Immunoreactive Endothelin-1 in the Neural Lobe of the Rat Pituitary following Hemorrhage and Dehydration.

Abstract

Abstract. Previously we found intragranular colocalization of immunoreactive endothelin-1 and neurohypophysial hormones in the axon terminals of the rat neural lobe. To investigate the function of endothelin-1 in the rat neural lobe, immunoreactive endothelin-1 in plasma and the neural lobe was measured by enzyme immunoassay in rats subjected to hemorrhage and in other rats who were deprived of water for 2 days to induce dehydration. Changes in plasma arginine vasopressin were determined by radioimmunoassay.In addition, morphometric analysis was performed in the neural lobe of rats exposed to these stresses. Plasma concentrations of immunoreactive endothelin-1 were unchanged following hemorrhage or dehydration, whereas those of immunoreactive vasopressin were remarkably increased. In the neural lobe, immunoreactive endothelin-1 content and the number of neurosecretory granules decreased significantly after dehydration.However, immunoreactive endothelin-1 in tissue increased nearly three-fold in hemorrhaged rats, whereas the endothelin-1-immunolabeling in the axon terminals was unchanged. These results suggest that endothelin-1 in the hypothalamo-hypophysial system may be involved in the local modulation of vasopressin secretion when an animal is exposed to hypovolemic and/or osmotic stress.

Regulation of Blood Pressure and Salt Homeostasis by Endothelin

“…This has led to speculation as to whether mature ET-1 is involved in hypothalamic neurotransmission and Big ET-1 is released from the nerve terminals. Neural lobe ET immunoreactivity decreases with water deprivation (864), although plasma concentrations of ET-1 remain unchanged despite clear elevations in circulating AVP (788). In contrast, during hemorrhage, which is a powerful stimulus for AVP release, ET-1 immunoreactivity increased up to threefold in hypothalamic tissue, but remained unchanged in the axon terminals (788).…”

“…Neural lobe ET immunoreactivity decreases with water deprivation (864), although plasma concentrations of ET-1 remain unchanged despite clear elevations in circulating AVP (788). In contrast, during hemorrhage, which is a powerful stimulus for AVP release, ET-1 immunoreactivity increased up to threefold in hypothalamic tissue, but remained unchanged in the axon terminals (788). Although these findings suggest that the ET system itself is modulated under conditions of osmotic and/or hypovolemic stress when BP is threatened, this has not been further explored.…”

Response of Substances Co-Expressed in Hypothalamic Magnocellular Neurons to Osmotic Challenges in Normal and Brattleboro Rats

“…Plasma concentration of immunoreactive ET-1 is unchanged following hemorrhage or dehydration, whereas immunoreactive AVP is remarkably increased. It suggests that ET-1 in the hypothalamo-hypophysial system may be involved in the local modulation of vasopressin secretion during hypovolemic and/or osmotic stress challenges (Uemura et al 1994).…”

Localization of endothelin A receptors in the rat pituitary TSH cells: light- and electron-microscopic immunohistochemical studies

“…Endothelins have been reported to induce thyroid-stimulating hormone (TSH), lutenizing hormone (LH), follicle-stimulating hormone (FSH) and adrenocorticotropic hormone (ACTH), but to inhibit prolactin release in vitro (Samson et al 1990; Kanyicska et al 1991;Samson 1992;Kanyicska and Freeman 1993;Calogero et al 1994;Zheng et al 1995;Stojilkovic and Catt 1996;Kanyicska et al 1998). Moreover, ET immunoreactivity has been detected not only in the neural lobe (Nakamura et al 1993;Uemura et al 1994), but in the gonadotrophs (Naruse et al 1992;Suzuki et al 1997). Endothelins in the pituitary are considered as modulators of secretory responses, or autocrine and/or paracrine hormones (Kanyicska et al 1998).…”