Action of parathyroid hormone, with special reference to its anabolic effect on different kinds of tissues in rats (II).

The effect of parathyroid hormone (PTH) on the formation of the incisor in the rats was investigated using a time marker by the injection of lead acetate. 1) When intact immature rats were fed on a low calcium diet, the rate of the longitudinal and appositional formation of the incisal dentin was increased. 2) Both formations were inhibited by parathyroidectomy (PTX) or thyro-parathyroidectomy (TPTX), the inhibition being stronger in the appositional than in the longitudinal formation. The mechanism generating the characteristic responses (thin dentin and irregularity of dentin formation) which appeared after the operations was made clear. 3) All of the effects in 2) were reversed by the injection of PTH. However, the restoration in the appositional formation was faster in appearance and higher in rate than in the longitudinal formation. The results of 1) to 3) indicate that PTH has an anabolic effect on the hard tissues. 4) The sensitivity of the tissues to PTH varies according to their embryological origin.