Biomedical subjects

P R Conlin

Publications and source records attributed to P R Conlin.

At least 37 records · Page 2Linked to original sources

PubMed1999

Recruitment and baseline characteristics of participants in the Dietary Approaches to Stop Hypertension trial. DASH Collaborative Research Group.

Dietary Approaches to Stop Hypertension (DASH) was a randomized, multicenter feeding study designed to assess the effects of modifying dietary patterns on blood pressure. Among the most challenging aspects of conducting the DASH trial was the recruitment of participants at the 4 clinical centers. As part of the recruitment drive, 347,500 brochures were mailed, 250,500 coupons were distributed in coupon packs, 114 advertisements were published in newspapers or bulletins, 140 radio and 74 television advertisements were broadcast, and 68 screening events and presentations were conducted. These efforts yielded a total of 459 enrolled participants, ahead of schedule. The most common source of participants was mass mailing of individual brochures (n = 194, 42.3%), followed by word-of-mouth (n = 82, 17.8%), and then other types of mass mailing (n = 44, 9.6%). Recruitment of minority participants followed a similar pattern. Among the 3,192 persons attending the first in-person screening visit, the major reason for nonenrollment was low blood pressure (56%) rather than a diet-related factor. The study population was demographically heterogeneous (49% women, 60% African American, 48% married, and 77% employed full-time). On average, the diet of participants before the DASH feeding study was more similar to the trial control diet than to the combination diet, which reduced blood pressure more effectively. In summary, recruitment of a heterogeneous study population that includes a substantial number of minority participants is a feasible undertaking. However, the effort is considerable and requires a major commitment of resources.

Adult↗

PubMed1999

Effect of dietary patterns on ambulatory blood pressure : results from the Dietary Approaches to Stop Hypertension (DASH) Trial. DASH Collaborative Research Group.

We measured ambulatory blood pressure (ABP) in 354 participants in the Dietary Approaches to Stop Hypertension (DASH) Trial to determine the effect of dietary treatment on ABP (24-hour, day and night) and to assess participants' acceptance of and compliance with the ABP monitoring (ABPM) technique. After a 3-week run-in period on a control "typical" American diet, subjects (diastolic blood pressure [BP], 80 to 95 mm Hg; systolic BP, <160 mm Hg; mean age, 45 years) were randomly assigned to 1 of 3 diets for an 8-week intervention period: a continuation of the control diet; a diet rich in fruits and vegetables; and a "combination" diet that emphasized fruits, vegetables, and low-fat dairy products. We measured ABP at the end of the run-in and intervention periods. Both the fruit/vegetable and combination diets lowered 24-hour ABP significantly compared with the control diet (P<0. 0001 for systolic and diastolic pressures on both diets: control diet, -0.2/+0.1 mm Hg; fruit/vegetable diet, -3.2/-1.9 mm Hg; combination diet, -4.6/-2. 6 mm Hg). The combination diet lowered pressure during both day and night. Hypertensive subjects had a significantly greater response than normotensives to the combination diet (24-hour ABP, -10.1/-5.5 versus -2.3/-1.6 mm Hg, respectively). After correction for the control diet responses, the magnitude of BP lowering was not significantly different whether measured by ABPM or random-zero sphygmomanometry. Participant acceptance of ABPM was excellent: only 1 participant refused to wear the ABP monitor, and 7 subjects (2%) provided incomplete recordings. These results demonstrate that the DASH combination diet provides significant round-the-clock reduction in BP, especially in hypertensive participants.

Adult↗

PubMed1998

Protein kinase C activation stimulates calcium transport in adrenal zona glomerulosa cells.

