Altered protein kinase C regulation of phosphoinositide-coupled receptors in deoxycorticosterone acetate-salt hypertensive rats

Obesity-Induced Hypertension Develops in Young Rats Independently of the Renin-Angiotensin-Aldosterone System

A correlation exists between obesity and hypertension. In the currently available models of diet-induced obesity, the treatment of rats with a high fat (HF) diet does not begin until adulthood. Our aim was to develop and characterize a model of pre-pubescent obesity-induced hypertension. Male Sprague-Dawley rats were fed a HF diet (35% fat) for 10 weeks, beginning at age 3 weeks. Blood pressure was measured by tail-cuff, and a terminal blood sample was obtained to measure fasting blood glucose, insulin, plasma renin, aldosterone, thiobarbitutic acid reactive substances (TBARS), and free 8-isoprostanes levels. The vascular reactivity in the aorta was assessed using a myograph. Blood pressure was increased in rats fed the HF diet (HF, 161 ± 2 mm Hg vs. control, 137 ± 2 mm Hg, P < 0.05). Blood glucose (HF, 155 ± 4 mg/dL vs. control, 123 ± 5 mg/dL, P < 0.05), insulin (HF, 232 ± 63 pM vs. control, 60 ± 11 pM, P < 0.05), TBARS (expressed as nM of malondialdehyde [MDA]/ml [HF, 1.8 ± 0.37 nM MDA/ml vs. control 1.05 ± 0.09 nM MDA/ml, P < 0.05]), and free 8-isoprostanes (HF, 229 ± 68 pg/ml vs. control, 112 ± 9 pg/ml, P < 0.05) levels were elevated in the HF diet group. Interestingly, plasma renin and aldosterone levels were not different between the groups. The maximum vasoconstriction to phenylephrine (10−4 M) was increased in the HF diet group (HF, 26.1 ± 1.5 mN vs. control 22.3 ± 1.2 mN, P < 0.05). In conclusion, pre-pubescent rats become hypertensive and have increased oxidative stress and enhanced vasoconstriction when fed a HF diet. Surprisingly, this occurs without the increase in renin or aldosterone levels seen in the adult models of diet-induced obesity.

A review of deoxycorticosterone acetate-salt hypertension and its relevance for cardiovascular physiotherapy research

[Purpose] The purpose of this review was to elucidate the deoxycorticosterone acetate (DOCA)-salt-related hypertensive mechanism and to contribute to future studies of cardiovascular physiotherapy. [Methods] This paper focuses on the signal transductions that control hypertension and its mechanisms. We include results reported by our laboratory in a literature review. [Results] Our results and the literature show the various mechanisms of DOCA-salt hypertension. [Conclusion] In this review paper, we carefully discuss the signal transduction in hypertension based on our studies and with reference to cardiovascular physiotherapy research.

Elevated mean arterial pressure in the ovariectomized rat was normalized by ET(A) receptor antagonist therapy: absence of cardiac hypertrophy and fibrosis

1. The influence of menopause on ventricular function and remodelling remains undefined. The following study examined the effect of ovariectomy on ventricular contractility, cardiac hypertrophy and extracellular matrix protein expression. 2. Elevated circulating levels of the vasoconstrictor endothelin-1 have been reported in post-menopausal women. Moreover, endothelin-1 has been shown to influence blood pressure, ventricular function and cardiac remodelling. In this regard, the potential pathophysiological role of endothelin-1 in the ovariectomized rat was assessed via the administration of the selective endothelin(A) receptor (ET(A)) antagonist BMS-182874. 3. In 3 and 6 week ovariectomized female Sprague - Dawley rats, uterus atrophy was associated with a significant increase in mean arterial pressure, and left ventricular systolic pressure, as compared to sham. By contrast, right ventricular contractile indices were normal in the ovariectomized rat. Despite increased systolic load, left ventricular hypertrophy was not evident, prepro-atrial natriuretic peptide (prepro-ANP) mRNA levels and collagen protein content were similar to sham. 4. The treatment of ovariectomized rats with BMS-182874 (60 mg kg(-1) per day) did not reverse uterus atrophy. However, BMS-182874 normalized mean arterial pressure, and left ventricular systolic pressure in the ovariectomized rat. 5. Thus, despite elevated blood pressure, ovariectomized rats were not associated with either cardiac hypertrophy or fibrosis. Lastly, endothelin-1, acting via the stimulation of the ET(A) receptor represents an integral mechanism implicated in the increase of mean arterial pressure following ovariectomy.

A farnesyltransferase inhibitor attenuates cardiac myocyte hypertrophy and gene expression

