Perfusion rate dependent prostaglandin release from isolated rabbit kidneys

Isolated rabbit kidneys were perfused with 37 degrees C Krebs-Henseleit solution aerated with 95% O2 + 5% CO2. Perfusion rate was varied from 1 to 10 ml/min. This was accompanied by parallel changes of perfusion pressure, prostaglandin excretion and release of radioactivity from kidneys with 14C-arachidonic acid incorporated into the tissue lipid pool. It is suggested that enhancement of perfusion rate raises the intrarenal pressure which increases renal prostaglandin release due to increased substrate availability.     

Light activation of fructose bisphosphatase in photosynthetically competent pea chloroplasts.

The ipsilateral kidney was removed from a rabbit 48h after unilateral partial renal-vein-constriction and was perfused with Krebs–Henseleit media at 37°C. Hourly administration of a fixed dose of bradykinin to the renal-vein-constricted kidney demonstrated a marked time-dependent increase in the release of bioassayable prostaglandin E₂ and thromboxane A₂ into the venous effluent as compared with the response of the contralateral control kidney. The renal-vein-constricted kidney produced up to 60 times more prostaglandin E₂ in response to bradykinin after 6h of perfusion as compared with the contralateral kidney; thromboxane A₂ was not demonstratable in the contralateral kidney. Inhibition of protein synthesis de novo in the perfused renal-vein-constricted kidney with cycloheximide lessened the hormone-stimulated increase in prostaglandin E₂ by 94% and in thromboxane A₂ by 90% at 6h of perfusion. Covalent acetylation of the renal cyclo-oxygenase by prior oral administration of aspirin to the rabbit inhibited initial bradykinin-stimulated prostaglandin E₂ biosynthesis 71% at 1h of perfusion. However, there was total recovery from aspirin in the renal-vein-constricted kidney by 2h of perfusion after bradykinin stimulation. Total cyclo-oxygenase activity as measured by [¹⁴C]arachidonate metabolism to labelled prostaglandins by renal cortical and renal medullary microsomal fractions prepared from 6h-perfused kidneys demonstrated that renal-vein-constricted kidney-cortical cyclo-oxygenase activity was significantly greater than the contralateral-kidney-cortical conversion, whereas medullary arachidonate metabolism was comparable in both the renal-vein-constricted kidney and contralateral kidney. These data suggest that perfusion of a renal-vein-constricted kidney initiates a time-dependent induction of synthesis of prostaglandin-producing enzymes, which appear to be primarily localized in the renal cortex. The presence of the synthetic capacity to generate very potent vasodilator and vasoconstrictor prostaglandins in the renal cortex suggests that these substances could mediate or modulate changes in renal vascular resistance in pathological states.     

PGE2 secretion from organ cultured gastric mucosa: Correlation with cyclooxygenase activity and endogenous substrate release

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE₂ release in organ cultured gastric mucosa of the rabbit, determining PGE₂ secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [¹⁴C]-arachidonic acid.Freshly taken biopsies secreted PGE₂ at an initial high rate, that decreased during the following 4 hrs of culture. This PGE₂ release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE₂ secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE₂ release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca⁺⁺-ionophore A23187. However, Ca⁺⁺/A23187 were unable to maintain PGE₂ secretion at the initial rate.PGE₂ secretion was undisturbed in calcium-free medium but was reduced to 50–60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N′,N′,-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE₂ release to 72% of controls. In contrast, PGE₂ release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromid, neomycine or low dose quinacrine, indicating that the reduction of PGE₂ release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE₂ secretion by quinacrine at high concentrations (≥ 0.8mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE₂ secretion, also at low concentrations and minor degrees of inhibition.From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE₂ secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A₂. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

The effect of acute hypoxia on prostaglandin release in perfused human fetal placenta

