The renal endothelin system in the Prague hypertensive rat, a new model of spontaneous hypertension

Abstract

In a new model of spontaneous hypertension, namely the Prague hypertensive rat (PHR), hypertension is transferred with a kidney transplanted from the PHR to its normotensive counterpart (PNR) by an as yet unknown mechanism. One candidate may be endothelin (ET), since this potent vasoconstrictor affects vascular tone, renal haemodynamics and renal excretory function, and all members of this peptide family are located within the kidney and act in an autocrine/paracrine fashion. In the present study we investigated, in the renal tissue of PHRs and PNRs: (1) preproET-1 and preproET-3 mRNAs as well as ET-1 and ET-3 peptide distribution, (2) endothelin-converting enzyme (ECE)-1 mRNA expression, and (3) ET receptors and their characteristics in membranes of glomeruli and papillae. In addition, plasma ET concentration and urinary ET excretion were determined. Quantitative measurements by competitive reverse transcription-polymerase chain reaction revealed ET-1 mRNA levels in the renal cortex from PHRs and PNRs of 1.09+/-0.13 and 1. 29+/-0.18 amol/microgram of total RNA respectively, and in red medulla of 2.72+/-0.82 and 3.30+/-0.68 amol/microgram respectively. In contrast, renal papilla from PHRs showed significantly lower levels of preproET-1 mRNA (1.81+/-0.64 amol/microgram of total RNA, compared with 4.25+/-0.82 amol/microgram in PNRs; each n=5; P<0.05). The ET-1 peptide concentration in papillary tissue was also significantly lower in PHRs than in PNRs (120.2+/-30.8 and 491.3+/-53.4 fmol/mg of protein respectively; n=5; P<0.01), whereas it was similar in cortex and medulla from PHRs and PNRs. The preproET-3 mRNA content in renal tissue was much lower than that of preproET-1 mRNA. It was significantly higher in red medulla from PHRs compared with that from PNRs (0.25+/-0.05 and 0.13+/-0.02 amol/microgram of total RNA respectively; P<0.05), but was similar in papillae of PHRs and PNRs (0.04+/-0.02 and 0.05+/-0.01 amol/microgram respectively; n=5). Cortical preproET-3 mRNA was at the lower limit of detection. Similarly, the ET-3 peptide concentration was slightly but significantly higher in the red medulla of PHRs compared with PNRs (15.4+/-2.0 and 8.8+/-0.8 fmol/mg of protein respectively; n=5; P<0. 05), whereas no differences in ET-3 peptide concentration were found in papillae from PHRs and PNRs. ECE-1 mRNA levels were similar in the renal cortex, red medulla and papillae from PHRs and PNRs, ranging between 0.34+/-0.03 and 0.56+/-0.12 amol/microgram of total RNA. Of the total ET receptors in glomerular membranes, 39% were ETA receptors, whereas papillary membranes contained exclusively ETB receptors. PHRs and PNRs showed similar Bmax and Kd values for ET-1 in renal glomerular membranes (Bmax, 6.5+/-1.3 and 4.9+/-1.2 pmol/mg of protein respectively; Kd, 0.69+/-0.10 and 0.56+/-0.10 nM respectively) and papillary membranes (Bmax, 9.7+/-1.1 and 11.3+/-1. 6 pmol/mg of protein respectively; Kd, 0.30+/-0.04 and 0.42+/-0.07 nM respectively). Plasma ET-1/2 concentrations (10.4+/-1.3 and 12. 2+/-1.2 fmol/ml in PHRs and PNRs re...

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats

“…More important, however, is the finding that the ET-1 content in the renal papilla of our spontaneously hypertensive rats was significantly lower than that of their WKY counterparts. These data confirm our previous observation of significantly lower levels of ET-1 peptide and of preproET-1 mRNA expression in the renal papilla of genetically hypertensive rats [Prague hypertensive (Wistar) rats] than in renal papillary tissue of their normotensive controls (Prague normotensive rats) [17]. As in this previous study the present study again failed to demonstrate a difference in ET-1 content in renal cortical tissue between spontaneously hypertensive rats and WKY rats.…”

“…With respect to an interaction between the renal ET system and renal nerves our findings show for the first time that BRD decreases papillary ET concentration in WKY but not in spontaneously hypertensive rats, whose tissue ET concentration is already low as we reported earlier [17] and as was confirmed in the present study. In support of these changes in papillary ET-1 content, we found parallel changes in urinary ET-1 excretion, which thus probably reflects tissue ET-1 synthesis.…”

“…Several studies have provided evidence that implicates locally produced ET-1 in the renal medulla and papilla in the development of hypertension [17,18]. In the present study we found high ET-1 concentrations in the renal papilla as compared to renal cortical tissue in both normotensive (WKY) and hypertensive rats.…”

“…In six rats of each group, plasma and urine as well as tissue concentrations of ET-1 were determined by enzymelinked immunosorbent assay (ELISA) (Endothelin-1 ELISASystem) (Amersham Buchler, Braunschweig, Germany) as previously described [17]. For ET-1 determination in renal cortex and papilla, tissues were homogenized on ice at 4 • C in distilled water containing 100 kallikrein-inhibitory units/mL of aprotinin using a 2 mL glass homogenizer (Kontes, Vineland).…”

Diabetes‐induced overexpression of endothelin‐1 and endothelin receptors in the rat renal cortex is mediated via poly(ADP‐ribose) polymerase activation

“…It is noteworthy, however, that the values of tissue ET-1 reported to date vary considerably. Our renal ET-1 values are in the range of those reported by four other groups (52)(53)(54)(55) who employed different techniques, that is, radioimmunoassay (RIA) or reverse-phase HPLC coupled to RIA. Increased gene expression of both ET(A) and ET(B) receptors in the renal cortex of rats with one-month diabetes in our study is consistent with another study in the rat model (51), as well as increased ET (A) receptor binding in rabbits with short-term diabetes compared with controls (56).…”