Serotonin hypersensitivity in aorta of two kidney-two clip hypertensive rats: calcium contribution and prostanoids-nitric oxide interactions.

Previous studies from our own laboratory have shown that abdominal aorta rings from two kidney - two clip hypertensive rats (HT) develop hypersensitivity to serotonin (SER) which is related to a decreased nitric oxide (NO) availability and enhanced thromboxane A2 production. In the present study we investigated whether calcium and prostanoid-NO interactions are involved in these findings. To this purpose, the aortic responses to SER were analyzed in calcium-free medium and in calcium-depleted aorta placed in normal medium. Moreover, effects of ridogrel (RID, an antagonist of TxA 2/PGH2 receptors and inhibitor of thromboxane synthetase) were analysed by cumulative dose-response curves to SER in the presence and in the absence of the NO synthase inhibitor N(omega)-nitro-L-arginine (NOLA). Vascular responses to SER in vessels from HT rats were associated with increased intracellular calcium mobilization. In addition, hypersensitivity to SER in HT group respect to sham group (SH) disappeared in the presence of RID, NOLA and RID plus NOLA. RID decreases the maximum tension to SER and this effect was prevented by NOLA. This inhibition was of a greater magnitude in rings from sham rats (SH): 34 +/- 6% than in HT rats: 15 +/- 6% (p < 0.05). Besides, RID decreased the sensibility to SER in the presence of NOLA only in the HT group. In conclusion, the present study suggests that SER hypersensitivity observed in HT rats is related to a facilitated intracellular calcium mobilization and enhanced TxA2-endoperoxide response. Changes in membrane SER-gated calcium channels opening are observed only during the early hypertensive period. Besides, the lower depressor effect of RID on the maximal tension to SER in aorta rings from HT rats are related with a decreased NO availability in this model of renovascular hypertension.

Effect of oral L-arginine administration for three weeks in two kidney-two clip hypertensive rats.

Nitric oxide (NO) has been identified as an effective vascular relaxant. This study analyses the contribution of the precursor L-arginine (L-arg) by oral administration in two kidney-two clip hypertension in the rat (2K-2C). Two groups were studied: sham (SH, n=21) and hypertensive (HT, n=15). After 4 weeks of surgery, a group of rats remained as controls (SHc and HTc, respectively), while others were supplemented with L-arg (1.25 g/L) in drinking water (SHa and HTa) for 3 weeks. Blood pressure was significantly increased in 2K-2C rats but remained unchanged after L-arg treatment. Plasma nitrite/nitrate concentrations were not different among groups. The contractile response of aorta to KCl, serotonin and the protein kinase C (PKC) stimulant, phorbol 12,13-dibutyrate (PDBu) was also evaluated. Higher contractile responses to PDBu (p<0.001) and lower relaxation to acetylcholine (Ach 10(-6) M, p<0.05 and 10(-5)M, p<0.02) were observed in aortic rings of HTc vs SHc; L-arg supplementation significantly diminished tension development to all agonists (p<0.05) but failed to modify the lower relaxation to Ach in HTa. Thromboxane (TxA(2)) - synthesis in rings of HTc was higher than in SHc under basal conditions (p<0.05). In the groups with supplement of L-arg, PDBu significantly stimulated prostacyclin (PGI(2)) synthesis more in HTa rats than in SHa ones (p<0.05). To conclude: 1) L-arg fails to modify hypertension development in 2K-2C rats; and 2) L-arg exerts a beneficial effect on the vascular wall, by reducing contractility in rings from HTa rats; it also improved PGI(2) synthesis under PDBu stimulation. 3) greater PKC activation and TxA(2) production rather than lower NO availability might result in systemic hypertension in 2K-2C rats.

Atrial natriuretic factor in two kidney--two clip renovascular hypertension in the rat.