The release of prostaglandin E₂ and F_2α, thromboxane B₂ and 6-keto-prostaglandin F_1α was measured in isolated human placental cotyledons perfused under high- and low-oxygen conditions. Also the effect of reoxygenation on prostaglandin production was studied. During the high-oxygen period, prostaglandin E₂ accounted for 44 % and 6-keto-prostaglandin F_1α for 28 % of all prostaglandin release, and the rank order of prostaglandin release was E₂ > 6-keto-prostaglandin F_1α > thromboxane B₂ > prostaglandin F_2α. Hypoxia had no significant effect on quantitative prostaglandin release, but the ration of prostaglandin E₂ to prostaglandin F_2α was significantly increased. After the hypoxic period during reoxygenation the release of 6-keto-prostaglandin F_1α was significantly decreased, as was the ratio of 6-keto-prostaglandin F_1α to thromboxane B₂. Also the ratio of the vasodilating prostaglandins (E₂, 6-keto-prostaglandin F_1α) to the vasocontricting prostaglandins (thromboxane B₂, prostaglandin F_2α) was decreased during reoxygenation period. With the constant flow rate, the perfusion pressure increased during hypoxia in six and was unchanged in three preparation. The results indicate that changes in the tissue oxygenation in the placenta affect prostaglandin release in the fetal placental circulation. This may also have circulatory consequences.     

Effect of prostaglandin E2on the pressor response to peri-arterial stimulation and norepinephrine of the isolated perfused rabbit kidney

The interaction of prostaglandin E₂ (PGE₂) and aspirin with the responses to peri-arterial stimulation (PS) and norepinephrine (NE) was studied in the isolated kidney of rabbit perfused through the renal artery at constant flow with Krebs' solution. NE and PS increased vascular perfusion pressure of kidney and caused a contraction on the isolated rabbit aortic strip superfused with the effluent from kidney. Addition of PGE₂ to the perfusion medium decreased the PS-induced rise in perfusion pressure without changing the effect of exogenous NE. In contrast, addition of aspirin to the perfusion medium induced a potentiation of the response to PS but not to NE. These results suggest that PGE₂ modulates the effect of PS probably by inhibiting the release of NE from sympathetic nerve endings.     

Regulation by prostaglandin E2 of interleukin release by T lymphocytes in mucosa

Regulation of immune cell activation in lymphocyte-bearing human tissues is a pivotal host function, and metabolites of arachidonic acid (prostaglandin E₂ in particular) have been reported to serve this function at non-mucosal sites. However, it is unknown whether prostaglandin E₂ is immunoregulatory for the large lymphocyte population in the lamina propria of intestine; whether low (nM) concentrations of prostaglandin E₂ modulate immune responses occurring there; and whether adjacent inflammation per se abrogates prostaglandin E₂'s regulatory effects. To address these issues, intestine-derived lymphocytes and T hybridoma cells were assessed, T cell activation was monitored by release of independently quantitated lymphokines, and dose-response studies were performed over an 8-log prostaglandin E₂concentration range. IL-3 release by normal intestinal lamina propria mononuclear cells was reduced (up to 78%) in a dose-dependent manner by prostaglandin E₂, when present in as low a concentration as 10⁻¹⁰M. PGE₂ also inhibited(by ≥ 60%) mucosal T lymphocytes' ability to destabilize the barrier function of human epithelial monolayers. Further, with an intestine-derived T lymphocyte hybridoma cell line, a prostaglandin E₂ dose-dependent reduction in IL-3 and IL-2 (90 and 95%, respectively) was found; this was true for both mitogen- and antigen-driven T cell lymphokine release. Concomitant [³H] thymidine uptake studies suggested this was not due to a prostaglandin E²-induced reduction in T cell proliferation or viability. In contrast, cells from chronically inflamed intestinal mucosa were substantially less sensitive to prostaglandin E², e.g., high concentrations (10⁻⁶ M) of prostaglandin E² inhibited IL-3 release by only 41%. We conclude that prostaglandin E² in nM concentrations is an important modulator of cytokine release from T lymphocytes derived from the gastrointestinal tract, and it may play a central role in regulation of lamina propria immunocyte populations residing there. © 1996 Wiley-Liss, Inc.     

