Chronic furosemide treatment alters renal responses to furosemide in conscious lambs

Despite the widespread chronic use of furosemide in the clinical management of a variety of fluid and electrolyte disorders in human infants, the phys iological responses to furosemide in the newborn after chronic furosemide t reatment are not known. The present experiments were conducted to determine the effects of chronic furosemide treatment on renal responses to acute fu rosemide challenge in conscious, chronically instrumented lambs. Experiment s were carried out on day 1 (before chronic treatment) and on day 7 (after chronic treatment) in lambs given intravenous injections of either furosemi de (1 mg/kg per 12 h for 5 days, n=9) or vehicle (0 mg/kg per 12 h for 5 da ys, n=4). Furosemide-treated animals responded to acute furosemide challeng e on day 7 with attenuation of natriuresis and diuresis, and augmentation o f kaliuresis compared with responses on day 1. Baseline renin production wa s elevated. although the renin response to furosemide was similar in chroni c furosemide-treated and vehicle-treated lambs. Baseline aldosterone levels were not altered by chronic furosemide treatment, but the aldosterone resp onse to acute furosemide injection was decreased after chronic furosemide t reatment. Therefore, chronic furosemide treatment alters renal responses to furosemide in conscious lambs, and alters the aldosterone response to acut e furosemide challenge.