What vasopressor drugs are used in treatment of hypertension under spinal anesthesia?

Multitudinous. I think you mean hypotension (drop in blood pressure), since spinal anesthesia paralyses the nerves maintaining blood pressure, and so, naturally, it drops. By implication, these drugs "squeeze" blood vessels, to raise resistance, and therefore increase pressure. Commonly used drugs might be ephedrine, (ephedrine sulfate) or phenylephrine. In more extreme cases, epinephrine or norepinephrine might be used.