A comparison of the effects of prostacyclin and 6-keto-prostaglandin E1 on renin release in the isolated rat and rabbit kidney

A direct comparison of the relative potencies of the prostaglandins PGI₂ and 6-kto-PGE₁ to induce renin release was made in the isolated rat kidney, which was perfused with a synthetic medium at constant perfusion pressure.Both prostaglandins stimulated renin release in a dose-dependent manner (0.01 to 1 μM) and with equal potency.Also in the isolated rabbit kidney, PGI₂ and 6-keto-PGE₁ had the same potency to induce renin release at 1 μM final concentration.Following infusion of 6-keto-PGE₁ a small increase of vascular resistance in the rat kidney was observed, whereas in the rabbit kidney no constrictor effect was seen.When perfusate of PGI₂ or 6-keto-PGE₁-infused rat kidneys were tested for antiaggregatory activity in the ADP induced aggregation of human platelets and compared with authentic standards, the results showed 6-keto-PGE₁ passes the kidney essentially unchanged, whereas only 25–40% of the infused PGI₂ appear in the venous perfusates, as judged from the recovery of antiaggregatory activity.Analysis of venous perfusates from ³H-PGI₂ infused kidneys by high performance liquid chromatography indicates that about 25% of the infused PGI₂ remains intact, a major portion of the perfused radioactivity was identified as 6-keto-PGF_1α by combined gaschromatography-mass-spectrometry (19).We conclude that the renin-stimulating effect of PGI₂ is not secondary to its metabolism to 6-keto-PGE₁, as has been suggested in the literature (8).     

Zero extracellular K+ and prostaglandin E release in the guinea-pig taenia coli

Prostaglandin E release rates from isolated strips of guinea-pig taenia coli increased during exposure to zero K⁺ bathing fluid, from control values of $\text{0.78 ± 0.11}\text{ng/g}$ per min to levels as high as 29.2 ng/per min. Release rates increased for 40–50 min and then remained constant or fell despite progressive increases in intracellular sodium [Na_i⁺] or fall in intracellular potassium [K_i⁺]. Readmittance of K⁺ to the bathing solution resulted in rapid reversal of elevated prostaglandin E release rates. [Na⁺_i] and [K⁺_i] were markedly more abnormal in strips exposed to zero K⁺ for 70–201 min compared to 30-min exposures. Upon the readdition of K⁺ after long zero K⁺ exposure, the rate of prostaglandin E release fell long before [Na⁺_i] and [K⁺_i] returned to control levels. After K⁺ was readded to the bathing solution, the ion concentration of tissues exposed to zero K⁺ for 30 min returned to normal much more quickly than did those of tissues exposed for the longer time periods, yet the exponential rate constants for fall of prostaglandin E release rate after K⁺ was added were not significantly different after short or long zero K⁺ exposure. Thus there was a dissociation between the return of [Na⁺_i] and [K⁺_i] and the fall of prostaglandin E release rate to control levels. Ouabain augmented prostaglandin E release under conditions where [K⁺_i] could not fall. Addition of known neurotransmitters present in this tissue to the bathing fluid did not augment prostaglandin E release. Guinea-pig taenia coli strips that had been incubated with [³H]arachidonic acid, constantly released [³H]arachidonic acid and [³H]prostaglandin E and a prostaglandin which cochromatographed with prostaglandin E but could not be converted to prostaglandin B by alkali and was shown to be 6-ketoprostaglandin F_1α. Release of [³H]arachidonic acid and [³H]prostaglandin E plus 6-[³H]ketoprostaglandin F_1α was increased when strips were exposed to zero K⁺. Data obtained in this study suggest the augmented prostaglandin E release seen during zero K⁺ or ouabain is related to increased availability of unbound arachidonic acid at the site of cyclooxygenase in the cell. Augmented prostaglandin E release is apparently not related to alterations in intracellular electrolyte concentrations or release of known neurotransmitters.     

