Effect of renin-angiotensin system blockade on the expression of the angiotensinogen gene and induction of hypertrophy in rat kidney proximal tubular cells

Studies have shown that high levels of glucose and angiotensin II (Ang II) stimulate hypertrophy and the expression of matrix protein genes in mouse proximal tubular cells in vitro. The present study tested the hypothesis that blockade of the renin-angiotensin system (RAS) inhibits the stimulatory effect of high levels of glucose on the expression of the renal angiotensinogen (ANG) gene and the formation of Ang II and subsequently attenuates the induction of hypertrophy in kidney proximal tubular cells. Immortalized rat proximal tubular cells (IRPTC) were cultured in monolayer. The levels of expression of rat ANG and ANG mRNA in the IRPTC were quantified by specific radioimmunoassays for rat ANG (RIA-rANG) and by a reverse-transcription polymerase chain reaction (RT-PCR) assay, respectively. Hypertrophy of IRPTC was analyzed by flow cytometry (FACScan) and cellular protein assay. Our studies showed that losartan (an Ang II (AT(1))-receptor blocker), perindopril and captopril (inhibitors of angiotensin-converting enzyme) blocked the stimulatory effect of a high level of glucose (i.e. 25 mM) on the expression of the rat ANG gene and hypertrophy in IRPTC but not by the Ang II (AT(2))-receptor blocker. Our studies indicate that the blockade of RAS is effective in inhibiting the stimulatory effect of hyperglycemia on the expression of the ANG gene and hypertrophy in IRPTC, supporting the notion that the local formation of intrarenal Ang II may play a role in the development of renal hypertrophy during early diabetes.

Catecholamines and angiotensinogen gene expression in kidney proximal tubular cells

To investigate the molecular mechanism(s) of action of catecholamines on the expression of the angiotensinogen (ANG) gene in kidney proximal tubular cells, we used opossum kidney (OK) cells with a fusion gene containing the 5'-flanking regulatory sequence of the rat ANG gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (rANG N-1498/+18), permanently integrated into their genomes. The level of expression of the ANG-GH fusion gene was quantified by the amount of immunoreactive-hGH (IR-hGH) secreted into the medium. The addition of norepinephrine (NE), isoproterenol (a beta1/beta2-adrenergic receptor (AR) agonist) and iodoclonidine (an alpha2-AR agonist) stimulated the expression of the ANG-GH fusion gene in a dose-dependent manner, whereas the addition of epinephrine and phenylephrine (alpha1-AR agonist) had no effect. The stimulatory effect of NE was blocked by the presence of propranolol (beta-AR blocker), atenolol (beta1-AR blocker), yohimbine (alpha2-AR blocker), Rp-cAMP (an inhibitor of cAMP-dependent protein kinase AI & AII) and staurosporine (an inhibitor of protein kinase C), but was not blocked by ICI 118, 551 (beta2-AR blocker) and prazosin (alpha1-AR blocker). The addition of a combination of isoproterenol and iodoclonidine or a combination of 8-Bromo-cAMP (8-Br-cAMP) and phorbol 12-myristate (PMA) synergistically stimulated the expression of the ANG-GH fusion gene as compared to the addition of isoproterenol, iodoclonidine, 8-Br-cAMP or PMA alone. Furthermore, the addition of NE, 8-Br-cAMP or PMA stimulated the expression of pOGH (rANG N-806/-779/-53/+18), a fusion gene containing the putative cAMP responsive element (CRE, ANG N-806/-779) upstream of the ANG promoter (ANG N-53/+18) in OK cells, but had no effect on the expression of fusion genes containing the mutant of the CRE. Gel mobility shift assays revealed that the ANG-CRE binds with the DNA-binding domain (bZIP254-327) of the cAMP-responsive binding protein (CREB). The binding of the labeled ANG-CRE to CREB (bZIP254-327) was displaced by unlabeled ANG-CRE and the CRE of the somatostatin gene but not by the mutants of the ANG-CRE. Finally, NE stimulated the phosphorylation of CREB in OK cells. These studies demonstrate that the molecular mechanism(s) of NE action on the expression of the ANG gene in OK cells may be mediated via both the PKA and PKC signalling pathways and via the phosphorylation of CREB. The phosphorylated CREB then interacts with the CRE in the 5'-flanking region of the ANG gene and subsequently stimulates the gene expression.

Dopaminergic receptors and angiotensinogen gene expression in opossum kidney cells

To investigate whether expression of the renal angiotensinogen gene is regulated by dopaminergic receptors, we used opossum kidney (OK 27) cells with a fusion gene containing the 5'- flanking regulatory sequence of the rat angiotensinogen gene fused with a human growth hormone (hGH) gene as a reporter [pOGH, angiotensinogen nucleotide (N) -1498/+18], permanently integrated into their genomes. The level of expression of pOGH (angiotensinogen N-1498/+18) in OK 27 was evaluated by the amount of immunoreactive hGH (ir-hGH) secreted into the culture medium. In the absence of 3-isobutyl-1-methylxanthine (IBMX), addition of dopamine (10(-13) to 10(-5)M) had minimal effect on the expression of the pOGH (angiotensinogen N-1498/+18) in OK 27 cells. In the presence of IBMX, addition of low concentrations (10(-13) and 10(-7) M) of dopamine stimulated the expression of pOGH angiotensinogen N-1498/+18) in OK 27 cells in a dose-dependent manner, whereas high concentrations (i.e., > 10(-7) M) had minimal effect. The stimulatory effect of dopamine on the expression of pOGH (angiotensinogen N-1498/+18) was inhibited by the presence of SCH-23390 (D1-dopaminergic receptor antagonist) and spiperone (D2-dopaminergic receptor antagonist), but not by ketanserin (5 HT2/5HT1c-serotonergic receptor antagonist). Moreover, the stimulatory effect of dopamine was inhibited by the presence of U-73122 (an inhibitor of phospholipase C and phospholipase A2) or staurosporine (an inhibitor of protein kinase C) or (R)-p-adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMP[S]; an inhibitor of cAMP-dependent protein kinase AI and II). Addition of low concentrations (10(-13) to 10(-9)M) of SKF-82958 (D1-dopaminergic receptor agonist) or PPHT (D2-dopaminergic receptor agonist) also stimulated the expression of pOGH (angiotensinogen N-1498/+18). The stimulatory effect of SKF-82958 was inhibited by the presence of SCH-23390 or Rp-cAMP[S], whereas the effect of PPHT was inhibited by the presence of spiperone or staurosporine. These studies demonstrate that the expression of pOGH (angiotensinogen N-1498/+18) in OK 27 cells is modulated by dopaminergic receptor agonists.

