Renal cyclic 3',5'-guanosine monophosphate and sodium excretion in Dahl salt-resistant and Dahl salt-sensitive rats: comparison of the roles of bradykinin and nitric oxide.

OBJECTIVE: The purpose of this study was to determine the relative importance of bradykinin and nitric oxide (NO) in mediating renal responses to altered sodium intake in Dahl salt-resistant (Dahl-SR) and salt-sensitive (Dahl-SS) rats. DESIGN AND METHODS: Dahl-SR and Dahl-SS rats consumed a diet containing 0.15% (low) or 4.0% (high) sodium chloride for 10 days. A microdialysis technique was then used to measure renal cortical interstitial fluid (RIF) cyclic 3',5'-guanosine monophosphate (cGMP) production in anesthetized rats, under baseline conditions and during acute cortical infusion of either the bradykinin B2 receptor antagonist icatibant or the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME). Urine sodium excretion was monitored simultaneously by ureter cannulation. Results Baseline sodium excretion was similar in the two types of rats, but RIF cGMP was significantly elevated in Dahl-SR compared to Dahl-SS rats on both low and high sodium diets. Icatibant infusion significantly reduced both RIF cGMP and sodium excretion in Dahl-SR rats during low sodium intake, but had no effect in Dahl-SS rats on either diet L-NAME infusion significantly reduced sodium excretion in Dahl-SR and Dahl-SS rats, during both low and high sodium intake. L-NAME infusion caused a significant reduction in RIF cGMP in Dahl-SR and Dahl-SS rats on low sodium diet, but reduced RIF cGMP only in Dahl-SR rats on high sodium diet. Conclusion These data suggest a potential role for cortical bradykinin, but not NO, in mediating the differences in the renal response to low sodium intake between Dahl-SR and Dahl-SS rats.

Thyrocyte release of asymmetric dimethylarginine does not account for human thyrocyte inhibition of endothelial cell cyclic GMP.

BACKGROUND: The thyroid gland produces and responds to the signalling molecule nitric oxide (NO). The activity of NO synthase (NOS) may be regulated by endogenous NOS inhibitors such as asymmetric dimethylarginine (ADMA). OBJECTIVE: To investigate whether human thyrocytes are capable of regulating NOS activity via the production of ADMA. DESIGN: Human thyrocytes were incubated with human umbilical vein endothelial cells (HUVEC) in order to determine the effect on HUVEC NOS activity. HUVEC cGMP production over a 3-h period was measured as an indicator of NOS activity in the absence and presence of thyrocytes. To determine thyrocyte production of ADMA, samples of conditioned media were analysed by HPLC. RESULTS: The presence of primary human thyrocytes or immortalized human thyrocyte SGHTL-189 cells caused a significant inhibition of both basal (approximately 57% inhibition) and thrombin-stimulated (approximately 42% inhibition) HUVEC cGMP production. Both primary human thyrocytes and SGHTL-189 cells released ADMA (approximately 0. 28 microg per 10(6) thyrocytes over a 3-day period). However, excess L-arginine, the natural substrate for NOS, was unable to overcome thyrocyte inhibition of HUVEC cGMP production. CONCLUSION: These data indicate that human thyrocytes potently reduce endothelial cell cGMP concentrations, and that thyrocytes produce the endogenous NOS inhibitor, ADMA. However, the inhibition of endothelial cGMP is not mediated via thyrocyte production of a competitive NOS inhibitor.

Age-related changes in renal cyclic nucleotides and eicosanoids in response to sodium intake.

The signaling molecules cGMP, cAMP, prostaglandin E(2) (PGE(2)), and prostaglandin F(2alpha) (PGF(2alpha)) play important roles in mediating the response of the kidney to changes in dietary sodium intake. We used a renal microdialysis technique in conscious rats to address the hypothesis that the renal ability to produce these mediators in response to dietary sodium intake is altered during maturation. Young (4-week-old) or adult (6-month-old) rats were studied after the consumption for 5 days of diets containing low (0. 04% NaCl), normal (0.28% NaCl), or high (4.0% NaCl) levels of sodium. Plasma renin activity was significantly increased by low-sodium diet and significantly decreased by high-sodium diet, with no significant difference between the responses of the 2 age groups. Renal interstitial fluid (RIF) levels of cGMP, cAMP, PGE(2), and PGF(2alpha) on normal-sodium diet were similar in the 2 age groups. Low-sodium diet caused a significant increase in RIF levels of all 4 mediators, with no significant differences between the responses of the 2 age groups. High-sodium diet also caused a significant increase in RIF levels of all 4 mediators. However, RIF production of cGMP, cAMP, and PGE(2) was significantly greater, and RIF PGF(2alpha) production was significantly lower, in young rats compared with adult rats. These data demonstrate that the kidneys of young and adult rats respond to dietary sodium restriction in a similar manner but that there are age-related changes in the renal response to sodium loading.

Angiotensin II and nitric oxide: a question of balance.

