High urine flow rate increases prostaglandin E excretion in the conscious dog

Although previous studies from this and other laboratories have shown that urinary prostaglandin E excretion (U_PGEV) can vary independent of urine flow rate, recent studies during water diuresis in the conscious dog have suggested that high urine flow rate per se may increase U_PGEV. To examine the effect of urine flow rate on U_PGEV we administered either mannitol, chlorothiazide or Ringer's solution to mongrel dogs and measured U_PGEV. During anesthesia neither mannitol or chlorothiazide increased U_PGEV. There was, however, a consistent increase with all three agents in awake animals. This increase in U_PGEV was independent of alterations in glomerular filtration rate. There was a consistent increase in urinary sodium excretion and decrease in urinary osmolality with all three agents. The changes in PGE, however, were similar to those found during water diuresis when no increase in sodium excretion was found. It is not presently clear whether these findings reflect a true increase in renal PGE synthesis due to some change in flow or pressure within the renal medulla or rather represent unchanged PGE synthesis by renal tubular cells, the high tubule fluid flow rate causing increased entry into the tubular lumen in contrast to the renal interstitium.     

Prostaglandin E1 increases blood flow to the cervix uteri

PGE₁ occurs in high concentration in seminal fluid and is apparently necessary for normal fertility, although its specific function(s) is not known. We investigated the possibility that PGE₁, at seminal fluid concentration, could increase cervical blood flow and, thus, potentially alter cervical mucus properties, including 0₂ concentration. Fifteen μg PGE₁/ml placed directly on the cervix uteri increased cervical blood flow in anesthetized dogs from 0.8±0.7 to 5.7±5.1 ml/gomin 5 min following application without affecting arterial pressure or hepatic or renal blood flow. Seminal PGE₁ may have effects upon oxygen tension in the cervical mucus, as well as aiding leukocyte accumulation in the cervical canal, by increasing cervical blood flow.     

Prostaglandin E1 increases in vivo and in vitro calcitriol biosynthesis in rabbits

INTRODUCTION: Prostaglandins have an anabolic effect on bone. Possible mediation of this effect is via calcitriol. This study determines in vivo and in vitro effects of PGE(1) on calcitriol synthesis. METHODOLOGY: In vivo: rabbits received intravenous vehicle or prostaglandin E(1) (50 microg/day) for 20 days before measurements of serum total and ionic calcium, magnesium and phosphorus levels, total and bone-specific alkaline phosphatases, 25(OH)D(3), calcitriol, parathyroid hormone and calcitonin. In vitro: rabbit proximal renal tubules were incubated with 25(OH)D(3) (8 microM) together with PGE(1) (2.82 x 10(-6) M) and the prostaglandin receptor inhibitor AH6809 (10(-4) M) in selected samples. After 5 or 30 min incubation, calcitriol production was measured by radioimmunoassay and data analysed statistically. RESULTS: In vivo, in groups receiving PGE(1), levels of total Ca, Mg and calcitriol increased significantly and 25 dihydroxyvitamin D(3), parathyroid hormone and calcitonin remained unchanged. In vitro, PGE(1) increased calcitriol biosynthesis and the prostaglandin inhibitor AH6809 reduced calcitriol levels significantly after prolonged incubation. CONCLUSIONS: In vivo and in vitro results demonstrate that PGE(1) stimulates calcitriol synthesis. This study represent a major advancement in knowledge of bone metabolism.     

