John C. McGiff

Release of a prostaglandin E-like substance from canine kidney by bradykinin.

Renal vasodilation produced by two dissimilar vasodepressor polypeptides, bradykinin and eledoisin, was correlated with changes in renal venous concentrations of substances having the properties of prostaglandins of the E and F series in anesthetized dogs. Samples of renal venous blood were extracted for acidic lipids, and the prostaglandin E and prostaglandin F zones of the chromatographed extracts were eluted and assayed in vitro for prostaglandins of the E and F series by a parallel bioassay system (sensitivity 0.015 ng/ml blood). During the first 2 minutes of infusion, bradykinin increased the concentration of a prostaglandin E-like substance in renal venous blood from a mean control level of 0.16 ng/ml to 1.05 ng/ml (P<0.01); this increase occurred simultaneously with the greatest increase in renal blood flow to 432 ml/min from a control value of 282 ml/min. After 12 minutes of bradykinin infusion, the concentration of the prostaglandin E-like substance had decreased to 0.30 ng/ml, and renal blood flow had fallen to 398 ml/min. In contrast, eledoisin infused in equidilator doses did not increase the concentration of the prostaglandin E-like substance. The concentration of prostaglandin F-like substances was not affected by either polypeptide. A transient increase in urine flow occurred during the first 2 minutes of bradykinin infusion only. These results suggest that a prostaglandin E-like substance participates in the renal vasodilator and the diuretic responses to bradykinin.

Dependency of Renal Blood Flow on Prostaglandin Synthesis in the Dog

Inhibition of prostaglandin synthesis in chloralose-anesthetized dogs reduced renal blood flow, and this reduction closely correlated (r=0.92, P<0.01) with a decline in the renal efflux of a substance having the properties of PGE2. We used solvent extraction and thin-layer chromatography coupled with parallel bioassay to identify and assay the PGE- and PGF-like substances (expressed as PGE2 and PGF2α equivalents). Either of two antiinflammatory acids, indomethacin or meclofenamate, that inhibited conversion of 14C-arachidonic acid to prostaglandins in renal homogenates decreased the basal concentration of a PGE-like substance in renal venous blood to 0.06 ± 0.02 ng/ml from a mean control value of 0.34 ± 0.10 ng/ml (P<0.01). This change was associated with a mean reduction in renal blood flow of 45% in spite of increased renal perfusion pressure. Femoral blood flow and cardiac output were variably and insignificantly affected. Changes in the renal efflux of a PGF-like substance induced by indomethacin were unrelated to the decline in renal blood flow. Changes in the efflux of a PGE-like substance from the femoral vascular bed were unrelated to the small and variable changes in femoral blood flow. Extrarenal factors, i.e., humoral, nervous, or cardiopulmonary factors, did not account for the decline in renal blood flow produced by the inhibitors of prostaglandin synthesis, since the inhibitors produced identical effects in the isolated blood-perfused canine kidney. We concluded that PGE2 participates in maintaining renal vascular tone which heretofore has been ascribed to autonomous, intrinsic renal arteriolar activity.

Prostaglandin synthesis by bovine mesenteric arteries and veins.

Prostaglandins (PG) were synthesized at similar rates by bovine mesenteric arteries and veins; viz., ca. 200 ng/g wet weight after one hour of incubation. After synthesis, PGE and PGF compounds were released from slices of arteries and veins into the incubating medium; PG were not detected in the walls of these blood vessels. Arachidonic acid, the precursor to PGE2 and PGF2α, did not affect PG synthesis, whereas meclofenamate, an aspirin-like agent, decreased synthesis in arteries and veins by 90%. The PG biosynthetic capacity of these blood vessels is high, as indicated by greater than 20% conversion of [l-14C]-arachidonic acid to radiolabeled PG. Under control conditions in both arteries and veins, synthesis of PGE2 exceeded that of PGF2α twofold. Bradykinin selectively increased the synthesis of a PGE-like substance in arteries and of a PGF-like substance in veins.

Disappearance of bradykinin in the renal circulation of dogs. Effects of kininase inhibition.