A nitric oxide synthesis inhibitor decreased prostaglandin production in rat mesenteric vasculature

Endothelial cells synthesize and release nitric oxide (NO) and prostacyclin (PGI₂) which are involved in the regulation o f vascular tone and blood pressure. Our objective was to evaluate the effects of inhibiting NO synthesis on vascular prostaglandin (PG) and cyclic nucleotide production, as well as the pressor response to norepinephrine (NE). Isolated mesenteric arterial beds were perfused with Krebs-Henseleit solution containing 100 μM N^G-monomethyl-L-arginine (L-NMMA), 100 μM L-arginine (LA), or vehicle. After a 30 min equilibration 0.1, 0.5, 1, or 5 μM NE was infused into the superior mesenteric artery and the perfusion pressure was monitored. The basal perfusion pressure did not differ significantly between groups. The pressure-response curve was shifted to the right in the L-NMMA group vs. the LA and control groups. Perfusion was similarly performed with a Krebs-Henseleit solution containing 100 μM L-NMMA, LA, D-arginine, or vehicle. Perfusates were collected before and after NE infusion for the measurement of PGE₂, 6-keto-PGF_1α, TxB₂, cAMP, and cGMP. In the L-NMMA group the release of PGE₂ and 6-keto-PGF1α was decreased, and the release of cGMP was prevented. Production of cAMP did not differ between the four groups before NE infusion, and NE increased cAMP release in the L-NMMA group and controls. The results indicate that inhibition of NO synthesis by L-NMMA enhanced the pressor response to NE, possibly mediated by the decreased cGMP and PGI₂ production in resistance vessels.     

Hormonal stimulation of arachidonic release from isolated perfused organs relationship to prostaglandin biosynthesis

The lipids of isolated Krebs perfused rabbit kidneys and hearts were labeled with [¹⁴C]arachidonic acid. Subsequent hormonal stimulation (e.g. bradykinin, ATP) of the pre-labelled tissue resulted in dose-dependent release of [¹⁴C]prostaglandins; little or no release of the precursor [¹⁴]arachidonic acid was observed. When fatty acid-free bovine serum albumin was added to the perfusion medium as a trap for fatty acids substantial release of [¹⁴C]arachidonic acid was detected following hormonal stimulation. The release of [¹⁴C]arachidonic acid was dose-dependent and >;3 fold that of [¹⁴C]prostaglandin release. Indomethacin by inhibiting the cyclo-oxygenase, completely inhibited release of [¹⁴C]prostaglandins and only slightly inhibited release of [¹⁴C]arachidonic acid. These results demonstrate that in both rabbit kidney and heart much more substrate is released by hormonal stimulation than is converted to prostaglandins. This suggests that either the deacylation reaction is not tightly coupled to the prostaglandin synthetase system or that there are two deacrylation mechanisms, one which is coupled to prostaglandin synthesis while the other is non-specific. It has previously been shown that prostaglandin release due to hormones such as bradykinin is transient despite continued presence of the hormone (tachyphylaxis). By utilizing albumin to trap released fatty acid, it was found that hormone-stimulated release of arachidonic acid is also transient. This directly demonstrates that tachyphylaxis occurs at a step prior to the cyclo-oxygenase.     