beta-Adrenoceptors and dexamethasone synergistically stimulate the expression of the angiotensinogen gene in opossum kidney cells

We transiently co-transfected opossom kidney (OK) cells with the plasmid containing the cDNA for beta 1-adrenoceptor (pBC-beta 1 AR) or beta 2-adrenoceptor (pBC-beta 2 AR) and a fusion gene with the 5'-flanking region of the angiotensinogen (ANG) gene linked to a bacterial chloramphenicol acetyl transferase (CAT) coding sequence as a reporter, pOCAT (ANG N-1498/ +18). Co-transfection of plasmid pBC-beta 1 AR or pBC-beta 2 AR alone enhanced the expression of pOCAT (ANG N-1498/+18). The addition of isoproterenol further stimulated the expression of pOCAT (ANG N-1498/ +18) when co-transfected with pBC-beta 1AR, but not with pBC-beta 2AR. Moreover, the addition of a combination of dexamethasone and isoproterenol synergistically stimulated the expression of pOCAT (ANG N-1498/+18) when co-transfected with pBC-beta 1AR, but not when cotransfected with pBC-beta 2AR. The synergistic effect of dexamethasone and isoproterenol was inhibited by the presence of RU 486 (an antagonist of glucocorticoid) or Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A I and II). To localize the putative cAMP-responsive element (CRE) and glucocorticoid responsive element (GRE) in the ANG gene, we constructed the fusion gene by inserting the DNA fragment, ANG N-806 to N-465 upstream of the thymidine kinase (TK) promoter fused to a CAT gene and introduced them with pBC-beta 1AR into OK cells. The addition of dexamethasone or isoproterenol alone stimulated the expression of pTKCAT (ANG N-806/-465). The addition of isoproterenol and dexamethasone synergistically stimulated the transcriptional activity of pTKCAT (N-806/-465). These studies demonstrate that the beta 1-adrenoceptor and dexamethasone act synergistically to stimulate the expression of the ANG gene in OK cells via the putative CRE and GREs in the 5'-flanking region of the rat ANG gene. These data should aid in the understanding of the molecular mechanism(s) of the stimulatory effect of catecholamines/glucocorticoid induced expression of the ANG gene in the kidney.

Alpha-adrenoceptors and angiotensinogen gene expression in opossum kidney cells

To investigate whether alpha (alpha)-adrenoceptor agonists have a stimulatory effect on the expression of the angiotensinogen (Ang) gene in opossum kidney (OK) cells, we used OK 27 cells with a fusion gene containing the 5'-flanking regulatory sequence of the rat angiotensinogen gene fused with a human growth hormone (hGH) gene as a reporter, pOGH (Ang N-1498/+18), permanently integrated into their genomes. The level of expression of the pOGH (Ang N-1498/+18) was quantitated by the amount of immunoreactive-human growth hormone (IR-hGH) secreted into the medium. The addition of iodoclonidine (alpha 2-adrenoceptor agonist, 10(-13) to 10(-9) M) and phorbol 12-myristate 13-acetate (PMA, 10(-13) to 10(-5) M) stimulated the expression of pOGH (Ang N-1498/+18) in a dose-dependent manner, whereas the addition of phenylephrine (alpha 1-adrenoceptor agonist, 10(-13) to 10(-5) M) had no effect. The stimulatory effect of iodoclonidine was blocked by the presence of yohimbine (alpha 2-adrenoceptor antagonist) and staurosporine (an inhibitor of protein kinase C) but not blocked by the presence of prazosin (alpha 1-adrenoceptor antagonist) or Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A). The addition of iodoclonidine, phenylephrine or PMA had no effect on the expression of pTKGH in OK 13 cells, an OK cell line, into which had been stably integrated a fusion gene, pTKGH containing the promoter/enhancer DNA sequence of the viral thymidine-kinase (TK) gene fused with a human growth hormone gene as a reporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the angiotensinogen gene is synergistically stimulated by 8-BrcAMP and Dex in opossum kidney cells

