Rosemary Wangensteen

Increased Pressor Sensitivity to Chronic Nitric Oxide Deficiency in Hyperthyroid Rats

Abstract—We studied the effects of a possible interaction between partial nitric oxide deficiency and thyroid hormone excess on the long-term control of blood pressure (BP) and morphological and renal variables and examined the role of the renin-angiotensin system in the increased BP of this interaction. Eight groups (n=8 each) of male Wistar rats were used: a control group; 3 groups that were treated with thyroxine (50 &mgr;g/d), Nw-nitro-l-arginine methyl ester (l-NAME; subpressor dose, 1.5 mg · kg−1 · d−1), or thyroxine plus l-NAME; and another 4 similarly treated groups that received losartan (20 mg · kg−1 · d−1) in their drinking fluid. All treatments were maintained for 3 weeks. The time course of tail systolic BP was recorded once a week. At the end of the experimental period, we measured mean arterial pressure in conscious rats and assessed the morphological, metabolic, plasma, and renal variables. Thyroxine produced a mild BP increase from the second week of treatment and an increase in plasma angiotensin II and plasma nitrates/nitrites by the end of the study. Simultaneous administration of thyroxine and a subpressor dose of l-NAME produced a marked BP increase that reached significance from the first week of treatment. Losartan produced normotension in thyroxine-treated rats and attenuated the BP elevation in thyroxine+l-NAME–treated rats. Hyperthyroid rats showed relative renal and ventricular hypertrophy, absence of absolute left ventricular hypertrophy, and proteinuria. These alterations were not changed by losartan. We conclude that an impaired nitric oxide system might have a counterregulatory homeostatic role against the prohypertensive effects of thyroid hormone and that the renin-angiotensin system plays an important role in thyroxine+l-NAME hypertension.

Role of sex, gonadectomy and sex hormones in the development of nitric oxide inhibition‐induced hypertension

In this study we have evaluated the influence of sex, gonadectomy and sex hormones on the development of l‐NAME‐induced hypertension in the rat, focusing our investigation on blood pressure (BP), plasma renin activity (PRA), cardiac hypertrophy and proteinuria. Three experiments were performed to investigate: (i) the influence of sex on the development of l‐NAME‐induced hypertension; (ii) the effects of gonadectomy on the dimorphism of l‐NAME‐induced hypertension; and (iii) the effects of testosterone in ovariectomized female and of 17β‐oestradiol in orchidectomized male rats. Male l‐NAME‐treated rats had higher BP values than females. Orchidectomy of l‐NAME‐treated rats reduced BP to the levels of females and ovariectomy did not affect hypertension in females. Oestrogenized and orchidectomized males had a BP level similar to intact female l‐NAME‐treated rats. However, androgenization and ovariectomy did not change BP in female l‐NAME‐treated rats. PRA was greater in intact male l‐NAME hypertensive rats than in female rats, and gonadectomy protected against the increase in PRA such that PRA was similar among all the groups. Intact female hypertensive rats showed significantly greater ventricular hypertrophy compared with male hypertensive rats. Male l‐NAME hypertensive rats had increased proteinuria that was not present in female rats. Moreover, testosterone increased proteinuria in males and females regardless of the BP level. Male l‐NAME‐treated rats developed higher BP, PRA and proteinuria than female rats, but were more resistant to the development of cardiac hypertrophy. The higher PRA of male l‐NAME‐treated rats might be involved in the sex‐dependent dimorphism of this model of hypertension.

Interaction Between Nitric Oxide and Mineralocorticoids in the Long-Term Control of Blood Pressure

We analyzed the effects of a possible interaction between nitric oxide deficiency and mineralocorticoids on the long-term control of blood pressure and renal and endocrine variables. Six groups of uninephrectomized male Wistar rats were used: control animals and rats that received (1) N(G)-nitro-L-arginine methyl ester (L-NAME) subpressor (0.5 mg/100 mL drinking fluid), (2) L-NAME pressor (35 mg/100 mL drinking fluid), (3) deoxycorticosterone acetate (DOCA; 12. 5 mg/wk per rat), (4) DOCA plus L-NAME subpressor, or (5) L-NAME pressor plus DOCA. For all groups, the drinking fluid was tap water or 1% NaCl solution. We measured the time course of tail systolic blood pressure (SBP) and body weight for 3 weeks in all rats. At the end of the experimental period, we measured mean arterial pressure (direct recording) and endocrine and renal variables. Tail SBP rose significantly in the DOCA plus L-NAME subpressor-treated group but remained at normotensive levels in the DOCA-treated group. The addition of L-NAME to the subpressor dose accelerated the blood pressure increase in DOCA-salt hypertensive rats. The simultaneous administration of DOCA and L-NAME increased blood pressure and mortality rates in rats that drank water or saline compared with the rats treated with L-NAME alone. The subpressor dose of L-NAME did not increase blood pressure in saline-drinking rats. We conclude that impaired NO synthesis results in increased sensitivity to the pressor effect of mineralocorticoids in the presence or absence of an increased saline intake. Hence, nitric oxide contributes to the adaptative response to mineralocorticoid excess, perhaps through the facilitation of natriuresis and, thus, control of blood pressure.

