Summary
After incubation with 2.3 μM 3H-(±)-adrenaline(3H-AD) or 3H-(-)-noradrenaline(3H-NA) for 60 min in the presence of hydrocortisone and U-0521, dog saphenous vein strips were perifused (the fluid containing cocaine+hydrocortisone+U-0521) and electrically stimulated. Tritium fractional release per shock was calculated for 1 and 5 Hz.
Phentolamine (3 μM) enhanced the overflow of tritium evoked by electrical stimulation at both frequencies but at 1 Hz the enhancement was higher for strips loaded with 3H-AD than for strips loaded with 3H-NA.
Propranolol (1 μM) reduced the overflow evoked by electrical stimulation at 1 Hz from the strips loaded with 3H-AD but not from those loaded with 3H-NA.
Isoprenaline (0.04 μM) increased the overflow of tritium evoked by electrical stimulation at 1 Hz from the strips loaded with 3H-NA but did not change that from strips loaded with 3H-AD.
It is concluded that: a) the α-adrenoceptor-mediated feedback mechanism is also present in the dog saphenous vein; b) this feedback mechanism also functions with the “false transmitter” AD; c) the use of 3H-AD as false transmitter revealed the existence of a β-adrenoceptor-mediated positive feedback mechanism in this tissue.
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Guimarães, S., Brandão, F. & Paiva, M.Q. A study of the adrenoceptor-mediated feedback mechanisms by using adrenaline as a false transmitter. Naunyn-Schmiedeberg's Arch. Pharmacol. 305, 185–188 (1978). https://doi.org/10.1007/BF00508291
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DOI: https://doi.org/10.1007/BF00508291