We transiently transfected fusion genes with the 5'-flanking region of the angiotensinogen gene linked to a bacterial chloramphenicol acetyltransferase (CAT) coding sequence as a reporter into opossum kidney (OK) cells. The addition of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) (10(-3)-10(-7) M) or forskolin (10(-9)-10(-5) M) stimulated the expression of the plasmid pOCAT [angiotensinogen nucleotide (N) -1498/+18] fusion gene in OK cells in a dose-dependent manner. The addition of dexamethasone (Dex) (10(-6) M) further enhanced the stimulatory effect of 8-BrcAMP or forskolin, whereas the addition of (R)-p-adenosine 3',5'-cyclic monophosphorothioate [(Rp)-cAMP[S], an inhibitor of cAMP-dependent protein kinase A, I and II] blocked the stimulatory effect of 8-BrcAMP. Furthermore, the addition of 8-BrcAMP (10(-3) M) or Dex (10(-6) M) or a combination of both stimulated the expression of pOCAT (angiotensinogen N -1138/+18), pOCAT (angiotensinogen N -960/+18), pOCAT (angiotensinogen N -814/+18), and pOCAT (angiotensinogen N -688/+18), but had no effect on the expression of pOCAT (angiotensinogen N -280/+18), pOCAT (angiotensinogen N -198/+18), pOCAT (angiotensinogen N -110/+18), pOCAT (angiotensinogen N -53/+18), and pOCAT (angiotensinogen N -35/+18). To further localize the putative cAMP-responsive element (CRE) in the angiotensinogen gene, we constructed fusion genes by inserting the DNA fragments angiotensinogen N -814 to N -689, angiotensinogen N -814 to N -761, and angiotensinogen N -760 to N -689 of the 5'-flanking region of the angiotensinogen gene upstream of the thymidine kinase (TK) promoter fused to a CAT gene and introduced them into OK cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic receptors and angiotensinogen gene expression in mouse hepatoma cells in vitro

We have previously reported that addition of 8-bromocyclic AMP enhances the stimulatory effect of dexamethasone on the expression of the angiotensinogen gene in mouse hepatoma cells in vitro. Isoproterenol is known to stimulate the synthesis of hepatic intracellular cyclic AMP via beta-adrenergic receptors. To study the possible effect of beta-adrenergic receptors on the expression of the angiotensinogen gene in mouse hepatoma cells, we transiently transfected them with a fusion gene with the 5'-flanking region of the angiotensinogen gene linked to a bacterial chloramphenicol acetyltransferase coding sequence as a reporter, pOCAT (ANG N-1498/+18). The addition of isoproterenol (10(-9) to 10(-5) mol/L) alone had no stimulatory effect on the expression of pOCAT (ANG N-1498/+18). In the presence of dexamethasone (10(-6) mol/L), however, isoproterenol enhanced the stimulatory effect on the dexamethasone on the expression of pOCAT (ANG N-1498/+18). The enhancing effect of isoproterenol was inhibited by the presence of propranolol (beta 1- and beta 2-adrenergic receptor antagonist) and ICI 118,551 (beta 2-adrenergic receptor antagonist) but not by the presence of atenolol (beta 1-adrenergic receptor antagonist). Furthermore, the addition of Rp-cAMP (an inhibitor of protein kinase A I and II) blocked the enhancing effect of isoproterenol. These studies demonstrated that isoproterenol enhances the stimulatory effect of dexamethasone on the expression of the angiotensinogen gene in mouse hepatoma cells via beta 2-adrenergic receptor and cyclic AMP-dependent protein kinase pathways. Our data may be important in understanding the molecular mechanism(s) of the stimulatory effect of catecholamines/glucocorticoid-induced expression of the angiotensinogen gene in the liver.

Isoproterenol and 8-bromo-cyclic adenosine monophosphate stimulate the expression of the angiotensinogen gene in opossum kidney cells

To investigate whether the expression of the renal angiotensinogen (ANG) gene is regulated by beta-adrenoceptors and the cAMP-dependent protein kinase A pathway, we introduced stably the fusion gene containing the 5'-flanking regulatory sequence of the ANG gene with a human growth hormone (hGH) gene as a reporter, pOGH (ANG N-1498/+18), into opossum kidney (OK) cells. We successfully obtained several stable transformants with a high expression of the pOGH (ANG N-1498/+18) fusion gene. One stable transformant (OK 27) that is able to maintain the expression of pOGH (ANG N-1498/+18) in culture for more than a year was used in the present study. The level of expression of the pOGH (ANG N-1498/+18) in OK 27 was evaluated by the amount of immunoreactive-hGH (IR-hGH) secreted into the culture medium. The addition of isoproterenol (10(-11) M to 10(-9) M) stimulated the expression of pOGH (ANG N-1498/+18) and increased the accumulation of intracellular cAMP. Higher concentrations of isoproterenol (that is, greater than 10(-9) M) had low or minimal effect. In contrast, the addition of 8-bromo-cAMP (8-Br-cAMP) and forskolin stimulated the expression of pOGH (ANG N-1498/+18) in a dose-dependent manner. The stimulatory effect of isoproterenol was blocked by the presence of propranolol, atenolol and ICI 118,551. The addition of ICI 118,551, however, was less effective than atenolol. Furthermore, the stimulatory effect of isoproterenol and 8-Br-cAMP on the expression of the pOGH (ANG N-1498/+18) was inhibited by the presence of Rp-cAMP (an inhibitor of cAMP-dependent protein kinase A I and II).(ABSTRACT TRUNCATED AT 250 WORDS)

ACMC: past, present and future

In this article, the president of the Association of Canadian Medical Colleges (ACMC) and its director of research review the issues that have confronted ACMC since its inception: the founding of ACMC; development of the clinical teaching unit; creation of the Medical Research Council and expansion of the research mission; the Royal Commission on Health Services and the founding of new faculties of medicine; ACMC's in-house research program; accreditation and ACMC's links with medical education in the United States; and French-language medical education in Canada. The review points out the perennial nature of many of these issues, and how often perceived solutions to the problems later become problems themselves. It ends on the optimistic note that ACMC can successfully meet the challenges of the future.