Effect of the effluent released from the canine internal mammary artery after intraluminal and extraluminal perfusion of acetylcholine and adenosine diphosphate

Segments of the canine internal mammary artery (35 mm in length) were suspended in vitro in an organ chamber containing physiological salt solution (95% O₂/5% CO₂, pH = 7.4, 37°C). Segments were individually cannulated and perfused at 5 ml/minute using a roller pump. Vasorelaxant activity of the effluent from the perfused internal mammary arteries was bioassayed by measuring the decrease in tension induced by the effluent of the coronary artery endothelium-free ring which had been contracted with prostaglandin F_2α (2 × 10^-6 M). Intraluminal perfusion of adenosine diphosphate (10^-5 M) induced significant increase in relaxant activity in the effluent from the perfused blood vessel. However, when adenosine diphosphate (10^-5 M) was added extraluminally to the internal mammary artery, no change in relaxant activity in the effluent was noted. In contrast, acetylcholine produced significant increase in the relaxant activity on the effluent of the perfused internal mammary artery with both intraluminal and extraluminal perfusion. The intraluminal and extraluminal release of endothelium-derived relaxing factor (EDRF) by acetylcholine (10^-5 M) can be inhibited by site-specific administration of atropine (10^-5 M). These experiments indicate that certain agonists can induce the release of EDRF only by binding to intravascular receptors while other agonists can induce endothelium-dependent vasodilatation by acting on neural side receptors.     

Prostaglandin E2 and muscle protein turnover inPseudomonas aeruginosa sepsis

Rats were injected intraperitoneally withPseudomonas aeruginosa (septic group) or sterile 0.9% NaCl (controls). Soleus muscles were excised 7 h later, and muscle prostaglandin E₂ release and tyrosine release were measured in vitro. Muscles of septic rats exhibited 226–326% higher release of prostaglandin E₂ and 54–84% higher net proteolysis than muscles of controls. Inclusion of aspirin or indomethacin in the incubation medium almost completely inhibited prostaglandin E₂ production, but had no effect on net proteolysis in muscles from either group. Inclusion of cycloheximide, a protein synthesis inhibitor, increased tyrosine release of control muscles by 42%, whereas no statistically significant increase was observed in muscles from infected rats. However, total proteolytic rate, indexed by tyrosine release in the presence of cycloheximide, was 22% higher in muscles of septic rats compared to that of control animals. Concomitantly, inclusion of cycloheximide inhibited prostaglandin E₂ release by muscles of infected rats by 91% and that of controls by 65%. It is concluded that (a) muscles of septic animals exhibit a pronounced stimulation of prostaglandin E₂ release and net proteolysis, combined with a small increase in total proteolytic rate, (b) the stimulation of net proteolysis is mainly due to inhibition of protein synthesis, (c) the increases in net and total proteolysis appear to be independent of prostaglandin E₂ production, (d) cycloheximide has a previously unrecognized inhibitory effect on muscle prostaglandin E₂ production.     

Multinuclear NMR studies of intracellular cations in the prehypertensive rat kidney

We previously reported a significant derangement of intracellular free calcium ion concentration in the isolated perfused kidney of adult spontaneously hypertensive rat (SHR) (J. Biol. Chem. 267, 3637–3643, 1992). In order to investigate whether an abnormality in intracellular free calcium or another ion precedes the development of elevated blood pressure in SHR, we have now compared intracellular free Ca²⁺, Na⁺ and pH, using ³¹P, ¹⁹F, and triple quantum-filtered (TQ) ²³Na NMR, in perfused kidneys from prehypertensive young SHR and normotensive young Wistar-Kyoto (WKY) rats (5–6 weeks old) which showed no significant difference in blood pressure B.P.=120±5 mmHg and 115±3 mmHg, for SHR and WKY rats, respectively). Like the adult kidney, no significant differences in intracellular ATP concentration or intracellular pH were found between young prehypertensive SHR and normotensive WKY rat kidneys. The TQ ²³Na NMR signal was 47% higher in the SHR kidney, but, due to biological variability and measurement errors, this difference could not be shown to be statistically significant. However, a significant (40%; P<0.05) increase was found in O₂ consumption rate, a measure of the Na⁺/K⁺-ATPase activity, of the young prehypertensive SHR kidney in comparison to the age-matched WKY rat kidney (7.25±0.75 for SHR vs. 5.17±0.18 μmola O₂/min g for WKY rat, n = 6). Furthermore, a highly significant (92%; P<0.02) increase in intracellular free Ca²⁺ concentration was observed in kidneys from young SHR that had noy yet been developed high blood pressure in comparison to the kidneys from young normotensive WKY rats (648±76 nM vs. 339±39 nM, n = 4, despite the fact that there was no significant difference in blood pressure. Increased intracellular free Ca²⁺ thus appears to be part of a primary defect, in the prehypertesive young SHR kidney, which may, by way of increased release of arachidonic acid, and subsequent increased production of vasoconstricting arachidonic acid metabolites via the cytochrome P450 pathway, induce elevated blood pressure in the adult SHR.     

