (5-HT) were analysed.

Segments 2-mm long from rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries were prepared for isometric tension recording in an organ bath at 37 and 24°C (cooling). 5-HT (10−9-3 times 10−4 M) induced concentration-dependent contraction of the arteries. The sensitivity and maximal contraction of ear arteries and only the maximal contraction of femoral arteries to this amine were reduced at 24°C.

Endothelium removal or pretreatment with the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 10−5  m) did not affect the response at 37°C but reversed the decreased sensitivity at 24°C in ear arteries, and neither procedure modified the reactivity at 24 or 37°C in femoral arteries to 5-HT. At both temperatures, the response of ear arteries to 5-HT was shifted to the right by phentolamine (10−6M) more than by the 5-HT antagonist, ketanserin (3 times 10−7M), and that of femoral arteries was shifted to the right by ketanserin or the 5-HT1/5-HT2 antagonist methysergide (3 times 10−7 M) more than by phentolamine, in arteries with and without endothelium.

These data concur with the proposition that the contraction to 5-HT is mediated mainly by α-adrenergic receptors in ear arteries and mainly by 5-HT-ergic receptors in femoral arteries, and suggest that cooling reduces the sensitivity of cutaneous, but not of deep arteries to 5-HT, probably by endothelium-nitric oxide-dependent mechanisms.

The effect of cooling on the contractility of equine digital small lamellar arteries: modulating role of the endothelium

The equine hoof displays thermoregulatory functions, and the blood vessels lying under the hoof wall are temperature sensitive. The aim of this study was to investigate the effect of cooling on the contractile responses to α-adrenoceptor and 5-HT receptor stimulation in equine small lamellar arteries using wire myography. The role of the endothelium in the response mediated by 5-HT was also evaluated. Moderate cooling caused a reduction of the contraction induced by depolarizing Krebs solution (DKS, containing 118 mm KCl) and the maximal contraction caused by UK-14304 (α(2)-adrenoceptor agonist). The potency of methoxamine (α(1)-adrenoceptor agonist) was reduced by cooling [pD(2) (-log EC(50)) at 22°C, 5.7 (5.5-6.0) versus 30°C, 5.9 (5.7-6.1)]; however, the efficacy was maintained. The contractions evoked by sumatripan and α-methyl 5-HT (5-HT receptor agonists) were not modified by moderate cooling. In contrast, a cooling-enhanced contraction was observed in response to 5-HT [maximum response (E(max)) at 22°C, 213.2 ± 13% DKS versus 30°C, 179.9 ± 11% DKS]. Furthermore, this effect was more evident in endothelium-denuded lamellar arteries (E(max) at 22°C, 270.2 ± 26% DKS versus 30°C, 172.2 ± 20% DKS), suggesting a potential modulating role of the endothelium. The L-NAME/ibuprofen-resistant relaxation in response to carbachol was reduced by cooling in small lamellar arteries precontracted with 5-HT but not phenylephrine. Therefore, a moderate reduction of temperature modulates the reactivity of small lamellar arteries by enhancing the 5-HT-mediated contraction, but inhibits the α-adrenoceptor-mediated response. Furthermore, the endothelium of these blood vessels may play an important role in preventing excessive vasoconstriction in response to 5-HT and maintaining digital blood flow in cool environmental temperatures.

Rho kinase activation and ROS production contributes to the cooling enhanced contraction in cutaneous equine digital veins

A decrease in environmental temperature can directly affect the contractility of cutaneous vasculature, mediated in part by α2-adrenoceptors. Most of the cellular mechanisms underlying the cooling-enhanced contractility to α2-adrenoceptor agonists have been reported in cutaneous arteries but little information is available on cutaneous veins. To investigate the cellular mechanisms associated with the cooling-enhanced contraction to UK-14304 (α2-adrenoceptor agonist), isolated equine digital veins (EDVs) were studied at 30°C and 22°C. The effects of inhibitors were studied on the contractile response to UK-14304 (0.1 μM). The cooling-enhanced responses were inhibited by Rho kinase inhibitors [maximum response to UK-14304 95.2 ± 8% of response to depolarizing Krebs solution (DKS) in control vessels cooled to 22°C, compared with 31.4 ± 6% in the presence of fasudil 1 μM and 75.8 ± 6% with Y-27632 0.1 μM] and the effects of these inhibitors were considerably less at 30°C (control response 56.4 ± 5% of DKS; 34.9 ± 6% with fasudil 1 μM and 50.6 ± 9% with Y-27632 0.1 μM). Furthermore, Western blotting showed that one of the downstream targets for Rho kinase activity, ezrin/radixin/moesin, was phosphorylated after cooling and reduced by fasudil (1 μM) only at 22°C. The activation of protein kinase C contributed to the contractile response, but predominantly at 30°C (maximum response 82.3 ± 9% of DKS for control; 57.7 ± 10% in the presence of chelerythrine 10 μM) with no significant effect at 22°C. The reduction of the response at 22°C by antioxidants, rotenone (14% reduction), and tempol (21% reduction) suggested the contribution of reactive oxygen species (ROS). No evidence was obtained to support the participation of tyrosine kinase. These data demonstrate that Rho kinase activation and the production of ROS contributes to the cooling-enhanced contraction in these cutaneous digital veins.

