Pineal Structures and Functions in Mammalian Body Mechanisms Coping with Exogenous and Endogenous Changes

Various aspects of pineal structures and functions have been reviewed. mainly relating to our own observations and experiments. The pineal gland shows high amplitude circadian rhythms in cellular and metabolic activities. which are changeable under various circumstances. The pineal hormone appears to participate in the body's adaptive regulatory system mostly by cooperative and modulatory mechanisms. particularly in relation to environmental changes including stress/invasion. timing of physiological processes including reproductive activities. and possibly exogenous and endogenous pathological changes such as inflammatory disease and tumor. Pineal effects are variable due to the sensitivity/state of target mechanisms. For example. the pinealectomy effects on adreno-medullary adrenaline cells were more evident in comparison with the 'sham-pinealectomy' group than the normal group, and the pinealectomy effects on female reproductive activities were age-dependent. In any case, the pineal hormone retains physiological functions at least till middle age. Pineal actions are mainly inhibitory. but can be also stimulatory as shown in immune regulatory mechanisms. It has long been known that big differences in pineal structures and functions exist between mammals and submammals and that mammals show characteristic development of the brain, autonomic nervous system and unique style of reproduction including pregnancy and suckling. These and other related results seem to support a hypothetical view that the pineal hormone was involved in drastic reorganization of the regulatory system occurred in the evolutional process from submammals to mammals and became participated in the system which regulates complex body mechanisms in mammals