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Biomedical subjects

J L Osborn

Publications and source records attributed to J L Osborn.

At least 55 records · Page 3Linked to original sources
PubMed1984

Interactions among renal nerves, prostaglandins, and renal arterial pressure in the regulation of renin release.

To examine the interactions among the renal nerves, prostaglandins, and renal arterial pressure in the regulation of renin secretion, experiments using low-frequency renal nerve stimulation (LFRNS; supramaximal voltage, 0.5 ms, 0.5 Hz) were performed in anesthetized dogs. LFRNS, which did not affect renal hemodynamics or urinary sodium excretion, increased renin secretion rate before (79 +/- 16 ng/min) but significantly less after renal arterial administration of indomethacin or meclofenamate (26 +/- 7 ng/min). In a separate group of dogs, LFRNS increased both renin secretion rate (266 +/- 139 ng/min) and renal prostaglandin E2 secretion rate (2,080 +/- 635 ng/min). LFRNS does not alter input stimuli to the renal vascular baroreceptor or tubular macula densa receptor mechanisms for renin secretion and represents a direct neural stimulus for renin secretion; this also increases renal prostaglandin E2 secretion rate, which contributes to the increase in renin secretion rate. The renin secretion rate response of innervated and denervated kidneys to reduction in renal arterial pressure to 50 mmHg was examined before and after indomethacin/meclofenamate administration. The observation that indomethacin/meclofenamate decreased but did not abolish the renin secretion rate response to aortic constriction in innervated kidneys suggests the presence of a prostaglandin-independent mechanism that is mediated by an interaction between the renal nerves and the tubular macula densa receptor, as indomethacin/meclofenamate essentially abolished the renin secretion rate response to aortic constriction in denervated kidneys.

Animals↗
PubMed1983

Impaired blood flow autoregulation in nonfiltering kidneys: effects of theophylline administration.

To investigate blood flow autoregulation in filtering and nonfiltering kidneys, renal blood flow was determined during graded reductions in renal perfusion pressure in seven anesthetized dogs containing both a filtering and nonfiltering kidney. In each dog, one kidney was made nonfiltering by the method of EH Blaine, JO Davis, and RT Witty (Circ Res 27:1081-1089, 1970). Renal perfusion pressure was decreased from 129 to 115, 99, and 83 mm Hg by stepwise constriction of the suprarenal aorta. In filtering kidneys, the maximum decrease in renal perfusion pressure reduced renal blood flow only 20.1% of control whereas renal blood flow of nonfiltering kidneys decreased by 41.0% of control. During aortic constriction, renal vascular resistance of nonfiltering kidneys remained unchanged or slightly increased. These hemodynamic changes were associated with significantly greater autoregulation indices in nonfiltering kidneys. In eight dogs with nonfiltering kidneys, competitive inhibition of adenosine with theophylline (9 mg/kg iv) restored autoregulation of renal blood flow as shown by significant decreases in renal vascular resistance. These data indicate that in the nonfiltering kidney model, autoregulation of renal blood flow is impaired. It is suggested that this impaired autoregulatory response may result from renal ischemia and the vasoconstrictor influence of elevated intrarenal adenosine concentration.

Adenosine↗
PubMed1982

Role of macula densa in renal nerve modulation of renin secretion.

Low-frequency renal nerve stimulation (0.25 Hz) augments the renin secretion response to reduction of renal perfusion pressure to 50 mmHg by aortic constriction. The present experiments determined whether this modulating influence could be demonstrated when the macula densa receptor was inoperative. In 10 anesthetized dogs with a nonfiltering kidney and sectioned renal nerves, aortic constriction to 52 mmHg decreased renal blood flow and increased renin secretion from 126 +/- 94 to 192 +/- 55 ng/min. During low-frequency renal nerve stimulation and aortic constriction to 50 mmHg, renin secretion was not augmented (37 +/- 13 to 81 +/- 42 ng/min). In four anesthetized dogs with nonfiltering kidneys, aortic constriction to 52 mmHg increased renin secretion similarly before (16 +/- 8 to 68 +/- 17 ng/min) and after renal denervation (14 +/- 14 to 78 +/- 18 ng/min). Therefore, the augmentation of the renin secretion response to aortic constriction to 50 mmHg by low-frequency renal nerve stimulation in filtering kidneys does not result from an interaction with the renal vascular baroreceptor or the juxtaglomerular granular cells. Since neural augmentation of renin secretion during aortic constriction was not observed in the nonfiltering kidney where the macula densa is inoperative, we conclude that the macula densa is the probable site for the neural modulation of renin secretion.

