Ultrastructural and histochemical investigations of the development of the medullary part of the adrenal gland in domestic pig (Sus scrofa dom.) during the prenatal period.

The development of the adrenal medulla was investigated during the prenatal period in the pig. The observations were carried out on 221 embryos from 21 to 112 day post coitum. The histological, histochemical, ultrastructural and stereological methods were performed. First chromaffinoblasts infiltrated the adrenal cortex primordium around the 27-th day pc. They were mixed with cortical cells and just in the last days of pregnancy they were localized only in central part of adrenal. The chromaffinoblasts differentiated gradually from neuron-like cells to typical chromaffinocytes. A centripetal gradient of this differentiation was observed. All chromaffinoblasts contained the chromaffine granules. The size and numerical density of the chromaffin granules increased with development.