Administration Of DOCA Research Articles

Abstract P426: Novel Peptide B7-33 Demonstrates Efficacy In Rat Models Of Preeclampsia

Background: Preeclampsia (PreE) is a hypertensive pregnancy disorder, which occurs in approximately 10% of all gestations. The literature suggests potential therapeutic role of H2 relaxin in PreE. Due to the complex insulin-like structure of relaxin (A- and B- chains, 53 amino acids, 3 disulfide bonds), a novel H2 relaxin B-chain-only peptide variant B7-33 (27 amino acids without any disulfide bonds) has recently been developed. Objective: This single-chain peptide displayed equivalent efficacy to the natural H2 relaxin in several functional assays both in vitro and in vivo . The Aim of this study is to evaluate whether B7-33 attenuates preE syndrome in rat models of PreE. Methods: Rat Model 1. The efficacy of B7-33 was evaluated in the Reduction of Uterine Perfusion Pressure (RUPP) model as described previously. RUPP rats are randomly assigned to 4 groups (N=8/group): 1) vehicle, 2) B733; 3) B733-Fc; and 4) B733-HSA. Rats are dosed twice weekly (i.v.) from GD10 to GD 20. Rat Model 2. Timed-pregnant rats are used, and the model is conducted as previously described. DOCA and saline administration begin at approximately GD2. Three groups of animals are studied (n=8 per group). 1) normal pregnant rats; 2) pregnant animals injected (i.p.) initially with 12.5 mg of DOCA, followed by a weekly injection of 6.5 mg, and whose drinking water was replaced with 0.9% saline; 3) rats administered DOCA and saline as for Group 2, and given B733 35 ug i.p. biweekly from GD10-20. BP, proteinuria and inflammatory markers were evaluated. Statistical comparisons were performed using analysis of variance with Duncan’s post hoc test. Results: RUPP rats have increased MAP, plasma TNF-α, and plasma sFlt-1 along with decreased NO index compared to normal pregnancy. Treatment with B733 and B7-33 fusion proteins lowers MAP, TNF-α, and sFlt-1 back to that of normal pregnancy. B7-33 data are consistent with earlier data with serelaxin in the RUPP model. All fusions tested ameliorate hypertension in the RUPP animals. B7-33 normalizes BP and proteinuria in the DOCA rat model of preE. Conclusion: Both B7-33 and B7-33 fusion proteins attenuate preE syndrome in RUPP and DOCA rat models of PreE. We conclude that B7-33 is an ideal candidate for development as a novel therapeutic in preE.

VEGF-B hypertrophy predisposes to transition from diastolic to systolic heart failure in hypertensive rats.

Cardiac energy metabolism is centrally involved in heart failure (HF), although the direction of the metabolic alterations is complex and likely dependent on the particular stage of HF progression. Vascular endothelial growth factor B (VEGF-B) has been shown to modulate metabolic processes and to induce physiological cardiac hypertrophy; thus, it could be cardioprotective in the failing myocardium. This study investigates the role of VEGF-B in cardiac proteomic and metabolic adaptation in HF during aldosterone and high-salt hypertensive challenges. Male rats overexpressing the cardiac-specific VEGF-B transgene (VEGF-B TG) were treated for 3 or 6 weeks with deoxycorticosterone-acetate combined with a high-salt (HS) diet (DOCA + HS) to induce hypertension and cardiac damage. Extensive longitudinal echocardiographic studies of HF progression were conducted, starting at baseline. Sham-treated rats served as controls. To evaluate the metabolic alterations associated with HF, cardiac proteomics by mass spectrometry was performed. Hypertrophic non-treated VEGF-B TG hearts demonstrated high oxygen and adenosine triphosphate (ATP) demand with early onset of diastolic dysfunction. Administration of DOCA + HS to VEGF-B TG rats for 6 weeks amplified the progression from cardiac hypertrophy to HF, with a drastic drop in heart ATP concentration. Dobutamine stress echocardiographic analyses uncovered a significantly impaired systolic reserve. Mechanistically, the hallmark of the failing TG heart was an abnormal energy metabolism with decreased mitochondrial ATP, preceding the attenuated cardiac performance and leading to systolic HF. This study shows that the VEGF-B TG accelerates metabolic maladaptation which precedes structural cardiomyopathy in experimental hypertension and ultimately leads to systolic HF.