In chloralose-anesthetized dogs, we investigated the disappearance of bradykinin on passage across the renal circulation. The peptide was infused into a renal artery at various doses (5-200 ng/kg min−1); renal blood flow and the concentration of kinins in renal venous blood were then determined and the percent survival of bradykinin on passage through the kidney calculated. Bradykinin caused a dose-related increase in renal blood flow, urine flow, sodium excretion, and kinin content of renal venous blood. Intravenous administration of BPP9cr (300 μg/kg), a peptide kininase II inhibitor, potentiated the renal vasodilator, diuretic, and natriuretic actions of bradykinin and augmented the survival of the kinin on passage through the kidney from 12.72 ±1.64% in control dogs to 53.92 ±7.48% (P < 0.001). Furthermore, the values of peptide survival were positively correlated with the increases in renal blood flow (r = 0.92, P< 0.01), urine flow (r = 0.75, P < 0.01), and sodium excretion (r = 0.68, P < 0.01) produced by bradykinin. In addition, BPP9a by itself increased renal blood flow (16%, P < 0.01), urine flow (115%, P < 0.005), and sodium excretion (167%, P< 0.02). Similarly, the concentration of kinin in renal venous blood and the excretion of urinary kinins rose from 0.11 ±0.03 ng/ml and 4.4 ±1.1 ng/min to 0.24 ±0.05 ng/ml (P < 0.005) and 38.5 ±12.2 ng/min (P < 0.02). These studies suggest that kinins generated intrarenally play a role in the regulation of renal blood flow and salt-water excretion and that variations in the capacity of the kidney to inactivate kinins may be a determinant of the intrarenal activity of the kallikrein-kinin system.

Prostaglandins and the kidney.

• Although prostaglandins were discovered four decades ago, definition of their remarkable range of biological activity was delayed until the past decade when Bergstrom et al. (1) identified the structures of the major prostaglandins and set the foundation for their synthesis. What has happened thereafter is only too familiar: a full-scale invasion by prostaglandins into disciplines as disparate as demography and neurophysiology has resulted in a rapid accumulation of information, much of which appears contradictory and resists meaningful classification. For example, prostaglandins of the E series can either attenuate or augment the vasoconstrictor response to nerve stimulation, although augmentation occurs only at high doses (2). PGE2, the major renal prostaglandin, can modulate the renal response to antidiuretic hormone (ADH) by inhibiting stimulation of adenyl cyclase by ADH, although a prostaglandin of the E series can itself activate adenyl cyclase (3). Therefore, when considering biological activities, the prostaglandin in question must be unequivocally identified among the more than 14 naturally occurring prostaglandins and its dose and route of administration must be noted, since major differences in the effects of a prostaglandin depend on these factors in a way that appears to be unique for biological systems even in comparison with steroids.

Effect of A Renal Prostaglandin on Distribution of Blood Flow in the Isolated Canine Kidney

In isolated blood-perfused canine kidneys, progressive increases in renal blood flow and its fractional distribution to the inner cortex were correlated with increases in perfusate concentrations of a prostaglandin E-like (PGE-like) substance. The ratio of blood flow to the outer and inner halves of the renal cortex measured by the radioactive-microsphere method changed from 77:23 to 68:32 (P < 0.001) after 90 minutes of perfusion; simultaneously, the concentration of the PGE-like substance increased from 0.04 ng/ml to 0.59 ng/ml (P < 0.02). Thus, the greatest rate of increase in the concentration of the PGE-like substance occurred coincidently with the largest increase in inner cortical blood flow, i.e., from 30 ml/min to 69 ml/min (P < 0.001). During the two subsequent 90-minute perfusion periods, the ratio of outer cortical blood flow to inner cortical blood flow fell to 61:39, and the concentration of the PGE-like substance increased further. When indomethacin was added to the perfusate, the concentration of the PGE-like substance decreased from 1.00 ng/ml to 0.24 ng/ml (P < 0.05), and renal blood flow decreased, especially in the inner cortex where the decline was from 34% to 19% of total renal blood flow (P < 0.05). Thus, renal blood flow was redistributed after indomethacin was administered. PGE2 was infused to determine whether substitution for the loss of circulating PGE-like substance could prevent the effects of indomethacin on the distribution of renal blood flow. Despite administration of exogenous PGE2, renal blood flow redistributed after administration of indomethacin, and the ratio of outer cortical blood flow to inner cortical blood flow increased from 68:32 to 80:20 (P < 0.05). These results suggest that the intrarenal site of synthesis and release of PGE2 determines its action as a local hormone affecting deep cortical blood flow.

