Insulin and insulin-like growth factor-I promotes angiotensinogen production and growth in vascular smooth muscle cells.

BACKGROUND: Circulating insulin and insulin-like growth factor-I (IGF-I) levels are increased in patients with hypertension and insulin resistance. Since both hormones are known to have cell growth-promoting effects, they may contribute to the progression of vascular hypertrophy in patients with insulin resistance. Insulin-mediated activation of the vascular renin-angiotensin system (RAS) stimulates growth in cultured rat vascular smooth muscle cells (VSMC). OBJECTIVE: In order to evaluate the role of IGF-I-mediated activation of components of the tissue RAS, we examined the effect of IGF-I receptor stimulation on cell proliferation, and production of angiotensinogen in cultured VSMC. STUDY DESIGN: Aortic VSMC were derived from male Sprague-Dawley rats. IGF-I and insulin-mediated DNA synthesis were estimated by 3H-thymidine uptake (3H-TdR) with or without the angiotensin I converting enzyme inhibitor, captopril. Moreover, angiotensinogen released by the cells to the culture medium was determined by radioimmunoassay with or without the anti-IGF-I receptor antibody alphaIR3 or captopril. RESULTS: Both IGF-I and insulin increased 3H-TdR uptake by cultured rat VSMC (P < 0.05). Captopril blocked IGF-I and insulin-mediated 3H-TdR uptake (-34.4 +/- 1.9% and -32.7 +/- 1.8%, P < 0.05, respectively). IGF-I increased the angiotensinogen level in the medium by 30.6 +/- 2.9% (P < 0.01). Insulin also stimulated angiotensinogen synthesis by 26.3 +/- 2.2% (P < 0.01). Captopril and alphaIR3 significantly suppressed angiotensinogen production stimulated by both IGF-I and insulin. CONCLUSIONS: These results indicate that IGF-I as well as insulin stimulates angiotensinogen production and growth in VSMC. Thus, both hormones may independently play a role in progression of the vascular hypertrophy and atherosclerosis in patients with hypertension and insulin resistance through activation of the tissue RAS.

Erythropoietin upregulates angiotensin receptors in cultured rat vascular smooth muscle cells.

OBJECTIVE: Plasma renin is not elevated in recombinant human erythropoietin (rhEPO)-induced hypertension but angiotensin converting enzyme inhibitors reduce blood pressure in both human and animal studies. Since rhEPO elevates renin and angiotensinogen messenger RNAs in angiotensin II target tissues such as the aorta, we explored the actions of rhEPO on renin-angiotensin system-related gene transcription of cultured rat vascular smooth muscle cells. DESIGN AND METHODS: To separate direct actions of rhEPO from those mediated secondarily by potential activation of the renin-angiotensin system, vascular smooth muscle cells were cultured with rhEPO and enalapril to inhibit the angiotensin converting enzyme and losartan to inhibit angiotensin II type 1 receptors. RESULTS: Vascular smooth muscle cells cultured with rhEPO (6-8 units/ml) demonstrated elevations (40-120%) in messenger RNAs of the renin-angiotensin system (renin, angiotensinogen, angiotensin receptor types 1 and 2) and increased levels of several messenger RNAs known to respond to angiotensin II (transforming growth factor-beta, insulin-like growth factor-II, epidermal growth factor, c-fos and platelet-derived growth factor). In contrast, cells cultured in the presence of rhEPO and enalapril or losartan showed elevations of messenger RNA for only the two types of angiotensin II receptor. This increase was higher than that obtained when cells were cultured with rhEPO or either antagonist alone. The increase in specific binding of angiotensin II to cells cultured in the presence of rhEPO and enalapril or rhEPO and losartan paralleled the changes in receptor messenger RNA. CONCLUSIONS: rhEPO exerts its primary action on vascular smooth muscle cells via an increase in angiotensin receptor messenger RNA, resulting in a parallel increase in angiotensin II receptor expression. We suggest that increased receptor expression secondarily mediates the expression of other renin-angiotensin system messenger RNAs, which leads to angiotensin II-responsive gene transcription. The elevation in angiotensin II receptors, as observed in response to rhEPO, may provide a mechanism by which other forms of renin-dependent hypertension are initiated.

Insulin-mediated growth in aortic smooth muscle and the vascular renin-angiotensin system.

