Function of mammalian-type and reptilian-type nephrons in kidney of desert quail.

WRAUN, ELDON J., ~%LLCAM 1% J)ANTZLER. Function of mamunalian-type and reptilian-type nephrons in kidney of desert quail. Am. J. Physiol. 222(3): 617-629. I972.---Bird kidneys have mammaliantype (MT) as well as reptilian-type (RT) nephrons. Wholekidney and individual nephron functions were studied in the desert quail during a control diuresis and during 6% NaCl infusion. Glomerular filtration rate (GFR) decreased after ca. 20 mEq NaCl/kg and fell to 20% of control after cit. 40 mEq NaCl/ kg. Tubular maximum for para-aminohippurate secretion decreased with GFR, suggesting that changes in GFR resulted from changes in number of functioning nephrons. Histological data showed 71 y. of RT proximal convoluted tubule (PCT) lumina open in hydrated birds and 84”/, lumina closed in salt-loaded birds, suggesting that it was RT nephrons which ceased filtering during salt loading. Single-nephron filtration rates (SNGFR) during control diuresis were 15.8, 10.9, and 6.4 nl/min for large mammalian-type (MT-L), small mammalian-type (MT-S), and RT nephrons, respectively. During salt loading, SNGFR values were 13.4 and 12.4 nl/min for MT-L and MT-S. No RT nephrons were filtering during salt loading. Birds with limited concentrating ability and without salt glands can respond to osmotic stress by reducing number of functioning RT nephrons. Possible regulatory mechanisms for this differential functioning of nephrons and the relationships between SNGFR, PCT length, and glomerular volume are discussed.