The overexpression of either oncogenic ras or calmodulin in cardiac myocytes can elicit a hypertrophic response, albeit their recruitment by physiologically relevant stimuli remains unresolved. The present study utilized a pharmacological approach to examine the role of ras and calmodulin in norepinephrine- and endothelin-1-stimulated hypertrophy of neonatal rat cardiac myocytes. The pretreatment of cardiac myocytes with the farnesyltransferase inhibitor BMS-191563 (25 microM) increased the level of unfarnesylated ras in the cytosolic fraction, and caused a concomitant 42 +/- 2% decrease in immunodetectable farnesylated ras in the particulate fraction. In parallel, BMS-191563 pretreatment inhibited norepinephrine-mediated 3H-leucine uptake (80 +/- 10% decrease: n = 6; P<0.01), whereas a significant but less pronounced effect on the endothelin-1 response (46 +/- 6% decrease: n = 6; P<0.05) was observed. The calmodulin inhibitor W7 caused a 50 +/- 10% decrease (n = 8; P<0.05) of norepinephrine stimulated protein synthesis, whereas the endothelin-1 response was unaffected. Consistent with the recruitment of ras, BMS-191563 pretreatment attenuated norepinephrine and endothelin-1-stimulated extracellular signal-regulated kinase (ERK) activity. However, PD098059-mediated inhibition of MEK-dependent stimulation of ERK did not alter the hypertrophic response of either agonist. At the molecular level, the pretreatment with either BMS-191563 or W7 attenuated the norepinephrine-mediated increase of prepro-ANP and -BNP mRNA. Likewise, BMS-191563 caused a significant decrease of endothelin-1-mediated expression of the natriuretic peptide mRNAs, but to a lesser extent, as compared to norepinephrine. Thus, the present study has shown the treatment of neonatal rat cardiac myocytes with a farnesyltransferase inhibitor can attenuate the hypertrophic phenotype in response to physiologically relevant stimuli, thereby supporting a role of the small GTP-binding protein ras. Moreover, these data further suggest alternative ras-independent signaling pathways are also implicated in the hypertrophic response, albeit, there appears to exist a stimulus-specific heterogeneity in their recruitment.

Cardiac and vascular responses in deoxycorticosterone acetate-salt hypertensive rats

1. Hypertension leads to ventricular hypertrophy and, eventually, to heart failure. The present study has investigated the functional consequences of deoxycorticosterone acetate (DOCA)-salt hypertension in rats by defining the inotropic, chronotropic and vascular responses to noradrenaline (NA; beta1-adrenoceptor agonist), forskolin (adenylate cyclase activator) and theophylline (phosphodiesterase inhibitor). 2. Administration of DOCA (25 mg, s.c., every 4th day) and excess salt (1% NaCl in drinking water) to uninephrectomized rats increased left ventricular wet weight by 35 and 71% after 4 and 8 weeks, respectively. Addition of KCl (0.4%) or CaCl2 (1%) in the drinking water for 4 weeks attenuated blood pressure increases, but not ventricular weight increases (46 and 28%, respectively). 3. Positive inotropic responses in papillary muscles from uninephrectomized rats to NA (-log EC50 6.73+/-0.38; n = 7), forskolin (-log EC50 6.15+/-0.31; n = 7) and CaCl2 (-log EC50 2.40+/-0.02; n = 14) were unchanged in hypertrophied left ventricles of DOCA and DOCA-CaCl2 rats, although maximal responses to NA were decreased in DOCA-KCI rats (1.2+/-0.6 mN, n = 8; DOCA-salt 2.9+/-0.5 mN, n = 6); theophylline was less potent in DOCA-salt rats. Positive chronotropic responses to NA, forskolin and theophylline in right atria and negative inotropic responses to carbachol in papillary muscles were unchanged. 4. Maximal vasoconstrictor responses to NA in thoracic aortic rings were reduced in DOCA-KCI rats to 2.4+/-0.9 mN (n = 5), but were increased in DOCA-CaCl2 rats to 26.6+/-2.2 mN (n = 7; DOCA-salt 7.8+/-2.2 mN, n = 9). Vasorelaxant responses to forskolin and theophylline were unchanged. 5. These results show that cardiac responses are only minimally affected during the development of DOCA-salt hypertension-induced hypertrophy, despite the reported decreases in adenylate cyclase activity, in these rats. This is in contrast with the decreased responses reported in other rat models of cardiac hypertrophy and in the failing human heart. Thus, hypertrophy in hearts of DOCA-salt hypertensive rats does not produce similar changes to the failing human heart.

Activation of phospholipase C delta1 through C2 domain by a Ca(2+)-enzyme-phosphatidylserine ternary complex

The concentration of free Ca(2+) and the composition of nonsubstrate phospholipids profoundly affect the activity of phospholipase C delta1 (PLCdelta1). The rate of PLCdelta1 hydrolysis of phosphatidylinositol 4,5-bisphosphate was stimulated 20-fold by phosphatidylserine (PS), 4-fold by phosphatidic acid (PA), and not at all by phosphatidylethanolamine or phosphatidylcholine (PC). PS reduced the Ca(2+) concentration required for half-maximal activation of PLCdelta1 from 5.4 to 0.5 microM. In the presence of Ca(2+), PLCdelta1 specifically bound to PS/PC but not to PA/PC vesicles in a dose-dependent and saturable manner. Ca(2+) also bound to PLCdelta1 and required the presence of PS/PC vesicles but not PA/PC vesicles. The free Ca(2+) concentration required for half-maximal Ca(2+) binding was estimated to be 8 microM. Surface dilution kinetic analysis revealed that the K(m) was reduced 20-fold by the presence of 25 mol % PS, whereas V(max) and K(d) were unaffected. Deletion of amino acid residues 646-654 from the C2 domain of PLCdelta1 impaired Ca(2+) binding and reduced its stimulation and binding by PS. Taken together, the results suggest that the formation of an enzyme-Ca(2+)-PS ternary complex through the C2 domain increases the affinity for substrate and consequently leads to enzyme activation.