Thrombin stimulates release of endothelin and vasopressin, but not substance P, from isolated rabbit tracheal epithelial cells

Increased Endothelin-1 Mrna Expression in Peripheral Blood Monocytes of Dialysis Patients

Objective

To compare plasma endothelin (ET)-1 level and ET-1 mRNA level in peripheral blood monocytes of patients undergoing hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD).

Design

Endothelin-1 mRNA level in peripheral blood monocytes and plasma ET -1 level were studied in 30 HD patients, 15 CAPD patients, 20 chronic renal failure patients not being dialyzed, and 20 normal healthy controls. Hemodialysis patients were dialyzed three times per week with a bicarbonate dialysate. Different types of dialyzer membrane, viz., cellulose triacetate, cuprophane, poly-sulfone, polyacrylonitrile, and ethylenevinylalcohol were used in 8,6,6,5, and 5 patients, respectively. Continuous ambulatory peritoneal dialysis patients were dialyzed with four daily exchanges of a 2-L dialysate containing glucose at a concentration of 1.5% to 2.5%.

Results

Higher levels of ET -1 mRNA in monocytes were observed in HD patients than in CAPD patients (p < 0.01), chronic renal failure patients (p < 0.01), or normal healthy controls (p < 0.001). The level of ET -1 mRNA in monocytes at the end of HD was not significantly higher than that at the start of HD. ln addition, these mRNA levels in HD patients showed littledifference with different types of dialysis membrane. Plasma ET -1 level in HD patients (10.2 ± 2.4 pg/mL) was also higher than that in CAPD patients (7.8 ± 1.6 pg/mL, p < 0.01), in chronic renal failure patients (4.8 ± 1.2 pg/mL, p < 0.01), or in normal controls (2.6 ± 0.8 pg/mL, p < 0.001).

Conclusion

Dialysis itself did not significantly affect ET -1 mRNA levels in monocytes. Chronic stimulation of peripheral blood monocytes may be associated with higher levels of ET -1 mRNA and plasma ET -1 in HD patients than in CAPD patients.

Anatomical and functional evidence for a role of arginine-vasopressin (AVP) in rat olfactory epithelium cells

The olfactory epithelium (OE) is composed of olfactory sensory neurons (OSNs) and sustentacular cells; it lies in the nasal cavity where it is protected by a thin mucus layer. The finely regulated composition of this mucus provides OSN with a suitable ionic environment. To maintain the functional integrity of the epithelium despite permanent physical, chemical and microbial aggressions, both OSNs and surrounding sustentacular cells are continuously renewed from globose basal cells. Moreover, the sense of smell is involved in so numerous behaviours (feeding, reproduction, etc.) that it has to cross-talk with the endocrine and neuroendocrine systems. Thus, besides its sensory function, the olfactory epithelium is thought to undergo a lot of complex regulatory processes. We therefore studied the effects of various neuropeptides on primary cultures of Sprague-Dawley rat olfactory epithelium cells. We found that arginine-vasopressin (AVP) triggered a robust, dose-dependent calcium increase in these cells. The cell response was essentially ascribed to the V1a AVP receptor, whose presence was confirmed by RT-PCR and immunolabelling. In the culture, V1a but not V1b receptors were present, mainly localized in neurons. In the epithelium, both subtypes were found differentially distributed. V1a-R were localized mainly in globose basal cells and at the apical side of the epithelium, in the area of the dendritic knobs of OSNs. V1b-R were strongly associated with Bowman's gland cells and globose basal cells. These localizations suggested potential multifaceted roles of a hormone, AVP, in the olfactory epithelium.

Choroid plexus: target for polypeptides and site of their synthesis

Choroid plexus (CP) is an important target organ for polypeptides. The fenestrated phenotype of choroidal endothelium facilitates the penetration of blood-borne polypeptides across the capillary walls. Thus, both circulating and cerebrospinal fluid (CSF)-borne polypeptides can reach their receptors on choroidal epithelium. Several polypeptides have been demonstrated to regulate CSF formation by controlling blood flow to choroid plexus and/or the activity of ion transport in choroidal epithelium. However, many ligand-receptor interactions occurring in the CP are not involved in the regulation of fluid secretion. Increasing evidence suggests that the choroidal epithelium plays an important role in hormonal signaling via a receptor-mediated transport into the brain (e.g., leptin) and helps to clear certain CSF-borne polypeptides (e.g., soluble amyloid beta-protein). Thus, impaired choroidal transport or insufficient clearance of polypeptides may contribute to pathogenesis of systemic or central nervous system (CNS) disorders, such as obesity or Alzheimer's disease. CP epithelium is not only a target but is also a source of neuropeptides, growth factors, and cytokines in the CNS. These polypeptides following their release into the CSF may exert distal, endocrine-like effects on target cells in the brain due to bulk flow of this fluid. Distinct temporal patterns of choroidal expression of several polypeptides are observed during brain development and in various CNS disorders, including traumatic brain injury and ischemia. Therefore, it is proposed that the CP plays an integral role not only in normal brain functioning, but also in the recovery from the injury. This review attempts to critically analyze the available data to support the above hypothesis.

