Studies on equine prematurity 4: Effect of salt and water loss on the renin-angiotensin-aldosterone system in the newborn foal.

The research investigates the impact of salt and water loss on the renin-angiotensin-aldosterone system in newborn pony foals. It suggests that ‘premature’ delivery following induced labour leads to more rapid sodium loss when the route of natriuretic agent frusemide is tested, even with exaggerated responses of the renin-angiotensin system.

Experiment Details

• An experiment was conducted on 18 four-day-old pony foals. The foals were split into two groups; one contained 13 foals that had been spontaneously delivered, and the other consisted of five foals whose labour had been induced in the mares.
• The experiment involved the administration of the natriuretic agent frusemide, which helps eradicate sodium and water from the body. The influence of this agent on the renin-angiotensin-aldosterone system (a hormone system) was studied in these foals.
• The concentration of plasma renin substrate – a primary element in the renin-angiotensin-aldosterone system that triggers the production of angiotensin and consequently aldosterone – was measured in all the 18 foals.
• Plasma aldosterone – which helps regulate sodium and potassium balance – concentration was measured in 12 of the spontaneously delivered foals.

Observations and Findings

• It was found that the renin substrate concentration increased significantly within the first 15 minutes after administration of frusemide and hit its highest concentration after an hour. The induced delivery foals showed more pronounced response than the spontaneously delivered ones.
• In the induced foals, the serum sodium concentration experienced a rapid decline (significant at P less than 0.002 by 60 mins), but was relatively well maintained in the spontaneous group.
• Individual serum potassium concentrations fluctuated greatly. They were noticeably higher in foals with induced delivery and in smaller (30 kg or less) foals from the spontaneous group.
• There was a positive correlation noted between plasma renin substrate concentration and plasma potassium level in both groups of foals.
• The concentration of aldosterone increased significantly within 30 mins (P less than 0.025) and kept increasing throughout the experiment. It showed significant correlation with renin substrate concentration in both lighter and heavier spontaneously delivered foals.

Conclusion

• The research proposes that the maturation of renal sodium and potassium handling takes place late in the gestation period in foals and may be related partly to body mass.
• The study concludes that the induced labour leading to ‘premature’ delivery comes with the risk of faster sodium loss when challenged with frusemide, despite the exaggerated response of the renin-angiotensin system.