AW-APSH-2: “MINERALOCORTICOID RECEPTOR (MR)-ASSOCIATED HYPERTENSION” IN “GREEDY ORGAN HYPOTHESIS”

Spironolactone has been used for more than 60 years. Eplerenone is MR-specific MRB and esaxerenone possesses non-steroidal structure with high affinity and specificity to MR and exhibits long half-life. We conducted a double-blind phase III study of esaxerenone compared with eplerenone in patients with essential hypertension in 2020. Esaxerenone 2.5 mg elicited comparable hypotensive effect to eplerenone 50 mg and 5 mg exhibited significantly stronger effect than 2.5 mg. We also investigated the efficacy of dosage-escalation of esaxerenone added to a RAS inhibitor in hypertensive patients with type 2 diabetes (DM) (HbA1c:6.8%) and albuminuria (212 mg/gCr). 5 mg esaxerenone induced 20/8mmHg blood pressure reduction and reduced albumin excretion significantly. Interestingly, in these studies, esaxerenone exerted similar hypotensive action in the patients with RAS inhibitors, compared to the groups without them. This observation indicates that MR can be activated being independent of renin-angiotensin-aldosterone system. In 2012, we proposed the concept of “MR-associated hypertension”, hypertension caused by over-activation of MR with wide range of plasma aldosterone level. Primary aldosteronism is the typical example of MR-associated hypertension, but even in low plasma aldosterone concentration state, such as obesity, DM, CKD, MR can be over-activated. There are several postulated mechanisms of over-activation of MR. Increased expression of MR, increased sensitivity of MR and MR protein stabilization. We are interested in the activation of MR by salt and sugar themselves. We focus on MR expressed in the intestine for sodium absorption. Administration of DOCA and high salt induced up-regulation of epithelial sodium channel, ENaC, the target molecule of MR. And intestine specific knock-out of MR mice exhibited blunted increase of blood pressure by DOCA and high salt loading. We also demonstrated that high sugar induces MR protein stabilization by PKC activation, O-GlcNac modification or EGFR-ERK activation. More recently, in relation to excessive salt and sugar intake and occurrence of non-communicable diseases (NCDs), including hypertension, we have proposed “Greedy Organ Hypothesis”. Excessive intake of salt and sugar are sensed by the kidney and the intestines, and these organs up-regulate SGLT, sodium-glucose co-transporters and come to absorb salt and sugar greedily. Excessive salt intake through SGLT2 makes the kidney greedy to induce hypertension/CKD. Excessive food intake through SGLT1 make the intestines greedy to induce obesity/DM. Furthermore, there is “crossing” relationships between “greedy organs” and NCDs. Greedy kidney and intestines over-activate MR and induce MR-associated hypertension. Therefore, MRB are effective to alleviate Greedy Organs and to suppress NCDs.

Secreted protein acidic and rich in cysteine (SPARC) and a disintegrin and metalloproteinase with thrombospondin type 1 motif (ADAMTS1) increments by the renin-angiotensin system induce renal fibrosis in deoxycorticosterone acetate-salt hypertensive rats

Secreted protein acidic and rich in cysteine (SPARC), an extracellular matrix (ECM) protein, was recently shown to induce collagen deposition through the production of a disintegrin and metalloproteinase with thrombospondin type 1 motif (ADAMTS1) in the aging heart. ADAMTS1 regulates ECM turnover by degrading ECM components, and its excessive activation contributes to various pathological states, including fibrosis. The present study investigated the pathophysiological regulation and role of SPARC and ADAMTS1 in renal fibrosis using uninephrectomized rats treated with deoxycorticosterone acetate (DOCA, 40 mg/kg/week, subcutaneously) and salt (1% in drinking water). The administration of DOCA and salt gradually and significantly elevated systolic blood pressure during the 3-week treatment period, induced proteinuria, decreased creatinine clearance, and increased NADPH oxidase-derived superoxide production, malondialdehyde concentrations, and monocyte chemoattractant protein-1 and osteopontin expression in the kidneys. Glomerulosclerosis, fibrillar collagen deposition, and transforming growth factor-β expression increased in a time-dependent manner, and SPARC and ADAMTS1 expression showed a similar pattern to these changes. The angiotensin II type-1 receptor blocker losartan suppressed the overexpression of SPARC and ADAMTS1, and an in vitro exposure to angiotensin II induced the production of both SPARC and ADAMTS1 in renal fibroblast NRK-49F cells. Knockdown of the SPARC gene with small interfering RNA reduced all forms (the 110-kDa latent and 87- and 65-kDa bioactive forms) of ADAMTS1 expression as well as collagen production. These results suggest that SPARC is induced by the renin-angiotensin system and may be a fibrogenic factor, at least in part, by producing ADAMTS1 in hypertensive renal disease.

