Acciones óseas de las hormonas de la neurohipófisis / Bone actions of neuro hypophyseal hormones

La oxitocina (OXT) como la arginina-vasopresina (AVP) son dos hormonas primitivas secretadas por la hipófisis posterior. Sus receptores están mucho más ampliamente distribuidos en el organismo de lo que se pensaba originalmente, incluido el hueso. En los estudios preclínicos, la OXT ha mostrado ser anabólica para el hueso, promoviendo la osteogénesis sobre la adipogénesis y favoreciendo la actividad osteoblástica sobre la osteoclástica. Tanto los osteoblastos como los osteoclastos tienen receptores para la OXT, y los efectos de los estrógenos sobre la masa ósea en ratones está mediada por lo menos en parte por la OXT. El mecanismo preciso por el cual la activación de los receptores de oxitocina (OXTR) se traduce en un incremento de la formación ósea permanece poco claro. La AVP también podría afectar el esqueleto en forma directa. Dos de los receptores de la AVP, V1a y V2 están expresados en osteoblastos y osteoclastos. La inyección de AVP en ratones de tipo salvaje aumenta la formación osteoclastos que producen resorción y reduce los osteoblastos formadores de hueso. En forma opuesta, la exposición de precursores osteoblásticos a antagonistas de los receptores V1a o V2, incrementan la osteoblastogénesis, como también lo hace la deleción genética del receptor V1a. (AU)

Both oxytocin (OXT) and argininevasopressin (AVP) are primitive hormones secreted by the posterior pituitary gland. OXT receptors are much more widely distributed in the body than originally thought, including in bone. In preclinical studies, OXT has been shown to be anabolic for bone, promoting osteogenesis over adipogenesis and favoring osteoblastic over osteoclastic activity. Both osteoblasts and osteoclasts have receptors for OXT, and the effects of estrogen on bone mass in mice is mediated at least in part by OXT. The precise mechanism by which the activation of oxytocin receptors (OXTRs) results in an increase in bone formation remains unclear. AVP could also have direct actions on the skeleton. The two AVP receptors, V1a and V2, are expressed in osteoblasts and osteoclasts. Injection of AVP in wild-type mice increases the formation of osteoclasts increasing bone resorption, and reduces bone-forming osteoblasts. On the contrary, the exposure of osteoblastic precursors to V1a and V2 antagonists increase osteoblastogenesis, the same as the genetic deletion of the V1a receptor. (AU)

Diabetes insipidus nefrogênico: conceitos atuais de fisiopatologia e aspectos clínicos / Nephrogenic diabetes insipidus: actual concepts of fisiopathology and clinical aspects

O diabetes insipidus nefrogênico (DIN) é uma doença rara caracterizada pela incapacidade do rim de concentrar a urina, a despeito de concentrações normais ou aumentadas do hormônio antidiurético arginina-vasopressina (AVP). Recentes avanços da fisiopatologia renal mostraram que, após a ligação do AVP ao seu receptor AVPR2 (receptor de vasopressina tipo 2), uma cascata de eventos culmina com a reabsorção de água no túbulo coletor, por meio de canais permeáveis exclusivamente à água e localizados nas membranas apicais do túbulo coletor, sendo o mais importante deles a aquaporina-2 (AQP2). A identificação, caracterização e análise mutacional dos genes AVPR2 e AQP2 permitiram estabelecer as bases moleculares de vários tipos hereditários de diabetes insipidus nefrogênico. Aproximadamente 90 por cento desses pacientes apresentam mutações do AVPR2, 8 por cento apresentam mutações no AQP2 e o restante não tem causas identificadas. Nessa revisão apresentamos exemplos de alterações genéticas e sugerimos que o uso de técnicas de biologia molecular pode minimizar as complicações dessa doença heterogênea mas com fenótipo bastante semelhante.

Vasopressin and bradykinin receptors in the kidney: implications for tubular function

Vasopressin and bradykinin are two of the most important peptides in regulating vascular tone, water, and ionic balance in the body, adn thus they play a key role in controlling blood pressure. In addition to being a potent vasoconstrictor, Vasopressin also has an antidiuretic activity in the kidney, whereas kinins regulate renal blood flow in addition to their vasodilatory and natriuretic activity. We review here the primary evidence for the localization of the vasopressin and kinin receptors and their role in ionic and water regulation in the kidney.

Stress and water balance: the roles of ANP, AVP and isatin.

Stress is often associated with water retention and its resolution with diuresis. The biological systems for the control of stress and water balance are very closely related. Corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) are co-localised in the hypothalamus and often act synergistically. Atrial natriuretic peptide (ANP) can exert a feedback control on the hypothalamic/pituitary/adrenal axis. ANP has been shown to be anxiolytic, whereas AVP may be anxiogenic. AVP and ANP levels have been found to be abnormal in a range of stress disorders and psychiatric illnesses. Isatin is an endogenous anxiogenic factor which is also a potent inhibitor of the ANP receptor. It may provide a link between the function of monoamines during stress, and the control of water balance by ANP.

Arginine vasopressin as a neurotransmitter in brain.

Arginine vasopressin (AVP) which exerts diverse biological effects in mammals is no more restricted to the posterior pituitary. Neurons containing AVP are seen in many other areas and in CNS vasopressinergic neurons are identified from the neocortex to the spinal cord. With the characterization of three different types of vasopressin receptor subtypes V1a, V1b and V2 responsible for its actions, their cloning and identification in different areas--especially in the brain many more hitherto unknown functions of AVP in brain has come to light. Added to this is the recently available specific vasopressin receptor antagonists. At present AVP seems to be involved in memory retrieval, learning, circadian time keeping, modulating the actions of area postrema and many other functions in brain. In the suprachiasmatic nuclei (SCN)--the biological clock--an area of the brain where the role of VP is still not very clear, VP is found to participate not only in transmitting the circadian rhythms to the rest of the brain but also serves the function of synchronizing and amplifying the pacemaker output of SCN. AVP can act not only as a neurotransmitter but also can stimulate the production of chemicals/neurotransmitters and thereby act as a mediator. It may be concluded that there is a central vasopressinergic system which participates in a variety of physiological and behavioral functions of brain.