Hormonal regulation of expression of the angiotensinogen gene in cultured mouse hepatoma cells

To investigate the hormonal regulation of expression of the angiotensinogen (ANG) gene in the liver, we constructed fusion genes with various lengths of the 5'-flanking region of the rat ANG gene linked to a bacterial chloramphenicol acetyl transferase (CAT) gene as reporter and introduced them into mouse hepatoma cells (Hepa 1-6). As a negative control, we introduced them into a nonhepatic cell line, a mouse testicular Sertoli (TM4) cell line. The level of expression of ANG-CAT fusion genes, pOCAT (ANG N-1498/+18), pOCAT (ANG N-688/+18), pOCAT (ANG N-110/+18), pOCAT (ANG N-53/+18) and (ANG-35/+18) were 3.7, 4, 1.1, 4, and 3-fold higher than promoterless pOCAT in Hepa 1-6 cells. No significant expression of any of these ANG-CAT fusion genes over the promoterless pOCAT was observed in Sertoli TM4 cells. The addition of dexamethasone (10(-10) to 10(-4) mol/L) stimulated the expression of the pOCAT (ANG N-1498/+18) fusion gene in Hepa 1-6 cells in a dose-dependent manner with a maximum stimulation at 10(-4) mol/L and a half-maximal stimulation at 10(-8) mol/L. A combination of dexamethasone (10(-6) mol/L) and 8-bromo-cyclic AMP (cAMP) (10(-3) mol/L) further enhanced the effect of the dexamethasone alone although cAMP alone had no effect. Testosterone (10(-6) mol/L), estradiol (10(-6) mol/L), progesterone (10(-6) mol/L), and thyroid hormone (L-T3, 10(-6) mol/L) did not have this effect in either the presence or absence of cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of expression of the angiotensinogen gene in cultured opossum kidney proximal tubular cells

Angiotensinogen (ANG) messenger RNA is expressed in cultured opossum kidney (OK) proximal tubular cells. The aim of these studies was to investigate whether steroid hormones (dexamethasone, estradiol, testosterone, and progesterone) could stimulate the expression of renal ANG gene in vitro. Fusion genes consisting of various lengths of the 5'-flanking region of the rat ANG gene linked to a chloramphenicol acetyl transferase (CAT) reporter gene were constructed and introduced into cultured OK cells. The level of expression of fusion genes was determined by the level of cellular CAT enzymatic activity. The addition of dexamethasone (10(-12) to 10(-6) M) stimulates the expression of the pOCAT (ANG N-1498/+18) fusion gene in OK cells in a dose-dependent manner with a maximum stimulation at 10(-6) M and a half-maximal stimulation at 10(-9) M. Combination of dexamethasone (10(-6) M) and thyroid hormone, L-T3 (10(-6) M), further enhanced the effect of the dexamethasone alone. Testosterone (10(-6) M), estradiol (10(-6) M), and progesterone (10(-6) M) did not have this effect. Moreover, dexamethasone also stimulates the expression of the pOCAT (ANG N-688/+18) but not pOCAT (ANG N-110/+18), pOCAT (ANG N-53/+18) and pOCAT (ANG N-35/+18). These studies demonstrate that the glucocorticoid hormone is effective at stimulating the transcription of the ANG gene in OK cells, but stimulation is not observed from testosterone, estradiol, or progesterone. Moreover, glucocorticoid and L-T3 act synergistically to stimulate the transcription of the ANG gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormone, L-T3, stimulates the expression of the angiotensinogen gene in cultured opossum kidney (OK) cells

Angiotensinogen (ANG) messenger RNA is expressed in opossum kidney (OK) proximal tubular cells. To examine whether thyroid hormone, L-T3, could stimulate the expression of the ANG gene in OK proximal tubular cells, fusion genes, consisting of various lengths of the 5'-flanking region of the rat angiotensinogen gene linked to a human growth hormone reporter gene, were constructed and introduced into OK cells. As a negative control, they were introduced into a nonkidney cell line, a human choriocarcinoma cell line (JEG-3). The level of the expression of fusion genes in these cells were determined by the level of immunoreactive human growth hormone secreted into the culture medium. The expression of ANG-growth hormone (ANG-GH) fusion genes pOGH (ANG N-1498/+18), pOGH (ANG N-688/+18), pOGH (ANG N-110/+18), pOGH (ANG N-53/+18), and pOGH (ANG N-35/+18) was 226-, 4.5-, 1.0-, 12-, and 2.5-fold higher than promoterless pOGH in the expression of growth hormone activity in OK cells. No significant expression of any of these ANG-GH fusion genes over the promoterless pOGH was observed in JEG-3 cells. The addition of L-T3 stimulates the expression of pOGH (ANG N-1498/+18) in a dose-dependent manner with a maximal and half-maximal effect at 10(-7) M and at 10(-8) to 10(-9) M, respectively. Thyroid hormone (10(-7) M) also stimulates the expression of pOGH (ANG N-688/+18) but not pOGH (ANG N-110/+18), pOGH (ANG N-53/+18), or pOGH (ANG N-35/+18).(ABSTRACT TRUNCATED AT 250 WORDS)

Future prospects and strategies for academic medicine in Quebec

Complete reorganization of the Quebec health and social services system, as envisaged by a new bill to be studied by the provincial government, is of major importance for the future of academic medicine since it includes all aspects of the training of health care professionals. While the bill aims to stimulate fundamental and applied research to the highest standards of academic medicine, its clearly stated spending limitations are a major concern to academic physicians. With the proposed centralization of all health care institutions, the role of medical schools and universities will be significantly diminished. Scientific programs of international standing and high levels of teaching and training of medical students and residents, on the other hand, can only be achieved with the development of appropriate structures. Effective prioritization, planning and representation of academic institutions must therefore be given as much consideration as the equally important functions of health care, teaching, and research. Programs oriented toward personnel support and the development of research centres and institutes should continue to be fostered. The future of academic medicine, particularly in its clinical components, is closely linked to the health care system. Academic physicians must become involved in the strategic planning of health care delivery since the development of academic medicine will otherwise not flourish.