Renal vascular reactivity to P(2)-purinoceptor activation in spontaneously hypertensive rats.

This study was performed to determine the possible contribution of an imbalance between P2X (vasoconstriction) and P2Y (vasodilation)-purinergic reactivity to the increased vascular resistance of spontaneously hypertensive rats (SHR). The vasoactive responses to α,β-methylene ATP and 2-methylthio ATP specific agonists, respectively, for P2X and P2Y purinergic receptors were characterized in isolated perfused kidneys from Wistar Kyoto (WKY) and SHR. To analyze P2X- and P2Y-purinergic reactivity we used phenylephrine and barium chloride, or acethylcholine (ACh) and sodium nitroprusside (NP) as reference compounds, respectively. The renal vasculature from SHR showed markedly enhanced reactivity to α,β-methylene ATP, phenylephrine and barium chloride. The dose-response curves were characterized by a similar threshold, with a greater maximal response. There were no significant differences in the dose-response curves or in maximal vasodilation to 2-methylthio ATP, ACh or NP when both groups were compared, except at the dose of 10–6 g/g kidney weight of NP in which the SHR group showed an increased responsiveness. The results indicate that the increased responsiveness of kidneys from SHR to α,β-methylene ATP may be due to nonspecific functional changes in the renal vasculature rather than to a specific alteration in the activity of renal P2X-purinoceptors. Our results also indicate that P2Y-purinergic reactivity, nitric oxide-induced vasodilation and the cGMP-dependent mechanisms of vasodilation are well preserved in SHR.

Urinary Aminopeptidase Activities as Early and Predictive Biomarkers of Renal Dysfunction in Cisplatin-Treated Rats

This study analyzes the fluorimetric determination of alanyl- (Ala), glutamyl- (Glu), leucyl-cystinyl- (Cys) and aspartyl-aminopeptidase (AspAp) urinary enzymatic activities as early and predictive biomarkers of renal dysfunction in cisplatin-treated rats. Male Wistar rats (n = 8 each group) received a single subcutaneous injection of either saline or cisplatin 3.5 or 7 mg/kg, and urine samples were taken at 0, 1, 2, 3 and 14 days after treatment. In urine samples we determined Ala, Glu, Cys and AspAp activities, proteinuria, N-acetyl-β-D-glucosaminidase (NAG), albumin, and neutrophil gelatinase-associated lipocalin (NGAL). Plasma creatinine, creatinine clearance and renal morphological variables were measured at the end of the experiment. CysAp, NAG and albumin were increased 48 hours after treatment in the cisplatin 3.5 mg/kg treated group. At 24 hours, all urinary aminopeptidase activities and albuminuria were significantly increased in the cisplatin 7 mg/kg treated group. Aminopeptidase urinary activities correlated (p<0.011; r2>0.259) with plasma creatinine, creatinine clearance and/or kidney weight/body weight ratio at the end of the experiment and they could be considered as predictive biomarkers of renal injury severity. ROC-AUC analysis was made to study their sensitivity and specificity to distinguish between treated and untreated rats at day 1. All aminopeptidase activities showed an AUC>0.633. We conclude that Ala, Cys, Glu and AspAp enzymatic activities are early and predictive urinary biomarkers of the renal dysfunction induced by cisplatin. These determinations can be very useful in the prognostic and diagnostic of renal dysfunction in preclinical research and clinical practice.

Role of endothelium-derived relaxing factors in adrenomedullin-induced vasodilation in the rat kidney

The present study aimed to evaluate the contributions of endothelium-derived hyperpolarizing factor (EDHF), the nitric oxide (NO)-cGMP pathway, and prostaglandins to adrenomedullin-induced vasodilation in isolated rat kidney. Inhibition of the NO-cGMP pathway with N(omega)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadiazolo-[4,3a]quinoxalin-1-one (ODQ) reduced the maximal vasodilator response to adrenomedullin by approximately 50%. Pretreatment of the vessels with the potassium channel inhibitor, tetraethylammonium or increased extracellular K(+), also decreased the maximal response to adrenomedullin by approximately 50%. The simultaneous administration of blockers of both endothelium-derived relaxing factors had a combined effect that almost suppressed adrenomedullin-induced vasodilation. The administration of indomethacin did not modify the renal response to adrenomedullin. Our results suggest that the vasodilator response to adrenomedullin in the isolated perfused kidney of rats is mediated by EDHF and NO to a similar extent. Our data also provide evidence that prostaglandins play no role in the vasodilator response to adrenomedullin in the renal vasculature.

