Heparin, lipoproteins, and oxygenated fatty acids in blood: a cautionary note.

We measured 16 nonesterified oxygenated fatty acid derivatives (oxylipids) in plasmas from seven human subjects. Two arterial samples from each subject were analyzed, drawn approximately 2h apart. We observed a marked increase in levels of most oxylipids in the second sample, as high as 470-fold. Between the first and second samples, subjects received approximately 800-1000 IU of heparin to prevent clotting in intravascular catheters. We postulate that heparin activated lipoprotein lipases, which, in turn, released oxylipids from triglycerides and phospholipids in plasma lipoproteins. Some of that lipolysis may have occurred during sample storage. Measurements of nonesterified lipids in human plasma may be distorted if heparin is administered to subjects before blood is drawn and if lipase inhibitors are omitted from stored samples.

Nontraditional aspects of aldosterone physiology.

Aldosterone is the most important circulating mineralocorticoid. It is secreted by the zona glomerulosa of the adrenal gland and plays a major role in sodium and potassium metabolism by binding to epithelial mineralocorticoid receptors (MR) in the renal collecting duct, promoting sodium resorption and potassium excretion. The action of aldosterone on its classic target epithelia has been extensively studied, and many of the signaling events that mediate its effects have been described. Recently, there has been increased interest in aldosterone actions on the cardiovascular system, which are mediated through nonclassical actions. These include local tissue production, nongenomic actions, and effects on nonepithelial targets. In this review article, we focus on the effects of aldosterone in nonepithelial tissues that are mediated through MR, especially cardiovascular effects.

High-fat diet elevates blood pressure and cerebrovascular muscle Ca(2+) current.

Dietary fat contributes to the elevation of blood pressure and increases the risk of stroke and coronary artery disease. Previous observations have shown that voltage-gated Ca(2+) current density is significantly increased in hypertension and can be affected by free fatty acids (FAs). We hypothesized that a diet of elevated fat level would lead to an increase in blood pressure, an elevation of L-type Ca(2+) current, and an increase in saturated FA content in vascular smooth muscle cell membranes. Male Osborne-Mendel rats were fed normal rat chow or a high-fat diet (Ob/HT group) for 8 weeks. Blood pressures in the Ob/HT group increased moderately from 122.5+/-0.7 to 134.4+/-0.8 mm Hg (P<0.05, n=26). Voltage-clamp examination of cerebral arterial cells revealed significantly elevated L-type Ca(2+) current density in the Ob/HT group. Voltage-dependent inactivation of the Ob/HT L-type channels was significantly delayed. Total serum FA contents were significantly elevated in the Ob/HT group, and HPLC analyses of fractional pools of FAs from segments of abdominal aorta revealed that arachidonic acid levels were elevated in the phospholipid fraction in Ob/HT. No differences in vascular membrane cholesterol contents were noted. Plasma cholesterol was significantly elevated in portal venous and cardiac blood samples from Ob/HT rats. These findings suggest that an elevation of plasma FAs may contribute to the development of hypertension via a process involving the elevation of Ca(2+) current density and an alteration of channel kinetics in the vascular smooth muscle membrane.

Mechanisms in the pressor effects of hepatic portal venous fatty acid infusion.

Portal venous infusion of oleate solution has pressor effects. We have examined efferent mechanisms, measured the response to sustained infusion, and determined the effect of linoleate. Eight conscious animals received concurrent infusions of prazosin or vehicle with portal venous infusion of oleate. Oleate alone increased mean arterial pressure from 109.0 +/- 4.1 to 123.0 +/- 5.8 mmHg (P = 0.02), whereas no increase in blood pressure occurred when oleate was infused with prazosin. In 10 rats, concurrent infusion of losartan had no effect on the pressor activity of portal oleate infusion. Twenty-two animals received portal oleate or vehicle as a continuous infusion for 7 days. Mean arterial pressure (126.1 +/- 2.0 vs. 107.8 +/- 2.6 mmHg, P < 0.001) and heart rate (383 +/- 5 vs. 366 +/- 5, P = 0.0257) were increased in oleate-infused animals. No differences in plasma fatty acids, glucose, insulin, pressor hormones, liver enzymes, or in vitro arterial pressor responsiveness were observed. Portal venous infusion of linoleate increased arterial pressure by 12.2 +/- 3.2 mmHg (P = 0.033). These results indicate that alpha-adrenergic activity is necessary for the acute pressor effects of portal oleate, that sustained portal oleate infusion results in persistent blood pressure elevation, and that other long-chain fatty acids besides oleate have pressor effects.

