Fetal development of regulatory mechanisms for body fluid homeostasis

Influence of gestational salt restriction in fetal growth and in development of diseases in adulthood

Recent studies reported the critical role of the intrauterine environment of a fetus in growth or the development of disease in adulthood. In this article we discussed the implications of salt restriction in growth of a fetus and the development of growth-related disease in adulthood. Salt restriction causes retardation of fatal growth or intrauterine death thereby leading to low birth weight or decreased birth rate. Such retardation of growth along with the upregulation of the renin angiotensin system due to salt restriction results in the underdevelopment of cardiovascular organs or decreases the number of the nephron in the kidney and is responsible for onset of hypertension in adulthood. In addition, gestational salt restriction is associated with salt craving after weaning. Moreover, salt restriction is associated with a decrease in insulin sensitivity. A series of alterations in metabolism due to salt restriction are probably mediated by the upregulation of the renin angiotensin system and an epigenetic mechanism including proinflammatory substances or histone methylation. Part of the metabolic disease in adulthood may be programmed through such epigenetic changes. The modification of gene in a fetus may be switched on through environment factors or life style after birth. The benefits of salt restriction have been assumed thus far; however, more precise investigation is required of its influence on the health of fetuses and the onset of various diseases in adulthood.

Upper gastrointestinal motility: prenatal development and problems in infancy

Deglutition, or swallowing, refers to the process of propulsion of a food bolus from the mouth into the stomach and involves the highly coordinated interplay of swallowing and breathing. At 34 weeks gestational age most neonates are capable of successful oral feeding if born at this time; however, the maturation of respiration is still in progress at this stage. Infants can experience congenital and developmental pharyngeal and/or gastrointestinal motility disorders, which might manifest clinically as gastro-oesophageal reflux (GER) symptoms, feeding difficulties and/or refusal, choking episodes and airway changes secondary to micro or overt aspiration. These problems might lead to impaired nutritional intake and failure to thrive. These gastrointestinal motility disorders are mostly classified according to the phase of swallowing in which they occur, that is, the oral preparatory, oral, pharyngeal and oesophageal phases. GER is a common phenomenon in infancy and is referred to as GERD when it causes troublesome complications. GER is predominantly caused by transient relaxation of the lower oesophageal sphincter. In oesophageal atresia, oesophageal motility disorders develop in almost all patients after surgery; however, a congenital origin of disordered motility has also been proposed. This Review highlights the prenatal development of upper gastrointestinal motility and describes the most common motility disorders that occur in early infancy.

Ovine fetal hormonal and hypothalamic neuroendocrine responses to maternal water deprivation at late gestation

Angiotensin II (Ang II), aldosterone, and arginine-vasopressin (AVP) are three major neuropeptides or hormones that are important in the control of body fluid regulation. Dehydration during pregnancy induces alterations in maternal-fetal fluid homeostasis. It is still not clear about effects and mechanisms of maternal water deprivation on fetal neuroendocrine and hormonal responses. The present study deprived water from pregnant sheep at near-term for 24 h and 48 h, and determined maternal and fetal blood osmolality and sodium levels before and immediately after water deprivation. Fetal renal excretion and plasma hormones were measured. Fetal forebrain was analyzed for cellular activation marked with Fos and Fos-B. The results showed that maternal and fetal blood osmolality and sodium were increased by water deprivation. Maternal and fetal Ang II, aldosterone, and AVP levels were elevated by 24-h and 48-h water deprivation, while fetal plasma Ang I levels were increased only under the condition of 48-h water deprivation. Intensive Fos and Fos-B expression was detected in the median preoptic nuclei and paraventricular nuclei in the fetal brain following exposure to maternal water deprivation. Double labeling demonstrated that many Fos-positive cells were AVP-containing neurons in the fetal paraventricular nucleus. Together, the results suggest that neuroendocrine and hormonal regulatory mechanisms play a role in the control of body fluid homeostasis, and relatively matured and functional at the last third of gestation, as well as the fetal hypothalamus is functional in the control of the neuropeptide in response to maternal dehydration.