Serum ferritin measurement and the degree of agreement using four techniques.

Four commercial assay kits to measure serum ferritin were compared to establish the degree of agreement and interchangeability between the different techniques based on the intraclass correlation coefficient (ri). Radioimmunoassay, microparticle enzyme immunoassay, enzyme-linked immunosorbent assay, and chemiluminescent immunoassay systems were used. The Pearson product-moment correlation factor (r) between any two methods was at least 0.98, and the intercept of the regression equations ranged from -0.613 to 3.797, indicating that the methods were comparable. Furthermore, the intraclass correlation coefficient (ri) was at least 0.98, suggesting that the methods were interchangeable.

Role of mast cell chymase in the extracellular processing of big-endothelin-1 to endothelin-1 in the perfused rat lung.

Previous studies of endothelin-1 (ET) synthesis have shown that some cultured endothelial cells secrete an intermediate product, big-endothelin-1 (bigET), suggesting that the processing of secreted bigET to ET may be physiologically significant. In this study, two pertinent ET converting enzyme activities, mast cell chymase I (EC 3.4.21.39) and a phosphoramidon-sensitive, neutral metalloprotease, were identified in a rat lung particulate fraction. We perfused rat lungs with bigET and chymostatin or phosphoramidon to study the relevance of these two proteases to the processing of extracellular bigET in vivo. Addition of compound 48/80 (a compound which activates mast cells, causing degranulation and release of chymase) to the perfusion buffer greatly increased hydrolysis of exogenously added bigET to ET. ET formation was inhibited completely by 32 microM chymostatin, whereas inhibition by 50 microM phosphoramidon was incomplete and variable. Perfusate histamine levels were used to monitor the extent of mast cell degranulation, and inhibition of ET production by phosphoramidon was attributed to inhibition of degranulation, per se. There was a direct correlation between perfusate ET and histamine levels in both control and phosphoramidon-treated (but not chymostatin-treated) lungs. Our results suggest that chymase from lung mast cells is capable of physiologically relevant extracellular processing by bigET to ET in the perfused rat lung.

Control of renal function during intrarenal infusion of endothelin.

It has been demonstrated that bolus injections of a vasoconstrictor derived from endothelial cells, endothelin 1 (ET-1), constricts isolated arteries and increases blood pressure in animals when infused intravenously. The purpose of this study was to examine the direct effects of intrarenal infusions of ET-1 on renal function at doses that do not alter systemic arterial pressure. The effects of ET-1 on renal hemodynamics and electrolyte excretion were examined during 40 min of intrarenal infusions of ET-1 at rates of 1.15 and 5 ng.kg-1.min-1. Infusion of ET-1 (1.15 ng.kg-1.min-1) resulted in a transient increase in renal blood flow (RBF) followed by a progressive vasoconstriction, which reduced RBF by 23%. ET-1 decreased glomerular filtration rate (GFR) and had no significant effect on filtration fraction. Intrarenal infusion of ET-1 (1.15 ng.kg-1.min-1) had no effect on fractional excretion of sodium (FENa) or potassium. Infusion of ET-1 at a higher dose (5 ng.kg-1.min-1) produced further reductions in RBF, GFR, and FENa. These data indicate that ET-1 is a potent renal vasoconstrictor that could play a role in controlling renal hemodynamics.

Effects of long-term increases in plasma ANP on angiotensin II-induced hypertension.