POSSIBLE INFLUENCE OF INTRARENAL GENERATION OF KININS ON PROSTAGLANDIN RELEASE FROM THE RABBIT PERFUSED KIDNEY

1 The effects of bradykinin and kininogen on renal prostaglandin release were studied in rabbit isolated kidneys perfused with oxygenated Krebs solution. 2 The concentration of prostaglandin‐like material in kidney effluent was determined by bioassay after extraction of the samples with organic solvents. In 7 experiments the samples were assayed after separation of prostaglandins E and F by thin layer chromatography. 3 Addition of bradykinin to the perfusing fluid increased the venous and urinary effluxes of prostaglandin E‐like substance by sixfold and fivefold, respectively, but efflux of prostaglandin F‐like material was unaffected. 4 Addition of kininogen to the perfusing fluid augmented the venous and urinary release of prostaglandin E‐like substances by fifteenfold and ninefold respectively and caused a twofold increase in the efflux of prostaglandin F‐like material into the venous effluent. 5 Aprotinin, a kallikrein inhibitor, reduced the prostaglandin releasing action of kininogen but not of bradykinin. In contrast, inhibition of prostaglandin synthesis by indomethacin suppressed the release of prostaglandin evoked by either bradykinin or kininogen. 6 This study suggests that augmented release of prostaglandins in response to kininogen is a consequence of renal generation of kinins. Thus, changes in the intrarenal activity of the kallikreinkinin system may modulate renal prostaglandin release.

Differential inhibition by prostaglandins of the renal actions of pressor stimuli.

Abstract In chloralose-anesthetized dogs, either PGE 2 , PGA 2 or acetylcholine (ACh) infused into a renal artery inhibited reversibly in the experimental kidney vasoconstriction-antidiuresis produced by renal nerve stimulation (RNS) or by pressor hormones given intravenously. The renal actions of RNS were reversed by PGE 2 and PGA 2 , whereas, those of norepinephrine were least affected. PGF 2α did not modify the renal actions of pressor stimuli. ACh inhibited the renal effects of RNS and norepinephrine to the same degree. PGE 2 (100 ng/min) inhibited the renal actions of adrenergic stimuli and angiotensin II to the same degree as PGA 2 , at a dose one-fifth that of PGA 2 , and at concentrations (ca 0.5 ng/ml blood) comparable to those of a substance, having the properties of PGE 2 , reported in renal venous effluent during escape from the renal vasoconstrictor-antidiuretic actions of pressor hormones.

The relationship of the renal vasodilator action of bradykinin to the release of a prostaglandin E-like substance.

Nachweis, dass Bradykinin den renalen Blutstrom um 58% der Kontrollwerte (282±40 ml min) erhöht und gleichzeitig im venösen Nierenblut die Konzentration einer Substanz, welche die physicochemischen und biologischen Eigenschatten eines Prostaglandins der E-Serie besitzt, steigert, wobei die Konzentration einer PGF-ähnlichen Substanz unverändert blieb.

Relationship of Glucose Metabolism to Adrenergic Transmission in Rat Mesenteric Arteries Effects of Glucose Deprivation, Glucose Metabolites, and Changes in Ionic Composition on adrenergic Mechanisms

The vasoconstrictor response of perfused rat mesenteric arteries to stimulation of sympathetic nerve fibers is markedly potentiated by glucose deprivation; this potentiation is abolished or reduced when glucose or other sugars are added. The augmentation of the vasoconstrictor response to nerve stimulation produced by glucose deprivation presumably results from an increased release of the adrenergic transmitter, since (1) the response to injected norepinephrine is much less affected by glucose deprivation and (2) the increase in the vasoconstrictor response to either adrenergic stimulus produced by inhibition of neuronal reuptake by cocaine is unaltered by glucose deprivation. The inhibitory effect of glucose may involve its metabolite(s). Pyruvic and lactic acids inhibit the vasoconstrictor response to nerve stimulation previously augmented by glucose deprivation but do not affect adrenergic transmission in the presence of glucose. Also, the inhibitory effect of glucose on the potentiated response is abolished by the simultaneous infusion of 2-deoxy-D-glucose or iodoacetic acid, inhibitors of glucose metabolism. The inhibitory effect of glucose and its metabolite(s) on adrenergic transmission may also involve changes in the ionic permeability of the nerve terminal. In the absence of glucose, raising the Na+ and K+ concentrations affects the vasoconstrictor response differently, namely, Na+ potentiates and K+ attenuates the response. These effects are abolished by addition of glucose. In contrast, the effects of increased concentrations of either Ca2+ (facilitation) or Mg2+ (inhibition) on neurotransmission are unaffected by removal or restoration of glucose. We conclude that glucose deprivation does not affect adrenergic transmission by acting directly through Ca2+. Rather, glucose deprivation decreases pyruvate and possibly other products of glucose metabolism, and these decreases, in turn, alter the concentrations of Na+ and K+ within the neuron. These latter changes then enhance the availability of Ca2+ and, thereby, increase the release of the adrenergic transmitter.