Molecular cloning and expression of the rat angiotensinogen gene

To identify tissue- and hormonal-specific DNA control cis-elements in the rat gene, we have constructed fusion genes consisting of various lengths of the 5'-flanking region of the rat angiotensinogen gene linked to a human growth hormone (hGH) reporter gene and have introduced them into a subclone of rat pancreatic islet tumor cell line (1056A) which expresses the highest level of angiotensinogen mRNA. As a negative control, we have also introduced them into a human choriocarcinoma cell line (JEG-3), which does not express the endogenous angiotensinogen gene. The level of the expression of these fusion genes in these cells was determined by the level of immunoreactive hGH secreted into the culture medium. The expression of angiotensinogen-growth hormone (ANG-GH) fusion genes, pOGH (ANG N-1498/+18), pOGH (ANG N-688/+18), pOGH (ANG N-110/+18), pOGH (ANG N-53/+18), and pOGH (ANG N-35/+18) was 1.0, 1.8, 1.5, 12.0 and 3.0-fold higher, respectively, than the promoterless growth hormone expression vector (pOGH). The addition of dexamethasone (10(-6) M), aldosterone (10(-5) M), and thyroid hormone, L-T3 (10(-7) M), stimulated the expression of pOGH (ANG N-1498/+18) by 4.0-, 2.5-, and 2.0-fold above the control level, respectively. Combination of dexamethasone (10(-6) M), L-T3 (10(-7) M), and ethinyl-estradiol (10(-6) M) stimulated the expression of the pOGH (ANG N-1498/+18) to greater than 10-fold over the control. Ethinyl-estradiol (10(-6) M) or progesterone (10(-6) M) alone had no effect on the expression of the pOGH (ANG N-1498/+18).(ABSTRACT TRUNCATED AT 250 WORDS)

The kidney in essential hypertension: culprit or victim?

Clinical and experimental data clearly demonstrate that, at least in some forms of hypertension, removal of the kidney and its replacement by a non-hypertensinogenic organ may counteract the development of this disease. Although their specific involvement has yet to be determined, a number of vasoactive and sodium-retaining systems originating from the kidney are important in blood pressure control and play a key role in essential hypertension. Even if the triggering mechanisms do not lie within this organ, the kidney is at least an essential link for the expression of essential hypertension.

Catecholamine sulfates: end products or metabolic intermediates?

Dopamine-beta-hydroxylase catalyzes the beta-oxidation of dopamine to noradrenaline while phenylethanolamine-N-methyltransferase converts noradrenaline to adrenaline. Since catecholamine sulfates represent the predominant form of catecholamines in human tissues, we have studied the role of dopamine sulfate and noradrenaline sulfate as alternate substrates for dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, respectively. Dopamine 3-sulfate, dopamine 4-sulfate and noradrenaline 3-sulfate were chemically synthesized and exhaustively purified by ion-exchange chromatography. Dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase were partially purified from human adrenals. Using tyramine as substrate, dopamine-beta-hydroxylase is slightly inhibited by dopamine 3-sulfate according to some irreversible or mixed mechanisms. When dopamine-beta-hydroxylase was incubated with dopamine 3-sulfate or dopamine 4-sulfate, we were not able to find any synthesis of either noradrenaline sulfate or free noradrenaline. Using phenylethanolamine as substrate, the enzymatic activity of phenylethanolamine-N-methyltransferase remains unchanged with addition of dopamine 3-sulfate, dopamine 4-sulfate or noradrenaline 3-sulfate. It was concluded that dopamine sulfate is not an alternate substrate for either dopamine-beta-hydroxylase or phenylethanolamine-N-methyltransferase nor is noradrenaline 3-sulfate an alternate substrate for phenylethanolamine-N-methyltransferase.

The activity of human kidney arylsulfatases A and B towards catecholamine sulfates

Both arylsulfatases (EC 3.1.6.1, ARS) A and B purified from human kidney displayed Michaelis-Menten kinetics towards catecholamines sulfates as substrates with Km values in the range of 4-25 mM. ARS A hydrolyzed adrenaline 3-sulfate and noradrenaline 3-sulfate with a maximal rate lower than that observed for cerebroside 3-sulfate. In contrast, ARS B hydrolyzed adrenaline 3-sulfate and noradrenaline 3-sulfate with a maximal rate similar to that observed for UDP-N-acetylgalactosamine 4-sulfate.

Is the platelet phenolsulfotransferase involved in the sulfoconjugation of plasma catecholamines?

