Maternal age-related changes in renin-angiotensin-aldosterone system and electrolyte homeostasis during equine pregnancy.

Research Overview

• This study investigated how maternal age affects the activity of the renin-angiotensin-aldosterone system (RAAS) and electrolyte balance during pregnancy in mares.
• The researchers focused on hormonal changes (renin, angiotensin II, and aldosterone) and their impact on sodium and potassium levels across different age groups of pregnant mares.

Introduction to the Topic

• The renin-angiotensin-aldosterone system (RAAS) is critical for regulating fluid and electrolyte homeostasis, especially during pregnancy.
• RAAS controls the secretion of hormones such as renin (REN), angiotensin II (ANG-II), and aldosterone (ALD), which influence sodium (Na⁺) and potassium (K⁺) balance.
• Previous studies in humans and laboratory animals showed that maternal age can modulate RAAS activity, but little was known about this effect in horses.
• This study aimed to fill that knowledge gap by analyzing how maternal age influences RAAS hormones and electrolyte levels throughout equine pregnancy.

Methods

• Subjects: Forty-five Spanish Purebred mares divided equally into three age categories:
  • Young (6-9 years old)
  • Middle-aged (10-12 years old)
  • Older (13-16 years old)
• Monitoring: Hormone and electrolyte levels were recorded monthly over an 11-month gestation period.
• Measurements:
  • Plasma concentrations of REN, ANG-II, and ALD were measured using competitive immunoassays, a technique designed for high specificity in detecting these hormones.
  • Electrolyte concentrations (Na⁺ and K⁺) were measured with a validated analyzer to ensure accurate assessment of electrolyte homeostasis.

Results

• Renin (REN):
  • REN concentrations rose from mid-gestation (around month 5), peaking at month 6 in all mares.
  • Young mares had significantly higher REN levels between months 5 and 6 compared to middle-aged and older mares (p < 0.05).
• Angiotensin II (ANG-II):
  • ANG-II levels displayed fluctuations throughout pregnancy rather than a steady increase or decrease.
  • Older mares had significantly higher ANG-II concentrations during early to mid-pregnancy (months 2, 3, and 5) compared to younger groups (p < 0.05), after which levels gradually declined.
• Aldosterone (ALD):
  • ALD mirrored the REN pattern with peaks at months 1, 4, 5, and 7.
  • Young mares consistently had greater ALD concentrations than older mares (p < 0.05).
• Electrolytes (Na⁺ and K⁺):
  • Despite the variation in RAAS hormones, plasma sodium and potassium levels remained stable across all age groups and gestational stages.

Conclusions and Interpretation

• Maternal age influences the activity of RAAS during equine pregnancy, with distinct hormonal profiles observed in different age groups.
• Younger mares showed enhanced renin and aldosterone responses, suggesting a more robust RAAS activation during mid- to late-gestation.
• Older mares had elevated angiotensin II concentrations in early pregnancy, which then declined, indicating altered early gestational RAAS regulation compared to younger animals.
• Despite these hormonal differences, electrolyte homeostasis (Na⁺ and K⁺ balance) remained unaffected, implying that compensatory mechanisms maintain stable plasma electrolyte concentrations during pregnancy regardless of maternal age.
• These findings enhance understanding of age-related physiological changes during equine pregnancy and could inform management and care practices for mares of different ages.