THYROIDAL CONTENT OF THYROCALCITONIN IN LACTATING RATS

Abstract

ABSTRACT Thyrocalcitonin (TCT) content of thyroid glands was determined by bioassay in Sprague-Dawley-Rolfsmeyer rats at 1, 5, 10, 15 and 20 days of lactation and found to be 476, 523, 762, 553 and 564 MRC mU per gland (5 rats on each day of lactation). A control group of normal virgin rats had 438 MRC mU per gland. These experiments indicate that at day 10 of lactation TCT content of the gland is significantly (P < 0.05) higher than any other day. The possible explanation of TCT accumulation is that during lactation animals undergo a mild hypocalcaemia due to large amounts of calcium drain in milk. Hypocalcaemia and lack of hypercalcaemic stimulation of TCT secretion have been reported to cause TCT accumulation in the thyroid gland. Though gland content does not necessarily reflect secretory status of a hormone, it is possible that less TCT is discharged from the gland during the middle of lactation.