Membrane bounded dense bodies (MBB) of the domestic pig pinealocytes--current state of knowledge.

The results of our former investigations concerning the pig pinealocyte organelles named membrane bounded dense bodies (MBB) have been summarized. The presence of MBB is the most conspicuous morphological feature of pinealocytes of genus Suidae. The relative volume of MBB in the cell bodies of pinealocytes in adult domestic pigs ranges from 8% to 16% of whole cytoplasm. On the basis of their morphology, membrane bounded bodies were divided into two main types: MBB-1 and MBB-2. Dense bodies of MBB-1 type have various inner structure and are present both in perikaryons and processes of the pinealocytes. Dense bodies of MBB-2 type are characterised by regular, multilammellar structure and their presence is restricted to pinealocyte perikaryons. The origin and transformations of the MBB are enigmatic. The relative volume of dense bodies in the pig pinealocytes changes during postnatal development and under various physiological and experimental conditions. The system of dense bodies is controlled by sympathetic innervation and environmental light. Dense bodies are also influenced by changes in function of pituitary-gonadal axis in female pigs and by administration of melatonin. High number of the dense bodies in the pig pinealocytes, significant changes in their number and inner structure in various physiological and experimental conditions as well as their exocytosis from pinealocyte processes suggest that these structures are involved in secretory processes in the pig pinealocytes.