Estradiol potentiates hypothalamic vasopressin and oxytocin neuron activation and hormonal secretion induced by hypovolemic shock

Abstract

-Estrogen receptors are located in important brain areas that integrate cardiovascular and hydroelectrolytic responses, including the subfornical organ (SFO) and supraoptic (SON) and paraventricular (PVN) nuclei. The aim of this study was to evaluate the influence of estradiol on cardiovascular and neuroendocrine changes induced by hemorrhagic shock in ovariectomized rats. Female Wistar rats (220 -280 g) were ovariectomized and treated for 7 days with vehicle or estradiol cypionate (EC, 10 or 40 g/kg, sc). On the 8th day, animals were subjected to hemorrhage (1.5 ml/100 g for 1 min). Hemorrhage induced acute hypotension and bradycardia in the ovariectomized-oil group, but EC treatment inhibited these responses. We observed increases in plasma angiotensin II concentrations and decreases in plasma atrial natriuretic peptide levels after hemorrhage; EC treatment produced no effects on these responses. There were also increases in plasma vasopressin (AVP), oxytocin (OT), and prolactin levels after the induction of hemorrhage in all groups, and these responses were potentiated by EC administration. SFO neurons and parvocellular and magnocellular AVP and OT neurons in the PVN and SON were activated by hemorrhagic shock. EC treatment enhanced the activation of SFO neurons and AVP and OT magnocellular neurons in the PVN and SON and AVP neurons in the medial parvocellular region of the PVN. These results suggest that estradiol modulates the cardiovascular responses induced by hemorrhage, and this effect is likely mediated by an enhancement of AVP and OT neuron activity in the SON and PVN.hemorrhage; female rats; supraoptic nuclei; paraventricular nuclei; arterial pressure; heart rate THE PRECISE REGULATION OF body fluids is essential for the metabolic function of virtually all cells in the body. A variety of mechanisms are activated to maintain plasma osmolality and blood volume within a very narrow range of values (3). For example, hypovolemia and/or hypotension induce vasopressin (AVP) and oxytocin (OT) release from the magnocellular neurons of the supraoptic (SON) and paraventricular (PVN) nuclei in the hypothalamus (3, 56). It is estimated that a decrease of 10 -20% in total blood volume induces the release of AVP in several species. This neurosecretory response is modulated by peripheral baroreceptors in the aortic arch and carotid sinus, cardiopulmonary volume receptors, and angiotensin II (ANG II) (50, 65).The precise role of estrogen in maintaining body fluid homeostasis is not yet fully understood (16). Our group has previously reported that ANG II type 1 (AT 1 ) receptors are involved in the regulation of water and hypertonic saline intake in ovariectomized (OVX) rats during the nocturnal period (37, 38). In addition, several reports have suggested that estrogen has modulatory effects on cardiovascular function, as evidenced by the cardiovascular changes observed in postmenopausal women, OVX rats, and, possibly, females of other species during senescence (12, 46). These effects occur by estrogen's action on the...

Annual Research Review: The neurobiology and physiology of resilience and adaptation across the life course

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