Catecholamines are predominantly present in the sulfoconjugated forms in human plasma. Phenolsulfotransferase (EC 2.8.2.1), which catalyses the sulfation of phenolic compounds, is widely distributed in human tissues. In blood, a phenolsulfotransferase, more specific for catecholamine sulfation is found exclusively in platelets. Free and sulfoconjugated catecholamines were measured in plasma and platelets of healthy volunteers and compared with those present in patients with uremia or pheochromocytoma to determine the ability of platelet phenolsulfotransferase to sulfurylate plasma catecholamines. In patients with pheochromocytoma, the rise in free and sulfoconjugated plasma catecholamines is accompanied by a simultaneous rise of these molecules in platelets. In uremia, where the level of plasma catecholamines is normal, the rise in the sulfoconjugates is not accompanied by a concomitant increase in either free or sulfoconjugated catecholamines in platelets. Platelet phenolsulfotransferase activity remains unchanged in pheochromocytoma and uremia. These data indicate that the platelet phenolsulfotransferase is involved in the sulfation of the catecholamines present in platelets, but its contribution, if any, to the high level of sulfoconjugated catecholamines found in plasma is negligible. This assertion is confirmed by our observations in thrombocytopenic patients. Indeed, despite the very low number of platelets and the absence of plasma phenolsulfotransferase activity, thrombocytopenic patients have normal plasma levels of free and sulfoconjugated catecholamines.

Composition and physical properties of lipids from plasma membranes of dog kidney

Lipid composition, physical state of major phospholipid classes and transbilayer migration of phosphatidylcholine have been determined in plasma membranes of the dog kidney. The lipid composition of brush-border membranes markedly differs from that of antiluminal membranes with respect to: (a) the total phospholipid content; (b) the cholesterol to phospholipid ratio (C/P); (c) the distribution of the major phospholipid classes. Sphingomyelin present in large amounts in both luminal and antiluminal membranes extracts exhibits a transition of phase between 20 and 44 degrees C approximately. In the range of temperature studied (5-55 degrees C) no phase transitions were detected for the other phospholipid species. Our data suggest that: (1) at physiological temperature the higher C/P ratio of brush-border membranes is in large part responsible for their lower fluidity; (2) both the relatively low cholesterol and high sphingomyelin contents contribute to the thermotropic transitions observed in intact membranes. Finally transbilayer migration of phosphatidylcholine in brush-border membranes is a very slow process with a half time of 6.5 h at 37 degrees C which compares with that of other biological membranes.

Fluidity of brush border and basolateral membranes from human kidney cortex

The physical state of lipids in brush border and basolateral membrane vesicles prepared from normal human kidney cortex was investigated by fluorescence polarization and electron spin resonance. At physiologic temperature, lipids were significantly less ordered, i.e., more fluid, in basolateral than in brush border membranes. This difference was also observed using corresponding liposomes made from total lipid extracts. For both brush border and basolateral membranes, temperature-dependent experiments revealed the existence of a broad thermotropic transition extending approximately from 20 to 42 degrees C. These data are interpreted to indicate that plasma membranes from human kidney cortex function physiologically at the upper critical temperature of a transition that probably corresponds to a liquid crystalline-to-gel lipid phase separation.

Release of epinephrine during carotid artery occlusion following vagotomy in dogs

The blood pressure (BP), serum norepinephrine (NE), and epinephrine (E) responses to carotid artery occlusion (CAO) were examined in three different groups of anesthetized dogs. The response was first examined under control conditions in the three groups and then following vagotomy and adrenalectomy in the first group, following adrenalectomy and vagotomy in the second group, and following atropine administration and vagotomy in the third group. The results obtained in these three groups of dogs during the control period demonstrate that CAO produces significant increases in BP (from 144 ± 5 to 182 ± 8, 154 ± 7 to 202 ± 9, and 143 ± 3 to 185 ± 2 mmHg, respectively) (1 mmHg = 133.322 Pa) and in NE serum level (from 218 ± 36 to 337 ± 45, 215 ± 51 to 275 ± 46, and from 163 ± 23 to 247 ± 22 pg/mL, respectively), thus confirming previous studies. No rise in E serum level occurred in these three conditions (226 ± 100 vs. 275 ± 87, 280 ± 161 vs. 205 ± 88, and 183 ± 75 vs. 157 ± 46 pg/mL, respectively), as also previously reported. The first series of experiments demonstrated that following vagotomy, CAO induced a marked elevation of E serum levels from 275 ± 87 to 1145 ± 274 pg/mL (P < 0.005). These CAO-induced changes in E were abolished by previous (group 2) or subsequent (group 1) adrenalectomy which also attenuated BP and NE elevations, although these remained significant. By comparison with these changes, vagotomy only had a modest effect on BP and serum NE increase following CAO. These results demonstrate that vagal inhibition upon vasomotor tone was most important in controlling the adrenal release of catecholamines (CA), particularly E. In the third series of dogs atropine sulfate could not reproduce the BP, NE, and E changes observed after vagotomy, as the results were comparable to those observed under control conditions. Subsequent vagotomy produced results analogous to those observed in the first group of animals and confirmed that vagal afferent fibers are responsible for tonic inhibition of vasomotor centers.

Indapamide for out-patient treatment of hypertension: modifications in serum catecholamine levels

A study was carried out to evaluate the efficacy of indapamide in the treatment of 20 patients with mild hypertension and to determine whether a favourable response to treatment was related to initial hyperadrenergic status, to changes in serum catecholamine levels or modified by orthostatic stress. After 4 weeks on placebo, patients received 2.5 mg indapamide per day for 4 weeks and, if diastolic pressure was controlled below 100 mmHg, this regimen was continued for a further 8 weeks. Those not adequately controlled with indapamide alone were treated additionally with nadolol (mean dose 140 mg per day) for a period of 12 weeks. The results showed that indapamide alone produced a significant reduction in blood pressure both in the recumbent and upright position in 12 (60%) of the patients and that addition of the beta-blocker augmented the antihypertensive effect. No relationship was demonstrated between initial high serum catecholamine levels and a favourable response to indapamide. Recumbent serum norepinephrine levels after indapamide alone or with nadolol for 4 to 8 weeks remained comparable with placebo levels. However; the amplitude of the norepinephrine increase due to orthostatic stress was significantly reduced after 8 weeks of indapamide treatment. Possible explanations for this are discussed.