Insulin has been shown to directly affect blood vessel tone and to promote vascular hypertrophy, but the mechanism of these actions remains uncertain. Because angiotensin I (Ang I)-converting enzyme inhibitors have been shown to improve insulin action and to impede the progression of vascular hypertrophy in hypertensive animal models, it is possible that the vascular properties of insulin may be mediated through the tissue renin-angiotensin system (RAS). To evaluate this relationship, we first investigated the effect of insulin on components of the RAS using cultured rat vascular smooth muscle cells (VSMCs). Insulin treatment (1000 microU/mL) markedly increased angiotensinogen mRNA expression and angiotensinogen production. We next investigated the role of the RAS in insulin-mediated cell proliferation, using [3H]thymidine uptake. Studies were done both with insulin alone and in the presence of captopril (1x10(-7) to 10(-5) mol/L) and losartan (1x10(-9) to 10(-7) mol/L). [3H]Thymidine uptake was increased significantly by 1000 microU/mL insulin, and this stimulation was reduced by 1x10(-6) mol/L captopril (-38.8%, P<0.05) and by 1x10(-8) mol/L losartan (-37. 5%, P<0.05). Further studies showed that the degree of insulin-mediated [3H]thymidine uptake in VSMCs could be duplicated by 4x10(-10) mol/L Ang II. Losartan reduced the effects of both Ang II and insulin on [3H]thymidine uptake by about 40% to 45% of baseline (P<0.05). Captopril reduced insulin-mediated [3H]thymidine uptake but did not affect Ang II-mediated [3H]thymidine uptake. In summary, insulin induced significant stimulation of angiotensinogen expression and production and stimulated growth similar to that seen with Ang II in cultured rat VSMCs. Inhibition of Ang II production or its binding to the Ang II type 1 (AT1) receptor inhibited insulin-mediated growth in a fashion similar to that seen with inhibition of Ang II-mediated growth. Thus, insulin can modulate the vascular RAS, and the effect of insulin on vascular growth may be via direct effects on angiotensinogen expression and translation operative through both the AT1 receptor and the conversion of Ang I to Ang II.

Cigarette smoke increases gastric ulcer size in part by an angiotensin II-mediated mechanism in rats.

To assess the mechanism of the effect of cigarette smoke on ulcer disease we employed a rat model in which cigarette smoke increases the size of acetic acid-induced gastric ulcer and decreases the hyperemia at the ulcer margin. We postulate that cigarette smoke increases angiotensin II (a vasoconstrictor) in ulcer tissue. Since direct measurement of angiotensin II in small tissue samples is problematic, we compared the messenger ribonucleic acid (mRNA) for its precursors (angiotensinogen and renin) in ulcer and normal gastric tissue. We also evaluated the effect of enalapril, which blocks the conversion of angiotensin I to angiotensin II on ulcer size. In the ulcer tissue, cigarette smoke produced a significant increase in mRNA for angiotensinogen but not for renin. Enalapril decreased the size of the gastric ulcer in rats exposed to cigarette smoke. The data support the possibility that in ulcer tissue cigarette smoke stimulates an angiotensin II-mediated mechanism, which may in part be responsible for the impairment of ulcer margin hyperemia and aggravation of ulcer size.

Angiotensinogen messenger RNA stabilization by angiotensin II.

OBJECTIVE: To further characterize the molecular mechanism whereby angiotensin II stabilizes the angiotensinogen messenger (m)RNA through binding studies of the previously isolated polysomal stabilizing protein to partial and mutagenized sequences of the 3' untranslated region of the gene and to explore its importance to rodent genetic hypertension. DESIGN: Analysis of angiotensinogen mRNA mutants for half-life and binding to a polysomal protein with a molecular weight of 12000. METHODS: Protein/RNA interactions were determined in band shift assays employing radiolabelled 3' untranslated region of angiotensinogen mRNA. Measurement of the mRNA half-life used a cell-free incubation system and 3' untranslated region DNA sequences were polymerase chain reaction (PCR) cloned and sequenced. Sequences of normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rat (SHR) strains were compared. Point mutations were introduced by site directed mutagenesis. RESULTS: The angiotensinogen 3' untranslated region exhibited specific binding to the polysomal 12000 molecular weight protein which, in an in vitro incubation system, increased 10-fold the half-life of full-length angiotensinogen mRNA; no effect was observed with 3' deleted angiotensinogen mRNA indicating a regulatory function of protein at the 3' untranslated region. Sequence analysis of PCR amplified DNA fragments identified a (G-->C) point mutation in the La Jolla colony SHR. Following introduction of this point mutation into wild-type 3' untranslated regions, protein binding significantly increased (wild-type binding constant, 19 mumol/l; mutant binding constant 3.5 mumol/l), indicating that this point mutation affects 3' untranslated region secondary structure, binding of the RNA stabilizing protein and, consequently, the half-life of angiotensinogen mRNA. Deletion of a U-rich region (position 1609-1613, UCCUU) expressed twice in the 3' untranslated region almost completely abolished protein binding suggesting this sequence as one part of the putative binding motif in the 3' untranslated region. CONCLUSIONS: Angiotensin II regulates hepatic angiotensinogen synthesis and secretion by inhibiting degradation of angiotensinogen mRNA by the action of a polysomal protein. Mutations in the 3' untranslated region mRNA coding sequence alter binding and half-life and may significantly affect the half-life of angiotensinogen mRNA thereby altering the secretion rate of angiotensinogen.