Simultaneous scintigraphic depiction of aldosteronoma and adrenal infarction.

Primary aldosteronism is a potentially curable cause of hypertension, especially when caused by an adrenal adenoma. Aldosteronomas because of their small size often elude techniques to locate them. This case illustrates the advantages, disadvantages and complications of noninvasive techniques used for their diagnosis. A patient with hypertension and hypokalemia underwent an adrenal venous effluent sampling for measurement of aldosterone concentrations. This procedure was complicated by an injury to the right adrenal gland. Subsequently, it was difficult to control the patient's hypertension and hypokalemia with medical therapy alone. A re-assessment years after his initial diagnosis included a CT scan, which now visualized a left adrenal tumor. The functional status of this tumor and lack of function of the previously injured right adrenal gland were demonstrated by NP-59 scintigraphy. This information modified the surgical intervention (adenectomy rather than total adrenalectomy) and the residual left sided adrenal tissue prevented adrenocortical insufficiency. A year later the patient remains euadrenal.

Pressor effects of portal venous oleate infusion. A proposed mechanism for obesity hypertension.

Increased visceral fat accumulation is a strong predictor of arterial hypertension. In this study, we explored the hypothesis that increased hepatic portal venous free fatty acid delivery results in increased blood pressure. Such an effect might explain the link between visceral obesity and hypertension. In nine conscious, instrumented rats, we studied the effects of 1-hour infusions of sodium oleate solution into the portal and femoral veins and infusions of sodium caprylate solution into the portal vein on 3 separate days. Basal blood pressure was not significantly different on the 3 study days. Mean arterial pressure increased 29 +/- 4 mm Hg during portal oleate infusion and 13 +/- 2 mm Hg during femoral oleate infusion (both significant increases over basal, P < .001). Mean arterial pressure did not change during portal caprylate infusion. The increase during portal oleate infusion was greater than that during femoral oleate infusion (P = .028). Heart rate rose during all three infusions; the increase was greatest during portal oleate infusion (334 +/- 4 to 412 +/- 2 beats per minute). During portal venous oleate infusion in five rats, plasma norepinephrine rose from 2.17 +/- 0.34 to 3.58 +/- 0.50 nmol/L, epinephrine rose from 0.79 +/- 0.28 to 1.84 +/- 0.44 nmol/L, and corticosterone rose from 147 +/- 55 to 1130 +/- 289 nmol/L. Three rats given portal venous oleate infusions for 1 week had increased blood pressure compared with baseline (mean increase, 16 +/- 4 mm Hg). These studies indicate that increases in portal venous fatty acid concentrations have significant pressor effects, perhaps mediated by increased sympathetic tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Sustained hypertension induced by orally administered nitro-L-arginine.

To study the hemodynamic and metabolic effects of chronic inhibition of endothelium-derived nitric oxide, we treated conscious rats with an oral solution of N omega-nitro-L-arginine (LNA), an inhibitor of nitric oxide production by endothelial cells. After 3 days of treatment with 2.74 mM LNA, rats had higher blood pressures (136 +/- 5 versus 113 +/- 3 mm Hg, p < 0.0005) than did the control animals. This effect was maintained through 7 days of treatment (142 +/- 6 versus 109 +/- 4 mm Hg, p < 0.0005) and in three animals for 35 days (167 +/- 7 mm Hg). The blood pressure rise was dose dependent. The hypertensive effect of oral LNA was not enhanced by the administration of 20 mg intraperitoneal LNA and was prevented by pretreatment with L-arginine, although L-arginine also caused a transient but significant increase in urinary sodium excretion. When LNA treatment was discontinued, blood pressure fell gradually, with an effective biological half-life of 4.2 days. Metabolic balance studies did not identify differences in sodium or potassium balance between treated and control animals. Plasma renin activity was lower in LNA-treated animals, and aldosterone concentrations tended to be lower. In contrast, atrial natriuretic factor levels and serum electrolyte concentrations were unchanged after 7 days of treatment with LNA. These data support the premise that endothelium-derived nitric oxide plays an important role in basal hemodynamic homeostasis. Oral administration of LNA may serve as a model of chronic nitric oxide-deficient hypertension and allow for the future study of endothelium dependence in hypertension.