Prostaglandin E2 increases cardiac fibroblast proliferation and increases cyclin D expression via EP1 receptor

PGE(2) affects growth of many cell types. Thus, we hypothesized that PGE(2) would stimulate growth of cardiac fibroblasts. To test our hypothesis we used neonatal rat ventricular fibroblasts (NVF). RT-PCR demonstrated the presence of all 4 PGE(2) receptor (EPs) mRNAs in NVF. Using flow cytometry, we found that PGE(2) decreased the percentage of cells in G0/G1 and increased the number of cells in S phase. PGE(2) also increased expression of cyclin D3, a known regulator of the cell cycle and this effect was mimicked by the EP1/EP3 agonist sulprostone. Next, we found that treatment of NVF with PGE(2) increased phosphorylation of p42/44 MAPK and Akt and that PGE(2)-stimulation of cyclin D3 was antagonized with both a MEK inhibitor and a PI3 kinase inhibitor. In conclusion, PGE(2) stimulates cardiac fibroblast proliferation via EP1 and/or EP3, p42/44 MAPK and Akt-regulation of cyclin D3. These results may be relevant to cardiac fibrosis.     

Nonspecific inhibition of nitric oxide synthesis evokes endothelin-dependent increases in myocardial contractility

The role of endogenous nitric oxide (NO) in modulating myocardial contractility is still unclear, in part because of unknown, secondary effects of blocking NO release. We hypothesized that the nonspecific inhibition of nitric oxide synthase (NOS) enhances endothelin-1 (ET-1) effects, which can play a role in ET-A receptor-dependent myocardial contractile responses. The myocardial contractility was estimated from the slope of the left ventricular end-systolic pressure–diameter relationship in closed-chest, pentobarbital-anesthetized dogs. Group 1 (n = 7) was the saline-treated control, while in groups 2 (n = 7) and 3 (n = 7) N-nitro-l-arginine (NNA, 4 mg kg^?1), a nonselective NOS blocker, was administered with or without pretreatment with the ET-A receptor antagonist ETR-P1/fl peptide (100 nmol kg^?1 iv). Plasma ET-1, nitrite/nitrate (NO_x) and blood superoxide levels were measured, and myocardial ET-1 content and xanthine oxidoreductase (XOR) activity were determined from myocardial biopsies. The infusion of NNA over 120 min decreased the plasma NO_x, significantly elevated the plasma ET-1 and blood superoxide levels, and in parallel greatly increased the left ventricular contractility as compared with the untreated controls [47.5 vs 30 mm Hg mm^?1]. The myocardial ET-1 content decreased simultaneously, while the XOR activity and blood superoxide level were significantly elevated. These effects, including NNA-induced positive inotropy, were significantly suppressed by pretreatment with ETR-P1/fl peptide. These results demonstrate that a diminished NO synthesis leads to a preponderant ET-1 effect, which increases myocardial contractility through an ET-A receptor-dependent mechanism.     

Intracerebroventricular infusion of neuropeptide Y increases glucose dependent-insulinotropic peptide secretion in the fasting conscious dog

The rapid increase of incretins glucose-dependent insulinotropic peptide (GIP) and glucagon like peptide-1 (GLP-1), within 5-15 min, after food ingestion, suggests that a neural mechanism might be involved in the regulation of their secretion. The aim of this study is to determine whether intracerebroventricular (i.c.v) administration of neuropeptide Y (NPY), a widely distributed neurotransmmiter, can mediate this neural regulation of GIP secretion after food consumption. Six healthy mongrel dogs were utilized for this study. A prototype epicranial apparatus was placed surgically, allowing easy and exact localization of the third ventricle for infusions or sampling. Simultaneous blood sampling was obtained from cannulation of a hind limb vein. Plasma insulin, and GIP concentrations were measured after i.c.v infusion of 5, 10 and 25 microg of NPY dissolved in 0.5 ml of artificial cerebrospinal fluid (a CSF). The secretion of GIP and insulin were increased after the injection of NPY in a different pattern. Our data indicate that NPY might be involved in a possible neural control mechanism of GIP secretion after food consumption.     

