Radiological Imaging of the Lacrimal Gland in Sjogren's Syndrome: A Systematic Review and Meta-Analysis

PURPOSE

To critically appraise the evidence on the ability of the lacrimal gland ultrasonography (USG) or magnetic resonance imaging (MRI) to differentiate between Sjogren's syndrome and non-Sjogren's syndrome/healthy controls.

METHODS

A systematic review and meta-analysis (based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines) of online literature search was performed using PubMed, Scopus, and Cochrane databases. Cohort studies comparing the imaging features of the lacrimal glands of Sjogren's syndrome with a control group were included. Quantitative synthesis was performed using the RevMan (Version 5.4.1).

RESULTS

Six studies used USG as an imaging technique, and three used MRI for the lacrimal gland imaging. The lacrimal gland affected with Sjogren's syndrome shows glandular heterogeneity on USG and MRI. Heterogeneity on USG had 6.18 times higher odds of the lacrimal gland being involved with Sjogren's syndrome (95% CI, 3.31-11.55). Gland hyperechogenicity cannot reliably differentiate the glandular involvement in Sjogren's syndrome. There is insufficient data for analysis on the gland size, hypoechoic areas, fibrous bands, and increased lacrimal artery resistance in Sjogren's syndrome patients. Of the three MRI-based studies, reduced apparent diffusion coefficient and heterogeneity were the characteristics of Sjogren's syndrome. Clinical parameters such as dry eye symptomatology and Schirmer values had variable associations with USG or MRI parameters. Ultrasonography parameters were no different between dry eye versus no dry eye in Sjogren's syndrome patients, whereas small-sized glands had low Schirmer on MRI-based studies.

CONCLUSION

Glandular heterogeneity on USG is significantly associated with lacrimal gland involvement in Sjogren's syndrome patients. However, the role of radiology in predicting lacrimal gland involvement is unclear as the evidence is insufficient and heterogeneous.

Cryptogenic posterior circulation stroke in children

We aimed to evaluate the percentage of posterior circulation arterial ischaemic stroke (PCAIS) caused by craniovertebral junction (CVJ) anomalies and describe their clinical course. Children admitted to a tertiary care paediatric hospital with PCAIS between July 2017 and December 2020 were assessed retrospectively for disease aetiology. We reviewed the clinical, radiological, and surgical details of children with evidence of CVJ anomalies. Fourteen (24.1%) of 58 children admitted with arterial ischaemic stroke had posterior circulation involvement. The mean age of patients presenting with posterior circulation stroke was 6 years 6 months (range 3 months-15 years), 11 were male. Six of 14 cases with PCAIS were due to CVJ anomaly, their ages ranged from 4 months to 15 years (two age ranges were noted, 4 months-4 years and 11-15 years), four were male. Two children had atlantoaxial dislocation with basilar invagination, two had Bow Hunter syndrome with Chiari malformation type 1 (one with completed stroke), one had Chiari malformation type 1 alone, and one presented with Farber disease with proatlas segmentation anomaly in CVJ. The time lag to stroke and CVJ diagnosis ranged from 2 weeks to 24 months. A dynamic angiogram was required to evaluate biomechanical changes on scans with inconclusive findings on standard stroke imaging. CVJ anomalies are an important treatable cause of paediatric posterior circulation stroke. Cervical spine x-ray in flexion and extension should be done in all patients with posterior circulation stroke beyond the acute period. In cryptogenic aetiology, provocative angiography with guarded neck rotation should be considered to evaluate possible dynamic vertebral artery compression.

Magnetic resonance imaging in rhino-orbital-cerebral mucormycosis

Coronavirus disease-associated mucormycosis (CAM) is an established clinical entity in India. In the past 4 months, there has been a sharp upsurge in the number of CAM cases in most parts of the country. Early diagnosis can be lifesaving. Magnetic resonance imaging (MRI) imaging remains the corner stone of management in patients with ROCM. This review discussed the utility of MRI imaging in ROCM with an emphasis on the ideal MRI protocol in a suspected case of ROCM, the pathways of spread of infection, the classic diagnostic features, MRI for staging of the disease, MRI for prognostication, MRI for follow up, and imaging features of common differentials in ROCM. The pit falls of MRI imaging and a comparison of CT and MRI imaging in ROCM are discussed. The clinical interpretation of areas of contrast uptake and those of necrosis and its relevance to treatment are discussed. This review aims to familiarize every member of the multidisciplinary team involved in managing these patients to be able to interpret the findings on MRI in ROCM.