Enzymic coupling of acylhydrolase and prostaglandin synthase activities in subcellular fractions from rabbit renal medulla

We have recently shown that mitochondrial and plasma-membrane fractions from kidney medulla possess Ca²⁺-stimulated acylhydrolase and prostaglandin synthase activities. The nature of the enzymic coupling between the Ca²⁺-stimulated arachidonic acid release and its subsequent conversion into prostaglandins was investigated in subcellular fractions from rabbit kidney medulla. Plasma-membrane, mitochondrial and microsomal fractions were found to have similar apparent K_m values for conversion of added exogenous arachidonate into prostaglandins. The rate of prostaglandin biosynthesis (V_max.) from added arachidonic acid in the microsomal fraction was approx. 2-fold higher than in the other subcellular fractions. In contrast, prostaglandin E₂ synthesis from endogenous arachidonate in plasma-membrane and mitochondrial fractions was 3–4-fold higher than in microsomes. Furthermore, Ca²⁺ stimulated endogenous arachidonate deacylation and prostaglandin E₂ generation in the former two fractions but not in microsomes. In mitochondrial or crude plasma-membrane fractions, in which prostaglandin biosynthesis was inhibited with aspirin, arachidonate released from these fractions was converted into prostaglandins by the microsomal prostaglandin synthase. Thus an intracellular prostaglandin generation process that involves inter-fraction transfer of arachidonic acid can operate. Prostaglandin generation by such an inter-fraction process is, however, less efficient than by an intra-fraction process, where arachidonic acid released by mitochondria or crude plasma membranes is converted into prostaglandins by prostaglandin synthase present in the same fraction. This demonstrates the presence of a tight intra-fraction enzymic coupling between Ca²⁺-stimulated acylhydrolase and prostaglandin synthase enzyme systems in both mitochondrial and plasma-membrane fractions.     

Differential role of cyclooxygenase-1 and -2 on renal vasoconstriction to α1-adrenoceptor stimulation in normotensive and hypertensive rats

Aims

Hypertension is associated with the impairment of renal cyclooxygenase (COX) activity, which regulates vascular tone, salt and water balance and renin release. We aimed to evaluate the functional role of COX isoforms in kidneys isolated from spontaneously hypertensive rats (SHR) after α₁-adrenoceptor (α₁-AR) stimulation.

Main methods

Male six-month-old SHR and normotensive Wistar-Kyoto rats (WKY) were used. The kidneys were isolated to measure perfusion pressure and COX-1- or COX-2-derived prostanoids in response to α₁-AR activation.

Key findings

The basal perfusion pressure was higher in SHR kidneys compared with WKY kidneys (95 ± 11 vs. 68 ± 6 mm Hg, P < 0.05). Phenylephrine induced a greater vasopressor response in SHR kidneys (EC₅₀ of 1.89 ± 0.58 nmol) than WKY kidneys (EC₅₀ of 3.30 ± 0.54 nmol, P < 0.05 vs. SHR). COX-1 inhibition decreased the α₁-AR-induced vasoconstrictor response in WKY but did not affect SHR response, while COX-2 inhibition diminished the response in SHR. Both basal prostacyclin (PGI₂) and thromboxane A₂ (TxA₂) values were higher in SHR kidney perfusates (P < 0.05) and were reduced by COX-1 and COX-2 inhibitors in both strains. Furthermore, phenylephrine increased PGI₂ through COX-2 in WKY and through COX-1 in SHR, but the agonist did not significantly modify TxA₂ in both strains.