In vitro studies have suggested that atrial natriuretic peptide (ANP) is a potent antagonist of the vasoconstrictor actions of angiotensin II (ANG II). The purpose of this study was to determine the long-term effects of physiological increases in circulating levels of ANP on arterial pressure (AP) regulation in conscious dogs (n = 9) with ANG II-induced hypertension. Infusion of ANG II at a rate of 10 ng.kg-1.min-1 for 7 days increased AP from 85 +/- 3 to 133 +/- 4 mmHg. This increase in AP was associated with an increase in total peripheral resistance (TPR) and a decrease in cardiac output (CO). After 7 days of ANG II infusion, ANP103-126 was then infused simultaneously at a rate of 20 ng.kg-1.min-1 for 7 days. Plasma levels of ANP increased from 59 +/- 15 to 285 +/- 28 pg/ml. Increasing plasma ANP levels for 7 days had no significant long-term effect on AP (133 +/- 4 vs. 125 +/- 6 mmHg), TPR, or CO. There were also no significant changes in glomerular filtration rate or sodium excretion during the 7 days of ANP infusion. These data indicate that long-term increases in circulating levels of ANP have minimal chronic hypotensive effects in dogs with ANG II hypertension. In addition, the results from this study suggest that physiological increases in plasma ANP do not exhibit long-term antagonistic effects toward the vasoconstrictor actions of ANG II.

Effects of chronic hypertension and its reversal on arteries and arterioles.

The reversibility of functional and structural microvascular alterations in chronic renal hypertension has not been established. Twelve weeks after surgery to induce hypertension, in vivo arteriolar and venular dimensions were measured in the cremaster muscle of rats with one-kidney, one-clip hypertension (1K1C), rats in which the clip was removed after 8 weeks (1KNT), and controls. Systolic blood pressure was significantly elevated after 3 days in 1K1C rats and reached a plateau by 6 weeks. In 1KNT rats, systolic blood pressures were similar to 1K1C rats but were normalized 1 day after unclipping. A marked medial-intimal hypertrophy was found by histological techniques in the thoracic and abdominal aortae (45% and 69%, respectively) but not in cremaster feeding arteries of 1K1C rats. These arterial changes were reversed after unclipping. In 1K1C rats, medial-intimal area decreased in first- through fourth-order (1A, 2A, 3A, and 4A) arterioles along with a decline in relaxed diameter (41%, 30%, 20%, and 21%, respectively), which was only partially restored after unclipping. Heart weight was increased by 67% in 1K1C rats, but it did not differ between 1KNT and controls. Therefore, the reversal of chronic renal hypertension can normalize gross structural alterations in the heart and large vessels, but more time may be required to normalize completely the arteriolar changes. These data indicate that long-term structural adaptations in renal hypertension are different in arterioles and arteries, and they may be related to chronic changes in blood flow and/or pressure.

Mechanism mediating hypotensive effect of ANF in sodium-depleted dogs.

Previous studies have indicated that suppression of renin release and antagonism of the vasoconstrictor actions of angiotensin II (ANG II) may be important mechanisms whereby atrial natriuretic factor (ANF) decreases arterial pressure (AP). The objective of this study was to determine the importance of renin suppression and ANG II antagonism in mediating the hypotensive effects of ANF in Na-depleted, high-renin dogs. Infusion of ANF (300 ng.kg-1.min-1) for 45 min in Na-depleted dogs decreased plasma renin activity (PRA) from 7.5 +/- 2.3 to 3.1 +/- 1.1 ng ANG I.ml-1.h-1. Associated with this fall in PRA was a significant reduction in AP and total peripheral resistance (TPR). Although cardiac output (CO) tended to fall, statistically significant reductions in CO (2.11 +/- 0.19 vs. 1.99 +/- 0.10 l/min) did not occur. In contrast to these findings, infusion of ANF (300 ng.kg-1.min-1) in Na-depleted dogs with fixed circulating levels of ANG II had no significant effect on AP or TPR. Results from this study suggest that renin suppression may be an important mechanism whereby ANF reduces AP in Na-depleted dogs. The results also suggest that antagonism of the vasoconstrictor actions of ANG II is not a potent mechanism whereby ANF decreases AP.

Arteriolar changes in developing and chronic stages of two-kidney, one clip hypertension.