Adrenal zona glomerulosa (ZG) cells produce aldosterone in response to angiotensin II and extracellular potassium through different mechanisms which involve changes in cytosolic free calcium (Cai). Protein kinase C (PKC) activation is part of the angiotensin II signalling cascade but its effects on Cai are unknown. PKC activation with 1 microM phorbol 12-myristate 13-acetate (PMA) and 8 mM Ko significantly increased the rate of calcium influx (P < 0.001). Both the PKC- and the Ko-induced calcium influx occurred via a nifedipine-sensitive pathway. When both were combined, PKC activation and 8 mM Ko were not additive over either agent alone. PKC activation and 8 mM Ko also stimulated calcium efflux (P < 0.01). When combined together PKC activation and 8 mM Ko had additive effects on calcium efflux (P < 0.05). PKC activation did not increase Cai nor the exchangeable calcium pool in contrast to 8 mM Ko which significantly increased both (P < 0.001). Thus, PKC activation in ZG cells induces a pattern of calcium transport characterized by accelerated calcium recycling across the cell membrane without increasing cell calcium content.

Adrenal Glands↗

PubMed1998

A study of losartan, alone or with hydrochlorothiazide vs nifedipine GITS in elderly patients with diastolic hypertension.

We conducted a randomised, double-blind, parallel design study comparing the efficacy and tolerability of the angiotensin II receptor antagonist, losartan, alone or with low-dose hydrochlorothiazide (HCTZ) to the dihydropyridine calcium channel blocker, nifedipine GITS (gastro-intestinal therapeutic system), in elderly patients (> or =65 years old) with a diastolic blood pressure (DBP) between 95 and 115 mm Hg. After a placebo wash out period, 140 patients were randomly assigned to receive either losartan 50 mg or nifedipine GITS 30 mg. Patients were evaluated at 4-week intervals during a 12-week treatment period. Patients receiving losartan had HCTZ 12.5 mg added and increased to 25 mg to reduce DBP <90 mm Hg. Patients receiving nifedipine GITS had their dose increased to 60 mg and 90 mg to reduce DBP <90 mm Hg. Efficacy, tolerability and quality of life were assessed during the 12 weeks on each regimen. Patients treated with the losartan regimen (n = 73) had reductions in trough sitting DBP of -10, -13, and -13 mm Hg after 4, 8, and 12 weeks of therapy, respectively. Patients receiving the nifedipine GITS regimen (n = 67) had DBP reductions of -14, -15, and -15 mm Hg, respectively. There were no significant differences in the DBP response between the treatment groups except at week 4 (P < 0.05). Similar reductions in systolic BP (SBP) between the two treatment groups were observed at all time points. The percentages of patients in the two treatment groups reaching goal DBP (<90 mm Hg or DBP > or =90 mm Hg with a reduction from a baseline of > or =10 mm Hg) were comparable (81% on the losartan regimen and 90% on the nifedipine GITS regimen). There were significantly more adverse events reported in patients receiving nifedipine GITS when compared to the losartan regimen (54% vs 36%, P < 0.05). A patient-reported symptom inventory also showed that swollen ankles was bothersome in significantly more patients treated with the nifedipine GITS regimen when compared to the losartan regimen (24% vs 5%, P = 0.001). Thus, in elderly patients with diastolic hypertension, a regimen of losartan alone or with HCTZ has similar efficacy to a regimen of nifedipine GITS with greater tolerability and less symptom bother due to swollen ankles.

Aged↗

PubMed1998

Dissociation of vascular and adrenal responsiveness to angiotensin II following calcium channel blockade.

Calcium channel blockers as a class reduce both vascular resistance and systemic blood pressure. However, it is not known if different classes of calcium channel blockers have similar effects on the renin-angiotensin-aldosterone system. We investigated vascular and adrenal responses to endogenous and exogenous angiotensin II in normotensive subjects before and after receiving isradipine or diltiazem. Subjects achieved low salt balance before study and underwent an angiotensin II infusion and upright posture study. After re-achieving salt balance the subjects received either isradipine (n=10), or diltiazem (n=7) for three days before repeating the study. Both agents lowered blood pressure and significantly shifted the dose response relationship of angiotensin II and mean blood pressure (P<0.01). In contrast, aldosterone secretion in response to upright posture and angiotensin II infusion was significantly reduced (P<0.01) by isradipine but not by diltiazem. The in vitro effects of both agents on aldosterone secretion from bovine adrenal glomerulosa cells paralleled the in vivo observations showing that angiotensin II-stimulated aldosterone secretion was markedly blunted by isradipine and minimally by diltiazem. These results suggest a tissue specificity for the effects of different classes of calcium channel blockers. Dihydropyridine calcium channel blockers may exert their antihypertensive effect by blocking both vascular and adrenal responses to angiotensin II.