Significance

The data suggest that COX-1contributes to vasoconstrictor effects in WKY kidneys and that COX-2 has the same effect in SHR kidneys. The results also suggest that basal release of COX-2-derived vasoconstrictor prostanoids is involved in renal vascular hypersensitivity in SHR.     

Relationship between oxygen tension, coronary vasodilation and prostaglandin biosynthesis in the isolated rabbit heart

In isolated perfused rabbit hearts, coronary vasodilation, produced by reduced oxygen tension seems to be independent of myocardial prostaglandin biosynthesis. a) Anoxia (N₂: CO₂ 95: 5%) produced coronary vasodilation without causing prostaglandin-like substance (PLS) biosynthesis and release; b) the decrease in coronary resistance during hypoxia (N₂:O₂:CO₂ — 80:15:5 %) was sustained during myocardial perfusion with the low oxygen media despite the transitory nature of its PLS release; and c) indomethacin, which abolished basal or ADP stimulated myocardial PLS release, did not abolish the coronary vasodilation produced by ischemia, hypoxia, or anoxia.     

Functional preservation of the mammalian kidney. IV. Functional effects of perfusion with dimethyl sulfoxide (DMSO) at normothermia

Rabbit kidneys were perfused at 37 °C with various concentrations of DMSO in a K⁺-Mg²⁺-rich perfusate. The effects of DMSO on various functional parameters of the rabbit kidney perfused for 60 min were compared with the functional effects of perfusion without DMSO under the same conditions. DMSO produced deviations in vascular resistance and perfusate flow rate from control values. In kidneys perfused with 1.4 and 2.8 m DMSO these vascular changes resulted in changes in GFR at relatively unchanged filtration fractions. The closely parallel relationship between changes in GFR and urine flow rate in all groups indicates that perfusion per se or perfusion with DMSO may shift the regulation of urine flow rate from tubular reabsorption, which obtains in the in vivo situation, to glomerular filtration. This view was supported by the relatively unchanged parameters of Na⁺ reabsorption and fractional water excretion during perfusion with all concentrations of DMSO. Additionally, DMSO perfusion resulted in significantly greater weight gains than those observed in kidneys perfused without DMSO, and significantly depressed clearances of PAH, with 2.1 and 2.8 m DMSO.     

Regulation of prostaglandin synthesis during differentiation of cultured mouse myeloid leukemia cells

Mouse myeloid leukemia cells (Ml) were induced to differentiate into mature macrophages and granulocytes by various inducers. The differentiated Ml cells synthesized and released prostaglandins, whereas untreated Ml cells did not. When the cells were prelabelled with [¹⁴C]arachidonate, the major prostaglandins released into the culture media were found to be prostaglandin E₂, D₂, and F_2α in an early stage of differentiation, but the mature cells produced predominantly prostaglandin E₂. The synthesis and release of prostaglandins were completely inhibited by indomethacin. Dexamethasone, a potent inducer of differentiation of Ml cells, did not induce production of prostaglandins in resistant Ml cells that could not differentiate even with a high concentration of dexamethasone. These results suggest that production of prostaglandins in Ml cells is closely associated with differentiation of the cells. Homogenates of dexamethasone-treated Ml cells converted arachidonate to prostaglandins, but this conversion was scarcely observed with homogenates of untreated Ml cells. Dexamethasone and the other inducers stimulated the release of arachidonate from phospholipids. Therefore, induction of prostaglandin synthesis during differentiation of Ml cells may result from induction of prostaglandin synthesis activity and stimulation of the release of arachidonate from cellular lipids. Lysozyme activity, which is a typical biochemical marker of macrophages, was induced in Ml cells by prostaglandin E₂ or D₂ alone, as well as by inducers of differentiation of the cells, but it was not induced by arachidonate or prostaglandin F_2α. These results suggest that prostaglandin synthesis is important in differentiation of myeloid leukemia cells.     

