Effects of orexins A and B on the secretory and proliferative activity of immature and regenerating rat adrenal glands L.K. Malendowicz1, N. Jedrzejczak1, A.S. Belloni2, M. Trejter1, A. Hochól1 and G.G. Nussdorfer2 1Department of Histology and Embryology, School of Medicine,
Poznan, Poland and Offprint requests to: Prof. G.G. Nussdorfer, Department of Human Anatomy and Physiology, Section of Anatomy, Via Gabelli 65, I-35121 Padova (Italy). Fax: (+39) 049-827-2319. e-mail: ggnanat@ipdunidx.unipd.it
Summary. Orexins A and B are two hypothalamic peptides, involved in the central regulation of feeding, which act through two receptor subtypes, named OX1R and OX2R. OX1R is selective for orexin-A, and OX2R binds both orexins. We have investigated the effects of three subcutaneous injections of 10 nmol/kg body weight of orexins on the secretion and proliferative activity of immature (20-day-old) and regenerating rat adrenal cortex. The presence of both OX1R and OX2R mRNAs has been detected by reverse transcription-polymerase chain reaction in adult, immature and regenerating adrenals. Orexin-A increased corticosterone plasma concentration in immature rats, but not in animals with regenerating adrenals. Both orexins raised metaphase index ( of metaphase-arrested cells) in immature rat adrenals, orexin-B being more effective than orexin-A. In contrast, both orexins equipotently lowered adrenal metaphase index at day 5 (but not day 8) of adrenal regeneration. We conclude that orexins (1) stimulate secretion and proliferative activity of immature rat adrenals, acting through OX1R and OX2R, respectively; and (2) do not affect secretion, but inhibit proliferative activity of regenerating adrenals, mainly via the activation of OX2R. Histol. Histopathol. 16, 713-717 (2001) Key words: Orexins, Orexin receptors, Steroid secretion,
Cell proliferation, Adrenal cortex, Adrenal regeneration |