Adrenal Glands↗

PubMed1998

Use of calcium channel blockers in hypertension.

During the past 20 years the number of subclasses of calcium channel blockers has increased from one to four. Three classes have only a single clinically approved compound: verapamil, diltiazem, and mibefradil. The fourth class, dihydropyridines, contains numerous compounds. All agents are effective in lowering blood pressure in short-term studies, and side effects that trouble the patient are infrequent. Long-term studies in hypertensive patients are limited. Short-acting agents such as nifedipine have been associated with an increased cardiovascular risk in some, but not all studies. These agents also probably create a compliance problem for hypertensive patients because of the need for multiple daily doses and their unpleasant side effects, e.g., ankle edema, palpitations, and flushing. Therefore, they are not useful or indicated for the treatment of hypertensive patients. No data have suggested that long-acting dihydropyridines or nondihydropyridine calcium channel blockers share the same fate. Indeed, several lines of evidence suggest the opposite: they have a cardioprotective effect. However, definitive information will require the completion of several long-term trials, including ALLHAT, CONVINCE, HOT, INSIGHT and NORDIL. Finally, it is important to reflect on the lessons learned from the controversy associated with the potential risks of calcium channel blockers. First, disagreements are common when one uses case-controlled studies and are reflective of the poor precision of the methods used. What is statistically relevant in one study may not hold true for another and may have no clinical relevance, particularly if the relative risk is less than 2. Investigators need to temper their enthusiasm to reflect this reality. Second, at the cutting edge of science there is probably relatively little agreement about what is correct among equally competent scientists. All have bias in their positions and should both recognize and admit so to themselves and their colleagues. Inferring that those who disagree have an unstated secondary agenda that will bring personal financial rewards or government accolades is inappropriate and counterproductive. Third, the randomized clinical trial, despite all its imperfections, is still the best tool to establish common ground on controversial issues. Finally, what may seem best from the public health perspective may not be in the best interest of the individual patient--a possibility that physicians have to constantly consider. For example, no public health benefit occurs if patients remain hypertensive because they fail to take their medications, no matter what the medication.

Antihypertensive Agents↗

PubMed1998

Recruitment and retention of minority participants in the DASH controlled feeding trial. DASH Collaborative Research Group. Dietary Approaches to Stop Hypertension.

The Dietary Approaches to Stop Hypertension (DASH) study was a National Heart, Lung, and Blood Institute multicenter trial that compared the impact of three dietary patterns on blood pressure (BP) among adults with high normal blood pressure or mild (Stage I) hypertension. DASH's high minority representation (two-thirds of the 459 randomized participants came from minority populations, and 60% of the cohort were African American) offered a valuable opportunity to assess factors affecting minority enrollment and retention in clinical trials of lifestyle modification. Recruitment strategies included targeted mailings to specific groups, mass mailings, community and worksite screenings, and mass media advertising; the four DASH clinical centers also reimbursed participants from $150 to $160. The most productive recruitment strategies tended to be mass mailings directed at a broad audience that was weighted toward, but not limited to, minority participants. DASH's African-American participants overwhelmingly (89%) cited health and dietary factors, such as learning more about blood pressure and healthy eating habits, as their primary reason for participating, while only six percent listed the financial incentives as their primary reason for participating. Eighty-eight percent of African-American respondents reported they would participate again in a similar study. The insights from DASH should help inform future efforts to recruit minority participants.

Adult↗

PubMed1996

Elevated lymphocyte cytosolic calcium in a subgroup of essential hypertensive subjects.

