CALCITONIN-POSITIVE AND SOMATOSTATIN-POSITIVE CELLS IN THYROID-GLAND OF PIGS AT DIFFERENT AGES

Immunohistochemical studies were carried out on calcitonin-, somatosta tin- and serotonin-reactive cells in newborn pigs and pigs at 3 weeks and 7 months old. The aim of these studies was to examine if the expre ssion of various bioactive substances by parafollicular cells in the p ig thyroid varied during development. The volume density of the follic ular epithelium was nearly the same in newborn and 3-week-old piglets and significantly lower in 7-month-old animals. The volume density of calcitonin-positive cells, expressed as a percentage of the follicular epithelium density, was similar in young animals, being 12.10% and 13 .03% in newborn and 3-week-old piglets, respectively. A small but sign ificant increase to 14.40% was seen in 7-month-old pigs. Somatostatin- positive cells formed a much smaller population at all time points, bu t these also showed a significant increase with age (0.13%, 0.17% and 0.52% of follicular epithelium density in newborn, 3-week- and 7-month -old pigs, respectively). However the changes in the volume density of somatostatin-positive cells correlated inversely with thyroid activit y, the density being highest when the activation index was lowest, sug gesting that thyroid activity may be regulated by an increase in the s ynthesis of this inhibitory peptide. Serotonin-positive cells were ext remely rare at all time points and their volume density was not calcul ated.