Pentosan polysulfate preserves renal microvascular P2X1 receptor reactivity and autoregulatory behavior in DOCA-salt hypertensive rats.

Inflammation contributes to ANG II-associated impairment of renal autoregulation and microvascular P2X1 receptor signaling, but its role in renal autoregulation in mineralocorticoid-induced hypertension is unknown. Autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. Hypertension was induced in uninephrectomized control rats (UNx) by subcutaneous implantation of a DOCA pellet plus administration of 1% NaCl in the drinking water (DOCA-salt) for 3 wk. DOCA-salt rats developed hypertension that was unaltered by anti-inflammatory treatment with pentosan polysulfate (DOCA-salt+PPS) but was suppressed with "triple therapy" (hydrochlorothiazide, hydralazine, and reserpine; DOCA-salt+TTx). Baseline arteriolar diameters were similar across all groups. UNx rats exhibited pressure-dependent vasoconstriction with diameters declining to 69 ± 2% of control at 170 mmHg, indicating intact autoregulation. DOCA-salt treatment significantly blunted this pressure-mediated vasoconstriction. Diameters remained between 91 ± 4 and 98 ± 3% of control over 65-170 mmHg, indicating impaired autoregulation. In contrast, pressure-mediated vasoconstriction was preserved in DOCA-salt+PPS and DOCA-salt+TTx rats, reaching 77 ± 7 and 75 ± 3% of control at 170 mmHg, respectively. ATP is required for autoregulation via P2X1 receptor activation. ATP- and β,γ-methylene ATP (P2X1 receptor agonist)-mediated vasoconstriction were markedly attenuated in DOCA-salt rats compared with UNx (P < 0.05), but significantly improved by PPS or TTx (P < 0.05 vs. DOCA-salt) treatment. Arteriolar responses to adenosine and UTP (P2Y2 receptor agonist) were unaffected by DOCA-salt treatment. PPS and TTx significantly reduced MCP-1 and protein excretion in DOCA-salt rats. These results support the hypothesis that hypertension triggers inflammatory cascades but anti-inflammatory treatment preserves renal autoregulation in DOCA-salt rats, most likely by normalizing renal microvascular reactivity to P2X1 receptor activation.

Spironolactone inhibits the activity of the Na+/H+ exchanger in the aorta of mineralocorticoid-induced hypertensive rats.

Aldosterone can induce changes in the expression or activity of Na(+)/H(+) exchanger isoform 1 (NHE-1) in vascular smooth muscle cells. We aimed to clarify whether chronic mineralocorticoid receptor activation exerts an effect on the activity of NHE-1 in the aorta of mineralocorticoid-induced hypertensive rats. Uninephrectomized male Sprague-Dawley rats received subcutaneously 10 mg/week of desoxycorticosterone (DOCA) with or without 20 mg/kg of spironolactone, or vehicle alone (n = 20). After four weeks of treatment, the animals were sacrificed; the aorta was excised for subsequent studies, including histological analysis, RT-PCR, Western blot, measurement of NHE-1 activity and vascular contractility in the presence or absence of the selective NHE-1 inhibitor ethyl-isopropyl amiloride (EIPA). Chronic DOCA treatment increased the NHE-1 activity, systolic and diastolic blood pressure, and aortic wall thickness. All these effects were prevented by co-treatment with Spironolactone (p < 0.05). Phenylephrine-induced vascular contractility was significantly reduced in the DOCA group when EIPA was added in the media (p < 0.05). No significant differences in NHE-1 mRNA or protein levels were detected between groups. Chronic DOCA administration induced functional and morphological alterations in the rat aorta that are partially explained by enhanced NHE-1 activity and prevented by spironolactone. However, we did not observe changes in the NHE-1 transcript or protein levels, suggesting that the effect may be due to post-transcriptional modifications induced by mineralocorticoid receptor activation.