Abnormalities of intracellular calcium homeostasis and sodium-proton exchange have been implicated in the pathophysiology of essential hypertension. To further define the nature of cytosolic calcium abnormalities and whether they relate to increased sodium-proton exchange in hypertension, we have studied peripheral lymphocytes from normotensive and hypertensive subjects. Lymphocyte cytosolic calcium was significantly increased (P < .01) in hypertensive compared with normotensive subjects while consuming a high salt diet. Using maximum likelihood analysis, we found that cytosolic calcium levels in our study population were not normally distributed and observed three modes (P < .02). The means of the first mode and the two upper modes were separated (+/-2 SD) at a cytosolic calcium level of 120 nmol/L. We conducted further analysis in the subgroups with cytosolic calcium levels > 120 nmol/L or < 120 nmol/L. The majority of the normotensive subjects (86%) and half of the hypertensive subjects (52%) had levels < 120 nmol/L. Clinical characteristics of the two subgroups did not differ. Subjects with levels < 120 nmol/L had a rise in cytosolic calcium when changed to a low salt diet; those with levels > 120 nmol/L did not show a change in cytosolic calcium but their blood pressure fell significantly with salt restriction. Hypertensive subjects also had increased sodium-proton exchange activity compared with normotensive subjects when both groups were studied in a high salt balance. A positive correlation between sodium-proton exchange and cytosolic calcium was observed in subjects with levels < 120 nmol/L. There was insufficient power to draw conclusions on this relationship in subjects with levels > 120 nmol/L. Thus, many hypertensive subjects have increased cytosolic calcium, but this abnormality is not associated with sodium-proton exchange activity in all individuals. The salt-induced change in cytosolic calcium in subjects with levels < 120 nmol/L and its link to sodium-proton exchange suggest regulation by factors involved in salt-volume homeostasis. Individuals with cytosolic calcium > 120 nmol/L, most of whom were hypertensive, may have abnormalities in this regulation, contributing to hypertension.

Adult↗

PubMed1994

Racial differences in parathyroid hormone dynamics.

Elevations in PTH levels have been reported in black subjects. Such observations have not been consistent, however, and seem paradoxical in view of the known bone-resorptive action of this hormone and the fact that black subjects have a higher bone mineral density and fewer fractures than their white counterparts. In this study, we used dynamic stimulation of the calcium-PTH axis to fully characterize potential racial differences in PTH dynamics. We, therefore, defined the inverse sigmoidal curve that describes the relationship between serum ionized calcium concentration and intact PTH levels in six normal white and six normal black volunteers and determined the four parameters that characterize this relationship. An elevation in any one of these parameters can result in hyperparathyroidism. Black subjects had higher maximal and minimal PTH responses to hypo- and hypercalcemia (mean intact PTH levels of 9.2 +/- 13 and 0.7 +/- 0.1 pmol/L respectively) than white subjects (6.9 +/- 0.6 and 0.3 +/- 0.1 pmol/L, respectively). There were no differences in the set-points or slopes of the curves. Despite the higher baseline and stimulated endogenous PTH levels in black subjects, their baseline and stimulated osteocalcin levels were lower. Our dynamic studies, therefore, document mild hyperparathyroidism in black subjects and suggest mild skeletal resistance to PTH.

Adult↗

PubMed1993

Stimulation of plasminogen activator inhibitor in vivo by infusion of angiotensin II. Evidence of a potential interaction between the renin-angiotensin system and fibrinolytic function.