Endothelins and asthma

In the decade since endothelin-1 (ET-1) and related endogenous peptides were first identified as vascular endothelium-derived spasmogens, with potential pathophysiological roles in vascular diseases, there has been a significant accumulation of evidence pointing to mediator roles in obstructive respiratory diseases such as asthma. Critical pieces of evidence for this concept include the fact that ET-1 is an extremely potent spasmogen in human and animal airway smooth muscle and that it is synthesised in and released from the bronchial epithelium. Importantly, symptomatic asthma involves a marked enhancement of these processes, whereas asthmatics treated with anti-inflammatory glucocorticoids exhibit reductions in these previously elevated indices. Despite this profile, a causal link between ET-1 and asthma has not been definitively established. This review attempts to bring together some of the evidence suggesting the potential mediator roles for ET-1 in this disease.

Vasopressin gene expression in rat choroid plexus

Vasopressin (VP) levels in cerebrospinal fluid (CSF) change in response to physiological stimuli and under various pathological conditions. The sources of CSF VP have yet to be clarified, however. In the present study, we provide evidence indicating that VP is synthesized in the choroid plexus, the primary site of CSF formation. All experiments were performed on adult male Sprague-Dawley rats. The presence of VP mRNA in choroid plexus epithelium was demonstrated by in situ hybridization histochemistry using the 35S-labeled riboprobe that was complementary to cDNA fragment of rat VP encoding the C-terminus part of proVP. In situ hybridization findings were confirmed by reverse transcriptase-polymerase chain reaction analysis. Immunohistochemistry for VP-associated neurophysin (VP-NP), a polypeptide component of proVP, revealed subapical accumulation of VP-NP-immunopositive product in choroidal epithelial cells. Immunoprecipitation and immunoblotting of choroidal protein extracts with anti-VP-NP antibody demonstrated the presence of a approximately 10-kD polypeptide that was also detected in hypothalamus. We hypothesize that the choroid plexus-derived VP exerts autocrine and/or paracrine effects on tissues near the CSF system.

Vasopressin stimulates ciliary motility of rabbit tracheal epithelium: role of V1b receptor-mediated Ca2+ mobilization

Arginine vasopressin (AVP) has recently been shown to exist in and to be released from airway epithelial cells, but the physiologic role of this hormone in airway epithelial function is unknown. To determine whether AVP affects ciliary motility, and if so, to elucidate the mechanism of action and the subtype of AVP receptors involved, we measured ciliary beat frequency (CBF) and the intracellular Ca2+ concentration ([Ca2+]i) of cultured rabbit tracheal epithelium with a photoelectric method and the fura-2 fluorescence method, respectively. Addition of AVP caused a rapid increase in CBF, followed by a decline and a subsequent sustained response. The ciliary stimulatory action was dose dependent, the maximal peak increase from the baseline CBF being 20.6 +/- 4.7% (mean +/- SE, P < 0.001), and this effect was reduced to 5.9 +/- 2. 0% by the V1 receptor antagonist OPC-21268 (P < 0.01), but not by the V2 receptor antagonist OPC-31260. The AVP-induced increase in CBF was not altered by the protein kinase A (PKA) inhibitor Rp-adenosine-3',5'-cyclic monophosphorothioate triethylamine (Rp-cAMPS) or by Ca2+-free solution containing ethylene glycol-bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), but was abolished by pretreatment with thapsigargin. Exposure of cells to AVP elicited a transient increase in [Ca2+]i, an effect that was likewise abolished by thapsigargin. The rank-order potency of AVP analogues to increase [Ca2+]i was AVP = [deamino1, D-3-(pyridyl) Ala2-Arg8] vasopressin (DP-VP), a specific V1b receptor agonist > [Phe2, Ile3, Orn8] vasopressin (PO-VT), a V1a agonist > 1-desamino-8-D-arginine vasopressin (dDAVP), a V2 agonist. Moreover, OPC-21268 greatly attenuated the action of AVP, whereas OPC-31260 was without effect. These results suggest that AVP stimulates ciliary motility of rabbit tracheal epithelium through mobilization of Ca2+ from thapsigargin-sensitive stores, and that this effect may be mediated by V1b receptors.

