Endocrine Journal 1994, 41(5), 491-507 Review Recent Advances in Endothelin Research on Cardiovascular and Endocrine Systems MITSUHIDE NARUSE, KIYoxo NARUSE, AND HIR0SH1 DEMURA Department of Medicine, Institute of Clinical Endocrinology, TokyoWomen's Medical College, Tokyo162, Japan Introduction Structure of ET and ET Receptor Since the quite exciting discovery in 1988 of The molecular and biochemical aspects of ET endothelin (ET) in the culture medium of aortic en- family peptides and ET receptors have been re- dothelial cells by Yanagisawa and coworkers [1], viewed by Masaki and Yanagisawa [13] and others evidence has accumulated to support its important [14-16]. We here describe the fundamentals. roles in the regulation of blood pressure and body fluid homeostasis and its pathophysiological sig- 1. ET Peptides nificance in various cardiovascular diseases. The discovery of ET and the opponent substances in- The ET molecule consists of 21 amino acid resi- cluding nitric oxide [2] and natriuretic peptides [3] dues with two intramolecular disulfide bonds be- during the last decade was epoch-making in the tween cystein residues at 1 and 15 and 3 and 11, field of "Cardiovascular Endocrinology". respectively. The ring structure and the hydropho- Because of its impressive potency and the long bic amino acid residues at the C-terminus are in- duration of its pressor action [1], the roles of ET in dispensable to its full biological activities. There the regulation of cardiovascular homeostasis have are three distinct isof orms of ET: ET-1, ET-2, and been extensively studied. However, the co-expres- ET-3 [13]. The difference in the amino acid se- sion or close localization of ET and its receptors in quence is seen in the ring structure, while they various tissues other than the vascular vessels sug- share the same sequence in the linear C-terminal gest non-vascular roles of ET [4-6]. In the present portion. Interspecies differences are minimal [13- review, we firstly integrate the information rel- 16]. Interestingly, the amino acid sequence of a evant to its physiological role in blood pressure family of rare snake venoms, the sarafotoxins, is regulation and possible pathogenic role in hyper- very similar to the sequence of ET [16], composing tension. We secondarily focus on the possible the ET-sarafotoxin family and suggesting the im- roles of ET in the endocrine system, especially in portance of the peptide in evolution. the pituitary and adrenal. Substantial review ar- PreproET-1, the precursor of the peptide, is syn- ticles on ET in the kidney [7, 8], ET and the heart thesized through the gene transcription and trans- [9], the growth regulating properties of ET [10], lation. Expression of the preproET-1 mRNA in the and ET in bronchial diseases [11, 12] have been endothelial cells is stimulated by various humoral published. and physical factors: thrombin, TGF-f3, interleukin- 1, TNF-a, angiotensin II (Ang II), vasopressin, and shear stress (for review see [13-15]). Production of This review was written as a memorial article for the Re- ET-1 in the endothelial cells is mediated by an in- search Encouragement Prize of the Japan Endocrine Soci- ety awarded to the author on June 3, 1993. crease in [Ca2+]i and activation of protein kinase Correspondence to: Dr. Mitsuhide NARUSE, Department C. On the other hand, increased cGMP caused by of Medicine, Institute of Clinical Endocrinology, Tokyo natriuretic peptides and nitric oxide inhibits the Women's Medical College, 8-1 Kawada-cho, Shinjuku-ku, production of ET-1 [17-19], suggesting a close in- Tokyo 162, Japan terrelationship between the vasoconstrictive and 492 NARU5E et a1. vasodilatory systems. vascular smooth muscle cells predominantly ex- After deletion of the signal peptide, the pro-seg- press the ETA receptor, while there is also an ETB ment of the proET-1 is initially cleaved by an en- receptor [25, 26]. The vascular endothelial cells dopeptidase specific for a pair of dibasic amino ac- predominantly express ETB receptor. In addition, ids to produce an inactive 38-amino acid peptide, both receptors are expressed in various tissues in- big-ET-1, which is finally cleaved into the mature cluding lung, heart, brain, kidney and adrenal form, ET-1, by a specific ET-converting enzyme. gland. The enzyme is a phosphoramidon-sensitive mem- The primary structures of the receptors deter- brane-bound metalloprotease [20]. Both big ET-1 mined from the sequences of the cDNA clones in- and ET-1 are secreted into the culture medium. dicate that both receptors are single chain peptides The immunocytochemical demonstration of ET-1 containing seven stretches of hydrophobic amino in cytoplasmic vesicles suggests a constitutive acid residues. The homology of the amino acid pathway for the secretion of ET-1 [21]. sequence of ETA and ETB is about 60%. The se- Northern blot analysis demonstrated that quence of the transmembrane