Animals↗
PubMed1982

Role of renal alpha-adrenoceptors mediating renin secretion.

The increase in renin secretion resulting from low-frequency renal nerve stimulation (0.5 Hz) occurs in the absence of changes in urinary sodium excretion or renal blood flow and is apparently derived from a direct effect of renal sympathetic nerves on juxtaglomerular granular cells. We sought to determine the role of renal alpha-adrenoceptors in this neurally evoked renin secretion. The neurally evoked renin secretion was unaffected by renal alpha-adrenoceptor blockade with phentolamine or prazosin; however, two dose levels of phenoxybenzamine equally inhibited the renin secretion. The renal vasoconstrictor response to graded renal nerve stimulation was similarly diminished by phentolamine, prazosin, and the higher phenoxybenzamine dose, whereas the lower phenoxybenzamine dose was significantly less effective. Renal alpha-adrenoceptor stimulation with methoxamine infusion at doses that were just subthreshold for altering renal blood flow and urinary sodium excretion or at doses that just reduced urinary sodium excretion also did not change renin secretion. Higher doses of methoxamine that decreased both renal blood flow and sodium excretion increased renin secretion. Based on the inability of phentolamine and prazosin to prevent neurally mediated renin secretion and on the dose-response relationship between methoxamine and changes in renin secretion, renal blood flow, and urinary sodium excretion, we conclude that renal alpha-adrenoceptors do not mediate renin secretion elicited by direct neural activation of the juxtaglomerular granular cells. The data suggest that phenoxybenzamine inhibits neurally mediated renin secretion by a mechanism other than renal alpha-adrenoceptor blockade.

Adrenergic alpha-Antagonists↗
PubMed1982

Prostaglandin in renin release during sodium deprivation.

This study was designed to examine the role of prostaglandins in the macula densa-mediated increase in plasma renin activity (PRA) during dietary sodium deprivation in rats. Micropuncture collections of early distal (ED) tubular fluid (TF) and measurements of PRA, arterial pressure (AP), and renal blood flow (RBF) were obtained in four groups of animals. Groups I and II received a normal Na diet and groups II and IV received a low Na diet; groups II and IV received indomethacin. Studies were performed after surgical denervation of the kidneys; AP and RBF were not different among the four groups of animals. EDTFna delivery was lower in groups III (0.20 +/- 0.04 neq/min) and in group IV (0.16 +/- 0.01 neq/min) animals on the low Na diet as compared with group I (0.34 +/- 0.02 neq/min) and group II (0.32 +/- 0.05 neq/min) animals on the normal Na diet. In association with the lower EDTFna delivery, the animals receiving vehicle in group III had an elevated PRA (31.46 +/- 8.81 ng/ml) as compared with group I animals on the normal Na diet receiving vehicle (4.78 +/- 1.64 ng/ml). This rise in PRA was abolished in the animals in group IV (4.06 +/- 0.81 ng/ml) that received indomethacin. We conclude that the increase in PRA, possibly resulting from macula densa receptor stimulation, during dietary Na deprivation is dependent on prostaglandin synthesis.

Animals↗
PubMed1981

The effect of vagotomy on sodium reabsorption and renin release in anaesthetized dogs subjected to 60 degrees head-up tilt.

1. Anaesthetized dogs were subjected to two 15 min periods of 60 degrees head-up tilt. Renal perfusion pressure was regulated to minimize changes during tilting. 2. In both intact and vagotomized animals there was a fall in systemic arterial pressure and a rise in heart rate. In both intact and vagotomized animals glomerular filtration rate fell slightly during the first tilt but remained unchanged in the second tilt period. Renal blood flow was unchanged throughout. 3. Both absolute and fractional excretions of sodium were reduced in intact animals subjected to the two consecutive periods of tilt. Following vagotomy these responses were as large as those observed in intact animals. 4. Tilting caused an increase in renin secretion from the kidney in both tilting periods to which the intact animals were subjected. In the vagotomized animals the increase in renin secretion was as large as that observed in intact animals. 5. The results of the present study show that, under the experimental conditions used, vagal afferent activity had no measurable effect on the decreases in sodium excretion or increases in renin secretion mediated by the renal nerves during short periods of 60 degrees head-up tilt.

