RENAL HEMODYNAMIC AND FUNCTIONAL-EFFECTS OF 10 DAYS PARTIAL URINARY OBSTRUCTION IN THE FETAL LAMB

We studied fetal lambs to define the renal pathophysiology of chronic in utero partial bladder outlet obstruction. These fetal lambs, 115 to 120 days gestation (term = 145 days), underwent urethral ligation, placement of a urachal catheter and positioning of an ultrasonic flow transducer around the left renal artery. Partial obstruction was created by placing a narrow connector between the urachal and an amniotic catheter. In control animals a large connector was placed to allow free drainage of the bladder into the amniotic cavity. Renal blood flow was measured daily, and urine was collected at days 5 and 10 to evaluate renal function. In control animals, no significant changes in any parameters were observed. In the partially obstructed fetal lambs, renal blood flow increased to 165% of baseline after 5 days; from 5 to 10 days, it decreased, but remained above baseline values through 10 days (128%). Urine production dropped significantly after 10 days (67%). Glomerular filtration rate increased slightly after 5 days (127%), but decreased after 10 (56%). Filtration fraction steadily decreased after 5 (70%) and 10 days (33%). Fractional and total sodium excretion did not change. Renal blood flow increases, filtration fraction decreases and renal function trends progressively diminish in response to partial bladder outlet obstruction over a period of 10 days in the fetal lamb.