Hepatic angiotensin II nuclear receptors and transcription of growth-related factors.

OBJECTIVES: To investigate the influence of angiotensin II (All) receptors in isolated hepatic nuclei on other genes regulated by All and to determine whether the function of these intracellular receptors is influenced by alterations in the endocrine renin system. METHODS: Nuclei were isolated from hepatic tissue of normal and bilaterally nephrectomized or adrenalectomized Wistar rats. Following nuclear run-off, in the presence of varying All concentrations, specific messenger RNAs (mRNA) were determined by slot blot hybridization. Tissue levels of renin system components were measured by radioimmunoassay and nuclear receptors characterized by displacement of radiolabeled All with specific All receptor antagonists. RESULTS: All binding in the presence of DUP 753 and PD 123177 confirmed that nuclear All receptors can be classified as AT1 receptors and that as much as 10% of the specific binding is attributable to nuclear chromatin. All stimulated not only the production of mRNA for renin system components such as renin and angiotensinogen, but also that of mRNA for growth-related factors such as platelet-derived growth factor and the oncogene c-myc. Maximal stimulation occurred at 10(-9) mol/l All; higher concentrations reduced this response. After stimulation or suppression of the plasma renin system by adrenalectomy or bilateral nephrectomy, nuclei isolated from rat hepatic tissue contained elevated endogenous levels of growth-related and renin system mRNA including AT1 and AT2 All receptors. However, despite the level of receptor mRNA having been elevated, the total All receptor density of isolated nuclei decreased. In addition, after both maneuvers, isolated nuclei were refractory to All-induced gene transcription. CONCLUSION: The existence of mechanisms producing intracellular All and regulating its level, which in turn exert local regulatory responses via nuclear All receptors, lends significance to the presence of a functional intracrine renin system that could act in concert with or independently of the endocrine renin system.

Cloning and functional characterization of the amphibian mesotocin receptor, a member of the oxytocin/vasopressin receptor superfamily.

Mesotocin is the oxytocin-like hormone found in most terrestrial vertebrates from lungfishes to marsupials, which includes all non-mammalian tetrapods (amphibians, reptiles, and birds). It has the largest distribution in vertebrates after vasotocin found in all non-mammalian vertebrates and isotocin identified in bony fishes. In this study, we report the cloning and functional characterization of the cDNA for the mesotocin receptor (MTR) from the urinary bladder of the toad Bufo marinus. The cloned cDNA encodes a polypeptide of 389 amino acids that shows the greatest similarity to the teleost fish isotocin receptor and to mammalian oxytocin receptors with mutations in extracellular loops which are involved in ligand binding. When expressed in COSM6 cells, MTR exhibits the following relative order of ligand affinity: mesotocin > vasotocin = oxytocin > vasopressin > hydrin 1, isotocin, hydrin 2. Injection of MTR cRNA into Xenopus laevis oocytes induces membrane chloride currents in response to mesotocin, which indicates the coupling of the mesotocin receptor to the inositol phosphate/calcium pathway. This response is inhibited by an oxytocin antagonist, but not by a vasopressin antagonist specific for V2 vasopressin receptors. MTR mRNA is not only found in toad urinary bladder, but also in kidney, muscle, and brain tissue of the toad as revealed by northern blot analysis and reverse-transcriptase PCR. The results suggest a variety of function for mesotocin and its receptor including, in particular, an involvement in the regulation of water and salt transport.

Tonic inhibition of renin secretion by the 12 lipoxygenase pathway: augmentation by high salt intake.

