Is endothelin-induced vasoconstriction mediated only by ET(sub A) receptors in humans?

Blocking of endothelin receptors, which consist of subtypes ET (sub A) and ET (sub B), is being studied by scientists to promote the dilation of blood vessels. To mediate vasoconstriction, it is improtant to determine the receptor subtypes that can be acted upon by the receptor antagonist agents. Encoding of mRNA revealed that not only ETA receptors are present in humans, but also ETB. Comparison of the agonist and antagonist patterns of the two subtypes confirmed that both ETA and ETB are expressed in human blood vessels.