Corticoid regulation of atrial natriuretic factor secretion and gene expression.

This study investigated the acute effects of glucocorticoids and mineralocorticoids on atrial natriuretic factor (ANF) biosynthesis in vivo. Groups of male Sprague-Dawley rats were injected with 1 mg dexamethasone (Dex), 10 mg deoxycorticosterone acetate (DOCA) or vehicle alone. Different groups were studied after periods of 30 min to 8 h. Plasma and left atrial ANF concentrations and ANF mRNA levels were measured 2-8 h after corticoid injection. From 30 min to 2 h after injection, ANF mRNA was analyzed by quantitative and qualitative assessments. There was a two- to threefold increase in plasma levels of ANF in Dex-treated rats compared with controls at all time periods (P < 0.05). Although ANF plasma levels increased over time following DOCA treatment, they were not significantly different from control values. Dex treatment also increased normalized ANF mRNA levels 77% above control levels during the first 4 h after injection (P < 0.05). Thereafter there was a return of mRNA levels to that seen in controls. There was no qualitative difference in the ANF mRNA at any time as assessed by Northern hybridization. In contrast, DOCA increased ANF mRNA levels only after 8 h (P < 0.05). No significant changes in left atrial ANF content were noted during this study. In a separate study, Dex was administered to isolated left atria in vitro in a superfusion system. Superfusion with 2 x 10(-5) M Dex produced a 40% increase in ANF secretory rate within 20 min (P = 0.036). We conclude that Dex induces a direct rapid increase in ANF mRNA levels and ANF secretion in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the secretion of atrial natriuretic factor in atria from aged rats.

We measured plasma atrial natriuretic factor levels and atrial natriuretic factor secretion by isolated left atria from aging rats to determine the secretory response to stretch and adrenergic stimulation. Systolic arterial pressure and right atrial pressure were measured in vivo. Twenty-four hours later, atria were removed and studied in vitro in a perifusion system. After removal, stabilization at 0.7 g tension, and equilibration for 65 minutes, atria were stretched by increasing external tension for 20 minutes. After reequilibration atria were perifused with phenylephrine, 10(-5) M, for an additional 30 minutes. Right atrial pressure was not different between young (3 months) and aged (16-24 months) rats. Aged rats had higher plasma atrial natriuretic factor levels (52 +/- 8 versus 21 +/- 6 pmol/l; p less than 0.05) than young rats. Basal atrial natriuretic factor secretory rate in vitro was greater in atria from aged rats than young rats (875 +/- 35 versus 402 +/- 22 pg/min; p less than 0.05). Atria from aged rats had an increased response to phenylephrine compared with young rats (1,687 +/- 143 versus 788 +/- 113 pg/min; p less than 0.05) when means were adjusted for basal secretory rate. The secretory response to stretch was less than that of young rats (673 +/- 37 versus 773 +/- 27 pg/min), although this difference was not significant (p = 0.07). Atrial natriuretic factor secretion in response to adrenergic stimulation is increased with aging, and these secretory responses may contribute to increased plasma levels that occur during aging. In contrast to increased adrenergic responses, atrial natriuretic factor secretion after external stretch is not increased in aging rats.

Atrial natriuretic factor in the elderly: diminished response to epinephrine.

