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

Abstract

Summary Plasma renin substrate concentration was measured in 18, four‐day‐old pony foals after the administration of the natriuretic agent frusemide. Thirteen foals had been delivered spontaneously; labour had been induced in the remaining five mares. Plasma aldosterone concentration was measured in 12 of the spontaneously delivered foals. Renin substrate concentration had risen sharply within 15 mins (P<0.005) and peaked at 1 h. The response was consistently greater in the induced foals. Serum sodium concentration fell rapidly in the induced foals (P<0.002 by 60 mins) but was better maintained in the spontaneous group. Individual serum potassium concentrations varied widely and were higher in both the induced group and smaller (30 kg or less) spontaneous foals. Plasma renin substrate concentration was positively correlated with plasma potassium in both groups (P<0.05, P<0.001 respectively). Plasma aldosterone rose significantly within 30 mins (P<0.025) and did not stabilise during the experiment. Plasma aldosterone was significantly correlated with renin substrate concentration in both lighter (P<0.005) and heavier (P<0.05) spontaneously delivered foals. It is suggested that maturation of renal sodium and potassium handling occurs late in gestation in the foal and is in part related to body mass. ‘Premature’ delivery following induced labour is associated with a more rapid loss of sodium when challenged with frusemide, even though the response of the renin‐angiotensin system may be exaggerated.

Effect of altrenogest‐treatment of mares in late gestation on adrenocortical function, blood count and plasma electrolytes in their foals

“…[Paper received for publication 26.03.08; Accepted 17.11.08] delivery, there is an exaggerated response of this system and foals fail to maintain serum electrolyte concentration (Pipkin et al 1984). Alterations of serum electrolyte concentrations can be associated with a variety of disorders in the neonatal foal (Bauer 1990).…”