Effect of meal feeding on plasma volume and urinary electrolyte clearance in ponies.

This study explores how different feeding practices, namely meal size and regularity, impact plasma volume and urinary sodium and potassium clearance in ponies.

Research Methodology

• The scientists conducted the study on ponies, choosing them for their controlled dietary intake and their distinct urinary and plasma parameters.
• A two-pronged feeding regimen was deployed. Some ponies were subjected to a multiple-feeding plan, receiving 12 equal parts of hay-grain pellets at two-hour intervals. Others were subjected to a single-large-feeding plan, receiving a substantial portion of their ration every 12 hours at predetermined times.
• The focus of the study was the impact of the single morning feeding aspect of the single-large-feeding regimen.
• To make serial measurements of plasma volume, an indicator-dilution technique was used in tandem with indocyanine green. This combination allowed for periodic measurements every two hours.

Feeding Impact on Plasma Volume and Protein Concentration

• Intake of the single large meal caused a notable 15% decrease in plasma volume over the course of the one-hour feeding period.
• This sudden drop in plasma volume, or feeding hypovolemia, was reinforced by a simultaneous 12% increase in plasma protein concentration.
• The researchers further substantiated their findings by examining the post-feeding shift in the elimination of Evans blue dye in different experiments.

Impact on Plasma Aldosterone Concentration & Urinary Electrolyte Clearance

• Plasma aldosterone concentration, which regulates sodium and fluid balance, noticeably increased between two and five hours after feeding.
• Urinary sodium clearance decreased following meal intake and remained lower than the usual rate up to nine hours post-feeding.
• In contrast, urinary potassium clearance displayed an upward trend from pre-feeding levels and peaked between five and seven hours after feeding. This outcome suggests a complex interplay in sodium and potassium urinary clearance post-feeding in ponies.
• Creatinine clearance, however, maintained a steady rate, unaffected by the feeding regimen.
• Worth noting is that the variables that showed significant changes in the single-large-feeding regimen stayed unchanged within the multiple-feeding regimen.

Conclusion

• The results suggest that the consumption of a single large concentrate meal in ponies leads to a temporary reduction in plasma volume (periprandial hypovolemia).
• This stimulates the renin-angiotensin-aldosterone system, which controls blood pressure and fluid balance.
• The aftermath of this process is a major antinatriuresis-kaliuresis event that lasts several hours after meal consumption, impacting the management of urinary sodium and potassium clearance in the pony’s body.