Hig levels of circulating atrial natriuretic factor (ANF) have been reported in several physiopathologic conditions like hypertension, heart and renal failure, pregnancy and high sodium intake. Nevertheless, neither relationships with water-sodium space regulation nor the role of an ANF vascular relaxant effect have been yet defined. The aim of present experiments was to characterize the contribution of circulating ANF and its vascular relaxing effects in the two kidney-two clip (2K2C) experimental model of renovascular hypertension. Complementary, plasma metabolites nitrite/nitrate of nitric oxide (NO) was examined because of mediation for both (NO an ANF) through cGMP. Three results showed (two-four weeks after surgery): indirect systolic blood pressure (mmHg), 186 +/- 4 in HT and 122 +/- 1 in SH (p < 0.001); a significant increase of plasma ANF (fmol/ml) in HT (n = 7, 1221 +/- 253) vs. SH (n = 9, 476 +/- 82; p < 0.02). Nitrate/nitrite plasma concentrations (mumol/l) were mpt different between SH and. The relaxant effect of ANF (10(-9), 10(-8) and 10(-7) M) on phenylephrine (3,5 x 10(-6) M) contracted rings from HT rats was smaller than SH rats (10(-8) M, p < 0.05). Contractions to phorbol 12, 13-dibutyrate (seven weeks after surgery) were significantly higher in rings from HT rats (p < 0.001). We conclude: 1) in addition to decreased granularity in atrial myocardiocytes, high circulating values of ANF here described suggest an increased turnover of the peptide in 2K2C hypertensive rats; 2) lower significant vascular relaxant effects in HT rats would indicate down regulation of ANF receptors in this model; the latter would derive from high plasma ANF concentration and, tentatively, because of greater activity of protein kinase C in the vascular wall; 39 similar values of plasma nitrite/nitrate in SH and HT rats would indicate a comparable NO circulating availability in both groups.

Nitric oxide and superoxide anions in vascular reactivity of renovascular hypertensive rats.

The present study intends to define the role of the endothelium derived relaxing factor nitric-oxide (EDRF-NO) and the reactive oxygen intermediates in hypersensitivity to 5-hydroxytryptamine (5-HT) observed in abdominal aorta rings of two kidney-two clip hypertensive rats. Methylene Blue (which blocks production of cGMP by EDRF-NO) and Nw-nitro-L-arginine (which inhibits EDRF-NO synthesis), both shifted 5-HT dose-response curves to the left and completely abolished the differences in sensitivity to the agonist. The aortic perfusion with Krebs-Alcohol 20% (v/v) suppressed vascular relaxation to Ach (10(-5) M) and also abolished differences in sensitivity to 5-HT. These results suggest that a lower availability of EDRF-NO accounts for a higher 5-HT sensitivity in vessels of hypertensive rats. On the contrary, ridogrel (inhibitor of tromboxane-synthase and blocker of PGH2 and TxA2 receptors) did not suppress the hypersensitivity to 5-HT. In addition, since the superoxide anion (O2-) inactivates EDRF-NO, the effects of Superoxide dismutase (SOD) and Catalase (CAT) added in the bath were analyzed. Significant changes in sensitivity (P < 0.005) were found only for vessels of hypertensive rats (SOD depressing and CAT increasing sensitivity to 5-HT). Complementary, SOD activity was evaluated in the aorta homogenates and was found to be significantly lower in the hypertensive rats [(differences between hypertensive and sham rats, mU.mg wet weight tissue-1: 7 days after clipping, -183 +/- 67 (n = 11), P < 0.02; 21 days, -160 +/- 70 (n = 9), p < 0.05]. Results would indicate: 1. Lower EDRF-NO availability in vessels of the hypertensive animals which would account for higher sensitivity to 5-HT; 2. Such a lower EDRF-NO might depend, in part, upon its greater inactivation by O2- anions; 3. A greater presence of O2- anions in the vessels of hipertensive rats that might be favored by the lower SOD activity concentration in the vascular wall.

Ultrastructural study of atrial specific granules in experimental renovascular hypertension elicited by the constriction of both renal arteries.

