Neuroendocrine Control of Body Fluid Metabolism

Abstract

Mammals control the volume and osmolality of their body fluids from stimuli that arise from both the intracellular and extracellular fluid compartments. These stimuli are sensed by two kinds of receptors: osmoreceptor-Na+ receptors and volume or pressure receptors. This information is conveyed to specific areas of the central nervous system responsible for an integrated response, which depends on the integrity of the anteroventral region of the third ventricle, e.g., organum vasculosum of the lamina terminalis, median preoptic nucleus, and subfornical organ. The hypothalamo-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin and oxytocin in response to osmotic and nonosmotic stimuli. Since the discovery of the atrial natriuretic peptide (ANP), a large number of publications have demonstrated that this peptide provides a potent defense mechanism against volume overload in mammals, including humans. ANP is mostly localized in the heart, but ANP and its receptor are also found in hypothalamic and brain stem areas involved in body fluid volume and blood pressure regulation. Blood volume expansion acts not only directly on the heart, by stretch of atrial myocytes to increase the release of ANP, but also on the brain ANPergic neurons through afferent inputs from baroreceptors. Angiotensin II also plays an important role in the regulation of body fluids, being a potent inducer of thirst and, in general, antagonizes the actions of ANP. This review emphasizes the role played by brain ANP and its interaction with neurohypophysial hormones in the control of body fluid homeostasis.

Corpus Callosal Abnormalities in Dogs

“…Vertebrates maintain plasma osmolality and extracellular volume primarily by regulating the ingestion and urinary excretion of water and electrolytes. An increase in the plasma osmolality, and consequent cellular dehydration, is the most potent stimulus of thirst 18. In the genesis of thirst, there is an important role for osmoreceptor‐Na + receptor cells located in the circumventricular organs of the anterior aspect of the third ventricle.…”

“…These structures contain sensory cells that respond to variations in the plasma osmotic pressure or the sodium concentration of plasma and cerebral spinal fluid 19. Lesions of the anteroventral third ventricle (AV3V), which includes 2 of the circumventricular organs, the median preoptic nucleus and the organum vasculosum lamina terminalis, induce permanent or temporary adipsia 18. Besides the AV3V, other midline structures such as the subfornical organ, medial septal area, anterior lateral hypothalamus, paraventricular nucleus, and the stria medullaris are also involved in the regulation of water/sodium intake and excretion18 and may be affected in these cohort of patients.…”

Chronic excitotoxic lesion of the dorsal raphe nucleus induces sodium appetite

“…The organum vasculosum laminae terminalis, median preoptic nucleus and subfornical organ (SFO), structures participating in hydroelectrolytic and cardiovascular homeostasis, receive input from serotonergic neurons of the dorsal raphe nucleus (DRN) (1)(2)(3)(4)(5)(6). There is a reciprocal connection linking DRN and SFO (7)(8)(9) which suggests that the DRN participates in cardiovascular as well as in extracellular fluid (ECF) volume and electrolyte homeostasis.…”

Selective Gene Expression in Magnocellular Neurons in Rat Supraoptic Nucleus

“…The hypothalamo-neurohypophysial system is the major neuroendocrine system through which the brain maintains body fluid homeostasis (Robertson, 1995;Antunes-Rodrigues et al, 2004). The axons of the vasopressin (VP)-and oxytocin (OT)-synthesizing magnocellular neurons (MCNs) located in the supraoptic and paraventricular hypothalamic nuclei of the hypothalamus terminate on the capillaries of the posterior pituitary, into which the peptides are secreted (Brownstein et al, 1980;Sladek, 1999).…”