Prazosin modulates rapid eye movement sleep deprivation-induced changes in body temperature in rats

Prolonged rapid eye movement sleep deprivation (REMSD) causes hypothermia and death; however, the effect of deprivation within 24 h and its mechanism(s) of action were unknown. Based on existing reports we argued that REMSD should, at least initially, induce hyperthermia and the death upon prolonged deprivation could be due to persistent hypothermia. We proposed that noradrenaline (NA), which modulates body temperature and is increased upon REMSD, may be involved in REMSD- associated body temperature changes. Adult male Wistar rats were REM sleep deprived for 6-9 days by the classical flower pot method; suitable free moving, large platform and recovery controls were carried out. The rectal temperature (Trec) was recorded every minute for 1 h, or once daily, or before and after i.p. injection of prazosin, an alpha-1 adrenergic antagonist. The Trec was indeed elevated within 24 h of REMSD which decreased steadily, despite continuation of deprivation. Prazosin injection into the deprived rats reduced the Trec within 30 min, and the duration of effect was comparable to its pharmacological half life. The findings have been explained on the basis of REMSD-induced elevated NA level, which has opposite actions on the peripheral and the central nervous systems. We propose that REMSD-associated immediate increase in Trec is due to increased Na-K ATPase as well as metabolic activities and peripheral vasoconstriction. However, upon prolonged deprivation, probably the persistent effect of NA on the central thermoregulatory sites induced sustained hypothermia, which if remained uncontrolled, results in death. Thus, our findings suggest that peripheral prazosin injection in REMSD would not bring the body temperature to normal, rather might become counterproductive.

Changes in cardiovascular beta-adrenoceptor responses during hypothermia

The purpose of this study was to determine cardiovascular beta-adrenergic responses during hypothermia. In the present study, we used isoproterenol (Iso), a nonselective, potent beta-adrenoceptor agonist, well known for its positive chronotropic and inotropic pharmacologic actions at normothermia. Rats were instrumented to measure mean arterial pressure (MAP) and left ventricular (LV) pressure-volume changes using a Millar pressure-volume conductance catheter. Core temperature was manipulated from 37 (normothermia) to 24 degrees C (hypothermia) and back to 37 degrees C (rewarming) using both internal and external heat exchangers. During cooling at each temperature (33, 30, 27, and 24 degrees C), central hemodynamic variables and MAP were measured while intravenously infusing Iso (doses of 1.7, 5, 10, and 20 ng/min). Seven animals underwent all phases of the protocol. At normothermia Iso infusion resulted in a significant, dose-dependent increase in heart rate (HR), stroke volume (SV), cardiac output (CO), LV dP/dt(max) (left ventricular maximum derivative of systolic pressure over time) but no change in MAP. During cooling Iso infusion caused no dose-dependent change in any of the hemodynamic variables. After rewarming, baseline HR and LV dP/dt(max) were increased, whereas SV was significantly reduced when compared with their pre-hypothermic baseline values. This study shows that physiological cardiovascular responses mediated by the beta-adrenoceptor are significantly diminished during core hypothermia.

