Norethindrone acetate (NETA), one of the hormones replacement drug Femhrt, protects the heart from damage, whereas medroxyprogesterone acetate (MPA), a hormone found in the drug Prempro, makes the heart more vulnerable to injury, according to findings from an animal study.

“In our previous work in monkeys we showed that two different hormone replacement therapies differed” in how they affected blood vessel function and plaque build-up, lead researcher Dr. J. Koudy Williams told AMN Health.

In the present study, Williams, a scientist at Wake Forest University Baptist Medical Center in Winston-Salem, North Carolina, and colleagues compared the effects of MPA and NETA in female monkeys that were subjected to an experimental form of heart attack in the laboratory.

The findings were presented Friday at the annual meeting of the North American Menopause Society in Washington, DC.

Animals treated with NETA experienced much less damage from the heart attack than the animals that received MPA. “I really was not expecting this profound difference,” Williams said.

NETA seemed to protect the heart by reducing the amount of inflammation that occurred after the attack, the researchers note.

The take-home message from this study is that not all hormone replacement therapies are created equal, Williams said, but the findings are still too preliminary to make any recommendations at this time.