Developmental changes in blood pressure and the renin-angiotensin system in pony fetuses during the second half of gestation.

Researchers studied developmental changes in blood pressure and the hormone system known as the renin-angiotensin system in pony fetuses during the latter half of gestation. They found that blood pressure increased close to birth, corresponding with increases in the hormone cortisol and components of the renin-angiotensin system, suggesting these systems may contribute to the increase in fetal blood pressure.

Study design and methodology

• The researchers measured blood pressure, heart rate, and the plasma concentrations of cortisol and components of the renin-angiotensin system in 15 Pony mares and their fetuses during the second half of gestation. The team specifically noted measurements from day 153 to 336 of gestation. The gestational term for ponies typically falls between day 320 and 340.
• Fetal blood pressure and other components were monitored, plotted and statistically analyzed to identify any trends or correlations.

Main Findings

• There was an increasing trend in fetal blood pressure toward the end of gestation, which correlated with the prepartum surge in plasma cortisol concentration. The researchers saw a significant correlation between fetal blood pressure and both gestational age and plasma cortisol concentration. The correlations indicate that as gestation advances and cortisol increases in the fetus, the blood pressure also tends to increase.
• The researchers concluded that the levels of components of the renin-angiotensin system, angiotensin-converting enzyme (ACE) and angiotensinogen, increased toward the end of gestation in the fetuses. ACE was observed to correlate with gestational age, cortisol levels and blood pressure.
• Fetal heart rate was found to be inversely correlated with gestational age, ACE concentration and angiotensinogen concentration. This suggests that as these parameters increase, fetal heart rate tends to decrease.
• A positive correlation was seen between plasma concentrations of angiotensin II and renin in the fetuses. However, no gestational changes were observed in these parameters for either the mares or fetuses, implying that their concentrations remain steady throughout the gestation period.

Conclusions and Insights

• Maternal factors, such as blood pressure, heart rate, plasma ACE and angiotensinogen concentrations did not change over the pregnancy term, thus the observed changes were specific to the fetuses.
• The study concluded that in pony fetuses, developmental changes in the renin-angiotensin system occur towards the end of gestation and coincide with the prepartum cortisol surge, suggesting that these changes may be partially responsible for the observed increase in fetal blood pressure.
• The study provides important insights into fetal development and the hormonal mechanisms involved in preparing the fetus for birth.