Cell volume regulation in the proximal convoluted tubule

To evaluate the effect of hyper- and hypotonicity on proximal convoluted tubule (PCT) cell volume, nonperfused PCT were studied in vitro with hypertonic solutions containing sodium chloride, urea, or mannitol (450 mosmol/kg H2O) and with hypotonic low sodium chloride solutions (160 mosmol/kg H2O). When the tubules were subjected to hypertonic peritubular solutions containing NaCl, cell volume immediately decreased by 15.5% and remained constant throughout the experimental period (60 min). With mannitol, the initial decrease was identical to that with NaCl (17.7%), but the PCT volume increased slightly during the experimental period. With urea, the decrease in cell volume was smaller (7%) and transient. In hypotonicity, the PCT swelled rapidly, but this swelling was followed by a rapid regulatory phase in which PCT volume nearly returned to control values after less than 10 min. With a potassium-free peritubular medium or 10(-3) M ouabain, the regulatory phase of hypotonicity completely disappeared, whereas the cells did not maintain their reduced volume in NaCl-induced hypertonicity. These results suggest that Na-K-ATPase plays an important role in the maintenance of a reduced cellular volume in hypertonicity and in the regulatory phase of hypotonicity, probably by an active extrusion of sodium and water from the cell.

Effect of maleate on membrane physical state of brush border and basolateral membranes of the dog kidney

The effects of maleate on the physical state of isolated brush border and basolateral membranes from dog kidney cortex have been studied by fluorescence polarization and ESR methods. Anisotropy of 1,6-diphenyl-1.3.5.-hexatriene and hyperfine splitting (2T parallel) of 5-doxylstearic acid in brush border and basolateral membranes were not significantly modified by the addition of 10(-2) M maleate after 60-90 min treatment. These findings further support the view that maleic acid nephropathy is not due to a direct effect of maleate on tubular membranes per se.

Membrane fluidity and enzyme activities in brush border and basolateral membranes of the dog kidney

The physical state of membrane lipids and relationships with the activity of Na+-K+-ATPase and alkaline phosphatase were studied in basolateral and brush border membranes of the dog kidney. Fluorescence polarization and electron spin resonance experiments demonstrate that basolateral membranes are much more fluid than brush border membranes. This can be accounted for by a difference in fluidity of the lipid part of the membranes. Broad (43-17 degrees C) thermotropic transitions are observed in liposomes made from total lipid extracts of brush border and basolateral membranes. Fluorescence data strongly suggest that thermotropic transitions also occur in intact membranes and that a change in membrane physical state may take place around the physiological temperature. A nonlinear Arrhenius plot for the Na+-K+-ATPase activity in basolateral membranes (breakpoint 21 degrees C) provides additional support for the existence of a lipid liquid leads to gel transition in antiluminal plasma membranes. A break in the Arrhenius plot of alkaline phosphatase activity is also observed but at a temperature significantly higher (26 degrees C) than that of the end of the thermotropic transition. "Room temperature" appears as a critical zone for lipid physical state and activities of both enzymes.

Catecholamine neurons of the central nervous system in organotypic culture

A standardized dissection has been designed to produce explants from the locus coeruleus of the newborn mouse brain. This area, termed the peduncular region, may be explanted with or without cerebellar neurons. Organotypic cultures with peduncular cells contain a cluster of 20-50 (or more) closely-packed large neurons, characterized by intracellular refractile granules in the living state. When treated with the glyoxylic acid method, somata of the granule-containing neurons exhibited catecholamine fluorescence, and a profuse plexus of varicose fluorescent fibers permeated the explant and its outgrowth. Intracellular staining of these cells with horseradish peroxidase demonstrated bipolar and multipolar neurons (25-30 micrometers), with stout dendrites and varicose axons. Granule-containing neurons stained for acetylcholinesterase. Electron microscopically, large dense granules were seen, which appear to correspond to the granules seen in living neurons. Cultures with these cells also have a high concentration of catecholamines in the medium. It is concluded that the granule-bearing neurons of the living culture are in fact neurons of the locus coeruleus.

Determination of free and conjugated catecholamines and L-3,4-dihydroxyphenylalanine in plasma and urine: evidence for a catechol-O-methyltransferase inhibitor in uraemia

A sensitive, accurate and reproducible method has been developed for the determination of free and conjugated catecholamines and L-3,4-dihydroxyphenylalanine in plasma and urine. The assay involves the enzymatic conversion of these compounds to their radio-labelled O-methylated derivatives using catechol-O-methyltransferase and S-adenosyl-L-[methyl-(3)H]methionine. Recoveries of 75 + /- 5% for dopamine, 70 + /- 5% for adrenaline and 65 + /- 5% for noradrenaline were obtained. The sensitivities were 0.5 pg for adrenaline and noradrenaline and 5-7 pg for dopamine, and dihydroxyphenylalanine. Measurements of conjugated catecholamines were performed after mild acid hydrolysis for 20 min at 95 degrees C. During this procedure no degradation of the catecholamines was observed. This assay led to the discovery of a dialyzable factor in the plasma of chronic uraemic patients which inhibits catechol-O-methyltransferase activity in vitro. The mean 22% inhibition observed for unhydrolyzed plasma increased to 42% after hydrolysis. The identity of this inhibitor which exists as an inactive conjugated form, probably a sulphate ester, and its implication in physiopathological disorders remain to be established.

