Local renin–angiotensin system in the pineal gland

Abstract

Besides the classical endocrine renin–angiotensin system (RAS), a local RAS has been described also in the brain. We attempted to clarify the existence of a local RAS in the pineal gland. Through the use of a ribonuclease protection assay, it proved possible to detect the mRNA for angiotensinogen (AOGEN), for the angiotensin receptor type 1A (AT 1a) and 1B (AT 1b) and for the angiotensin-converting enzyme (ACE) in pineal glands from rats. Renin mRNA, however, could not be found by this method. By in situ hybridization and immunocytochemistry, AOGEN mRNA was co-localized with the astrocyte marker glial fibrillary acidic protein. AT 1b mRNA expression exceeded the expression of AT 1a mRNA and was co-localized with the pinealocyte-specific tryptophan hydroxylase. Thus, in the mammalian pineal gland there is a local formation of the components of the RAS. The presence of angiotensin II receptors further substantiates a role for angiotensins and the pineal RAS in the physiology of this gland.