region is very simi- mRNAs corresponding to the three distinct ETs are lar for each receptor, while that of the N-terminal expressed in different proportions in non-vascular extracellular domain shows practically no homol- tissues as well as vascular tissues where ET-1 is ogy. Both receptors have two N-linked predominantly produced. In addition, the exist- glycosilation sites in the N-terminal domain, and ence of ET was also shown by immunoassay in a serine/threonine residues in the intracellular third variety of tissues other than the vascular endothe- loop and C-terminus. The third type of receptor lium [22]. The ET-1 content is the highest in the more specific to ET-3 has been predicted but is still posterior pituitary and the lung followed by the unidentified. anterior pituitary, brain, and adrenal gland. The The distribution of the ET determined from pep- ET-3 content is highest in the posterior and ante- tide content and mRNA expression is very similar rior pituitaries. The ET-1 content is significantly to that of the ET receptor determined by the bind- higher than that of ET-3 in all the tissues except for ing study and the expression of mRNA [4-6]. the anterior pituitary (Fig. 1). These findings suggest that ET acts mainly in a paracrine/autocrine fashion rather than in a classi- 2. ET Receptors cal endocrine fashion. There are at least two subtypes of ET receptors: ETA receptor with a higher affinity for ET-1 and Biological Actions ET-2 than for ET-3 and ETs receptor with an equivalent affinity for all three ETs [23, 24]. The The three ETs show somewhat different biologi- cal activities in relation to the affinity to and the distribution of each receptor subtype; ET-1 and ET- 2 are more potent than ET-3 in pressor response, while ET-3 is relatively more potent in vasodila- tion. In addition to the vasoconstrictive actions, ETs have diverse biological actions on the cardio- vascular, neural, renal, endocrine, metabolic, gas- trointestinal, and genitourinary systems (Table 1), but the physiological significance of these effects remains to be elucidated. ET elicits the biological actions by activating phospholipase C to produce inositol triphosphate and diacylglycerol which in turn activates protein kinase C, and by increasing the influx of calcium Fig. 1. Tissue content of immunoreactive ET-1 and ET-3 in ion via activation of the calcium channel. These rats. Note ubiquitous but tissue-specific distribution two major mechanisms are closely interrelated to of ETs. each other. The ET-stimulated intracellular signal REVIEW: RECENT PROGRESS IN ENDOTHELIN RESEARCH 493 Table 1. Diverse b iological actions of ET transduction mechanism is detailed in other re- The acute administration of ET-1 to rats view articles [13-15]. produces a transient decrease in blood pressure followed by a strong and long-lasting increase in blood pressure [1]. The first depressor effect is ET in the Cardiovascular System attributed to the release of vasodilator substances including prostacyclin and endothelium-derived The anatomically close site of production to the nitric oxide through the ETB receptor on the vascular smooth muscle cells and the potent vaso- endothelial cells, while the latter pressor effect is constrictive property indicate the potential impor- through the ETA receptor on the vascular smooth tance of ETs in the regulation of cardiovascular ho- muscle cells. The ETB receptor on the vascular meostasis and their pathophysiological signifi- smooth muscle cells was recently shown to cance in various cardiovascular diseases, especially contribute also to vasoconstriction [25, 26]. in hypertension. In addition to the direct action on the vascular smooth muscle cells, ET-1 has non-vascular actions 1. Significanceof ETs in SystemicHypertension which might affect blood pressure: central activation of the sympathetic nervous system [27], 1) Essential Hypertension secretion of vasopressin [28], aldosterone [29] and 494 NARUSE et al. catecholamine [30], positive isotropic and normotensive rats with antiserum to ET-1 does not chronotropic actions [31], and a decrease in the affect the blood pressure, providing evidence glomerular filtration rate and renal blood flow (for against the physiological role of ET-1 in regulating review see [6]). ET-1 potentiates the actions of vascular tone in a steady state condition [36]. Even other vasoconstrictive substances such as an increase in blood pressure in rats with the ET-1 norepinephrine and serotonin [32]. In addition, gene knocked out by gene targeting techniques is ET-1 promotes a proliferation of vascular smooth in agreement with this concept [37]. This is quite muscle cells and fibroblasts (for review see [9]), in contrast to the case of nitric oxide which plays which may result in the morphological changes in an important role in the maintenance of basal vas- the vascular wall. All these direct and indirect cular tone [38, 39].