RESPONSE OF THE FETAL LAMB KIDNEY TO VASOPRESSIN AND NOREPINEPHRINE

Abstract

Following asphyxia from occlusion of the umbilical cord there is a loss of electrolytes in the urine of the fetal lamb. Since both vasopressin (VP) and catecholamine levels are elevated in fetal blood during asphyxia, experiments hove been conducted on 14 fetal lambs, chronically instrumented to determine whether there is a relationship between these hormones and the changes in renal function. Administration of VP (5.0-10 mU/kg over 1 min) increased urinary output from 0.17 to a maximum of 0.58 ml/kg/min., and urine osmolality from 149 to 310 mOsm/kg at the end of one hour. Urine sodium & chloride concentrations increased & free water clearance decreased from 0.08 to 0.02 ml/kg/min. These changes persisted over two hours after the administration of VP. Fetal BP increased only transiently by a maximum of 15 mmHg following VP. Administration of norepinephrine at a rate of 0.5 μg/kg/min. over 30 minutes resulted in an increase in urine output from 0.25 to 0.55 ml/kg/min. Urine osmolality decreased from 150 to 128 mOsm/kg. Free water clearance increased from 0.13 to 0.27 ml/kg/min., while urine sodium and chloride concentrations remained the same. Control values were achieved one hour after the end of the infusion. At this rate of administration norepinephrine had minimal and only transient effect on fetal BP, HR and plasma renin activity. Thus, in the doses given vasopressin elicited a sodium diuresis and norepinephrine a water diuresis. The combined effect of these two hormones could thus lead to a loss of water and electrolytes.

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