We have previously found that epinephrine (EPI) increases plasma immunoreactive atrial natriuretic factor (irANF) in young human subjects. Because elderly humans have decreased sensitivity to adrenergic stimulation, we compared plasma irANF responses to intravenous infusion of EPI, 5 micrograms/min for 80 min in six young (ages 20-29) and nine old (ages 62-75) healthy subjects. In addition, we measured plasma irANF responses of the nine old subjects to 1 liter of normal saline infused over 30 min. Young and old subjects had similar basal EPI levels [108 +/- 18 vs. 106 +/- 10 (SE) pg/ml], but basal irANF levels tended to be higher in the old (32 +/- 7 vs. 50 +/- 8 pmol/l, P = 0.15). The young subjects had a significant increase in irANF levels after the EPI infusion (32 +/- 7 vs. 59 +/- 11 pmol/l, P less than 0.02), but there was no change in irANF in the old (50 +/- 8 vs. 48 +/- 7 pmol/l) despite similar plasma EPI levels in young and old (1,125 +/- 57 vs. 1,183 +/- 52 pg/ml). In contrast, the irANF response of the old subjects to saline infusion was striking: all nine subjects demonstrated a rise in irANF (P less than 0.01); mean levels increased from 54 +/- 4 pmol/l to a peak of 122 +/- 23 pmol/l. We conclude that healthy elderly subjects have a defect in EPI-stimulated ANF secretion, a finding compatible with other evidence for diminished sensitivity to adrenergic stimulation in aging.(ABSTRACT TRUNCATED AT 250 WORDS)

Idiopathic aldosteronism masquerading as discrete aldosterone-secreting adrenal cortical neoplasms among patients with primary aldosteronism.

The medical records of 32 patients with primary aldosteronism who underwent adrenalectomy at the University of Michigan Medical Center from January 1975 to February 1988 were reviewed. All 32 patients had the preoperative diagnosis of aldosterone-secreting adrenal cortical neoplasms. Based on pathology reports, however, 21 of 32 (66%) patients were confirmed to have adrenal cortical neoplasms. Ten of 32 (31%) patients had nodular hyperplasia, and 1 of 32 (3%) had diffuse hyperplasia. This report focuses on the results in 11 patients with idiopathic aldosteronism. In six of nine (67%) patients, aldosterone levels rose within 4 hours of patients assuming an upright posture after salt loading. Seven patients had selective adrenal venous aldosterone/cortisol ratios that were interpreted to lateralize to one adrenal gland; however, only four of seven (57%) had ratios of 3:1 or greater than the contralateral adrenal gland. In 6 of 11 (55%) patients, adrenal scans (NP-59) initially demonstrated unilateral uptake. Three of four computerized axial tomographic scans demonstrated a unilateral adrenal mass. Only 3 of 11 (27%) patients with idiopathic aldosteronism were normotensive after surgery. Four of 11 (36%) patients' conditions were improved, in that they became normotensive with antihypertensive medication. These data suggest that if both imaging and functional studies lateralize to one adrenal gland, it is reasonable to expect either a cure or an improvement after adrenalectomy among patients with primary aldosteronism caused by idiopathic aldosteronism. Unilateral adrenalectomy may be the treatment of choice in carefully selected patients with nodular hyperplasia causing primary aldosteronism.

Steroid secretion by a virilizing lipoid cell ovarian tumor: origins of dehydroepiandrosterone sulfate.

A 78-year-old woman had a 3-year history of severe virilization caused by a lipoid cell ovarian tumor localized by pelvic ultrasound examination and NP-59 scan. Steroid secretion was evaluated by the following: 1) peripheral plasma levels before and after hormonal stimulation with ACTH or hCG, 2) venous catheterization and measurement of steroid levels in the left and right ovarian veins during surgery, 3) measurements of enzymatic activities in the tumor tissue compared with those in normal ovarian tissue, and 4) steroid secretion studies in vitro of the tumor tissue, surrounding tissue, and contralateral ovarian tissue. The tumor tissue secreted both delta 5 and delta 4 androgens, including dehydroepiandrosterone sulfate. Dehydroepiandrosterone sulfate was also secreted by the surrounding and contralateral ovarian tissue.

Clonidine and morphine increase atrial natriuretic peptide secretion in anesthetized rats.

