Fluid balance, electrolyte profiles and plasma parathyroid hormone concentrations in ewes treated with epidermal...

The infusion of low doses of epidermal growth factor (EGF) into lactating ewes stimulates water intake and urine volume. The plasma concentrations and daily output of various electrolytes in milk and urine are also affected. We have investigated this further by recording the effects of EGF infusion on fluid balance, electrolyte profiles and plasma concentrations of glucose and parathyroid hormone (PTH) in non-pregnant, non-lactating ewes. Twenty-four animals (n = 8 per group) received infusions of 100 ml saline/day into the jugular vein for 10 days (days 1-10) followed by EGF at a dose rate of either 1 (low dose), 5 (medium dose) or 10 (high dose) micrograms/kg liveweight per day in 100 ml saline for 5 days (days 11-15). All ewes then received an infusion of 100 ml saline/day for 10 days (days 16-25). Most plasma and urine samples had undetectable concentrations of EGF-immunoreactive material during the periods of saline infusion. During EGF infusion, the highest amounts of EGF infusate excreted in urine were 1.6, 5.9 and 5.6% for ewes in low, medium and high dose groups respectively. Water intake increased by 17% (0.5 kg), 88% (2.5 kg) and 89% (2.3 kg) and urine volume increased by 29% (0.5 kg), 108% (2.2 kg) and 134% (2.1 kg) for the three groups respectively. Fluid balance and feed intake were not affected by EGF infusion, but the output of faecal dry matter was reduced in ewes receiving the two higher doses of EGF. All levels of EGF resulted in hypocalcaemia, increased plasma PTH concentrations and hypermagnesaemia. There was no effect of EGF on plasma concentrations of K+ and glucose or on daily urinary excretion of K+ and Mg2+. The only response to the low dose was a reduced plasma concentration of Na+ and an increased daily urinary urate excretion. The two higher doses increased the daily urinary excretion of Na+, PO4(3-) and urate, but had no effect on the respective concentrations in plasma. Urinary Ca2+ excretion was reduced only during infusion of the medium dose of EGF. The responses of most variables were similar during infusion of the medium and high doses of EGF. All three doses of EGF induced polydipsic and diuretic responses in ewes, and infusions of 5-10 micrograms EGF/kg liveweight per day affected renal excretion of Ca2+, Na+ and PO4(3-). We interpret the responses of the kidney and plasma PTH concentrations as a means of maintaining the homeostasis of plasma profiles of electrolytes.