Table 4.  Effects of 5-HT on the Vascular Wall

              Vasoconstrictor

         Vasodilator

1)

S₂ receptor:  Director activation of vascular

1)

S₁ Receptor:  Activation of

smooth muscle.

endothelial cells which release

endothelial relaxing factors.

2)

Release of norepinephrine from

2)

S₁ receptor:  Inhibition of

adrenergic nerves.

adrenergic neurotransmission

via action on prejunctional

receptors.

3)

Augmentation of other endogenous

3)

Release of other endogenous

vasoconstrictors.

mediators.

4)

Direct inhibition of vascular

smooth muscle.