Reflex regulation of hormonal responses during pregnancy

Area of Science:

• Reproductive physiology
• Cardiovascular regulation
• Endocrinology

Background:

• During pregnancy, resting levels of plasma angiotensin II and ACTH (corticotropin) increase, along with vasopressin relative to osmolality.
• Despite increased blood volume, mean arterial pressure decreases in the pregnant state.
• Baroreflex sensitivity is known to decrease during pregnancy.

Purpose of the Study:

• To investigate alterations in hormonal and cardiovascular responses to hypotension during pregnancy.
• To determine if changes in arterial pressure regulation during pregnancy affect hormonal responses to hypotension.
• To examine stimulus-specific alterations in hormonal responses.

Main Methods:

• Studies in pregnant ewes and dogs involved inducing hypotension via hemorrhage.
• Hormonal levels (vasopressin, ACTH, cortisol) and heart rate were measured in response to hypotension.
• Relationships between mean arterial pressure and hormone responses were analyzed.

Main Results:

• Vasopressin and ACTH responses to hypotension are shifted leftward in pregnant ewes, indicating a changed set-point for arterial pressure regulation.
• Vasopressin and cortisol responses to hypotensive hemorrhage are blunted in pregnant dogs.
• Heart rate responses to hypotension are decreased in pregnant ewes, consistent with reduced baroreflex sensitivity.

Conclusions:

• Pregnancy alters hormonal and cardiovascular responses to hypotension.
• A change in arterial pressure regulation during pregnancy modifies hormonal responses to hypotension.
• These findings suggest a recalibration of the baroreflex and hormonal systems during gestation.