The Renin-Angiotensin System: New Insight into Old Therapies

Although the renin-angiotensin system (RAS) is already an old acquaintance, there are often exciting discoveries that improve our knowledge of it and open new therapeutic possibilities. Moreover, well-established drugs, such as angiotensin-converting enzyme inhibitors (ACEI), angiotensin receptor blockers (ARB), or beta-blockers, show that their mechanism of action may be the result of parallel pathways other than the ones initially established. A detailed analysis of the RAS can be carried out in part through the study of the enzymes, named angiotensinases, involved in its cascade, whose activity is a reflection of the functionality of their peptide substrates. The study of these enzymes offers the possibility of controlling the effects of angiotensins through various pharmacological manipulations. For example, angiotensinase inhibitors or activators are being used or have been proposed as antihypertensive agents. They have also been suggested as analgesic and antidepressant drugs or targets for drug development against different pathologies such as Alzheimers disease, epilepsy or ischemia. On the other hand, the analysis of brain asymmetry has revealed surprising results about the laterality of central and peripheral components of the RAS. Such studies indicate that the neurovisceral integration, already proposed by Claude Bernard (1867) should also be analyzed from a bilateral perspective. In this review, the RAS and the role of various angiotensinases implicated in the cascade are revisited. Therapeutic strategies involving some components of the RAS with an unusual vision resulting from a bilateral perspective added to their study are discussed.

Chronic Blockade of Neuronal Nitric Oxide Synthase Does Not Affect Long‐Term Control of Blood Pressure in Normal, Saline‐Drinking or Deoxycorticosterone‐Treated Rats

It has been reported that long‐term selective inhibition of neuronal nitric oxide synthase (nNOS) produces elevated blood pressure (BP) in normal rats. The present study was designed to analyse the possible influences of the sodium‐retaining hormone deoxycorticosterone acetate (DOCA) and of an increased sodium intake on BP effects induced by the chronic blockade of nNOS with 7‐nitroindazole (7NI). Two experiments were performed using 7NI at a dose of either 10 mg kg−1 day−1 (experiment 1) or 30 mg kg−1 day−1 (experiment 2). The following groups were used in both experiments: control rats, and rats that received either 1% saline drinking water (Salt), deoxycorticosterone acetate (DOCA), 7NI, 7NI plus 1% saline (7NI + Salt) or 7NI plus DOCA (7NI + DOCA). The tail systolic BP (SBP) was measured in all rats once a week. At the end of the experimental period, the mean arterial pressure (MAP) and metabolic, morphological and renal variables were measured. There were no significant differences in the tail SBP, final MAP or glomerular filtration rate between the experimental groups and the control group. In both experiments, the plasma renin activity (PRA) was significantly inhibited in the Salt groups and suppressed in the DOCA groups. The PRA significantly increased in the 7NI groups, whereas the 7NI + Salt and 7NI + DOCA groups showed a significant inhibition in PRA, especially compared to the 7NI groups in the two experiments. We conclude that chronic nNOS blockade is unable to increase BP in normal, saline‐drinking or DOCA‐treated rats. Furthermore, the nNOS blockade does not interfere with the counterbalance between renin and an increased sodium intake or retention.

Contribution of endothelium-derived relaxing factors to P2Y-purinoceptor-induced vasodilation in the isolated rat kidney

We examined the role of endothelium-derived relaxing factors nitric oxide (NO), endothelium-derived hyperpolarising factor (EDHF), and prostaglandins (PGs) to P(2Y1)- and P(2Y2)-purinoceptor-induced vasodilation in isolated rat kidney. To do it, we analysed the renal response to ATP, 2-methylthio ATP, and UTP in rat renal vasculature under normal conditions and after the administration of: N(w)-nitro-L-arginine (L-NAME), increased K(+) concentration, indomethacin, and L-NAME and increased K(+) together. Our results indicate that the vasodilator response to P(2Y1)- and P(2Y2)-purinoceptor activation in the isolated perfused kidney of rats is subserved by EDHF and NO.

Long-Term Consequences of Uninephrectomy in Male and Female Rats

We investigated the effects of uninephrectomy (UNX) in 6-week-old male and female rats on blood pressure (BP), renal sodium handling, salt sensitivity, oxidative stress, and renal injury over 18 months postsurgery, studying control sham-operated and UNX-operated rats at 6, 12, and 18 months postsurgery, evaluating their renal sodium handling, BP, urinary isoprostanes, N-acetyl-&bgr;-D-glucosaminidase, and proteinuria before and after a 2-week high-salt intake period. At 18 months, plasma variables were measured and kidney samples were taken for the analysis of renal morphology and tissue variables. BP was increased at 6 months in male UNX rats versus controls and at 12 and 18 months in both male and female UNX rats and was increased in male versus female UNX groups at 18 months. UNX did not affect water and sodium excretion under basal conditions and after the different test in male and female rats at different ages. However, the renal function curve was shifted to the right in both male and female UNX rats. High-salt intake increased BP in both UNX groups at 6, 12, and 18 months and in the female control group at 18 months, and it increased proteinuria, N-acetyl-&bgr;-D-glucosaminidase, and isoprostanes in both UNX groups throughout the study. Renal lesions at 18 months were more severe in male versus female UNX rats. In summary, long-term UNX increased the BP, creatinine, proteinuria, pathological signs of renal injury, and salt sensitivity. Earlier BP elevation was observed and morphological lesions were more severe in male than in female UNX rats.