The heart has an endocrine activity which depends on the secretion of a natriuretic, diuretic and hypotensive factor contained in osmophilic, secretory granules localized in the myocardiocytes and called "atrial specific granules" (the atrial natriuretic factor, ANF). In this paper, the relationship between these specific granules and renovascular hypertension elicited by the constriction of both renal arteries was investigated at the electron microscope level during the acute, subacute and chronic phases of hypertension. Male Wistar CHbb THOM rats were divided in three groups: 1) clipped rats; 2) sham operated rats; 3) ether anesthesia as unique manoeuver 48 h before decapitation. Blood pressure increased progressively after the constriction of both renal arteries. The atrial specific granules were not affected by ether anesthesia alone; 48-72 h after clipping the granules almost disappeared and this situation persisted up to the 6th week. In sham operated rats the picture was very similar to the clip rats 48 and 72 h after surgery (severe granule disappearance); in contrast, at one, two and six weeks after surgery, the granularity of cardiomyocytes in sham rats was absolutely restored. It is concluded that: 1) similarities in morphology of atrial specific granules in sham and clip rats 48 and 72 h after surgery would suggest that stress plays a primary role in determining the observed images; 2) thereafter, the contrast between sham and clip rats 1, 2 and 6 weeks after surgery would indicate that the ANF is linked to the subacute and chronic regulation of renovascular hypertension.

Renal function conscious one kidney-one clip hypertensive rats. Effect of indomethacin.

These experiments have analyzed: a) Blood pressure (BP) and renal function in one kidney-one clip rats two weeks after clipping; b) The effect of cycloxygenase (CO) inhibition on BP and renal function regulation during the hypertensive period. Using the unanaesthetized, unrestrained and chronically instrumented animal, three groups of rats were studied: Sham, Clip 0.31 mm lumen and Clip 0.29 mm lumen. The animals were examined before (Control period) and during the infusion of indomethacin (IND, 5 mg/kg via aortic cannula, n = 11 for each group) or the buffer vehicle solution (BUF, n = 7 for each group). Effective inhibition of CO by IND was confirmed using radioimmunoassay of prostaglandin E2 (PGE2) in urine. Control BP (mmHg, mean +/- SE) differed significantly among the groups (p < 0.001): Sham, 114 +/- 3; Clip 0.31, 135 +/- 2; Clip 0.29, 154 +/- 4 and did not change by IND infusion. Along with the BP, Control Glomerular Filtration Rate and Renal Plasma Flow did not change by IND infusion, which suggests that CO eicosanoids, particularly PGG2, contribute little to basal renal hemodynamics in sham and hypertensive rats. Sodium excretion was lower in the Control period of Clip 0.29 rats (p < 0.01). A significant natriuretic effect observed in this Clip 0.29 group by the infusion of IND suggests the contribution of an AA related metabolite in renal handling of sodium in more severe renovascular hypertension.

Ultrastructural study of atrial specific granules in experimental renovascular hypertension elicited by the constriction of both renal arteries.

The heart has an endocrine activity which depends on the secretion of a natriuretic, diuretic and hypotensive factor contained in osmophilic, secretory granules localized in the myocardiocytes and called [quot ]atrial specific granules[quot ] (the atrial natriuretic factor, ANF). In this paper, the relationship between these specific granules and renovascular hypertension elicited by the constriction of both renal arteries was investigated at the electron microscope level during the acute, subacute and chronic phases of hypertension. Male Wistar CHbb THOM rats were divided in three groups: 1) clipped rats; 2) sham operated rats; 3) ether anesthesia as unique manoeuver 48 h before decapitation. Blood pressure increased progressively after the constriction of both renal arteries. The atrial specific granules were not affected by ether anesthesia alone; 48-72 h after clipping the granules almost disappeared and this situation persisted up to the 6th week. In sham operated rats the picture was very similar to the clip rats 48 and 72 h after surgery (severe granule disappearance); in contrast, at one, two and six weeks after surgery, the granularity of cardiomyocytes in sham rats was absolutely restored. It is concluded that: 1) similarities in morphology of atrial specific granules in sham and clip rats 48 and 72 h after surgery would suggest that stress plays a primary role in determining the observed images; 2) thereafter, the contrast between sham and clip rats 1, 2 and 6 weeks after surgery would indicate that the ANF is linked to the subacute and chronic regulation of renovascular hypertension.

Renal function conscious one kidney-one clip hypertensive rats. Effect of indomethacin.