Cooling augments vasoconstriction mediated by 5-HT1 and alpha2-adrenoceptors in the isolated equine digital vein: involvement of Rho kinase

The vasculature of the equine digit fulfils an important role in thermoregulation. In other species, it has been found that cooling may enhance the response of cutaneous vessels to 5-hydroxytryptamine (5-HT) and alpha(2)-adrenoceptor agonists. Translocation of alpha(2)-adrenoceptors to the smooth muscle cell membrane, mediated by Rho kinase, is thought to be involved in the cooling-enhanced response in mouse tail arteries. However, little is known about the effect of cooling on 5-HT receptor function. The present investigation compared the response of 5-bromo-6-(2-imidazolin-2-ylamino) quinoxaline (UK14304:1 nM to 30 microM), methoxamine (0.1 nM to 30 microM; in the presence of yohimbine 0.1 microM), 5-carboxamidotryptamine (5-CT; 0.1 nM to 10 microM) and alpha-methyl 5-HT (0.1 nM to 10 microM) in the isolated equine digital vein at 30 degrees C and 22 degrees C. The effect of the Rho kinase inhibitor, fasudil (1 microM), and the recovery of the response after the irreversible blockade of surface receptors with phenoxybenzamine (10 microM) or 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ;10 microM), was established. Moderate cooling significantly increased the maximum response to alpha-methyl 5-HT, 5-CT and UK14304 and shifted their response curves to the left. Cooling also augmented the phenoxybenzamine- and EEDQ-resistant response to UK14304 and 5-CT, respectively. Fasudil had no effect on the contractile response at 30 degrees C, but completely abrogated the effect of cooling on the response to 5-CT and UK14304. The response to methoxamine was not significantly affected by cooling. These results suggest that Rho kinase plays an important role in the cooling-enhanced response mediated by 5-HT(1B/D) receptors and alpha(2)-adrenoceptors. The exact mechanism by which Rho/Rho kinase enhances the functional responses mediated by these receptors in these vessels has yet to be determined.

Temperature Changes Stimulate Contraction in the Human Radial Artery and Affect Response to Vasoconstrictors

BACKGROUND

Radial artery conduits are increasingly used in coronary artery bypass grafting as an additional arterial graft to the internal thoracic artery. Their reactive nature remains a concern, often necessitating the routine use of topically applied vasodilators, such as glyceryl trinitrate, papaverine, phenoxybenzamine, or calcium channel antagonists, in theatre. During preparation prior to surgery and grafting, radial artery conduits are exposed to cooling and rewarming. We investigated how these temperature changes would affect radial artery contractility and how commonly used topical treatments might be used to prevent this.

METHODS

Human radial artery was obtained excess to surgery and arterial sections used in organ bath tension experiments or for the culture of smooth muscle cells from medial explants.

RESULTS

The radial artery responded to rapid cooling by the addition of 22 degrees C buffer with contraction. Gradual cooling, over a 20 to 30 minute period, reduced basal tension and the response to potassium chloride (KCl) and noradrenaline. Subsequent rewarming from 22 degrees C to 37 degrees C reestablished contraction at precooled levels and led to an elevation of the basal tension. Increases in tension measured in the radial artery were paralleled by increases in intracellular calcium in smooth muscle cells. Contraction induced by rapid temperature changes could be blocked by glyceryl trinitrate but not by phenoxybenzamine. Papaverine and calcium channel blockers had only limited activity.

CONCLUSIONS

Temperature changes commonly encountered in theatre during the preparation of radial artery grafts are likely to cause contraction. If rapid temperature change cannot be avoided during graft preparation, then topically applied glyceryl trinitrate will block these responses.

Effects of sympathetic stimulation during cooling on hypothermic as well as posthypothermic hemodynamic function

This experimental study was performed to explore hemodynamic effects of a moderate dose epinephrine (Epi) during hypothermia and to test the hypothesis whether sympathetic stimulation during cooling affects myocardial function following rewarming. Two groups of male Wistar rats (each, n = 7) were cooled to 15 °C, maintained at this temperature for 1 h, and then rewarmed. Group 1 received 1 μg/min Epi, i.v., for 1 h during cooling to 28 °C, a dose known to elevate cardiac output (CO) by approximately 25% at 37 °C. Group 2 served a saline solution control. At 37 °C, Epi infusion elevated CO, left ventricular systolic pressure, maximum rate of left ventricle pressure rise, and mean arterial pressure. During cooling to 28 °C, these variables, with the exception of mean arterial pressure, decreased in parallel to those in the saline solution group. In contrast, in the Epi group, mean arterial pressure remained increased and total peripheral resistance was significantly elevated at 28 °C. Compared with corresponding prehypothermic values, most hemodynamic variables were lowered after 1 h at 15 °C in both groups (except for stroke volume). After rewarming, alterations in hemodynamic variables in the Epi-treated group were more prominent than in saline solution controls. Thus, before cooling, continuous Epi infusion predominantly stimulates myocardial mechanical function, materialized as elevation of CO, left ventricular systolic pressure, and maximum rate of left ventricle pressure rise. Cooling, on the other hand, apparently eradicates central hemodynamic effects of Epi and during stable hypothermia, elevation of peripheral vascular vasopressor effects seem to take over. In contrast to temperature-matched, non-Epi stimulated control rats, a significant depression of myocardial mechanical function occurs during rewarming following a moderate sympathetic stimulus during initial cooling.