The presence of arginine vasopressin and its mRNA in rat choroid plexus epithelium

Arginine vasopressin (AVP) plays an important role in the regulation of secretory function and hemodynamics of choroid plexus, the primary site of cerebrospinal fluid (CSF) production. In the present study, localization of AVP and its transcripts in choroid plexus of adult male Sprague-Dawley rats was studied by immunohistochemistry and in situ hybridization histochemistry, respectively. For immunohistochemical analysis, AVP-specific polyclonal rabbit antibody was employed. Plasmid, pGrVP, containing a 232-bp fragment of rat AVP cDNA encoding the C-terminus of proAVP, was used as a probe to detect AVP mRNA. AVP-immunoreactive product was predominantly localized close to the apical (CSF-facing) membrane of choroidal epithelium while AVP transcripts were distributed throughout the cytoplasm of the cells. Our findings indicate that AVP is synthesized in choroid plexus epithelium, which suggests autocrine and/or paracrine actions of this peptide in choroidal tissue.

Effects of endothelin on hemodynamics, prostaglandins, blood coagulation and renal function

The interaction of the endogenous vasoconstrictors endothelin (ET), angiotensin II (Ang II) and catecholamines with the kallikrein-kinin-, prostaglandin and renin-aldosterone systems in the pathogenesis of acute renal failure (ARF) is still to be defined. In 18 anesthesized pigs the influence of i.v. bolus applications of ET (2 micrograms/kg), Ang II (10 micrograms/kg) and norepinephrine (NE; 20 micrograms/kg) on hemodynamics, plasmatic coagulation and fibrinolysis system, prostaglandins and renal function was studied. ET induced a biphasic change in blood pressure, starting with an initial short-lasting reduction followed by a long-lasting elevation of systolic and diastolic blood pressure. Endothelin bolus resulted in a significant increase of 6-keto-PGF1 alpha, PGE2 and TXB2 plasma levels (P < 0.05 against preinjection values), whereas prostaglandins remained unchanged in the Ang II and NE groups. There was a distinct correlation between the plasma ET and 6-keto-PGF1 alpha levels (r = 0.82). In contrast to Ang II or NE, ET induced a shortening of the activated partial thromboplastin time (aPTT) and increase of antithrombin III levels (ATIII), fibrin monomers (FM), prekallikrein (PKK) and factor VIII activity at the beginning. Finally a pronounced decrease of ATIII, FM and PKK occurred, indicating a consumptive coagulopathy. At the end of the experiment, elevated plasma renin activity and pCO2, significantly decreased creatinine clearance, blood pH, pO2, base excess, HCO3-, oxygen saturation (P < 0.01), a distinct glomerular proteinuria, and a final anuria were observated. These results reveal that ET activates the plasmatic coagulation system and induces an ARF accompanied by impairment of pulmonary function.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombin, phorbol ester, and cAMP regulate thrombin receptor protein and mRNA expression by different pathways

Human mesangial cells have been used to study the regulation of thrombin receptor protein and mRNA expression during cross-talk between different signal transduction pathways. Persistent activation of thrombin receptor by thrombin led to homologous down-regulation of thrombin receptor protein. However, thrombin receptor mRNA expression was not affected, suggesting that increased receptor degradation is responsible for homologous down-regulation. Chronic activation of protein kinase C by phorbol 12-myristate 13-acetate (PMA) and of adenylylcyclase by prostaglandin E1 (PGE1) resulted in heterologous down-regulation of thrombin receptor protein. In contrast to thrombin, PMA and PGE1 reduced in parallel thrombin receptor mRNA levels to 51% and 24% of control, respectively, indicating that heterologous down-regulation of thrombin receptor protein is, at least in part, due to inhibition of receptor mRNA expression. The mechanisms of heterologous down-regulation of thrombin receptor protein have been studied in detail and compared to homologous down-regulation. PMA-induced down-regulation was completely blocked by GF 109 203 X, an inhibitor of protein kinase C. However, the loss of thrombin receptor induced by thrombin was not prevented by GF 109 203 X, indicating that homologous regulation is not dependent on protein kinase C activation. The heterologous effect of PGE1 was mimicked by 8-bromo-cAMP, isobutylmethylxanthine, and forskolin, suggesting that an increase in intracellular cAMP level is involved in heterologous regulation. Interestingly, heterologous down-regulation induced by PGE1 seems not to require previous internalization of thrombin receptor. These data indicate that thrombin receptor protein and mRNA expression can be regulated in homologous and heterologous ways by different mechanisms.