Effect of Concomitant Administration of a-tocopherol and ACEI on Cardiovascular Performance and Nucleic Acid Changes in DOCA Hypertensive Rats

Background: Evidence for cardiovascular oxidative stress in animals with hypertension has been accumulated. Antioxidant agents have been used to treat endothelial dysfunction and arterial hypertension. Aim: The aim of present study is to elucidate the effect of concomitant administration of α-tocopherol (antioxidant) and angiotensin converting enzyme inhibitor (ACEI; anti-hyptertensive) on cardiac smooth muscle DNA and RNA changes in DOCA induced hypertension in rats. Methods: 48 male Sprague-Dawley rats were used in this study and were divided into 6 groups (n=8): C control rats; CE control rats received α-tocopherol (60 mg/kg) intragastrically (IG); DOCA rats were made hypertensive by SC injection of DOCA (50 mg/kg once weekly for 4 weeks); DOCA+E; DOCA hypertensive rats received α-tocopherol (60 mg/kg) IG; DOCA+ACEI; DOCA hypertensive rats received ACEI (captopril; 15 mg/kg) IG; and DOCA+E+ACEI; DOCA hypertensive rats received both α-tocopherol and captopril in the same doses as DOCA+E and DOCA+ACEI groups respectively. All IG treatments were given to the animals 6 days weekly for 6 weeks. At the end of experimental protocol, systolic blood pressure (MSP), renal vascular flow velocity (RFV), renal vascular resistance (RVR), myocardial contractility (MC) and heart rate (HR) were measured in rats of all groups. Also, serum sodium (Na + ), potassium (K + ) and total plasma antioxidant capacity (TOC) were measured. DNA and RNA analysis were done for the myocardial tissue homogenate. Results: While DOCA administration in rats produced significant increase in serum Na + , MSP, RVR, and RNA levels; it reduced significantly serum K + , TOC, MC and DNA levels compared with the control group. Concomitant administration of both α-tocopherol and ACEI resulted in significant reduction of serum Na + ,

Contribution of Cytochrome (CYP) P450 1B1 in Various Models of Hypertension in Rats and Mice: A Novel Target for the Development of Anti‐Hypertensive Agents

Previously, we reported that inhibition of CYP1B1 with 2, 4, 3′, 5′‐tetramethoxystilbene (TMS) in rats prevented the development and maintenance of angiotensin II (Ang II)‐induced hypertension. We have found that TMS (300 μg/kg, i.p. every 3rd day) also reduces mean arterial pressure (MAP) in DOCA/Salt‐hypertensive rats (154 ± 1 mmHg to 96 ± 1 mmHg, P &lt; 0.05) and in spontaneously hypertensive rats (163 ± 14 mmHg to 116 ± 4 mmHg, P &lt; 0.05). To further elucidate the role of CYP1B1 in hypertension, studies were conducted in CYP1B1 knockout (CYP1B1−/−) and wild‐type (CYP1B1+/+) mice. Ang II infused by mini osmotic pumps (1mg/kg/min sc.) for 13 days produced a significantly smaller increase in MAP (P &lt; 0.05) in CYP1B1−/− mice (112 ± 1 to 128 ± 2 mmHg) than in CYP1B1+/+ mice (113 ± 3 mmHg to 158 ±3 mmHg). In Ang II‐treated CYP1B1+/+ mice, responses of the mesenteric artery to phenylephrine and endothelin‐1, media to lumen ratio and aortic ROS production were significantly increased compared to Ang II‐treated CY1B1−/− mice. Administration of DOCA (35 mg/kg/week im. + 1% NaCl in drinking water) increased MAP from 102 ± 1 to 153 ± 4 mmHg in CYP1B1+/+ but not in CYP1B1−/− mice. These data suggest that CYP1B1 contributes to the development of hypertension, most likely via increased ROS generation and vascular reactivity and hypertrophy, and could serve as a novel target for the development of agents like TMS for the treatment of hypertension.

