Evidence for direct vasoconstrictor activity of melatonin in "pressurized" segments of isolated caudal artery from juvenile rats

Naunyn Schmiedebergs Arch Pharmacol. 1992 Sep;346(3):362-5. doi: 10.1007/BF00173553.


Responses of isolated, 60 mmHg 'pressurized' segments of the distal caudal artery of adult and juvenile Wistar rats to melatonin and the selective alpha 2-adrenoceptor agonist 5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline bitartrate (UK-14304) were examined using the Halpern pressure myograph. Melatonin showed no direct vasoconstrictor activity in vessels from adult rats, whereas UK-14304 produced moderate vasoconstriction (pD2-7.43 +/- 0.09). In the presence of phenylephrine-induced tone, melatonin produced a variable but small constrictor response (less than 10 microns reduction in diameter) in some vessels; the response to 1 mumol/l UK-14304 was less than in the absence of tone. In vessels isolated from juvenile rats, melatonin caused concentration-dependent vasoconstriction with a maximum response about 70% of the maximum response elicited by UK-14304. Vessels from juvenile rats were more sensitive to melatonin (pD2-9.40 +/- 0.07) than they were to UK-14304 (pD2-8.12 +/- 0.14). In the presence of phenylephrine-induced tone, the vasoconstrictor responses to both melatonin and IK-14304 were markedly less; the sensitivity to melatonin was not different from that seen in the absence of tone. These findings indicate that 'pressurized' segments of the isolated distal caudal artery may provide a simple and convenient, functional model of melatonin receptors. The findings also appear to implicate melatonin in thermoregulatory processes in juvenile rats.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / metabolism
  • Animals
  • Antihypertensive Agents / pharmacology
  • Arteries / drug effects
  • Brimonidine Tartrate
  • Female
  • In Vitro Techniques
  • Male
  • Melatonin / pharmacology*
  • Muscle, Smooth, Vascular / drug effects*
  • Quinoxalines / pharmacology
  • Rats
  • Rats, Wistar
  • Vasoconstrictor Agents / pharmacology*


  • Antihypertensive Agents
  • Quinoxalines
  • Vasoconstrictor Agents
  • Brimonidine Tartrate
  • Melatonin