Arteriolar internal and external diameters in the cremaster muscle of two-kidney, one clip hypertensive rats (2K1C) were measured in vivo with video microscopy, both before and after the topical application of adenosine (10(-4) M). Arteriolar density was determined by stereologic techniques. Mean arterial blood pressure was significantly elevated in the 2K1C rats, rising to 186 +/- 6 mm Hg by 8 weeks compared with 113 +/- 4 mm Hg in controls. Lumens of larger arterioles showed a structural reduction at 2 weeks of hypertension and remained at the same level through 8 weeks, while arterioles of control rats showed a progressive increase in diameter with age (101 +/- 6 microns in 2K1C vs. 158 +/- 8 microns in controls at 8 weeks after operation). Wall-to-lumen ratios of larger arterioles were significantly increased at 2, 4, and 8 weeks of hypertension, but cross-sectional wall area was significantly reduced at 8 weeks. Medial hypertrophy was not evident at any stage of hypertension. Arteriolar rarefaction of smaller arterioles was functional at 2 weeks and structural at 8 weeks of hypertension. Vascular tone of the smaller arterioles was elevated in the developing and chronic stages of hypertension. At 2 weeks of hypertension when the structural reduction in diameters of larger arterioles was progressing, the increased vasoconstriction and functional rarefaction may have contributed to the elevated resistance. At 8 weeks, the marked diameter reductions of larger arterioles (36% in first-order arterioles and 25% in second-order arterioles) account for most of the increased resistance to flow.

Attenuated microvascular alterations in coarctation hypertension.

Arteriolar vasoconstriction, structural reductions in dilated diameter, and rarefaction have been observed in vascular beds with chronic renal hypertension. To determine their pressure or flow dependence, these functional and structural parameters were studied in the developing and chronic stages of coarctation hypertension in the cremaster muscle, a normotensive skeletal muscle bed that is protected from the effects of elevated microvascular pressures. Hypertension was produced in rats by placing a silver clip around the abdominal aorta above the branches of the renal arteries. In hypertensive rats, resting diameters were reduced in second-order arterioles after 4 and 8 wk, in third-order arterioles after 2, 4, and 8 wk, and in fourth-order arterioles after 4 and 8 wk, vs. controls. Vascular tone was elevated in second-order arterioles after 2, 4, and 8 wk and in third- and fourth-order arterioles after 8 wk in hypertensive rats. No increases in medial-intimal area were found at any stage of hypertension in any arteriolar order. The density of small arterioles (3rd-5th orders) was reduced by 20% in hypertensive rats at 8 wk but was unchanged at the other time periods. These arteriolar alterations, especially the absence of structural reductions in diameter, are attenuated compared with those observed in one-kidney, one-clip hypertension and suggest that most of the arteriolar alterations that occur in renal hypertension are pressure or flow dependent.

Arteriolar reactivity to pressure stimuli in hamsters with renal hypertension.

The responses to alterations in extravascular pressure were studied in five orders of arterioles in the cheek pouch of normotensive and renal hypertensive hamsters. Renal hypertension was induced by bilateral compression of both kidneys using figure-of-eight ligatures. Ten to 16 days later, hamsters were anesthetized with pentobarbital (6.0 mg/100 g body weight) and a Plexiglas chamber was positioned in the cheek pouch. Chamber pressure, or extravascular pressure, was increased and decreased by +/- 10, 20, and 40 mm Hg, and arteriolar diameters were monitored continuously. The responses at -20 mm Hg and the slope of the linear portion of the chamber pressure-diameter curve (arteriolar gains) were compared between groups for each branching order of arteriole. Arteriolar responses at one chamber pressure and the arteriolar gains were enhanced in third and fourth order arterioles of the renal hypertensive group compared with the normotensive group, and the responses of these small arterioles were greater than those of larger arterioles in both groups. Control diameters of second and third order arterioles were significantly smaller in the renal hypertensive group, while the diameters after adenosine were not different. These results suggest that the enhanced responses of small arterioles in the renal hypertensive group were not related to structural alterations but may be related to an increased reactivity of smooth muscles in these small arterioles to volume expansion, thus a pressure stimulus.