BACKGROUND: Recent clinical trial data indicate that the use of angiotensin converting enzyme (ACE) inhibitors among patients with left ventricular dysfunction results in reduced rates of coronary thrombosis, a provocative finding that suggests a potential interaction between the renin-angiotensin system and fibrinolytic function. METHODS AND RESULTS: In four normotensive subjects and six hypertensive patients, we investigated whether infusion of angiotensin II (Ang II) affected circulating levels of plasminogen activator inhibitor-1 (PAI-1), the most important physiological inhibitor of tissue-type plasminogen activator (t-PA). Overall, mean levels of PAI-1 antigen increased significantly from 20.1 ng/mL before Ang II infusion to 36.0 ng/mL at the end of Ang II infusion (p = 0.008), whereas no change in PAI-1 was observed for control subjects infused with 5% dextrose (p = 0.46). Among the normotensive subjects for whom graded doses of Ang II were infused at 0, 1, 3, and 10 ng.kg-1.min-1, mean PAI-1 levels increased sequentially from 14.7 ng/mL to 23.0, 26.8, and 33.5 ng/mL, a dose-response relation that, compared with controls, was highly significant (p < 0.001). Among the hypertensive patients for whom a single 45-minute infusion of Ang II was given at a dose of 3 ng.kg-1.min-1, PAI-1 levels increased from 23.7 to 37.7 ng/mL, whereas PAI-1 levels among control subjects infused with 5% dextrose decreased from 16.9 to 10.8 ng/mL (p = 0.04). Finally, when compared with infusion of 5% dextrose solution, infusion of Ang II appeared to have little effect on circulating levels of t-PA antigen. CONCLUSIONS: These in vivo data suggest that infusion of Ang II results in a rapid increase in circulating levels of PAI-1, a finding that may help to explain clinical observations linking the renin-angiotensin system and thrombotic risk.

Angiotensin II↗

PubMed1993

Rapid modulation of renal and adrenal responsiveness to angiotensin II.

Reciprocal changes in adrenal and vascular responsiveness to angiotensin II (Ang II) are part of the normal adaptation to shifts in salt intake. When dietary salt intake is abruptly reduced from high to low, enhancement in aldosterone secretion requires several days to develop. Once established it is not known how quickly the enhancement is reversed with salt repletion. We investigated the time course and relative contributions of salt, volume expansion, or both to this process by studying 15 normotensive subjects; 5 were studied during both high-salt and low-salt balance, and 10 were studied only in low-salt balance. For rapid volume expansion to reverse low-salt balance, 5 subjects received in random order an infusion of normal saline or dextran. The adrenal glomerulosa and renal vascular responses to Ang II were assessed after each volume expansion maneuver. Saline and dextran infusions suppressed plasma renin activity and aldosterone equally, although dextran acted more slowly. Both also increased renal perfusion and renal vascular and pressor responses to Ang II, which in 3 to 7 hours became identical to responses seen during high-salt intake ("modulation"). Saline infusion also blunted adrenal responsiveness to Ang II during that same interval. Despite suppression of the renin-angiotensin system by dextran infusion, aldosterone responsiveness to Ang II remained enhanced. These observations suggest that the renal and vascular responses to Ang II are modulated rapidly by the effects of volume expansion per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1993

Calcium-mediated intracellular acidification and activation of Na(+)-H+ exchange in adrenal glomerulosa cells stimulated with potassium.

Intracellular pH (pHi) regulation by Na(+)-H+ exchange is important in cellular responses to hormones and growth factors, particularly those which raise cytosolic Ca2+ (Cai). Since elevation of Cai occurs when adrenal glomerulosa cells are stimulated by angiotensin II (Ang II) and high external K+ (Ko), we evaluated the relationship of Na(+)-H+ exchange to calcium movement particularly during high Ko stimulation of bovine glomerulosa cells. Inhibition of Na(+)-H+ exchange by dimethylamiloride markedly reduced aldosterone secretion in response to 8 mM Ko. This high Ko stimulation was accompanied by a rise in dimethylamiloride-sensitive Na+ influx and pHi acidification which was extracellular Ca2+ (Cao) dependent. High Ko also produced a rise in Ca2+ influx, Cai levels and Ca2+ efflux at 37 C. However, at 4 C, Ca2+ influx remained intact, but Ca2+ efflux and cellular acidification were inhibited. In contrast, Ang II produced protein kinase C (PKC) activation accompanied by a Na(+)-H+ exchange-dependent rise in pHi which was independent of Cao. After PKC depletion by phorbol ester pretreatment, Ang II also produced a Cao-dependent cell acidification as with high Ko. Thus, Na(+)-H+ exchange is activated by both Ang II and high Ko but by different mechanisms. High Ko stimulation induces an enhanced cellular acidification, whereas Ang II induces alkalinization driven by PKC activation of the antiporter. These findings suggest that a physiological role of Na(+)-H+ exchange may be, in part, to counteract the acidification produced by enhanced active Ca2+ efflux (via Ca2+ pumping) during both high Ko and Ang II stimulation of aldosterone secretion.