Recent evidence suggests that lipoxygenase (LO) metabolites inhibit renin production in vitro. However, the physiological significance of this effect has not been determined. This study examined the role of the LO pathway in the regulation of plasma renin concentration (PRC) in vivo. The acute administration of two structurally unrelated LO inhibitors, phenidone (30 and 60 mg/kg) and esculetin (60 mg/kg), resulted in suppression of platelet 12 hydroxyeicosatetraenoic acid (12HETE) production, reduction in systemic arterial pressure and a 2- to 3-fold increase in PRC. To determine whether the esculetin-induced increase in PRC was secondary to hypotension, esculetin was also administered to rats preinfused with a pressor dose of norepinephrine. In these acutely hypertensive rats, esculetin still induced a 2.5-fold increase in PRC, whereas blood pressure remained over 40 mm Hg above basal levels. Further, esculetin (10(-6)M) increased renin release in renal slices from 150 +/- 10 to 310 +/- 20 ng/ml.h (P < 0.05) and this rise was entirely blocked in the presence of 12HETE (10(-7)M; 130 +/- 40 ng/ml.h). In rats placed on high salt intake, 12HETE concentration in renal slices from the outer cortex was considerably higher than in renal slices from salt-restricted rats (116.5 +/- 15.7 vs. 65 +/- 12 pg/mg protein; P < 0.05). Chronic administration of the LO inhibitor phenidone also resulted in an increase of PRC, which was independent of changes in blood pressure. On either high salt (3.15%0 or low salt (0.05%) diet phenidone-treated rats had higher PRC levels than the respective control groups [high salt 9.7 +/- 3.5 vs. 1.9 +/- 1.4 ng/ml.h; P < 0.05; low salt 33.2 +/- 5.3 vs. 19.4 +/- 3.10 ng/ml.h; P < 0.05]. The finding that LO blockers are potent stimulators of PRC in vivo suggests the existence of a physiological tonic inhibition of renin secretion by LO products that is operative under a wide range of salt intake. High salt intake enhances this inhibitory tone by increasing renal cortical 12 LO activity and, in fact, normal suppression of PRC during high salt diet does not occur in LO-blocked animals. Thus, the LO pathway exerts a tonic inhibitory effect on renin release, which appears particularly important for renin suppression during high salt intake.

Angiotensin-converting enzyme inhibition in the treatment of renal transplant erythrocytosis. Clinical experience and observation of mechanism.

Recent observations indicate that angiotensin-converting enzyme (ACE) inhibition corrects renal transplant erythrocytosis (RTE). The mechanism for this association is not known. We examined the effect of ACE inhibition on hematocrit, erythropoietin (EPO), and renin substrate. ACE inhibition has been reported to suppress renin substrate, which is known to stimulate EPO and erythropoiesis. In 15 patients with RTE, hematocrit dropped from 52.8 +/- 0.6 (SEM) to 45.8 +/- 1.4% after 8 weeks of treatment with Enalapril, 2.5-20 mg/day. Serum EPO (normal range: 9-30 mU/ml) was high in one, normal in seven, and low in seven patients. ACE inhibition reduced EPO in patients with initial high or normal levels but induced no change in patients with initial low levels. ACE inhibition had no significant effect on renin substrate. In one patient who rejected his first graft, erythrocytosis recurred following a second, successful transplant. Treatment was discontinued because of cough in two patients and symptomatic drop in blood pressure in one patient. We conclude RTE is not caused by hypererythropoietinemia. In patients with normal circulating EPO, erythrocytosis may result from an increase sensitivity to EPO, and ACE inhibition lowered hematocrit by further reduction of this hormone. However, the finding of erythrocytosis in half our patients with suppressed EPO, suggests the participation of non-EPO-mediated mechanism(s). The recurrence of RTE in a patient after a second transplant raises the additional possibility of patient-specific factors in the pathogenesis of this disorder. In contrast to other reports, we documented side-effects (cough, hypotension) in three (20%) of our patients. Our clinical experience, coupled with prior reports of spontaneous resolution of RTE in some patients, suggests that intermittent courses of ACE-inhibition may be the optimal strategy in the use of this form of therapy for RTE.

A contraceptive vaginal ring releasing norethindrone acetate and ethinyl estradiol.