Absorption↗
PubMed1981

Effect of renal nerve stimulation on renal blood flow autoregulation and antinatriuresis during reductions in renal perfusion pressure.

Renal nerve stimulation increases renal vascular resistance and decreases glomerular filtration rate and urinary sodium excretion. The purpose of this study was to determine whether neurally mediated changes in renal vascular resistance, glomerular filtration rate, and urinary sodium excretion at control renal perfusion pressure modified the autoregulation of renal blood flow and glomerular filtration rate and the antinatriuresis observed during reductions in renal perfusion pressure in pentobarbital-anesthetized dogs. Renal blood flow, glomerular filtration rate, and urinary sodium excretion were determined during stepwise reductions in renal perfusion pressure from 137 to 55 mm Hg (suprarenal aortic constriction) before and during electrical stimulation of the renal nerve at 0.5, 1.0, 2.0, and 4.0 Hz. In the absence of renal nerve stimulation, renal blood flow and glomerular filtration rate remained constant until renal perfusion pressure was reduced to 70 and 85 mm Hg, respectively. Urinary sodium excretion decreased linearly as renal perfusion pressure decreased. Renal nerve stimulation at 0.5, 1.0, 2.0, and 4.0 Hz increased renal vascular resistance and decreased glomerular filtration rate and urinary sodium excretion. These frequencies of renal nerve stimulation, however, did not alter the decreases in renal vascular resistance and glomerular filtration rate or the antinatriuretic response to stepwise reductions in renal perfusion pressure to 55 mm Hg. These data demonstrate that increased renal vascular resistance at either the afferent or efferent arteriole does not change the responses of these vessels to reductions in renal perfusion pressure. Renal nerve stimulation at frequencies which decrease urinary sodium excretion at control renal perfusion pressure also does not enhance the antinatriuretic response to reductions in renal perfusion pressure.

Animals↗
PubMed1981

Beta-1 receptor mediation of renin secretion elicited by low-frequency renal nerve stimulation.

The purpose of this study was to determine if renin secretion resulting solely from low-frequency renal nerve stimulation (no change in renal blood flow or urinary sodium excretion) is mediated by activation of beta-1 (beta-1) or beta-2 (beta-2) adrenergic receptors. Beta-1 and beta-2 adrenergic receptor blockade were produced with atenolol and butoxamine, respectively. Low-frequency renal nerve stimulation (0.5 Hz) increased renin secretion without altering mean arterial pressure, renal blood flow, glomerular filtration rate or urinary sodium excretion. The increase in renin secretion in response to renal nerve stimulation was blocked by beta-1 blockade with intrarenal atenolol (2.0 micrograms/kg/min) infusion. This dose of atenolol reduced the renal vasodilator response to intrarenal isoproterenol by only 48%, thus indicating modest beta-2 receptor blockade. A lower dose of atenolol (30 micrograms/kg i.v.) markedly decreased the tachycardia in response to i.v. isoproterenol (2 micrograms) but had no effect on the renal vasodilator response to intrarenal isoproterenol injection (2 micrograms), thus indicating selective beta-1 blockade. This dose of atenolol abolished the increase in renin secretion during renal nerve stimulation. In contrast, beta-2 receptor blockade with butoxamine (20 micrograms/kg/min) did not alter the renin secretion response to renal nerve stimulation. This dose of butoxamine decreased the renal vasodilator response to intrarenal isoproterenol by 73%, thus demonstrating significant beta-2 receptor blockade. These results indicate the low-frequency renal nerve stimulation (0.5 Hz) increases renin secretion without altering renal hemodynamics or urinary sodium excretion. This neurally mediated renin secretion resulted from activation of beta-1 adrenergic receptors.

Animals↗
PubMed1980

Species differences in the kinetics of the renin-substrate reaction in plasma.

In view of the substrate-dependence of renin, it was of interest to examine the kinetics of the renin-angiotensinogen reaction in plasma of various species to establish differences in stoichiometry. The results also provide an indication of assay conditions appropriate for accurate measurement of the reaction velocity. Plasma from hogs, dogs, and rats served as the source of renin for incubation with homologous angiotensinogen. The rate of production of radioimmunoassayable angiotensin I increased with increasing concentrations of angiotensinogen. This substrate-dependence of renin conformed to conventional Michaelis-Menten kinetics. The concentration of angiotensinogen was less than that required for half maximum velocity in dog and rat plasma. In contrast, endogenous substrate in hog plasma was sufficient to sustain near maximal rates of generation of angiotensin I. Purification of angiotensinogen altered the catalytic properties of angiotensinogen making it a poor representative substrate for renin. Hog and rat renin were saturable with high concentrations of unextracted plasma angiotensinogen. In contrast, it was not possible to saturate the dog enzyme with unextracted substrate. The interspecies differences in stoichiometry of the reaction indicate that standardization of assay conditions for various species of renin is not justified.