Control of membrane lipids in Mycoplasma gallisepticum: effect on lipid order

Adaptation of Mycoplasma gallisepticum, a sterol-requiring Mycoplasma sp., to growth in a serum-free medium supplemented with cholesterol in decreasing concentrations and with various saturated or unsaturated fatty acids enabled us to control both the cholesterol levels and the membrane fatty acid composition. An estimate of the membrane physical state from fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the membrane lipids of native M. gallisepticum were highly ordered. Elongation of the saturated fatty acid chains from 14 to 18 carbon atoms caused only a small increase in the membrane lipid ordering, whereas the introduction of a cis double bond reduced it significantly. Lipid-phase transitions were observed in low-cholesterol-adapted organisms, whose membrane lipids were still highly ordered at the growth temperature.

Influence of sodium intake on catecholamine release by angiotensin and renal nerve stimulation in dogs

For 10 days, dogs were fed a normal salt diet containing 70 mequiv. Na+/day (NSD) followed by a high salt diet containing 170 mequiv. Na+/day (HSD) or 240 mequiv. Na+/day (VHSD), or the order was reversed. K+ in these diets was fixed at 40 mequiv./day. The different diets did not influence the basal level of serum catecholamines (CA). Intravenous angiotensin II (ATII) in subpressor doses produced, under NSD and HSD, an increase in serum CA accompanied by reductions in total renal blood flow as well as regional blood flow rates (microspheres), mostly in the deeper regions of the cortex. Under VHSD, ATII did not affect serum CA and barely decreased total renal blood flow, reducing regional blood flow rate in C3 and C4 only. The increase in renal vein serum CA produced by renal nerve stimulation was potentiated by ATII but under constant plasma levels of the latter, progressive increments of Na+ in the diet markedly exaggerated the liberation of CA following renal nerve stimulation and the hemodynamic response of the kidney. We conclude that the Na+ content in the diet markedly influences the increase in serum CA after renal nerve stimulation and greatly influences the response of that organ to renal nerve stimulation.

Carotid sinus reflex and norepinephrine release following acute volume depletion in dogs

Norepinephrine (NE) release and pressor response to sympathetic stimulation were studied in dogs under furosemide-induced acute volume depletion. The rise in blood pressure observed following carotid clamping proved similar before and after acute salt and water depletion in the first group of animals and NE rose comparably in these two conditions. Similar results were obtained in a second group of dogs that received an angiotensin II converting enzyme inhibitor (CEI). This study shows that contrary to isotonic saline loading, acute salt and water depletion cause a progressive increase in NE plasma levels. Moreover, these results clearly demonstrate that the decrease in sympatho--adrenergic response and the predominant role played by the renin--aniotensin system during chronic salt depletion are not observed in acute conditions.

Compensatory renal hypertrophy in dogs: single nephron glomerular filtration rate

Kidney weight, length of superficial and juxtamedullary proximal tubules, glomerular diameter, kidney filtration rate and PAH clearance, sodium excretion and intrarenal distribution of filtration (with (14)C-ferrocyanide) were measured in the remaining hypertrophic kidneys of dogs 10 days after unilateral nephrectomy. Whereas kidney weight increased to 75 percent of the original total renal mass, proximal tubule length and mean glomerular diameter remained unchanged. PAH and creatinine clearance, and absolute, but not fractional, sodium excretion, rose significantly. The ratio superficial/juxtamedullary filtration rate remained unchanged, indicating parallel increases of filtration in both cortical regions of hypertrophied kidneys.

Compensatory renal hypertrophy in dogs: single nephron glomerular filtration rate

Sodium ferrocyanide was used to measure the intrarenal distribution of single nephron glomerular filtration rate (SNGFR) in remaining kidneys of dogs, 10 d after contralateral nephrectomy. It was first demonstrated that the renal function of both kidneys in situ was comparable. Following right nephrectomy, the urine volume, p-aminohippuric acid clearance, creatine clearance, osmolar clearance, fractional excretion of potassium, and sodium excretion of the left kidney increased. Fractional excretion of sodium, free water clearance, and filtration fraction remained unchanged. Following that 10-d period, left kidney weight exceeded that of the previously removed contralateral kidney by 50%, indicating that most of the compensatory hypertrophy had already occurred. No significant difference in the length of the proximal tubule nor in the diameter of the glomeruli of superficial (SUP) and juxtamedullary (JM) nephrons of either kidney could be demonstrated. Most importantly, the ratio of radioactivity in the SUP/JM nephrons of the residual kidney was comparable with that previously observed in normal dog kidneys. Thus, the increase in total kidney GFR is explained through a proportional increase in the SNGFR of the SUP and JM nephrons.

Bumetanide, a new loop diuretic

The effect of bumetanide on renal function has been compared with that of furosemide and a placebo in a double-blind study of 9 healthy young men. The sequence for oral administration of the drug was subjected to a random assignation based upon the Latin-square methodology under three different conditions. (1) Normal hydration: The administration of bumetanide (2 mg) produced within the next 4 hr a diuresis comparable to that induced by 80 mg of furosemide. Urinary excretion of sodium, potassium, chloride, calcium, and uric acid also followed comparable patterns. Phosphaturia occurred only under bumetanide. The effect of bumetanide seemed longer lasting. (2) Water loading: The effects of bumetanide and furosemide were comparable with the exception of the phosphaturic effect induced by bumetanide. The action of both diuretics on the diluting segment of the nephron was well demonstrated by the marked depression of CH2O. (3) Water deprivation: The effects of the two diuretics were comparable, including depression tCH20. In none of these conditions did the placebo produce any significant effect.