These experiments have analyzed: a) Blood pressure (BP) and renal function in one kidney-one clip rats two weeks after clipping; b) The effect of cycloxygenase (CO) inhibition on BP and renal function regulation during the hypertensive period. Using the unanaesthetized, unrestrained and chronically instrumented animal, three groups of rats were studied: Sham, Clip 0.31 mm lumen and Clip 0.29 mm lumen. The animals were examined before (Control period) and during the infusion of indomethacin (IND, 5 mg/kg via aortic cannula, n = 11 for each group) or the buffer vehicle solution (BUF, n = 7 for each group). Effective inhibition of CO by IND was confirmed using radioimmunoassay of prostaglandin E2 (PGE2) in urine. Control BP (mmHg, mean +/- SE) differed significantly among the groups (p < 0.001): Sham, 114 +/- 3; Clip 0.31, 135 +/- 2; Clip 0.29, 154 +/- 4 and did not change by IND infusion. Along with the BP, Control Glomerular Filtration Rate and Renal Plasma Flow did not change by IND infusion, which suggests that CO eicosanoids, particularly PGG2, contribute little to basal renal hemodynamics in sham and hypertensive rats. Sodium excretion was lower in the Control period of Clip 0.29 rats (p < 0.01). A significant natriuretic effect observed in this Clip 0.29 group by the infusion of IND suggests the contribution of an AA related metabolite in renal handling of sodium in more severe renovascular hypertension.

Renal function conscious one kidney-one clip hypertensive rats. Effect on indomethacin

Los presentes experimentos han analizado: a) la Presión Arterial (PA) y la función renal en ratas un riñón-un clip (IRIC) dos semanas después de la estenosis arterial; b) efecto de la inhibición de la ciclooxigenasa (CO) sobre la PA y la regluación de la función renal durante el período hipertensivo. Se estudiaron tres grupos de ratas utilizando animales sin anestesia, con libertad de movimiento y crónicamente instrumentados: grupo "Sham" (con operación simulada), Clip 0.31mm de luz, Clip 0.29mm de luz. Los animales fueron examinados antes (período Control) y durante la infusión de indometacina (IND, 5 mg/Kg por la cánula aórtica, n = 11 en cada grupo). La efectiva inhibición de la CO por IND fue confirmada por la determinación de prostaglandín E2 (PGE) en orina. La PA Control (mmH, media ñ ES) difirió significativamente entre los grupos (P < 0.001): Sham, 114 ñ 3; Clip 0.31, l35 ñ 2; Clip 0.29, 154 ñ 4 y los valores no variaron la infusión de IND, sugiriendo que la participación de los eicosanoides derivados de la CO, particularmente la PGE2, en la regulación de la hemodinamia renal de las ratas sham e hipertensas no es significativa. La excreción de sodio fue menor en el período Control de las ratas Clip 0.29 (P<0.01). El significativo efecto natriurético observado en este grupo Clip 0.29 por la infusión de IND sugiere la contribución de um metabolito del AA para el manejo renal del sodio en la hipertensión renovascular más severa (AU)

Ultrastructural study of atrial specific granules in experimental renovascular hypertension elicited by the constriction of both renal arteries

El corazón tiene una actividad endocrina que depende de la secreción de un factor nafriurético, diurético e hipotensor contenido en gránulos osmiófilos secretorios localizados en los miocardiocitos y llamados " granulos atriales específicos" (atrial natriuretic factor, ANF). En este trabajo se investigó al microscópio electrónico la relación existente entre los gránulos atriales específicos y la hipertensión renovascular provocada por constricción de ambas arterias renales, examinándose los períodos agudo, subagudo y crónico de hipertensión. Se usaron ratas macho, Wistar CHbb Thom. Los animales fueron divididos en tres grupos: 1) ratas con compresión bilateral de la arteria renal; 2) ratas con operación simulada; 3) ratas con anestesia con éter como única maniobra, 48 hs antes de la decapitación. La presión arterial aumentó progresivamente después de la constricción de las arterias renales. Los gránulos atriales específicos no fueron afectados por la anestesia con éter. Por el contrário 48-72h después de la compresión de las arterias renales los gránulos atriales específicos prácticamente desaperecieron y esta situación persistía 1, 2 y 6 semanas después. En las ratas con operación simulada se observó un cuadro similar a las ratas con constricción arterial (severa desaparición de los gránulos) pero 1, 2 y 6 semanas más tarde la granularidad de los cardiomiocitos se había restaurado completamente. Se concluye: 1) la similitud de la respuesta en ratas con constricción de ambas arterias renales y en ratas con operación simulada 48-72 h después de la intervención sugiere que el estrés desempeña un papel inicial en los resultados observados. 2) el contraste observado 1, 2 y 6 semanas después entre ratas con constricción arterial pemanente y ratas con operación simulada indicaría que el factor natriurético atrial está vinculado con la regulación subaguda y crónica de la hipertensión renovascular (AU)