Angiotensin I↗
PubMed1980

Effect of saralasin and indomethacin on renal function in developing piglets.

To investigate the influence of angiotensin II (AII) and renal prostaglandins on neonatal renal hemodynamics and sodium excretion, unanesthetized piglets 1-5, 18-20, and 45-50 days of age were treated with saralasin and indomethacin prior to volume expansion (VE) with isotonic saline. Saralasin did not affect basal renal blood flow (RBF) or the intrarenal distribution of blood flow as calculated as the ratio of outer-to-inner slice counts (O/I) in piglets 1-50 days of age. VE increased fractional sodium excretion equally in all animals. In 1- to 5-day-old piglets, saralasin blunted this natriuresis without affecting renal hemodynamics. Therefore, low neonatal RBF and O/I do not appear to be due to AII. In addition, indomethacin did not change renal hemodynamics in newborn piglets and did not affect the natriuresis after VE in any age group. Indomethacin decreased RBF and increased O/I of conscious 45- to 50-day-old animals. Renal prostaglandins do not appear to be a factor in control of renal hemodynamic in newborn pigs and do not influence the natriuresis in neonates following saline loading.

Aging↗
PubMed1980

Regulation of plasma renin in developing piglets.

Plasma renin activity (PRA) was determined in conscious piglets between 1 and 50 days of age before and after treatment with saralasin and indomethacin. Following drug treatment, animals were volume expanded with isotonic saline. Saralasin increased PRA in piglets 1-5 and 18-22 days of age but not 45-50 days. Neither indomethacin nor VE changed PRA at any age. Volume expansion of saralasin- and indomethacin-treated pigs decreased PRA. Neonatal hyperreninemia does not appear to result from renin release stimulated by prostaglandins or by the absence of angiotensin II negative feedback. In addition, the plasma half-life of renin was not different between young and more mature animals suggesting that immature hapatic metabolism of renin cannot be entirely responsible for the high PRA in newborns.

Age Factors↗
PubMedDate not supplied

The effect of compression duration on hemodynamics during mechanical high-impulse CPR.

OBJECTIVE: To determine whether shorter compression durations combined with fixed increased compression velocity during mechanical high-impulse CPR (HI-CPR) improve resuscitation hemodynamics, compared with mechanical standard CPR (SCPR). METHODS: A porcine model of ventricular fibrillation was used, with each animal serving as its own control. Twelve anesthetized swine (20-25 kg each) were instrumented for hemodynamic monitoring. Ventricular fibrillation was induced and followed, after 3 minutes, by mechanical SCPR (50% duty cycle) for 10 minutes. Mechanical HI-CPR was then applied, with compression durations varied randomly at 2-minute intervals for 20% (COM20), 30% (COM30), and 40% (COM40) of the CPR cycle. A 2-minute mechanical SCPR control phase completed the experiment. RESULTS: Hemodynamic measurements were significantly better for COM20 and COM30 vs SCPR, including, respectively: mean arterial pressure (MAP), 45 +/- 8 and 43 +/- 7 vs 36 +/- 7 torr; coronary perfusion pressure (CPP), 21 +/- 6 and 21 +/- 8 vs 16 +/- 6 torr; and end-tidal CO2 (ETCO2), 7 +/- 2 and 6.6 +/- 2 vs 5 +/- 1.4 torr. MAP, CPP, and ETCO2 during COM40 were not significantly different from those during SCPR, and there was no difference between COM20 and COM30 for any hemodynamic parameter. Aortic flow velocity was significantly better in COM20, COM30, and COM40 vs SCPR: 2.3 +/- 0.7, 2.1 +/- 0.9, and 1.95 +/- 0.9 vs 1.3 +/- 0.5 cm/sec, respectively. CONCLUSION: In a swine model of mechanical HI-CPR, shorter compression durations combined with fixed increased compression velocity significantly improve resuscitation hemodynamics, compared with those afforded by mechanical SCPR.

Animals↗