Colfibrate attenuates blood pressure and sodium retention in DOCA-salt hypertension

Clofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR alpha) agonist, increases renal tubular cytochrome P450 4a (Cyp4a) expression thereby increasing 20-hydroxyeicosatetraenoic acid (20-HETE) production. To determine if clofibrate affects blood pressure regulation we studied mice with DOCA-salt induced hypertension in wild-type and PPAR alpha knockout mice. Wild-type mice treated with DOCA-salt had higher mean arterial pressures and higher cumulative sodium balance, but lower renal 20-HETE production than did vehicle-treated mice. Treating DOCA-salt mice with clofibrate attenuated the increase in mean arterial pressure and cumulative sodium balance while increasing 20-HETE production and renal Cyp4a expression. In contrast the PPAR alpha knockout mice treated with clofibrate and DOCA-salt showed no attenuation in the increase of blood pressure, cumulative sodium balance, renal 20-HETE production or Cyp4a protein expression. Expression of the PPAR alpha protein was greater in proximal tubules than in renal microvessels. Our results show that PPAR alpha pathway induces renal tubular 20-HETE production which affects sodium retention and blood pressure regulation in DOCA-salt-treated mice.

Sympathetic activation in the development of DOCA‐salt hypertension

Indirect evidence indicates that sympathetic activity (SNA) is increased in DOCA‐salt hypertension. Total body norepinephrine (NE) spillover provides an accurate estimate of whole‐body SNA. The purpose of this study was to assess SNA during the development of DOCA‐salt hypertension. Catheters were implanted in male rats for pressure measurements and blood sampling. Rats drank water containing 1% NaCl and 0.2% KCl. After a 7 day recovery and 3 day control period, a DOCA pellet (50 mg/kg, sc) was implanted in some rats, while others had sham surgery. NE spillover was measured following a 90 minute 3H‐NE infusion on control day 2, and days 7 and 14 after DOCA administration or sham surgery. During the control period, mean arterial pressure (MAP) was similar in sham (106 ± 4.2 mmHg) and DOCA (107 ± 4.5 mmHg) rats. MAP was higher in DOCA rats on day 7 and 14 (113 ± 7.5 and 124 ± 5.8 mmHg) than in sham rats (104 ± 2.0 and 108 ± 15.6 mmHg). However, plasma NE concentration, clearance and spillover were not different at any time in DOCA versus sham rats. To examine possible regional sympathetic activation, celiac ganglionectomy (CGX) was performed to selectively denervate the splanchnic organs. MAP was lower in CGX than in sham‐operated rats during DOCA‐salt treatment. In conclusion, global SNA is not increased during development of DOCA‐salt hypertension, but sympathetic activation may occur specifically in the splanchnic region.

Accelerated Decline in Circulating Progenitor Cells Due to Aldosterone Excess in Experimental Hypertension

Introduction: Bone marrow-derived progenitor cells may have a reparative and thus potentially therapeutic role in cardiovascular disease. Reduced reparative progenitor cell production or function may play a role in hypertension related vascular injury. Further, in vitro studies suggest that humoral activation (aldosterone) impairs production of progenitor cells, potentially limiting endogenous repair mechanisms and accelerating vascular damage during the transition to heart failure. Hypothesis: We hypothesized that circulating progenitor cells would be depleted in vivo in response to experimental hypertension and that these changes would be accelerated in the presence of concomitant aldosterone excess. Methods: Ten dogs underwent renal wrapping (RW) to induce hypertension. Blood pressure (BP) was measured weekly. After development of hypertension (5 weeks after RW), dogs were randomized to receive deoxycorticosterone acetate (1mg/kg/day for 3 weeks; HTN + DOCA) or not (HTN). Flow cytometric analysis for CD34+ (progenitor) cells was performed on whole blood harvested prior to and every 2 weeks after RW. ISHAGE criteria were used to enumerate CD34+ cells. Results: See Figure. Dogs were similarly hypertensive at 5 weeks; BP increased week 5-8 only in HTN + DOCA dogs. The CD34+ cell counts were similar prior to RW and decreased over time after RW in both groups. However, the decline in CD34+ cells was accelerated in the HTN + DOCA dogs after DOCA treatment. Conclusion: This study demonstrates a progressive decrease in circulating progenitor cells over time after the onset of experimental hypertension. This may represent impaired bone marrow production or homing to sites of hypertension related vascular injury. However, the dramatic drop in CD34+ cells after DOCA administration is consistent with the previous in vitro studies suggesting that aldosterone impairs bone marrow derived progenitor cell formation. These data support the concept that humoral activation accelerates vascular injury by limiting endogenous reparative mechanisms.

