Diuresis in Response to Hypoxia and Epinephrine in Infant Rats

¹ From the Department of Physiology, School of Medicine and Dentistry, The University of Rochester, Rochester, New York

Urine flow was measured in newborn and adult rats, urine being collected by means of a small plastic tube surgically inserted into the urinary bladder through the ventral body wall. Epinephrine in subcutaneous doses of 0.3 or 0.6 mg/kg of body weight produced a prompt diuresis which was nearly identical at all ages (1/4, 2, 6 days after birth; and adult). Arterial blood pressure was low in infant rats and was not increased by this dose of epinephrine. When infant rats breathed air low in oxygen (pO₂ = 38 mm Hg), prompt oliguria lasted one-half hour; primary diuresis followed; secondary diuresis suddenly developed whenever ordinary air was again supplied. Within 15 days after birth the oliguria and the secondary diuresis were lost; primary diuresis appeared earlier and lasted a shorter time. Whereas rats up to 39 days after birth did not respond to pO₂ of 56 mm Hg, adults responded to it with primary diuresis only. The urine produced during infant diureses was dilute as measured by chloride and refractive index, and remained acid. Pitressin did not interfere with these diureses. Adrenalectomy did not prevent the secondary diuresis. Though responses to epinephrine and hypoxia materialized at birth, their amount and character shifted with age, representing the terminal stages in fixiaton of a regulation.