Effects of Synthetic Salmon Calcitonin on C Cells of the Thyroid

The effects of long term administration of synthetic salmon calcitonin (TZ-CT) on thyroid C cells of rats were evaluated immunohistochemically and electron microscopically. Low dose (0.075, 0.75 and 7.5 IU/kg/day) administration caused no significant changes in the C cell population, whereas high doses (30 and 120 IU kg day) caused C cell suppression. The area ratio of C cells to total cells in the thyroid was measured on sections immunoperoxidase stained for calcitonin. The average C cell ratio was compared among the experimental groups. This mor-phometric analysis of the high-dose and control groups confirmed the differences in C cell populations statistically (30 IU/kg vs. control, pgO.05; 120 IU/kg vs. control, p ≦ 0.05). The suppressive effect of TZ CT on C cells was reversible after cessation of administration for one month. Electron microscopic examination on the C cells in the high dose groups revealed no particular ultrastructural differences. These results may suggest a negative feedback mechanism on C cells by exogenous CT. Acta Pathol Jpn 39: 545-550, 1989.