Influence of type of dietary fat on the prostaglandin release from isolated rabbit and rat hearts and from rat aortas

It has previously been found (1) that feeding rats a diet containing a high amount of sunflowerseed oil results in a higher coronary flow and left ventricular work of their isolated hearts as compared to hearts of rats fed hydrogenated coconut oil or lard. It was hypothesized that this phenomenon can be explained by an influence of dietary linoleic acid on prostaglandin synthesis in the heart. To verify this hypothesis rabbits and rats were fed for four weeks sunflowerseed oil (SSO), hydrogenated coconut oil (HCO) or lard (L) to a maximum of 30 to 40 per cent of the total digestable energy, and the prostaglandin release from the isolated perfused hearts and rat aortas was determined by gas chromatography and bio-assay (PGI₂).For the isolated hearts of rabbits fed SSO, the release of PGE₂, PGF_2α and 6-oxo-PGF_1α was 1.7, 0.7 and 3.0 ng min⁻¹ g⁻¹ dry weight respectively; when fed L, these values were 2.9, 1.1 and 5.6 ng min⁻¹ g⁻¹. For the isolated hearts of rats fed SSO, HCO or L, the total release of PGE₂, PGD₂, PGF_2α and thromboxane B₂ (TXB₂) was 5.9, 5.8 and 5.6 ng min⁻¹ g⁻¹ respectively; the release of 6-oxo-PGF_1α was 3.4, 5.7 and 6.4 ng min⁻¹ g⁻¹ respectively. Relatively, 26% PGE₂, 13% PGD₂, 8% PGF_2α, 6% TXB₂ and 47% 6-oxo-PGF_1α were released. For the isolated aortas of rats fed SSO or HCO, the release of PGI₂-like activity was 0.37 ± 0.05 and 0.49 ± 0.05 ng min⁻¹ cm⁻². The release of PGI₂-like activity from hearts of EFA-deficient rats was about 20% of that from control hearts.We conclude that, although feeding sunflowerseed oil, with respect to feeding hydrogenated coconut oil or lard, does increase coronary flow and left ventricular work, it does not increase the basal prostaglandin production in the isolated rat or rabbit heart; instead there is a tendency for a lower PGI₂ synthesis.     

Beta-adrenergic stimulation of prostaglandin production by human amnion tissue

Arachidonic acid is released from specific glycerophospholipids in human amnion and is used to synthesize prostaglandins that are involved in parturition. In an investigation of the regulation of prostaglandin production in amnion, the effects of isoproterenol on discs of amnion tissue maintained were examined. Isoproterenol caused a large but transitory increase in the amount of cyclic AMP in amnion discs and this was accompanied by a sustained stimulation of the release of arachidonic acid (but not palmitic acid or stearic acid) and prostaglandin E₂. The dependencies of cyclic AMP accumulation, arachidonic acid mobilization and prostaglandin E₂ release on the concentration of isoproterenol were similar, each response was maximal at 10⁻⁶ M isoproterenol and was inhibited by propranolol. Dibutyryl cyclic AMP stimulated the release of prostaglandin E₂ from amnion discs. Although prostaglandin E₂, when added to amnion discs caused an accumulation of cyclic AMP, it did not appear to mediate isoproterenol-induced accumulation of cyclic AMP since the latter effect was insensitive to indomethacin in concentrations at which prostaglandin production was inhibited greatly. These data support the proposition that catecholamines, found in increasing amounts in amniotic fluid during late gestation, my be regulators of prostaglandin production by the amnion.