Aldosterone↗

PubMed1992

Dose effect of adrenocorticotropin on aldosterone and cortisol biosynthesis in cultured bovine adrenal glomerulosa cells: in vitro correlate of hyperreninemic hypoaldosteronism.

In some critically ill patients, aldosterone secretion is diminished despite hyperreninemia. These same patients demonstrate appropriately elevated plasma ACTH and cortisol levels. In addition, infusion of ACTH or angiotensin-II (AII) fails to elicit the normal aldosterone response, implying that the defect is at the level of the zona glomerulosa (ZG) cell. To test the hypothesis that elevated ACTH levels induce this defect, Percoll-purified bovine ZG cells were plated in serum-free defined medium and cultured for 5 days. On days 1-4, cells were exposed to various concentrations of ACTH for 1 h. On the fifth day of culture, half of the wells pretreated with ACTH were treated for 1 h with AII (10(-7) M); the other half of the wells received another dose of ACTH for 1 h. Additionally, cells were exposed to daily 1-h pulses of AII (10(-7) M) alone or in combination with ACTH (10(-8) M) for 5 days. Acutely dispersed bovine ZG cells showed dose-dependent increases in aldosterone when incubated with ACTH, potassium, or AII, with minimal cortisol production. Acutely dispersed bovine fasciculata cells produced no aldosterone, but demonstrated a dose-dependent cortisol response to ACTH and AII, but not potassium. On day 1 of culture, the ZG cells demonstrated a significant (P less than 0.001 in all cases) dose-related increase in aldosterone secretion in response to ACTH. However, continued daily pulsation with ACTH resulted in a dose-dependent decrease in aldosterone secretion, with a concomitant dose- and time-related rise in cortisol production. Indeed, ACTH-induced cortisol production in ZG became similar to ACTH-induced cortisol production in zona fasciculata cells. The addition of AII to the daily ACTH pulse did not significantly alter the aldosterone or cortisol response patterns to ACTH alone. In contrast, ZG cells treated with AII alone for 5 days showed a minimal change in cortisol production and no reduction in aldosterone production until day 4. Northern blot analysis of total RNA isolated from ZG cells pulsed with ACTH for 5 days demonstrated a parallel dose-dependent increase in 17 alpha-hydroxylase mRNA, which did not occur in cells pulsed with AII alone. These in vitro results suggest that elevated ACTH levels over time induce 17 alpha-hydroxylase activity in ZG cells, thereby shifting steroid biosynthesis from an aldosterone-producing to a cortisol-producing pathway. It is likely that the chronically elevated ACTH levels in critically ill patients induce a similar change in ZG cell biosynthesis, resulting in their hyperreninemic hypoaldosterone state.

Adrenocorticotropic Hormone↗

PubMed1992

Abnormal norepinephrine and aldosterone responses to upright posture in nonmodulating hypertension.

The subgroup of patients with nonmodulating hypertension demonstrates a number of abnormalities of the renin-angiotensin-aldosterone axis. We previously identified abnormalities in plasma and urinary dopamine in nonmodulators and posited that this may be in part due to a generalized defect in sympathetic nervous system activity. In the present study we assessed the state of activation of the renin-angiotensin system and the sympathetic nervous system in normal subjects and patients with modulating, nonmodulating, and low renin essential hypertension during sodium depletion and change from supine to upright posture. Levels of plasma norepinephrine were higher in non-modulators during the posture study (P < 0.05). PRA rose with upright posture in all groups, but low renin subjects had a blunted response. Nonmodulators and low renin subjects had lower aldosterone levels both supine (P< 0.05) and upright (P< 0.01). However, the aldosterone/PRA increment ratio was increased in low renin subjects (P< 0.01), whereas it was decreased in nonmodulators. Twenty-four-hour urine collections for catecholamine determinations were obtained in a subgroup of the subjects, with nonmodulators showing higher levels of norepinephrine excretion which approached significance (P = 0.08). In vitro experiments using rat and human adrenal glomerulosa cells showed that norepinephrine does not affect aldosterone secretion per se. These observations extend the series of abnormalities observed in nonmodulating hypertension. However, it is likely that the alterations in norepinephrine levels during sodium depetion and upright posture are a secondary event and not linked to the altered aldosterone production in these patients.

