ATTENUATION OF RENAL EFFECTS OF ATRIAL-NATRIURETIC-FACTOR DURING RAT PREGNANCY

The influence of pregnancy on renal responses to atrial natriuretic fa ctor (ANF) was determined in urethane-anesthetized Sprague-Dawley rats . Infusions of ANF caused a significantly greater increase in urinary excretion of fluid, sodium, and potassium in virgin than in pregnant ( 13-15 days and 21 days) rats. Guanosine 3',5'-cyclic monophosphate (cG MP) excretion, mean arterial pressure, plasma immunoreactive ANF, and glomerular filtration rate (GFR) following ANF infusions were not diff erent in virgin and gravid rats, although increments in GFR over basal were greater in virgin than in gravid animals. Renal responses to ANF normalized during postpartum and were attenuated by progesterone trea tment of virgin rats. Natriuretic effects of infusions of ANF plus ANF -(4-23) (a ligand for clearance receptors) or of ANF plus thiorphan (a n endopeptidase inhibitor) in virgin and pregnant rats did not differ; ANF-(4-23) and thiorphan alone caused greater natriuresis in pregnant than in virgin rats. Effects of ANF on cGMP production by collecting duct cells isolated from virgin and pregnant rats did not differ. We c oncluded that the attenuation in the renal effects of ANF during pregn ancy might be mediated by progesterone by an increase in the intrarena l metabolism of ANF and might reflect physiological adjustment to faci litate fluid/electrolyte expansion.