A RADIOIMMUNOASSAY FOR OVINE CALCITONIN: AN EVALUATION OF CALCITONIN SECRETION DURING GESTATION, LACTATION AND FOETAL LIFE

Abstract

SUMMARY A radioimmunoassay capable of measuring ovine calcitonin in unextracted ovine plasma has been developed. Guinea-pig antisera to partially purified porcine calcitonin were highly specific for calcitonin and were capable of detecting 5 pg porcine calcitonin. One of these antisera cross-reacted significantly with pure ovine calcitonin and with foetal ovine plasma. The mean basal calcitonin secretion rate for the left thyroid lobe found in sheep foetuses 10 days before term was 3·36 ng/min/kg body weight. An infusion of calcium into the foetus was followed by an increase in the calcitonin secretion rate. The mean fasting calcitonin concentration in samples from the jugular vein of five pregnant ewes 10 days before term was 5·28 ng/ml. An infusion of calcium into the mother induced a sevenfold increase in plasma calcitonin concentration whereas the calcitonin concentration was unchanged in the foetal thyroid venous plasma. At parturition the plasma calcitonin concentration fell in the mother (1·85 ng/ml), and a sharp increase was observed during lactation (11·60 ng/ml). In the lamb from birth to 6 weeks post partum the calcitonin concentration was very high (8·10–10·40 ng/ml).