A core design contraceptive vaginal ring (CVR) releasing 650 mcg of norethindrone acetate (NA) and 10, 20, 30 or 65 mcg of ethinyl estradiol (EE) daily was developed and tested in 99 women. The CVR inhibited ovulation well with 30 or 65 mcg EE. Vaginal bleeding was better controlled than in 23 control women using NA/EE oral contraceptives. Side effects were comparable to controls for the 20 and 30 mcg EE CVR. The 65 mcg EE CVR resulted in an unacceptably high level of nausea. The 20 and 30 mcg EE CVR caused an increase in serum HDL cholesterol and triglycerides. Total cholesterol was unchanged. Angiotensinogen and sex hormone binding globulin-binding capacity were increased in a subgroup of the 20 and 30 mcg EE CVR subjects, similar to that of 20 controls using EE/gestodene oral contraceptives. This new CVR offers an excellent contraceptive alternative with the best performance provided by the 30 mcg EE dose.

Dose-finding study of a contraceptive ring releasing norethindrone acetate/ethinyl estradiol.

A core design contraceptive vaginal ring (CVR) with average daily release of 650 mcg of norethindrone acetate (NA) and 30 mcg of ethinyl estradiol (EE) inhibited ovulation and controlled vaginal bleeding well, but caused some nausea. This study was designed to minimally alter the dose of steroid to see if nausea could be reduced without loss of contraceptive efficacy. This 30/650 CVR was compared to a CVR releasing 20 mcg of EE and 1000 mcg of NA (20/1000) and another releasing 25 mcg of EE and 650 mcg of NA (25/650) in 69 subjects. Twenty-three subjects using an oral contraceptive containing NA/EE served as controls. Ovulation inhibition was excellent and comparable to the OC for all formulations. The CVR provided better control of vaginal bleeding than did the OC. Side effects were equivalent to the OC with the exception of a slight increase in nausea in CVR users. Lipid changes and globulin increases were comparable to oral contraceptive users. The 20/1000 CVR increased sex hormone binding globulin-binding capacity less than the other two CVRs. The performance of the three CVRs was not significantly different, but the 25/650 showed a trend of reduced performance relative to the other two formulations.

Nuclear angiotensin receptors induce transcription of renin and angiotensinogen mRNA.

The observation that nuclei from hepatic tissue exhibit specific angiotensin II (Ang II) binding led us to explore whether Ang II modulates mRNA in general, mRNA specific for renin system components, or both. Nuclei from hepatic tissue exhibited a single high-affinity (Kd = 0.4 nmol/L) Ang II-specific binding site, which was associated with increased RNA transcription. Whereas total RNA extracted from nuclei increased 1.5-fold in response to Ang II (10(-9) mol/L), specific mRNA for renin and angiotensinogen increased 7.8- and 2.5-fold, respectively. Ang II binding and induced transcription showed parallel Ang II dose responses that were both inhibited by 10(-5) mol/L DuP 753 or saralasin. Maximum Ang II binding and RNA transcription occurred at the same Ang II concentration (10(-9) mol/L). Higher doses of Ang II resulted in a progressive decrease in RNA transcription. Together, these results demonstrate that hepatic nuclei have functional Ang II-specific receptors. It is concluded that Ang II may elicit responses at nuclear receptors, which heretofore were associated only with Ang II receptors located on plasma membranes. However, the individual contribution of plasma and nuclear membrane Ang II receptors to the overall cellular Ang II transcriptional response and their possible interactions remain to be determined.

Inactivation of renin substrate by soybean trypsin inhibitors: implications for measurement of circulating inactive renin.

Semipurified soybean trypsin inhibitor added to rat and human plasma leads to a concentration dependent decrease in the rate of angiotensin I generation. This inhibition is due to binding of renin substrate to the inhibitor. Renin substrate present in nephrectomized rat plasma was more susceptible to binding than substrate of the normal rat suggesting structural differences in the substrate generated following nephrectomy. Because trypsin inhibition is necessary for measurement of active and inactive renin, we examined several alternate trypsin inhibitors. The Bowman-Birk inhibitor from soybean had similar actions as purified soybean trypsin inhibitor while trypsin inhibitors from lima bean and chicken did not depress renin substrate, but did have variable effects on the measured levels of active and total plasma renin. Surprisingly, crude soybean trypsin inhibitor did not suppress renin substrate and actually increased angiotensin I generation during PRA and PRC measurements. Since the crude preparation did not suppress renin substrate, changes in the specificity of the inhibitor may occur during its purification. The augmentation of PRA and PRC may be related to angiotensinase inhibitory actions.

