Evaluation of age effect on circulating catecholamines’ network in pregnant mares.

This study examined how pregnancy and age together shape changes in the stress-related hormones adrenaline, noradrenaline, and dopamine in Spanish Purebred mares. The authors found age-specific patterns across gestation: adrenaline dipped early then stabilized, noradrenaline rose late in younger mares, and dopamine peaked mid-pregnancy then fell toward foaling, with older mares showing more stable profiles.

What the researchers asked and why it matters

• Question: Does a mare’s age modify the normal pregnancy-related fluctuations in circulating catecholamines—adrenaline (A), noradrenaline (NA), and dopamine (DA)?
• Rationale: Catecholamines are key neuroendocrine regulators of cardiovascular tone, metabolism, and stress responses; both pregnancy and aging independently alter catecholaminergic activity. Understanding their combined effects can clarify maternal adaptation and guide peripartum management.
• Relevance: In horses, autonomic balance influences uterine blood flow, fetal environment, and behavioral/stress responses—factors important for welfare and breeding outcomes.

Study design at a glance

• Population: Spanish Purebred (Pura Raza Española) mares grouped by age:
  • 4–7 years (n=18)
  • 8–10 years (n=18)
  • 11–15 years (n=18)
• Sampling times across gestation:
  • T1: first trimester
  • T2: second trimester
  • T3: third trimester
  • B4: final bimester (last two months before foaling)
• Analytes measured: plasma adrenaline (A), noradrenaline (NA), dopamine (DA)
• Assay: horse-specific validated competitive enzyme immunoassay (3-CAT EIA)
• Statistics: Group and stage comparisons with significance reported at p<0.05 or p≤0.05 for main findings noted.

Key findings by hormone

• Adrenaline (A)
  • Overall pattern: Declined from T1 to T2 (p<0.05), then stabilized or slightly increased at T3–B4.
  • Age differences:
    • 8–10 years: highest A at T1 among age groups.
    • 11–15 years: maintained comparatively higher A at T2.
• Noradrenaline (NA)
  • Overall pattern: Age-dependent divergence late in gestation.
  • Age differences:
    • 4–7 years: elevated NA in late gestation (p≤0.05).
    • 8–10 years: lowest NA concentrations across stages, especially late gestation.
• Dopamine (DA)
  • Overall pattern: Peaked mid-gestation and decreased before parturition (p≤0.05).
  • Age differences:
    • Older mares (11–15 years): more stable DA profile across stages.

Physiological interpretation

• Pregnancy adaptation:
  • T1→T2 drop in adrenaline suggests an early gestational shift away from acute sympathetic surges, aligning with hemodynamic stabilization as placental circulation expands.
  • Mid-gestation DA peak may reflect dopaminergic modulation of prolactin and vascular tone during a period of rapid fetoplacental growth.
  • Late gestation fall in DA and partial rebound/stabilization of A could prepare for parturition-related metabolic and cardiovascular demands.
• Age modulation:
  • Younger mares’ higher late-gestation NA implies a stronger sympathetic response near term, potentially reflecting heightened reactivity or different autonomic set-points.
  • Older mares’ more stable DA (and sustained A at T2) suggests attenuated variability, consistent with age-related adjustments in catecholamine synthesis, clearance, or receptor sensitivity.
  • Middle-aged mares (8–10 years) showing lowest NA may occupy a “damped” sympathetic profile compared with younger mares.
• Network perspective:
  • The distinct timing of A, NA, and DA shifts indicates coordinated but non-identical regulation across pathways (adrenomedullary vs sympathetic neuronal vs dopaminergic).
  • Age appears to reweight this network, altering which catecholamine predominates at specific gestational windows.

Implications for equine management and breeding programs

• Monitoring and handling:
  • Consider minimizing stressors especially in late gestation for younger mares, who show higher NA reactivity near term.
  • Plan routine procedures (transport, environment changes) outside windows of peak reactivity when feasible.
• Nutritional and environmental support:
  • Stable routines and low-arousal environments may help modulate sympathetic activation in late gestation.
• Breeding strategy:
  • Awareness of age-related neuroendocrine profiles may inform individualized peripartum monitoring without implying pathology.

Strengths

• Clear age stratification across three clinically relevant cohorts.
• Stage-specific sampling spanning early pregnancy through the last two months.
• Use of a horse-validated 3-CAT competitive EIA tailored to the species.

Limitations and considerations

• Breed specificity (Spanish Purebred) may limit generalizability to other breeds.
• Abstract does not detail potential confounders (parity, body condition, time-of-day sampling, handling stress) that can influence catecholamine levels.
• Immunoassay-based catecholamine measurements can be affected by pre-analytical factors (sample handling, hemolysis) and cross-reactivity; high-frequency sampling or LC-MS/MS could refine temporal dynamics.
• Outcomes (maternal cardiovascular measures, fetal growth, foaling metrics) are not linked, so functional impact is inferred rather than demonstrated.

Future research directions

• Integrative profiling:
  • Combine catecholamines with cortisol, heart rate variability, and uterine/fetal Doppler to map autonomic-endocrine coupling.
• Mechanistic insights:
  • Assess enzymes (tyrosine hydroxylase, COMT, MAO) and receptor expression to parse age-related differences in synthesis and clearance.
• Design enhancements:
  • Control for parity, circadian timing, and environmental stress; add repeated within-stage sampling to capture short-term variability.
• Translational outcomes:
  • Relate catecholaminergic profiles to foaling outcomes, neonatal vigor, and postpartum recovery to determine practical predictive value.

Takeaway summary

• Adrenaline: early decline (T1→T2), then stabilizes/slightly rises toward term; peak T1 in 8–10 yrs; relatively higher T2 in 11–15 yrs.
• Noradrenaline: late-gestation rise in younger mares (4–7 yrs); consistently lowest in 8–10 yrs.
• Dopamine: mid-gestation peak followed by prepartum decline; older mares show greater stability.
• Conclusion: Pregnancy reshapes the catecholamine network in mares, and age further modulates these trajectories, indicating distinct autonomic strategies across the reproductive lifespan.