Relative roles of local and reflex components in cutaneous vasoconstriction during skin cooling in humans

The reduction in skin blood flow (SkBF) with cold exposure is partly due to the reflex vasoconstrictor response from whole body cooling (WBC) and partly to the direct effects of local cooling (LC). Although these have been examined independently, little is known regarding their roles when acting together, as occurs in environmental cooling. We tested the hypothesis that the vasoconstrictor response to combined LC and WBC would be additive, i.e., would equal the sum of their independent effects. We further hypothesized that LC would attenuate the reflex vasoconstrictor response to WBC. We studied 16 (7 women, 9 men) young (30.5+/-2 yr) healthy volunteers. LC and WBC were accomplished with metal Peltier cooler-heater probe holders and water-perfused suits, respectively. Forearm SkBF was monitored by laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF/blood pressure. Subjects underwent 15 min of LC alone or 15 min of WBC with and without simultaneous LC, either at equal levels (34-31 degrees C) or as equipotent stimuli (34-28 degrees C LC; 34-31 degrees C WBC). The fall in CVC with combined WBC and LC was greater (P<0.05) than for either alone (57.0+/-5% combined vs. 39.2+/-6% WBC; 34.4+/-4% LC) with equipotent cooling, but it was only significantly greater than for LC alone with equal levels of cooling (51.3+/-8% combined vs. 29.5+/-4% LC). The sum of the independent effects of WBC and LC was greater than their combined effects (74.9+/-4 vs. 51.3+/-8% equal and 73.6+/-7 vs. 57.0+/-5% equipotent; P<0.05). The fall in CVC with WBC at LC sites was reduced compared with control sites (17.6+/-2 vs. 42.4+/-8%; P<0.05). Hence, LC contributes importantly to the reduction in SkBF with body cooling, but also suppresses the reflex response, resulting in a nonadditive effect of these two components.

Cooling-induced contraction of the rat gastric fundus: mediation via transient receptor potential (TRP) cation channel TRPM8 receptor and Rho-kinase activation

1. Cooling has been shown to induce contractions of several smooth muscles in vitro. However, the mechanism involved in the response is not yet known. In the present study, we investigated the possible involvement of transient receptor potential (TRP) cation channel TRPM8 receptors and the Rho-kinase pathway in cooling-induced contraction of the rat fundus. 2. Cooling-induced contractions were inversely proportional to temperature. Contractions were significantly reduced (by 65.6 +/- 2.4%; P < 0.05) in a Ca2+-free (1 mmol/L EGTA) medium, but were not significantly inhibited by nifedipine (10(-6) mol/L). 3. Capsazepine (3 x 10(-6) and 3 x 10(-5) mol/L), a TRPM8 receptor antagonist, inhibited cooling-induced contraction of the rat gastric fundus. 4. The Rho-kinase inhibitor Y-27632 concentration-dependently inhibited cooling-induced contraction of the gastric fundus, producing approximately 90% inhibition at a concentration of 10(-5) mol/L. Contractions were also inhibited by genistein (3 x 10(-5) mol/L), a tyrosine kinase inhibitor, but not by GF 109203X (10(-7) mol/L), a protein kinase C inhibitor. 5. Using reverse transcription-polymerase chain reaction techniques, it was observed that the mRNA for the TRPM8 receptor and Rho-kinase were expressed in the rat gastric fundus. 6. These results would suggest that cooling-induced contraction of the rat fundus is mediated by activation of TRPM8 receptors via a mechanism involving activation of Rho-kinase.