The vasoconstrictor peptide angiotensin II (Ang II) and the endogenous vasodilator nitric oxide (NO) have many antagonistic effects, as well as influencing each other's production and functioning. In the short-term, Ang II stimulates NO release, thus modulating the vasoconstrictor actions of the peptide. In the long-term, Ang II influences the expression of all three NO synthase (NOS) isoforms, while NO downregulates the Ang II Type I (AT1) receptor, contributing to the protective role of NO in the vasculature. Within the cardiovascular system, Ang II and NO also have antagonistic effects on vascular remodeling and apoptosis. In the kidney, the distribution of the NOS isoforms coincides with the sites of the components of the renin-angiotensin system. NO influences renin secretion from the kidney, and NO-Ang II interactions are important in the control of glomerular and tubular function. In the adrenal gland, NO has been shown to affect Ang II-induced aldosterone synthesis, while in the brain NO appears to influence Ang II-induced drinking behavior, although conflicting data have been reported. In this review, we focus on the diverse ways in which Ang II and NO interact, and on the importance of maintaining a balance between these two important mediators.

Differential regulation of renal angiotensin subtype AT1A and AT2 receptor protein in rats with angiotensin-dependent hypertension.

-This study was designed to investigate distribution and regulation of the renal AT1A and AT2 subtype receptors in rats with either systemic angiotensin II (Ang II)-induced hypertension or acute phase renal hypertension (2-kidney, 1-clip [2K1C] or 2-kidney, 1-figure-of-8-wrap [2K1W]). In normal rat kidneys, positive immunostaining for the AT1A receptor was observed in the intrarenal vasculature, glomeruli, proximal and distal tubules, and collecting ducts. The AT2 receptor was localized mainly to the glomeruli. The AT1A but not AT2 receptor protein expression was significantly reduced in rats with 10-day systemic Ang II-induced hypertension. In both 7-day 2K1C and 3-day 2K1W rats, the AT1A receptor was significantly reduced in ischemic and contralateral kidneys compared with sham-operated control rats. Reduction in AT2 receptor expression was observed only in the ischemic kidneys in 2K1C and 2K1W renal hypertensive rats. These results demonstrate that the AT1A receptor is widely distributed in the glomerulus and all other nephron segments of the rat kidney. Renal AT1A but not AT2 receptor protein is downregulated in rats with Ang II-induced hypertension. In renal hypertensive rats, the AT1A receptor is bilaterally downregulated and the AT2 receptor is downregulated only in the ischemic kidney.

Nitric oxide enhances thyroid peroxidase activity in primary human thyrocytes.

Recent studies have demonstrated the production of the multi-functional messenger molecule nitric oxide (NO) by the thyroid gland. To examine a possible role for NO in thyroid function, we studied the acute and chronic effect of NO donors on thyroid peroxidase (TPO) activity in monolayer cultures of primary human thyrocytes, using a colorimetric assay technique. The presence of either S-nitrosoglutathione (GS-NO) or sodium nitroprusside (SNP) (10(-6)-10(-4) M) at the time of the assay caused a significant increase in TPO activity. Pre-incubation of thyrocytes with 10(-5) M GS-NO for 3 days had no effect on the level of TPO activity when the assay was performed in the absence of NO donors. However, GS-NO pre-incubation significantly enhanced the acute stimulatory effect of GS-NO and SNP on TPO activity. These results suggest a possible role for NO in the regulation of TPO activity and thus thyroid hormone synthesis.

Nitric oxide stimulates cyclic GMP in human thyrocytes.

Sodium nitroprusside spontaneously breaks down in solution to produce the vasodilator nitric oxide. In many cell types, this stimulates the cytosolic form of the enzyme guanylate cyclase, resulting in the elevation of cyclic GMP (cGMP). We have investigated the effect of sodium nitroprusside on the generation of cGMP in primary human thyrocytes and the SV40-transfected human thyroid cell line SGHTL-189. A dose-dependent increase in cGMP was obtained and the maximum response was observed with concentrations above 10 microM sodium nitroprusside in both cell types. Methylene blue (50 microM) had no significant effect on basal cGMP production but inhibited the effect of sodium nitroprusside at all concentrations tested, thus demonstrating that the effect was due to nitric oxide. Sodium nitroprusside had no effect on cyclic AMP (cAMP) production in these cells. TSH at 100 and 1000 microU/ml significantly stimulated the production of cAMP, but not that of cGMP, in primary human thyrocytes. Sodium nitroprusside had no significant effect on basal or TSH-stimulated triiodothyronine secretion in primary human thyrocytes. Forskolin (10 microM) significantly stimulated cAMP production in both primary thyrocytes and SGHTL-189 cells. Although forskolin had no significant effect on basal cGMP production, sodium nitroprusside-stimulated cGMP production was significantly reduced by forskolin. However, this inhibitory effect was not related to the production of cAMP.

The effect of basic fibroblast growth factor on the growth and function of human thyrocytes.

Basic fibroblast growth factor (bFGF) was quantitated in human primary thyrocyte cultures and thyroid cell lines produced by transfection with pSV3neo. Immunoreactive-bFGF (ir-bFGF) bound to heparin-Sepharose affinity columns eluted with 1.8-2.0 mol NaCl/l and had a molecular weight of approximately 17,000. Recombinant human bFGF in the presence of 5% serum increased the growth of transfected human thyrocytes but not the growth of primary human thyrocytes. Preincubation of cells with up to 100 micrograms bFGF/l potentiated TSH-stimulated cAMP release from the transfected cells but inhibited release from primary human thyroid cultures. bFGF may be an important modulator of thyroid cell function and growth.