1 The e ects 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 (248 ± 418C). 2 Transmural electrical stimulation (1 ± 8 Hz, at supramaximal voltage) produced frequency-dependent contraction, and this response, partially blocked by tetrodotoxin (1 mM) and phentolamine (1 mM), was reduced by cooling (308C ± 248C) and was not modi®ed by warming (418C), as compared to that recorded at 378C. 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 (348C ± 248C) than at 378C or warming (418C). 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 (348C ± 248C), but not at 378C or warming (418C). 5 Pretreatment with angiotensin II (0.1, 0.3 and 1 mM) 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.

1 To examine the role of the purinergic and noradrenergic components in the potentiation of endothelin-1 on the vascular response to sympathetic nerve stimulation, we recorded the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical ®eld stimulation (1 ± 8 Hz) under di erent conditions, at 378C and during cooling (308C). 2 Electrical ®eld stimulation produced frequency-dependent contraction, which was reduced during cooling (about 60% for 8 Hz). Both at 378C and 308C, phentolamine (1 mM) or blockade of a 1 -adrenoceptors with prazosin (1 mM) reduced, whereas blockade of a 2 -adrenoceptors with yohimbine (1 mM) increased, the contraction to electrical ®eld stimulation. This contraction was increased after desensitization of P2-receptors with a,b-methylene adenosine 5'-triphosphate (a,b-meATP, 3 mM) at 378C but not at 308C, and was not modi®ed by blockade of P2-receptors with pyridoxalphosphate-6-azophenyl-2,4'-disulphonic acid (PPADS, 30 mM) at either temperature. 3 Endothelin-1 (1, 3 and 10 nM) at 378C did not a ect, but at 308C it potentiated in a concentrationdependent manner the contraction to electrical ®eld stimulation (from 28+6 to 134+22%, for 8 Hz). At 378C, endothelin-1 in the presence of phentolamine or prazosin, but not in that of yohimbine, a,bmeATP or PPADS, potentiated the contraction to electrical stimulation. At 308C, phentolamine or yohimbine reduced, prazosin or PPADS did not modify and a,b-meATP slightly increased the potentiation by endothelin-1 of the response to electrical stimulation. 4 The arterial contraction to ATP (2 mM) and the a 2 -adrenoceptor agonist BHT-920 (10 mM), but not that to (7)-noradrenaline (1 mM), was potentiated by endothelin-1 at both 378C and 308C. 5 These results in the rabbit central ear artery suggest that the sympathetic response: (a) at 378C, could be mediated mainly by activation of a 1 -adrenoceptors, with low participation of P2-receptors, (b) is diminished during cooling, probably by a reduction in the participation of a 1 -adrenoceptors, and in this condition the response could be mediated in part by P2-receptors, and (c) is potentiated by endothelin-1 during cooling, probably by increasing the response of both postjunctional a 2 -adrenoceptors and P2-receptors.

To analyze the effect of hyperthermia on the vascular response, the isometric response of isolated rabbit femoral artery segments was recorded at 37 degreesC and hyperthermia (41 and 44 degreesC). Contraction to potassium (5 x 10(-3)-5 x 10(-2) M) was significantly greater at 41 and 44 than at 37 degreesC and increased by inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine (L-NNA; 10(-4) M) or endothelium removal at 37 degreesC but not at 41 or 44 degreesC. Norepinephrine (10(-9)-10(-4) M) produced a concentration-dependent contraction greater at 41 or 44 than at 37 degreesC and not modified by endothelium removal or L-NNA at either temperature. Phenylephrine (10(-9)-10(-4) M) produced a contraction increased by warming to 44 degreesC but not to 41 degreesC. The specific alpha2-adrenoceptor agonist BHT-920 produced a weak contraction, reduced by the alpha1-adrenoceptor antagonist prazosin (10(-6) M) and increased at 44 degreesC but not at 41 degreesC. The concentration-dependent contraction to endothelin-1 (ET-1; 10(-11)-10(-7) M) was increased by warming to 41 and 44 degreesC and by endothelium removal or L-NNA at 37 degreesC but not at 41 or 44 degreesC. Response to ET-1 was reduced by endothelin ETA-receptor antagonist BQ-123 (10(-5) M) and ETB-receptor antagonist BQ-788 (10(-5) M). In arteries precontracted with ET-1 (10(-8)-3 x 10(-8) M), relaxation to sodium nitroprusside (10(-8)-10(-4) M) was increased at 41 and 44 degreesC vs. at 37 degreesC, but that of ACh (10(-8)-10(-4) M) or adenosine (10(-8)-10(-4) M) was not different at all temperatures studied. Relaxation to ACh, but not adenosine, was reduced similarly by L-NNA at all temperatures studied. These results suggest hyperthermia in muscular arteries may inhibit production of, and increase dilatation to, NO, resulting in unchanged relaxation to ACh and increased constriction to KCl and ET-1, and may increase constriction to stimulation of alpha1-adrenoceptors by NO-independent mechanisms.

1 To examine further the potentiation by endothelin-1 on the vascular response to sympathetic stimulation, we studied the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical ®eld stimulation (1 ± 8 Hz), under di erent conditions, at 378C and during cooling (308C). 2 Electrical stimulation produced frequency-dependent contraction, which was reduced (about 63% for 8 Hz) during cooling. At 308C, but not at 378C, endothelin-1 (1, 3 and 10 nM) potentiated the contraction to electrical stimulation in a dose-dependent way (from 43+7% to 190+25% for 8 Hz). 3 This potentiation by endothelin-1 was reduced by the antagonist for endothelin ET A receptors BQ-123 (10 mM) but not by the antagonist for endothelin ET B receptors BQ-788 (10 mM). The agonist for endothelin ET B receptors IRL-1620 (0.1 mM) did not modify the contraction to electrical stimulation. 4 The blocker of L-type Ca 2+ channels verapamil (10 mM l 71 ) reduced (about 72% for 8 Hz) and the unspeci®c blocker of Ca 2+ -channels NiCl 2 (1 mM) practically abolished (about 98%), the potentiating e ects of endothelin-1 found at 308C. 5 Inhibition of nitric oxide synthesis with N G -nitro-L-arginine (L-NOARG, 0.1 mM) increased the contraction to electrical stimulation at 308C more than at 378C (for 8 Hz, this increment was 297+118% at 308C, and 66+15% at 378C). Endothelium removal increased the contraction to electrical stimulation at 308C (about 91% for 8 Hz) but not at 378C. Both L-NOARG and endothelium removal abolished the potentiating e ects of endothelin-1 on the response to electrical stimulation found at 308C. 6 These results in the rabbit ear artery suggest that during cooling, endothelin-1 potentiates the contraction to sympathetic stimulation, which could be mediated at least in part by increasing Ca 2+ entry after activation of endothelin ET A receptors. This potentiating e ect of endothelin-1 may require the presence of an inhibitory tone due to endothelial nitric oxide.