Female and male hearts respond differently to stress: study

Male and female hearts react differently to the stress hormone norepinephrine, according to a recent study published in Science Advances. The mouse study may have implications for human heart disorders such as arrhythmias and heart failure and how the different sexes respond to drugs.

According to the specialists, the research carried out in mice may have implications for human heart disorders such as arrhythmias and heart failure and how the different sexes respond to drugs.

Heart responds to hormones

The team built a new type of fluorescence imaging system that allows them to use light to see how a mouse heart responds to hormones and neurotransmitters in real-time.

The mice were exposed to noradrenaline, also known as norepinephrine. Norepinephrine is both a neurotransmitter and a hormone associated with the body's "fight or flight" response.

The results reveal that the hearts of male and female mice respond uniformly initially after norepinephrine exposure. However, some areas of the female heart return to normal more quickly than the male heart, resulting in differences in the heart's electrical activity.

The mice were exposed to norepinephrine, which is both a neurotransmitter and a hormone associated with the body's "fight or flight" response.

The results reveal that the hearts of male and female mice respond uniformly initially after norepinephrine exposure, however, some areas of the female heart return to normal more quickly than the male heart, leading to differences in the electrical activity of the heart.

“The differences in electrical activity that we observe are called repolarization in female hearts. This refers to how the heart resets between each beat and is closely linked to some types of arrhythmias,” explained Jessica L. Caldwell, first author of the study and a specialist at the UC Davis School of Medicine.

“We know that there are sex differences in the risk of certain types of arrhythmias. The study reveals a new factor that may contribute to different susceptibilities to arrhythmia between people of all genders,” she stressed.

Heart disease is leading cause of death in the US

Heart disease is the leading cause of death for both all genders in the United States, accounting for approximately one in four male deaths and one in five female deaths in 2020.

Including female mice leads to discoveries

The researchers had not planned to study responses based on gender, according to Crystal M. Ripplinger, the study's lead author. But the researchers began to see a pattern of different reactions, which led them to realize that the differences were based on gender.

Ripplinger, an electrical and biomedical engineer, is a professor in the Department of Pharmacology.

When he started his lab at the UC Davis School of Medicine more than a decade ago, he used exclusively male animals. That was the norm for most investigations at the time. But several years ago, he began to include both male and female animals in his studies.

"Sometimes the data between the two sexes is the same. But if the data starts to show variation, the first thing we do is look for sex differences. Using male and female mice has revealed clues about differences we never would have suspected. Researchers are realizing that you can't extrapolate to both sexes by studying only one," Ripplinger said.

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