Renal function conscious one kidney-one clip hypertensive rats. Effect on indomethacin

Los presentes experimentos han analizado: a) la Presión Arterial (PA) y la función renal en ratas un riñón-un clip (IRIC) dos semanas después de la estenosis arterial; b) efecto de la inhibición de la ciclooxigenasa (CO) sobre la PA y la regluación de la función renal durante el período hipertensivo. Se estudiaron tres grupos de ratas utilizando animales sin anestesia, con libertad de movimiento y crónicamente instrumentados: grupo "Sham" (con operación simulada), Clip 0.31mm de luz, Clip 0.29mm de luz. Los animales fueron examinados antes (período Control) y durante la infusión de indometacina (IND, 5 mg/Kg por la cánula aórtica, n = 11 en cada grupo). La efectiva inhibición de la CO por IND fue confirmada por la determinación de prostaglandín E2 (PGE) en orina. La PA Control (mmH, media ñ ES) difirió significativamente entre los grupos (P < 0.001): Sham, 114 ñ 3; Clip 0.31, l35 ñ 2; Clip 0.29, 154 ñ 4 y los valores no variaron la infusión de IND, sugiriendo que la participación de los eicosanoides derivados de la CO, particularmente la PGE2, en la regulación de la hemodinamia renal de las ratas sham e hipertensas no es significativa. La excreción de sodio fue menor en el período Control de las ratas Clip 0.29 (P<0.01). El significativo efecto natriurético observado en este grupo Clip 0.29 por la infusión de IND sugiere la contribución de um metabolito del AA para el manejo renal del sodio en la hipertensión renovascular más severa

Ultrastructural study of atrial specific granules in experimental renovascular hypertension elicited by the constriction of both renal arteries

El corazón tiene una actividad endocrina que depende de la secreción de un factor nafriurético, diurético e hipotensor contenido en gránulos osmiófilos secretorios localizados en los miocardiocitos y llamados " granulos atriales específicos" (atrial natriuretic factor, ANF). En este trabajo se investigó al microscópio electrónico la relación existente entre los gránulos atriales específicos y la hipertensión renovascular provocada por constricción de ambas arterias renales, examinándose los períodos agudo, subagudo y crónico de hipertensión. Se usaron ratas macho, Wistar CHbb Thom. Los animales fueron divididos en tres grupos: 1) ratas con compresión bilateral de la arteria renal; 2) ratas con operación simulada; 3) ratas con anestesia con éter como única maniobra, 48 hs antes de la decapitación. La presión arterial aumentó progresivamente después de la constricción de las arterias renales. Los gránulos atriales específicos no fueron afectados por la anestesia con éter. Por el contrário 48-72h después de la compresión de las arterias renales los gránulos atriales específicos prácticamente desaperecieron y esta situación persistía 1, 2 y 6 semanas después. En las ratas con operación simulada se observó un cuadro similar a las ratas con constricción arterial (severa desaparición de los gránulos) pero 1, 2 y 6 semanas más tarde la granularidad de los cardiomiocitos se había restaurado completamente. Se concluye: 1) la similitud de la respuesta en ratas con constricción de ambas arterias renales y en ratas con operación simulada 48-72 h después de la intervención sugiere que el estrés desempeña un papel inicial en los resultados observados. 2) el contraste observado 1, 2 y 6 semanas después entre ratas con constricción arterial pemanente y ratas con operación simulada indicaría que el factor natriurético atrial está vinculado con la regulación subaguda y crónica de la hipertensión renovascular