The lipoxygenase inhibitor phenidone is a potent hypotensive agent in the spontaneously hypertensive rat.

Previous studies from our laboratory indicated that the lipoxygenase inhibitor phenidone markedly attenuates angiotensin II (AII) induced vascular contractility. Phenidone was also shown to inhibit the formation of vascular lipoxygenase products and to reduce blood pressure in the AII-dependent renovascular hypertensive rat. We have now examined the effects of phenidone in the spontaneously hypertensive rat (SHR). A single dose of phenidone lowered intraarterial systolic pressure in a dose dependent manner in both SHR and Wistar-Kyoto (WKY) [(max 74 +/- 15 and 22 +/- 3 mm Hg, respectively; P < .001)], but the effect was substantially greater in SHR. Long-term oral phenidone administration arrested the evolution of hypertension in 6 week old SHR treated over a period of 4 weeks (control 190 +/- 2 mm Hg; phenidone treated rats 164 +/- 4 mm Hg; P < .01). To assess the role of AII related mechanisms in the hypotensive effect of phenidone, the acute effect was studied in SHR on high and low sodium intake. In addition, the effect of captopril was compared to that of phenidone alone or captopril and phenidone in salt restricted SHR. While a single dose of phenidone (30 mg/kg, intraperitoneally) elicited similar maximal effects in SHR on high and low sodium intake (54 +/- 6 and 52 +/- 5 mm Hg compared to basal blood pressure, respectively), the hypotensive effect in sodium restricted rats was more sustained. Phenidone had no further hypotensive effect in captopril treated, salt restricted SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of transdermal estradiol with and without medroxyprogesterone acetate.

OBJECTIVE: To study the long-term biological and metabolical effects of estradiol (E2) administered by transdermal therapeutic systems with and without the addition of medroxyprogesterone acetate (MPA). DESIGN: Open, randomized, comparative trial. SETTING: The reproductive endocrine unit of a tertiary care university-affiliated hospital. PATIENTS: Fifty-seven postmenopausal women were given E2 transdermally, whereas 28 were randomized to take MPA by mouth. Fifteen premenopausal women were studied for comparison. INTERVENTIONS: Estradiol, 0.1 mg, was administered by a transdermal therapeutic system for 24.5 of 28 days and was cycled for 96 weeks. Medroxyprogesterone acetate, 10 mg, was given for days 13 to 25 of each 28-day cycle (E+P group), whereas the remainder received E2 only. MAIN OUTCOME MEASURES: Serum E2, estrone (E1), luteinizing hormone, follicle-stimulating hormone, low-density, high-density, very low-density, and total cholesterol, triglycerides, blood pressure, renin substrate, plasma renin activity, and serum aldosterone levels were measured in all subjects at baseline and in the postmenopausal women every 24 weeks until the end of study. RESULTS: Mean +/- SE levels of E2 rose significantly from baseline at 24 weeks to 426 and 355 pmol/L for the E only and E+P groups, respectively. Smaller increases of estrone (E1) were observed to 263 and 244 pmol/L for the same respective groups. As expected, baseline levels of both gonadotropins were elevated, fell significantly with E2 administration, but remained increased in comparison with values observed in younger women. Decreases of total and low-density lipoprotein (LDL) cholesterol were observed in both groups that reached statistical significance at 48 weeks or later with the exception of LDL cholesterol in the E only group. No significant change of high-density lipoprotein or very low-density lipoprotein cholesterol or triglycerides was observed. There were reductions of mean systolic and diastolic blood pressures in both groups that reached significance at 72 weeks. Mean baseline plasma renin substrate, plasma renin activity, and serum aldosterone levels were within the ranges observed in younger, healthy women and did not change significantly with E2 administration in either group. CONCLUSION: These data support the long-term efficacy and safety of this form of replacement therapy, particularly in combination with MPA, in women with a uterus.

Rapid hypertensinogenic effect of lead: studies in the spontaneously hypertensive rat.