Cutaneous vasoconstrictor responses to norepinephrine are attenuated in older humans

Cutaneous vasoconstriction (VC) in response to cooling is impaired with human aging. On the basis of previous findings that older humans rely predominantly on norepinephrine (NE) for reflex VC of skin blood vessels, and that the VC effects of NE are blunted with age in many vascular beds, we tested the hypothesis that cutaneous VC responses to exogenous NE are attenuated in aged skin compared with young skin. In 11 young (18–30 yr) and 11 older (62–76 yr) men and women, skin blood flow was monitored at two forearm sites with laser Doppler (LD) flowmetry, while local skin temperature was clamped at 34°C. At one site, five doses of NE (10−10 to 10−2 M) were sequentially infused via intradermal microdialysis while the other site served as control (C; Ringer). Cutaneous vascular conductance (CVC; LD flux/mean arterial pressure) was expressed as percent change from baseline (%ΔCVCbase). At 10−10, 10−8, and 10−6 M NE, older VC responses were attenuated compared with young [10−10: −35 (95% confidence interval: −16, −52) vs. −49 (−40, −58) %ΔCVCbase, P = 0.02; 10−8: −38 (−20, −56) vs. −50 (−40, −61) %ΔCVCbase, P = 0.03; 10−6: −52 (−35, −70) vs. −67 (−60, −74) %ΔCVCbase, P = 0.01]. Older maximal VC responses were also blunted compared with young [−80 (confidence interval: −73,−87) vs. −88 (confidence interval: −87, −90) %ΔCVCbase, P = 0.03]. NE-mediated cutaneous VC is blunted at both physiological and superphysiological doses in older subjects compared with young subjects. Considering that NE is the only functional neurotransmitter mediating reflex VC in aged skin, attenuated NE-mediated VC may further predispose older humans to excess heat loss in the cold.

Attenuated noradrenergic sensitivity during local cooling in aged human skin

Reflex-mediated cutaneous vasoconstriction (VC) is impaired in older humans; however, it is unclear whether this blunted VC also occurs during local cooling, which mediates VC through different mechanisms. We tested the hypothesis that the sensitization of cutaneous vessels to noradrenaline (NA) during direct skin cooling seen in young skin is blunted in aged skin. In 11 young (18-30 years) and 11 older (62-76 years) men and women, skin blood flow was monitored at two forearm sites with laser Doppler (LD) flowmetry while local skin temperature was cooled and clamped at 24 degrees C. Cutaneous vascular conductance (CVC; LD flux/mean arterial pressure) was expressed as percentage change from baseline (% DeltaCVC(base)). At one site, five doses of NA (10(-10)-10(-2) m) were sequentially infused via intradermal microdialysis during cooling while the other 24 degrees C site served as control (Ringer solution + cooling). At control sites, VC due to cooling alone was similar in young versus older (-54 +/- 5 versus -56 +/- 3% DeltaCVC(base), P = 0.46). In young, NA infusions induced additional dose-dependent VC (10(-8), 10(-6), 10(-4) and 10(-2) m: -70 +/- 2, -72 +/- 3, -78 +/- 3 and -79 +/- 4% DeltaCVC(base); P < 0.05 versus control). In older subjects, further VC did not occur until the highest infused dose of NA (10(-2) m: -70 +/- 5% DeltaCVC(base); P < 0.05 versus control). When cutaneous arterioles are sensitized to NA by direct cooling, young skin exhibits the capacity to further constrict to NA in a dose-dependent manner. However, older skin does not display enhanced VC capacity until treated with saturating doses of NA, possibly due to age-associated decrements in Ca2+ availability or alpha2C-adrenoceptor function.

Effect of temperature on responses of dog isolated lingual and mesenteric arteries to vasoactive substances

1. The effects of temperature on submaximal vasoconstriction to an intraluminal administration of noradrenaline (NA), phenylephrine, tyramine and KCl were investigated in canine isolated and perfused lingual and mesenteric arteries, using the cannula-inserting method. 2. In lingual arteries, cooling (from 37 to 27 degrees C) caused significant depression of vasoconstriction to the four vasoactive substances used. Rewarming (to 37 degrees C) induced a significant augmentation of constriction by NA, phenylephrine and KCl, but not tyramine. 3. In mesenteric arteries, cooling depressed tyramine- and KCl-induced constrictions, but had no effect on NA- and phenylephrine-induced vasoconstriction. Only in the case of KCl-induced constrictions did rewarming induce a potentiation of the vasoconstrictor response. 4. We conclude that: (i) cooling induces a depression of voltage-dependent Ca2+ channels and rewarming may induce a potentiation of Ca2+ channels in both arteries; (ii) alpha1-adrenoceptor-operated Ca2+ channels are depressed by cooling in lingual arteries but not in mesenteric arteries; and (iii) cooling may induce an attenuation of the re-uptake function in sympathetic nerve terminals in both arteries and this attenuation may be not rapidly restored by acute rewarming.