In order to determine whether the activity of central alpha 2-adrenergic and opioid receptors influence plasma atrial natriuretic peptide (ANP) levels, clonidine and morphine were infused into the lateral cerebral ventricle for 45 min in anesthetized Sprague-Dawley rats. The central administration of a low dose of clonidine (10 ng/min) caused a significant increase in plasma ANP without changing arterial blood pressure or central venous pressure. Pretreatment with yohimbine (5 micrograms/min) completely blocked the effect of clonidine. Central infusion of morphine (100 ng/min) also elevated plasma ANP levels and naloxone (5 micrograms/min) blunted this effect. Intravenous infusion of the same dose of clonidine or morphine did not affect plasma ANP levels. Moreover, the effect of clonidine on plasma ANP was partially blocked by pretreatment with naloxone (5 micrograms/min). These results suggest that central alpha 2-adrenergic and opioid receptors may be involved in ANP secretion.

Sustained saline-induced secretion of atrial natriuretic hormone is not maintained by atrial stretch.

To determine the relationship between changes in right and left atrial pressures and changes in plasma levels of immunoreactive atrial natriuretic hormone (ANH), 11 normal men were studied during rapid infusion of 1 L 150 mmol/L NaCl. Right atrial pressure, pulmonary capillary wedge pressure, and peripheral plasma ANH levels were measured serially for 30 min in 6 men and for 90 min in 5 men. There were significant increases in right atrial pressure at 15 and 30 min [4.8 +/- 0.4 (+/- SE) vs. 8.9 +/- 0.3 and 6.5 +/- 0.4 mm Hg; P less than 0.001] and in pulmonary capillary wedge pressure at the same time intervals [8.5 +/- 0.6 vs. 13.6 +/- 0.8 (P less than 0.001) and 10.6 +/- 0.6 mm Hg (P less than 0.01)]. Plasma ANH increased significantly at 30 min (11.5 +/- 2.4 vs. 20.6 +/- 3.0 pmol/L; P less than 0.001). Regression analysis revealed no correlation between the increase in plasma ANH at 30 min and the increase in either right atrial or pulmonary capillary wedge pressure at 15 min (r = 0.46; P = 0.16 for right atrial pressure; r = 0.02; P = 0.96 for pulmonary capillary wedge pressure). In the 5 men studied for 90 min, right atrial and pulmonary capillary wedge pressures returned to basal values by 45 min. In contrast, plasma ANH levels remained significantly elevated at all sampling times from 30-90 min (P less than 0.001); the peak value occurred at 75 min. We conclude that ANH secretion persists after saline infusion and that the cause of this prolonged secretion is not atrial stretch.

Natriuresis associated with elevated plasma atrial natriuretic hormone during supraventricular tachycardia.

Elevated plasma levels of atrial natriuretic hormone (ANH) have been found in patients during paroxysmal supraventricular tachycardia (SVT) and other clinical syndromes. However, physiologic effects of this endogenous ANH have not been demonstrated. To determine whether the rise in ANH during SVT is associated with either a natriuresis or kaliuresis, urine sodium and potassium levels were measured in five patients at baseline and during SVT simulated by rapid atrioventricular pacing. Plasma ANH levels increased from 149 +/- 35 pmol/L at baseline to 187 +/- 31 pmol/L (p = 0.007) during SVT. Plasma vasopressin and renin levels were unchanged. Urine sodium levels increased 49% from 1.54 +/- 0.66 mEq/hr at baseline to 2.29 +/- 0.89 mEq/hr (p = 0.044) during SVT, and urine potassium levels increased 22% from 4.14 +/- 0.10 mEq/hr to 5.04 +/- 1.25 mEq/hr (p = 0.018). Urine sodium and potassium levels returned to baseline values 1 hour after pacing. Thus elevated plasma levels of ANH during SVT are associated with both a natriuresis and kaliuresis, which may represent physiologic effects of the endogenously secreted hormone.

Renal response of anesthetized rats to low-dose infusion of atrial natriuretic peptide.