Mechanical Asynchrony in Experimental Hypertensive Heart Disease

Introduction: Elderly patients (pts) with hypertensive heart disease (HHD) develop heart failure with preserved ejection fraction (HFpEF). Recently, left ventricular (LV) mechanical asynchrony (MA) has been reported in HFpEF. The factors which mediate development of MA and its role in progression from HHD to HFpEF remain unclear. Objective: Determine if aging or HHD is associated with MA and whether MA is related to alterations in LV structure or function. Methods: Elderly (n = 22; 8-12 years) dogs were studied before (Old) and 8 weeks after (Old-HTN) renal wrapping to produce chronic HHD with (n = 11) or without (n = 11) concomitant DOCA administration to vary degree of LV fibrosis.

Renal impairment in deoxycorticosterone acetate‐salt hypertensive rats

Summary: This study has compared renal function in deoxycorticosterone (DOCA)‐salt hypertensive Wistar rats (uninephrectomy followed by administration of DOCA 25 mg subcutaneously every fourth day and 1% NaCl in the drinking water) with various control rats using the isolated perfused kidney preparation. The systolic blood pressure of DOCA‐salt hypertensive rats was 180 ± 10 mmHg (uninephrectomy controls: 136 ± 9 mmHg) while normalization of calcium intake (DOCA‐Ca rats, 1% CaCl2 in water) attenuated this increase (systolic blood pressure, 146 ± 5 mmHg). Renal mass corrected for body weight increased by 25% after uninephrectomy, 55% in uninephrectomized rats given NaCl, 152% in DOCA‐salt rats and 147% in DOCA‐Ca rats. At a renal perfusion pressure of 135 mmHg, isolated perfused kidneys from DOCA‐salt rats showed decreases of 48% in glomerular filtration rate and 69% in sodium excretion with an increase of 44% in renal vascular resistance compared with uninephrectomized rats. There were no significant differences in renal function between DOCA‐salt and DOCA‐Ca rats. Histological assessment of renal pathology showed proximal tubular hypertrophy and hyperplasia, marked focal distal tubular atrophy, interstitial fibrosis and glomerular hypercellularity in DOCA rats compared with UNX rats. Lesions were less obvious in UNX‐salt or DOCA‐Ca rats. The lack of direct correlation between alterations in function and pathology may be explained by the compensatory effect of remaining healthy or hypertrophied nephrons. Thus, the DOCA‐salt model of hypertension in rats is associated with marked structural kidney damage and severely decreased kidney function. Marked attenuation of systemic hypertension by normalizing calcium intake in DOCA‐salt rats did not prevent impairment of kidney function.

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.

Regulation of brain renin-angiotensin system by benzamil-blockable sodium channels.

Changes in the renin-angiotensin system (RAS) mRNAs in the brain and the kidney of rats after administration of DOCA and/or sodium chloride were assessed by use of a competitive PCR method. Benzamil, a blocker of amiloride-sensitive sodium channels, was infused intracerebroventricularly or intravenously for 7 days in DOCA-salt or renal hypertensive rats, and the effects of benzamil on the brain RAS mRNAs were determined. Renin and ANG I-converting enzyme (ACE) mRNAs were not downregulated in the brain of rats administered DOCA and/or salt; however, these mRNAs were decreased in the kidney. Intracerebroventricular infusion of benzamil decreased renin, ACE, and ANG II type 1 receptor mRNAs in the brain of DOCA-salt hypertensive rats but not in the brain of renal hypertensive rats. The gene expression of the brain RAS, particularly renin and ACE, is regulated differently between the brain and the kidney in DOCA-salt hypertensive rats, and benzamil-blockable brain sodium channels may participate in the regulation of the brain RAS mRNAs.

Effect of pyridoxine and tryptophan, alone and combined, on the development of deoxycorticosterone acetate-induced hypertension in rats.

Chronic dietary administration of pyridoxine HCl (300 mg/kg/day), L-tryptophan (1.26 g/kg/day), or a combination of the two can attenuate the elevation of systolic blood pressure in DOCA-salt-treated rats. With these treatments, the characteristic increase in the weight of the heart accompanying chronic administration of DOCA (786 micrograms/kg/day) was also attenuated. Thus, both tryptophan and pyridoxine possess antihypertensive properties, and the combination of the two appeared to provide greater protection than either alone. The results are consistent with the possibility that pyridoxine, an important cofactor in the metabolic pathways for tryptophan, may facilitate the conversion of tryptophan to antihypertensive compounds. Additional studies will be required to determine which of the metabolites of tryptophan possess antihypertensive properties. Pyridoxal phosphate, one of the metabolites of pyridoxine, was also administered chronically in the diet (1.0 and 2.0% by weight) to rats whose blood pressures were elevated by administration of DOCA. The results of this study suggest that pyridoxal phosphate can also lower the blood pressure of rats with established hypertension. Thus, these studies reveal that pyridoxine, pyridoxal phosphate and tryptophan are potential antihypertensive agents.

