Female mice hearts respond differently to stress hormone

A new research paper has found that female and male mice hearts respond differently to the ‘fight or flight’ hormone.

Although it’s early days, the research may have implications for human heart disorders like arrhythmias and heart failure and how different sexes respond to medications.

“Sometimes the data between the two sexes is the same. But if the data start to show variation, the first thing we do is look at sex differences,” says UC Davis cardiac researcher, professor Crystal Ripplinger.

When Ripplinger started her lab she exclusively used male animals – as a lot of research still does. But several years ago, she began including male and female animals in her studies.

“Using both male and female mice has revealed clues into differences we would never have suspected. Researchers are realising you can’t extrapolate to both sexes from only studying one,” she added.

The team used a type of fluorescence imaging system, which allowed them to see how a mouse heart responds to hormones and neurotransmitters in real time.

The mice were exposed to noradrenaline (also known as norepinephrine). Noradrenaline is both a neurotransmitter and hormone associated with the body’s ‘fight or flight’ response.

The researchers found that male and female mouse hearts responded similarly at first after exposure to the stress hormone.

Female male mice hearts
The bottom of the heart — the apex — returns to normal more quickly in females than males.
Credit: UC Regents

However, the bottom of the female heart – which is known as the apex – returned to normal more quickly than the male heart. This difference produces changes in the heart’s electrical activity.

“The differences in electrical activity that we observed are called repolarisation in the female hearts,” said UC Davis researcher Dr Jessica Caldwell, first author of the study.

“Repolarisation refers to how the heart resets between each heartbeat and is closely linked to some types of arrhythmias.”

It’s important to note that the researchers are not yet sure if this difference is good or bad for the female mice, and more research will need to be undertaken to find out more.

“The response in the female mice may be protective — or it may not. But simply documenting that there is a measurable difference in the response to a stress hormone is significant. We are hoping to learn more in future studies,” Ripplinger said. The paper has been published in Science Advances.

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