Studies were performed in rats to determine the minimum infusion rate of atrial natriuretic peptide (ANP) associated with detectable changes in renal function and to determine the change in plasma levels of the peptide produced by these infusion rates. Synthetic ANP-(4-28) was administered to anesthetized euvolemic rats at rates ranging between 10 and 230 ng.kg-1.min-1 for 30 min. Significant natriuresis and diuresis were seen with an infusion of 20 ng.kg-1.min-1. At this rate of infusion, plasma ANP averaged 279 +/- 19.9 pmol/l (vs. 158 +/- 11.8 pmol/l in control rats). A transient increase in K excretion was seen with infusions higher than 100 ng.kg-1.min-1. There was no measurable change in glomerular filtration rate up to an infusion of 160 ng.kg-1.min-1. A significant decrease in mean arterial pressure was only seen with an infusion of 230 ng.kg-1.min-1. In volume-expanded rats, infusion of ANP at 10 ng.kg-1.min-1 induced a significant natriuresis. Our results indicate that natriuresis and diuresis are caused by an infusion of ANP which produces changes in plasma ANP concentration that may well result from stimulation of endogenous ANP release. In contrast, changes in K excretion, glomerular filtration rate, and arterial blood pressure may require changes in plasma ANP that are not easily achievable by physiological interventions.

Effect of vasopressors on atrial natriuretic factor and hemodynamic function in humans.

To assess the effects of vasopressors on plasma levels of immunoreactive atrial natriuretic factor (ANF), 13 normal men were studied on two occasions. On the experimental day, subjects received sequential 15-minute intravenous infusions of angiotensin II in doses of 4, 8, and 16 pmol/kg/min. Following a 30-minute recovery period, subjects received sequential 15-minute infusions of phenylephrine in doses of 0.4 and 0.8 micrograms/kg/min. Right atrial pressure, mean pulmonary capillary wedge pressure, pulmonary artery pressure, mean systemic arterial pressure, and plasma levels of renin activity, aldosterone, angiotensin II, and immunoreactive ANF were obtained sequentially throughout the protocol. During the control day, vehicle was infused and plasma samples were obtained for hormone measurements. Infusion of angiotensin II and phenylephrine increased mean systemic arterial pressure in a stepwise fashion. Both right atrial pressure and pulmonary capillary wedge pressure increased significantly during both doses of phenylephrine, but only the highest dose of angiotensin II significantly increased atrial pressures. Plasma levels of immunoreactive ANF increased parallel with the changes in right atrial pressure and pulmonary capillary wedge pressure, with significant increases occurring only at the highest dose of both pressors. Angiotensin II and aldosterone levels increased and renin activity decreased during infusion of angiotensin II. There were no significant changes in plasma levels of immunoreactive ANF during the control day. These studies demonstrate that infusion of vasopressors increases plasma levels of ANF, but only when the vasopressor effect is associated with significant increases in right atrial and pulmonary capillary wedge pressures. Atrial stretch is the most likely mediator of the increase in plasma levels of immunoreactive ANF during vasoconstriction.

Acromegaly from ectopic growth hormone-releasing hormone secretion by a malignant carcinoid tumor. Successful treatment with long-acting somatostatin analogue SMS 201-995.

A 26-year-old man with acromegaly secondary to ectopic growth hormone-releasing hormone (GHRH) secretion by a metastatic carcinoid tumor is the subject of this study. He previously failed to respond to conventional therapeutic modalities (partial hypophysectomy, pituitary irradiation, high-dose bromocriptine and a combination of streptozotocin and 5-fluorouracil) and was treated with long-acting somatostatin analogue SMS 201-995 (Sandoz, East Hanover, NJ). Growth hormone and somatomedin C concentrations became normal, and GHRH-LI (GHRH-like immunoreactivity) was suppressed by more than 60%. The growth hormone response to exogenous GHRH 1-40 was stopped and growth hormone rise to thyrotropin-releasing hormone (TRH) was significantly attenuated. A significant shrinkage of the pituitary gland was observed. Similarly, the size of the metastatic carcinoid lesions decreased dramatically and was accompanied by a normalization of liver function. After almost 2 years of SMS 201-995 therapy, the patient was well and had no clinical signs of acromegaly. Thus, SMS 201-995 appears to be a remarkably effective agent for treatment of acromegaly secondary to ectopic GHRH secretion.