The influence of parathyroid hormone and calcitonin on urinary excretion of calcium, magnesium and inorganic phosphorus in chronically catheterized foetal lambs in utero.

Nine single foetal lambs with catheters chronically implanted in utero on day 122 of gestation into the left carotid artery, the right external jugular vein and the bladder were used. In these foetuses, between days 130 and 142 of gestation, urine flow rate was 0.48 +/- 0.09 ml X min-1. In the same time, an intravenous infusion of bovine parathyroid hormone (150 U per foetus in 30 min) induced hypercalcaemia and hypophosphataemia, associated with an increase in urinary flow rate and urinary phosphate concentration. Although urinary calcium concentration was unchanged, the urinary excretion of both calcium and phosphate increased. An intravenous infusion of salmon calcitonin (200 MRC mU per foetus in 30 min) induced hypocalcaemia and hypophosphataemia, associated with an increased urinary phosphate concentration. Urinary flow rate and urinary calcium concentration were not modified by the calcitonin which increased only urinary excretion of phosphate. Thus the high plasma phosphate levels measured in lambs during the perinatal period do not seem to be related to a previous unresponsiveness (just before birth) to the hormones regulating phosphate urinary excretion.