In what year did MLB adopt the designated hitter in both leagues?

What is the distance from the pitcher's rubber to home plate in MLB? How many players are on the field for the defensive team? How many teams are in Major League Baseball? What are the two leagues in MLB? Which league first adopted the designated hitter in 1973? What rule did MLB introduce in 2023 to speed up the game? What is a home run with the bases loaded called? What does it mean when a batter "hits for the cycle"?