Influence of temperature and extracellular pH on contractile responses in isolated human hand veins.

The effects of moderate cooling and extracellular pH changes on concentration-response relationships for noradrenaline (NA), 5-hydroxytryptamine (5-HT) and prostaglandin F2 alpha (PGF2 alpha) were investigated in isolated human hand veins. pH changes were achieved by altering the NaHCO3 content of the Krebs solution. Cooling to 24 degrees reduced the maximum contractile responses to K+ (124 mM), NA and PGF2 alpha by 20-30%, whereas that to 5-HT was unchanged. The NA and 5-HT potencies were increased 8-10 times, whereas the PGF2 alpha potency was unaffected. A shift from alkalotic (pH 7.6) to acidotic (pH 6.9) conditions did not influence the contractile response to 124 mM K+, whereas the responses to NA, 5-HT and PGF2 alpha were inhibited with regard to both potency and maximum contraction. When related to neutral pH, acidosis significantly reduced only the 5-HT potency (4 times), whereas alkalosis selectively increased the NA and PGF2 alpha potencies (3 times). In the presence of prazosin (10(-7) M) cooling to 24 degrees significantly increased the NA potency, whereas no such increase was seen in the presence of rauwolscine (10(-7) M). Alkalosis significantly increased the NA potency in the presence of either antagonist. In conclusion, temperature and extracellular pH influenced the contractile responses to NA, 5-HT and PGF2 alpha in a differentiated manner. Alkalosis appeared to increase the response to both alpha 1- and alpha 2-adrenoceptor stimulation, whereas cooling preferentially increased that to alpha 2-adrenoceptor stimulation.