EFFECTS OF PROLONGED (48-H) INFUSION OF CORTISOL ON BLOOD-PRESSURE, RENAL-FUNCTION AND FETAL FLUIDS IN THE IMMATURE OVINE FETUS

1. This study describes the effects of prolonged (48 h) infusion of co rtisol into ovine foetuses (100-110 days of gestation: term is 150 day s) at a time when endogenous plasma cortisol concentrations are < 5 nm ol/L. 2. In four chronically cannulated foetuses (107 +/- 0.9 day) the infusion of saline (0.9% NaCl; w:v 0.19 mL/h, 48 h) had no effect on blood pressure, renal function, or composition of amniotic and allanto ic fluids. 3. Tn six foetuses (107 +/- 1 day) the infusion of cortisol (250 mu g/h) increased plasma cortisol concentrations from 4.1 +/- 0. 7 to 118 +/- 9 nmol/L (P < 0.001), increased mean arterial pressure fr om 34 +/- 1 to 40 +/- 1 mmHg (P < 0.001), increased glomerular filtrat ion rate (P < 0.05), urine flow rate, and free water clearance (P < 0. 01). 4. There was a significant increase in excretion rates of potassi um and creatinine as a result of cortisol infusion, but no natriuresis , indicating some functional maturation of the fetal kidney. 5. Cortis ol infusion had no effect on the volumes of amniotic and allantoic flu ids; allantoic fluid composition was unchanged; significant decreases occurred in amniotic fluid osmolality, sodium and chloride concentrati ons, and in lung liquid osmolality, potassium, creatinine, magnesium, glucose and fructose concentrations. 6. Thus prolonged exposure of the immature ovine foetus to elevated cortisol concentrations produced si gnificant alterations in the water and electrolyte balance of the foet us.