Potentiation of the 5-hydroxytryptamine-induced increases in myocardial contractility in Mercenaria mercenaria ventricle by forskolin

Forskolin (10(-5) M), an activator of adenylate cyclase in many mammalian cell types, potentiated the positive inotropic effects of 5-hydroxytryptamine (5-HT) on the bivalve, Mercenaria mercenaria, myocardium. Forskolin (10(-5) M) also significantly increased intracellular cyclic AMP concentrations when compared to 5-HT controls. Ro 20-1724 (10(-5) M), a putative inhibitor of cyclic AMP phosphodiesterase, had no effect on myocardial contractility or cyclic AMP concentration. A positive correlation between intracellular cyclic AMP concentration and the efficacy of 5-HT was obtained.     

Prostaglandin E2 increases growth and motility of colorectal carcinoma cells

Chronic use of nonsteroidal anti-inflammatory drugs results in a significant reduction of risk and mortality from colorectal cancer in humans. All of the mechanism(s) by which nonsteroidal anti-inflammatory drugs exert their protective effects are not completely understood, but they are known to inhibit cyclooxygenase activity. The cyclooxygenase enzymes catalyze a key reaction in the conversion of arachidonic acid to prostaglandins, such as prostaglandin E(2) (PGE(2)). Here we demonstrate that PGE(2) treatment of LS-174 human colorectal carcinoma cells leads to increased motility and changes in cell shape. The prostaglandin EP(4) receptor signaling pathway appears to play a role in transducing signals which regulate these effects. PGE(2) treatment results in an activation of phosphatidylinositol 3-kinase/protein kinase B pathway that is required for the PGE(2)-induced changes in carcinoma cell motility and colony morphology. Our results suggest that PGE(2) might enhance the invasive potential of colorectal carcinoma cells via activation of major intracellular signal transduction pathways not previously reported to be regulated by prostaglandins.     

Occupation of the prostaglandin E2-type 1 receptor increases rat atrial contractility via a Y-27632-sensitive pathway

This study investigated whether rat left atria (LA) contain the prostaglandin E2 type 1 receptor (EP1) and whether EP1 occupation induces positive inotropic responses in superfused LA. Western analysis demonstrated that LA contain EP1 and the EP1 splice variant. Exposing isolated, superfused LA to 17-phenyl trinor PGE2, an EP1 agonist, increased isometric contractile force and its corresponding dF/dTs to approximately 70% of the isoproterenol maximum with an EC50 of approximately 80 nM. In contrast, agonists for EP2, EP3, and EP4 caused little change in LA function. While the EP1 antagonists SC-51089 and SC-19220 blocked 17-phenyl trinor PGE2-induced inotropy, neither prazosin, nadolol, atropine nor EI-283, a pan-specific protein kinase C inhibitor, affected 17-phenyl trinor PGE2-induced inotropy. However, Y-27632 and HA-1077, inhibitors of rho A-activated protein kinases, prevented and reversed the increase in LA contractility that occurred in the presence of 17-phenyl trinor PGE2. Thus, atria contain EP1 and EP1 occupation increases LA contractility via a pathway sensitive to inhibitors of rho A-activated protein kinases.     

Pulmonary extraction of dopamine in the conscious dog

Thus far non-respiratory pulmonary functions have mainly been studied in isolated lungs or in intact anaesthetized animals. Therefore, we studied pulmonary handling of vasoactive hormones in the conscious dog. Dopamine, adrenaline and noradrenaline (3 nmol/ml) were injected together with cardiogreen (4 mg/ml) into the caval vein during 5, 10 and 15 s in three separate experiments. Indicator-dilution curves were derived from samples originating from the pulmonary artery and the aorta. During a single passage of the lung dopamine was removed to the greatest extent, noradrenaline somewhat less, and adrenaline not at all, irrespective of the injection duration. In particular, the extraction of dopamine, which was not emphasized in literature, was a remarkable finding.     

Prostaglandin E antagonist activity of 11-deoxy-16,16-trimethyleneprostaglandin E1

11-Deoxy-16,16-trimethyleneprostaglandin E1 is a potent inhibitor of prostaglandin E-induced contractions of the gerbil colon. The antagonism is directed specifically against the prostaglandin E receptor and is not manifested when contractions are induced by either prostaglandin F2 alpha or acetylcholine.