The Effect of Plantains (Musa paradisiaca) on DOCA-Induced Hypertension in Rats

AbstractDesoxycorticosterone acetate (DOCA) administration to rats placed on normal rat feed elevated the mean arterial blood pressure. The consumption of plantain diet by rats previously treated with DOCA lowered the mean arterial blood pressure to control values. DOCA administration to rats previously placed on plantain diet produced no significant change in the mean arterial blood pressure when compared with control.Chronic consumption of plantain diet is capable of lowering the DOCA-induced elevated mean arterial pressure in rats. Plantain diet can also prevent the onset of DOCA-induced hypertension in rats.

Nephron site responsible for the reduced kaliuretic response to mineralocorticoids during hypokalemia in rats

Rats with hypokalemia induced by eating a low-K diet have a diminished kaliuretic response to mineralocorticoids. The purpose of this study was to determine if this was the due to a lower rate of net secretion of K in the cortical collecting duct (CCD) and/or an enhanced rate of reabsorption of K in the medullary collecting duct (MCD). Secondary active secretion of K in the CCD raises the [K] in the lumen as compared to the plasma [TF/P)K). If the (TF/P)K is greater than 1, there was secondary active secretion of K in this nephron segment. The (TF/P)K in the CCD was measured by microcatheterization of the collecting duct. Three groups of rats were studied: rats on a low-K diet with and without the acute administration of DOCA, and rats on a normal-K diet treated with DOCA on a chronic basis. Rats on the low-K diet had a (TF/P)K of 0.8 +/- 0.11; this value did not rise to values significantly greater than 1 after the acute administration of DOCA (1.4 +/- 0.35). In contrast, chronic administration of DOCA to rats fed a normal-K diet did result in a (TF/P)K which was significantly greater than unity (3.1 +/- 0.39). The degree of hypokalemia was not significantly different in these rats. The absolute and fractional reabsorption of K in the MCD was not different in the rats on the low-K diet with or without DOCA. We conclude that the nephron segment which is responsible for the reduced kaliuretic response to mineralocorticoids is the CCD.

Neuromodulator mechanism of the inhibitory influence of deoxycorticosterone on the aggressive-defensive behavior of rats.

1. Deoxycorticosterone (DOCA) in a dose of 0.3 mg/kg has an inhibitory effect on the aggressive-defensive behavior provoked by pain stimulation, which is expressed in an increase in the thresholds of the major components of the reaction and a decrease in the number of instances of fighting. 2. Activation of the central N-cholino- or β-adrenoreceptors is accompanied by an inhibition of the aggressive-defensive behavior. Blockade of these receptors induces the opposite effect. 3. Administration of DOCA against a background of activation of the β-adrenoreceptors of the brain leads to a potentiation of the effect of their excitation and a sharp inhibition of the aggressive-defensive behavior. A change in the functional state of the central N-cholinoreceptors has no significant influence on the effects of the hormone. 4. The results obtained suggest that the mechanism of the inhibitory influence of DOCA on the aggressive-protective behavior of rats includes a facilitation of the activation of the central β-adrenoreceptors.

Parallel effects of DOCA on salt appetite, thirst, and blood pressure in sheep.

Salt appetite was quantified in sheep by measuring the relative amounts of high-salt (266 meq/kg) and low-salt (6 meq/kg) pelleted alfalfa that they ate. Given a choice of these two foods, normal sheep ate twice as much low-salt as high-salt pellets. Following DOCA administration the sheep rapidly developed an increased salt appetite, and after 10 days they ate approximately three times as much high-salt as low-salt pellets. Their choice rapidly reverted to control values after the end of the DOCA treatment. The changes in salt appetite were accompanied by changes in thirst and mean arterial pressure. We hypothesize that these effects of DOCA reflect changes that parallel those this mineralocorticoid causes in the hypothalamic regulatory centers for salt appetite, thirst, and blood pressure.