Adult↗

PubMed1991

Angiotensin II-induced activation of Na(+)-H+ exchange in adrenal glomerulosa cells is mediated by protein kinase C.

Modulation of Na(+)-H+ exchange (Na/H EXCH) by hormones and growth factors may be important in cell growth. We have previously shown that Na/H EXCH in adrenal glomerulosa cells is activated by angiotensin II (ANG II), a potent stimulator of aldosterone secretion. In the present paper, we have investigated the role of protein kinase C (PKC) in the activation of Na/H EXCH by ANG II. To accomplish this, we monitored cytosolic pH (pHi) in cells loaded with 2,7-biscarboxyethyl-5 (6)-carboxyflourescein and measured initial rates off 22Na uptake into glomerulosa cells in the presence or absence of dimethylamiloride. Both phorbol 12-myristate 13-acetate (PMA) and ANG II increased the activity of Na/H EXCH similarly when studied under basal conditions (pH 7.1). This was accompanied by alkalinization of pH and an increase in dimethylamiloride-sensitive Na+ influx. Study of kinetics of the antiporter activation showed that both ANG II and PMA led to an increase in the maximal rate (Vmax) and a decrease in the Michaelis-Menten constant (Km) for external Na+. The pHi dependence of Na+ influx was half-minimal (pK) at pHi 7.09 and remained unchanged in the presence of ANG II (pK 7.03) and PMA (pK 7.14). Depleting the cells of PKC by exposing them to PMA (1 microM) for 3 h caused a marked reduction in control and ANG II-stimulated Na+ influx and control pK (7.09 to 6.85, P less than 0.05). However, with PKC depletion, the kinetics of Na/H EXCH (Vmax, Km for external Na+, and pK) were unaffected by ANG II. Thus, Na/H EXCH in adrenal glomerulosa cells functions under basal conditions, and its relatively alkaline pK (7.09) is dependent upon PKC activity. In addition, the ANG II-induced activation of Na/H EXCH is modulated by PKC. These effects suggest an important role for PKC in pHi regulation of adrenal glomerulosa cells, particularly during ANG II stimulation of aldosterone secretion.

Aldosterone↗

PubMed1991

Acute changes in serum osteocalcin during induced hypocalcemia in humans.

Although levels of serum osteocalcin are thought to be an indicator of osteoblastic activity and bone formation, there is little information regarding the acute effects of changes in calcium or PTH levels on circulating osteocalcin concentrations. To study the effect of stepwise decreases in ionized calcium (CaI) on osteocalcin levels, we infused six normal subjects with citrate for four 30-min intervals using two different protocols. One protocol (pulse infusion) used alternating rates of infusion and resulted in rapid stepwise decrements in serum CaI. The second protocol (continuous infusion) used constant intermediate rates of citrate infusion and produced slower decrements in CaI, but with similar changes in magnitude. We monitored serum CaI, intact PTH, and osteocalcin concentrations during the course of these infusions. During each step of the pulse infusion the osteocalcin responses to changes in CaI in general were parallel to the changes in PTH (r = 0.462; P = 0.02) and were inversely correlated to CaI (r = -0.562; P = 0.003). The osteocalcin concentrations at the end of each 30-min period were higher than at the beginning of that period; over the total 120 min, osteocalcin levels rose from 3.46 +/- 0.63 to 6.88 +/- 1.08 micrograms/L (P less than 0.05). In contrast, during the first two periods of the continuous infusion, osteocalcin concentrations changed slightly. Only during the last two periods of the continuous infusion did osteocalcin respond in a manner characteristic of that observed with the pulse infusion. These data indicate that osteocalcin concentrations in the circulation may be acutely regulated by calcium and/or PTH.

