Sleep apnea is often comes with high blood pressurewhich, in turn, contributes to the heart health risks associated with both diseases. Now, scientists have identified two brain chemicals that play a role in this chain reaction and could pave the way for new therapies.
In a study of lab rats published in May in Journal of PhysiologyThe scientists focused on two chemicals produced by the brain that are known to affect blood pressure: oxytocinalso known for its roles in attachment and social bonding, and corticotropin-releasing hormone (CRH). They wanted to see how these two “neurohormones” influence the brainstem, a structure at the base of the brain responsible for controlling many involuntary functions, including arterial pressure.
People with sleep apnea temporarily stop breathing while they sleep. sleepbriefly depriving the body of oxygen. This places it in a hypoxic, or low-oxygen, state.
“When the body is lacking oxygen, a state called hypoxia, it causes a reflex that causes us to want to increase our breathing, which will bring our oxygen level back up,” said Dr. David Klineprofessor at the University of Missouri School of Veterinary Medicine, who oversaw the study. “It also causes a reflex to increase our blood pressure so that oxygenated blood gets to where it needs to go,” Kline told Live Science.
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However, although it is known that both oxytocin and CRH can alter blood pressure, their effects after these brief, repetitive bursts of hypoxia were not fully understood.
The researchers conducted their experiment with laboratory rats divided into two groups: the first group was kept in normal oxygen levels, while the second group was intermittently placed in low-oxygen conditions to mimic some aspects of sleep apnea episodes.
The experiment lasted for 10 days, after which the scientists took samples from the rats’ brainstems to analyze their neuronal activity using various techniques. Additional samples of brain tissue were taken to examine oxytocin and CRH activity using a microscope, and a count of the specific brain cells that respond to both chemicals was done manually.
Oxytocin and CRH are both produced by cells in a structure called the paraventricular nucleus (PVN). These cells in the PVN connect to a major sensory center in the brainstem that receives signals from the body telling it how to regulate the cardiovascular system, including blood pressure. Oxytocin and CRH play a role in sending these signals, but experience has shown that hypoxia enhances their influence.
Both chemicals had a greater effect on brainstem activity in hypoxic rats than in rats maintained at normal oxygen levels. After periods of low oxygen, there was an increase in the release of the chemicals from the PVN, as well as an increase in the number of receptors to which they connect in the brainstem. In turn, there was an increase in the number of signals emitted from the sensory center in the brainstem.
Based on these findings, Kline said sleep apnea may exaggerate the effects of oxytocin and CRH on the brain stem, which could then lead to increased blood pressure.
In other words, the release of chemicals after hypoxic episodes causes blood pressure to rise each time, Kline explained. Over weeks, if this happens too often, blood pressure remains elevated because the brain regions responsible for controlling blood pressure have been impaired, he hypothesized.
However, this study did not explicitly examine the underlying mechanisms; the group is now working on studies that could shed light on these unknowns.
Once more chemicals involved in the mechanism are identified, specific drugs can be developed to target them and reduce blood pressure in patients with sleep apnea, Kline said.
Generic drugs that affect the entire brain may not be the best option, he noted, because the effects of oxytocin and CRH depend on the regions of the brain with which they interact. can actually decrease arterial pressure if they target different parts of the brainstem than those studied by the team, for example.
However, in the area the researchers focused on, both chemicals had more of an uplifting effect, Procope Gama de Barcellos Filhoa postdoctoral researcher in Kline’s lab who led the study, told Live Science.
“I think all of this basic research is going to open up new insights that can be used by clinicians and pharmaceutical companies,” Kline said. He cautioned, however, that much work remains to be done to translate the findings into a therapeutic approach for human patients.
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