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Evidence that blood pressure controls heart rate in the chick embryo prior to neural control
Insights
Increased blood pressure directly elevates heart rate in chick embryos by stretching heart muscle, independent of neural control. This pressure-stretch mechanism is key to early cardiac regulation.
Area of Science:
- Developmental biology
- Cardiovascular physiology
- Embryology
Background:
- Early cardiac function in chick embryos precedes full neural development.
- Understanding the intrinsic mechanisms of heart rate regulation is crucial for developmental studies.
Purpose of the Study:
- To investigate the relationship between blood pressure and heart rate in developing chick embryos.
- To determine the role of mechanical stretch in mediating heart rate responses to pressure changes.
Main Methods:
- Experiments were conducted on intact chick embryos and surgically isolated hearts.
- Intraventricular fluid pressure was manipulated to observe effects on heart rate.
- Propranolol was administered to assess its impact on heart rate and blood pressure.
Main Results:
- Increased blood pressure elevated heart rate in intact embryos and isolated hearts.
- Pressure applied internally but not externally to isolated hearts increased beat rate, suggesting a stretch mechanism.
- Propranolol significantly reduced heart rate but did not affect blood pressure in intact embryos.
Conclusions:
- Cardiac mechanosensation, specifically the stretch of heart muscle, is a primary driver of increased heart rate in response to elevated blood pressure.
- Neural control is not required for this pressure-induced heart rate increase in early development.
- Blood pressure influences heart rate, but not vice versa, in this developmental stage.
Abstract:
Blood pressure increases will increase heart rate in intact chick embryos, prior to the development of neural control. Similarly, in surgically isolated hearts, increases in intraventricular fluid pressure will increase the rate of beat. However, fluid pressure applied equally to both interior and exterior surfaces of the isolated heart does not result in increased heart rate. Therefore, we conclude that the increased pressure stretches the heart muscle and that this stretch stimulates the increased heart rate. While heart rate is clearly influenced by blood pressure, the reverse is not true. Propranolol reduces the heart rate to about half normal in intact embryos but does not significantly alter the blood pressure.