Adult↗

PubMed1990

Dopamine and nonmodulating hypertension.

Sodium loading reduces aldosterone responses to angiotensin II (AII) when compared to the sodium restricted state. Recent investigations suggest that dopamine inhibits the aldosterone secretion and may contribute to the alteration in aldosterone response to AII with sodium intake, since administration of the dopamine antagonist, metoclopramide, enhances the aldosterone responses to AII on a high but not a low salt diet. Nonmodulating hypertension is characterized, in part, by a decreased aldosterone response to AII, raising the possibility that an increased dopaminergic inhibition of aldosterone secretion underlies the adrenal defect in nonmodulating hypertension. To assess this possibility, 69 patients with hypertension were characterized in relationship to their modulation status on a low sodium intake. Dopamine levels were significantly higher (P less than .05) in nonmodulators. To assess the physiologic relevance of these findings, the aldosterone response to AII infusion was assessed before and during administration of the dopamine antagonist, metoclopramide, in 13 patients. The adrenal response to AII did not change after metoclopramide in either hypertensive subgroup. Thus, it is unlikely that the adrenal defect is due to the increase in dopamine levels observed in nonmodulators. In the next study, the impact of dietary sodium intake on urinary dopamine levels was compared in normotensive and hypertensive subjects characterized as modulators and nonmodulators. Both modulators and normotensive subjects demonstrated an increase in urinary dopamine excretion in response to a high sodium intake--a feature that was not observed in the nonmodulators. Thus, the sodium retaining tendency of nonmodulators may reflect, at least in part, a reduction in intrarenal dopamine production in response to a sodium load.

Adrenal Glands↗

PubMed1990

Na(+)-H+ exchanger kinetics in adrenal glomerulosa cells and its activation by angiotensin II.

We have studied the kinetic properties of basal and angiotensin II (ANG II) stimulated Na(+)-H+ exchange in adrenal glomerulosa cells by measuring changes in cytosolic pH (pHi) and initial rates of 22Na uptake in the presence or absence of dimethylamiloride (DMA). The cells were studied 1) under basal conditions, 2) at constant pHi (6.8) with varied external sodium (Na+o), and 3) at varied pHi with constant Na+o (50 mM). In 2,7-biscarboxyethyl-5(6)-carboxyfluorescein loaded cells under basal conditions, pHi rose from 7.09 +/- 0.02 to 7.19 +/- 0.02 (P less than 0.05) with addition of ANG II (100 nM). Similarly, DMA-sensitive Na influx was enhanced from 9.2 +/- 1.3 to 14.8 +/- 2.1 nmol Na+/mg protein x min (P less than 0.01) by ANG II. In cells acid-loaded by preincubation in Na(+)-free media (pHi 6.8), addition of varying Na+o resulted in a rapid H+ efflux that was markedly inhibited by DMA. DMA-sensitive Na+ influx into these acidified cells with varied Na+o exhibited a Michaelis-Menten constant (Km) of 23 mM and a maximum velocity (Vmax) of 43 nmol Na+/mg protein x min. By varying pHi (from pHi 7.1 to 6.2), DMA-sensitive Na+ influx likewise showed activation with cellular acidification with a pK at pHi 7.09. At pHi 6.8, ANG II decreased the Km for Na+o from 23 to 17 mM and increased the Vmax from 43 to 53 nmol Na+/mg protein x min. The pHi dependence of DMA-sensitive Na+ influx was not affected by ANG II (pK at pHi 7.03). DMA also inhibited AII-stimulated aldosterone secretion and Na+ influx similarly. These results indicate that Na(+)-H+ exchange in adrenal glomerulosa cells is 1) functioning under basal conditions, and 2) is modulated by ANG II with enhanced Na+o affinity and Vmax but without a shift in pHi dependence (similar to ANG II effects on vascular smooth muscle cells). These effects suggest an important role for Na(+)-H+ exchange during ANG II stimulation of aldosterone production by glomerulosa cells.

Aldosterone↗