Effect of modulators of protein tyrosine kinase activity on gender-related differences in vascular reactivity at reduced temperature

We used the isolated-muscle-bath technique to examine the effect of protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) inhibitors on the response of rings of tail artery from male and female rats to cooling and reduced temperature in the absence and presence of two PTK-dependent (clonidine and serotonin) and one PTK-independent (phenylephrine, PE) agonists. At 37 degrees C, reactivity to clonidine, serotonin, and PE was the same in tail artery from female and male rats. At 25 degrees C, reactivity to clonidine and serotonin, but not PE, was greater in tail artery from female rats compared with those from male rats. Sodium orthovanadate (SOV) eliminated the gender-related difference in the contractile effect of clonidine and serotonin at 25 degrees C. The sensitivity to relaxation by genistein was considerably greater for clonidine and serotonin at both temperatures as compared with PE. At 25 degrees C the sensitivity to genistein was greater for the clonidine and serotonin-contracted rings from female rats. In the presence of SOV, temperature reduction led to contraction of rat-tail artery. This effect was greater in rings from female rats. Our results strongly implicate differences in the activity of the PTK transduction pathway as the cause of the observed gender-related differences in agonist-mediated contraction at 25 degrees C and in cold-induced vasoconstriction.

Peptidergic modulation of the sympathetic contraction in the rabbit ear artery: effects of temperature

1. The effects of neuropeptide Y, endothelin-1, arginine-vasopressin and angiotensin II on the vascular contraction to sympathetic nerve stimulation were studied in isolated segments, 2 mm long, from the rabbit central ear artery, a cutaneous vessel, during changes in temperature (24 degrees -41 degrees C). 2. Transmural electrical stimulation (1-8 Hz, at supramaximal voltage) produced frequency-dependent contraction, and this response, partially blocked by tetrodotoxin (1 microM) and phentolamine (1 microM), was reduced by cooling (30 degrees C -24 degrees C) and was not modified by warming (41 degrees C), as compared to that recorded at 37 degrees C. 3. Pretreatment with neuropeptide Y (10, 30 and 100 nM) increased in a concentration-dependent manner the vascular contraction to sympathetic stimulation at every temperature studied, but this potentiation was greater during cooling (34 degrees C -24 degrees C) than at 37 degrees C or warming (41 degrees C). 4. Pretreatment with endothelin-1 (3 and 10 nM) or vasopressin (0.1, 0.3 and 1 nM) increased in a concentration-dependent manner the vascular contraction to sympathetic stimulation during cooling (34 degrees C -24 degrees C), but not at 37 degrees C or warming (41 degrees C). 5. Pretreatment with angiotensin II (0.1, 0.3 and 1 microM) did not modify the contraction to sympathetic stimulation at any temperature studied. 6. These results suggest that neuropeptide Y, endothelin-1 and vasopressin, but not angiotensin II, modulate the cutaneous vasoconstriction to sympathetic nerve stimulation by potentiating this vasoconstriction during cooling.

Cooling effects on the histaminergic response of rabbit ear and femoral arteries: role of the endothelium