Chronic lead exposure may cause hypertension in normotensive rats. This hypertensinogenic effect has been attributed to perturbations in the renin-angiotensin axis, the contractile response of the vascular smooth muscle, or the intracellular Ca2+ homeostasis as a consequence of the inhibition of Na(+)-K(+)-ATPase activity. In this study we examined the short-term effect of lead exposure on blood pressure, plasma renin activity, vascular contractility, and renal Na(+)-K(+)-ATPase activity and abundance in the spontaneously hypertensive rat. Our data indicate that modest lead exposure caused blood pressure elevation within two weeks in this rat strain that is genetically susceptible to the development of hypertension. This rapid blood pressure-elevating effect did not appear to depend on the mechanisms described in hypertension associated with more chronic lead exposure listed above. This acute model provides an additional approach to the study of lead-induced hypertension.

Influence of recombinant human erythropoietin on blood pressure and tissue renin-angiotensin systems.

In humans, blockade of the renin-angiotensin system with angiotensin converting-enzyme inhibitors (ANG CEI) prevents the rise in blood pressure associated with the administration of recombinant human erythropoietin (rhEPO). This study was conducted to determine whether rhEPO elevates blood pressure in normal Wistar rats and whether the renin-ANG system is affected. Groups of 10 rats each were given rhEPO, ANG CEI (enalapril), rhEPO + ANG CEI, or vehicle. Renin and/or renin substrate mRNA was measured in aortas, kidney, and heart; renin activity (PRA), inactive renin, and renin substrate were measured in plasma. rhEPO raised blood pressure in the normal rat without changing the plasma renin system. ANG CEI prevented this blood pressure rise. Renin-specific mRNA was increased by rhEPO in renal tissue, and renin substrate mRNA was significantly elevated in the kidney and aorta. mRNA for renin and renin substrate were not altered in the heart. In both aorta and kidney, a significant correlation was observed between renin substrate mRNA and blood pressure. The data indicate that rhEPO modulates specific tissue renin-ANG systems, which may contribute to blood pressure elevation.

Trypsin activation of inactive renin: plasma blanks and angiotensin I radioimmunoassay.

Divergent conclusions exist as to whether inactive renin is present in nephrectomized rat plasma. A major factor contributing to this conflict may be related to significant changes in the "plasma blank" when trypsin-treated plasma is subjected to angiotensin I (AI) radioimmunoassay (RIA). In normal, but not nephrectomized rat plasma, AI-like substances are present in direct proportion to active renin. These substances are destroyed by trypsin. However, trypsin generates additional AI-like material, in both normal and nephrectomized rat plasma. This material, which is present in proportion to the renin substrate concentration, does not appear to be tetradecapeptide (TDP). In normal plasma, however, exogenous TDP is converted to AI in proportion to the active renin concentration and AI generation from TDP is increased by activation of inactive renin. However, in nephrectomized rat plasma, no AI generation from TDP was evident either before or after trypsin treatment. The coincident tryptic generation of a substance that quenches the levels of AI detected by RIA, combined with significant changes in the levels of endogenous and trypsin generated AI-like substances, may have significant bearing on the measured levels of inactive renin.

Parathyroid hormone, platelet calcium, and blood pressure in normotensive subjects.

Relations between platelet cytosolic calcium, parathyroid hormone, and blood pressure were investigated in 91 normotensive subjects: 47 men and 44 women ranging in age from 24 to 70 years. The men had higher mean arterial blood pressure, serum creatinine, and body mass index than the women. Serum total calcium, plasma ionized calcium, and parathyroid hormone (measured as both intact hormone and mid-molecule fragment) were not different between men and women; however, serum phosphate was higher in women than in men. Basal platelet cytosolic calcium was higher in men than in women (113.7 +/- 1.9 versus 105.9 +/- 1.7, respectively; p less than 0.01), but there was no difference in the peak platelet cytosolic calcium responses to thrombin between the two groups. In the combined group of male and female subjects, platelet cytosolic calcium correlated with diastolic blood pressure and mean arterial pressure (r = 0.37, p less than 0.001 and r = 0.32, p less than 0.01, respectively). Intact parathyroid hormone correlated with systolic and mean arterial blood pressure (r = 0.41, p less than 0.001 for both). Age correlated with both systolic blood pressure (r = 0.40, p less than 0.001) and intact parathyroid hormone (r = 0.51, p less than 0.001). When multiple regression analysis was performed using mean arterial pressure as the dependent variable, platelet cytosolic calcium and intact parathyroid hormone maintained significant correlations with mean arterial pressure. Platelet cytosolic calcium did not correlate with intact parathyroid hormone. These results suggest that both platelet cytosolic calcium and intact parathyroid hormone are associated with blood pressure regulation in normotensive subjects. However, the influences of these two factors on blood pressure are not interrelated.