The effects of cooling on the isometric response of rabbit isolated central ear (cutaneous) and femoral (non-cutaneous) arteries to histamine were determined at 37 degrees C and 24 degrees C (cooling). Under resting tension, both types of arteries contracted to histamine (10(-7)-10(-3) M), and the sensitivity of ear arteries, but not of femoral arteries was lower at 24 than at 37 degrees C. Chlorpheniramine (10(-7) M) blocked the contraction of both types of arteries to histamine at both temperatures. In ear arteries, endothelium removal or treatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) did not affect the contraction to histamine at 37 degrees C, but it reversed the decreased contraction at 24 degrees C. In femoral arteries, endothelium removal or L-NAME (10(-5) M) did not affect the response to histamine at 37 and 24 degrees C. Ear and femoral arteries precontracted with endothelin-1 (10(-8)-10(-7) M) and pretreated with chlorpheniramine (10(-5) M) relaxed to histamine (10(-7)-10(-4) M), and the sensitivity of this relaxation in ear arteries, but not in femoral arteries, increased at 24 degrees C. The relaxation of ear and femoral arteries to histamine was not modified by endothelium removal, L-NAME (10(-5) M) or meclofenamate (10(-5) M), but it was blocked by cimetidine (10(-6) M) at 37 degrees C and 24 degrees C. These results suggest: (1) ear and femoral arteries have contracting H1 and relaxing H2 receptors, probably located on smooth musculature, and (2) cooling reduces the contraction and increases the relaxation of cutaneous arteries to histamine: the reduction of this contraction could be caused by an augmented availability of endothelial nitric oxide, and the increment of this relaxation could be caused by an augmented sensitivity of H2 receptors of smooth musculature induced by cooling. These features do not seem to occur in deep vessels.

Effect of temperature reduction on the reactivity of the mouse vas deferens to adrenergic drugs

1. Dose-response curves for noradrenaline, phenylephrine and clonidine were determined isometrically on the mouse vas deferens at 26 degrees C, 15 degrees C and compared to the one obtained at 37 degrees C. 2. In the presence of noradrenaline, reducing temperature induced an increase of both maximal developed tension and sensitivity to the drug. Reduction by 50% of the extracellular calcium concentration abolished the maximal contraction potentiation. 3. When reducing temperature to 26 degrees C, the maximal contraction was increased and depressed in the presence of phenylephrine and clonidine respectively. 4. The results suggest (a) that cooling increases the reactivity of mouse vas deferens by activation of alpha 1 adrenoceptors and depresses it by activation of alpha 2 adrenoceptors (b) that calcium ions could play an important role in the potentiation of the maximal contraction.

Cooling and response to adrenoceptor agonists of rabbit ear and femoral artery: role of the endothelium

1. The effects of cooling on the response of the rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries to stimulation of adrenoceptors and the role of the endothelium in these effects, were studied in 2 mm long cylindrical segments. 2. Concentration-response curves for noradrenaline (10(-9)-3 x 10(-4) M), phenylephrine (alpha 1-adrenoceptor agonist, 10(-9)-3 x 10(-4) M) and B-HT 920 (alpha 2-adrenoceptor agonist, 10(-7)-10(-3) M) were recorded isometrically in arteries with and without endothelium at 37 degrees C and at 24 degrees C (cooling). To analyze further the endothelial mechanisms in the responses to adrenoceptor stimulation during cooling, the effects of the adrenoceptor agonists on ear arteries in the presence of NG-nitro-L-arginine methyl esther (L-NAME) (10(-5) M) were also determined. 3. In every condition tested, the three adrenoceptor agonists produced a concentration-dependent arterial contraction and the order of potency in ear and femoral arteries was noradrenaline greater than or equal to phenylephrine greater than B-HT 920. The response of ear and femoral arteries to phenylephrine or B-HT 920 was blocked by prazosin (10(-6) M). Yohimbine (10(-6) M) decreased slightly the response of ear arteries and increased that of femoral arteries to B-HT 920. 4. The sensitivity of both ear and femoral arteries to the three adrenoceptor agonists was significantly lower at 24 degrees C than at 37 degrees C. 5. In ear arteries, endothelium removal or treatment with L-NAME did not influence the response at 37 degrees C, but did increase it during cooling to adrenoceptor stimulation.In femoral arteries, endothelium removal increased the sensitivity to noradrenaline and, especially, to B-HT 920 at 37 degrees C, but did not affect the response at 24 degrees C.6. The results suggest that: (a) rabbit ear and femoral arteries are equipped mainly with alpha 1-adrenoceptors;(b) at 37 degrees C, the contraction of the ear artery to adrenoceptor agonists is mostly endothelium-independent, and in the femoral artery the contraction to alpha 2-adrenoceptor activation is endothelium-dependent; (c) cooling inhibits the contraction to adrenoceptor agonists in both ear and femoral arteries: in the ear artery probably by increasing the availability of endothelial nitric oxide, but in the femoral artery by depressing the sensitivity of alpha-adrenoceptors in the smooth musculature.7. The results suggest that the endothelium may modulate the adrenoceptor response of cutaneous arteries during changes in temperature.