Managing DICOM images: Tips and tricks for the radiologist

All modalities in radiology practice have become digital, and therefore deal with DICOM images. Image files that are compliant with part 10 of the DICOM standard are generally referred to as “DICOM format files” or simply “DICOM files” and are represented as “.dcm.” DICOM differs from other image formats in that it groups information into data sets. A DICOM file consists of a header and image data sets packed into a single file. The information within the header is organized as a constant and standardized series of tags. By extracting data from these tags one can access important information regarding the patient demographics, study parameters, etc. In the interest of patient confidentiality, all information that can be used to identify the patient should be removed before DICOM images are transmitted over a network for educational or other purposes. In addition to the DICOM format, the radiologist routinely encounters images of several file formats such as JPEG, TIFF, GIF, and PNG. Each format has its own unique advantages and disadvantages, which must be taken into consideration when images are archived, used in teaching files, or submitted for publication. Knowledge about these formats and their attributes, such as image resolution, image compression, and image metadata, helps the radiologist in optimizing the archival, organization, and display of images. This article aims to increase the awareness among radiologists regarding DICOM and other image file formats encountered in clinical practice. It also suggests several tips and tricks that can be used by the radiologist so that the digital potential of these images can be fully utilized for maximization of workflow in the radiology practice.

Case Report: Magnetic resonance imaging in rabies encephalitis

Rabies encephalitis is an invariably fatal disease characterized by typical clinical symptoms. Although the diagnosis of this condition can be made on the basis of the patient's history and the classical clinical presentation, neuroimaging may still play a role, especially for establishing an early diagnosis in cases with atypical presentations or when the history of animal bite is not forthcoming. We report the MRI findings in a case of furious rabies encephalitis and describe the utility of diffusion imaging in its diagnosis.

Effects of exposure of parents to toxic gases in Bhopal on the offspring

BACKGROUND

Exposure to methyl isocyanate and other toxic gases in Bhopal, India, on December 3, 1984 resulted in thousands of acute deaths, pregnancy loss and long-term effects.

METHODS

From 1985 to 2007, we conducted successive surveys of vital status and health to determine whether the exposure of parents to toxic gases in the Bhopal incident affected the 5-year survival and anthropometric variables of their offspring.

RESULTS

Initial 5-year mortality of offspring of exposed parents was very high. Male but not female offspring who were exposed to gases in utero or who were born to exposed parents were stunted in growth until puberty, which was followed by a period of accelerated growth. Results also suggest a post-puberty effect on head circumference of females exposed to gases in utero.

CONCLUSION

Exposure of pregnant women to toxic gases in Bhopal in 1984 resulted in high pregnancy loss, increased first 5-year mortality and delayed development of male progeny.

Corticobasal syndrome due to a thalamic tuberculoma and focal cortical atrophy

Corticobasal syndrome (CBS) is characterised by asymmetric apraxia, cortical sensory loss, extrapyramidal features and cognitive decline. Although CBS is classically described as a taupathy, heterogeneity of its aetiology is increasingly recognised. Clinical presentation of CBS appears to reflect areas of the brain involved and not necessarily the nature of the underlying pathology. We report a patient in whom resolution of a thalamic tuberculoma was associated with progressive atrophy of the parietotemporal cortex, resulting in an unusual presentation of CBS.

Evaluation, management, and long-term follow up of vein of Galen malformations

OBJECT

Vein of Galen malformations (VGMs) are extremely rare intracranial lesions. Clinical presentation and management strategies vary significantly in different areas of the world. The authors report their experience in evaluation, management, and long-term follow up of these lesions in India.

METHODS

Between October 1983 and June 2003, 25 patients with VGMs were referred to the authors' institution for evaluation and management. Ten children younger than 2 years of age presented with rapidly increasing head size as the chief complaint. Among 11 children 2 years of age or older, the most common presenting symptom was chronic headache. Four patients who presented during adulthood had chronic headache for many years before presentation. Angiographic evaluation of the lesion was performed in 21 patients. Fifteen patients were treated using endovascular techniques. Injection of the embolic material was performed after induction of systemic hypotension when the flow in the fistula was high. Complete occlusion of the arteriovenous shunt could be achieved in two patients with vein of Galen aneurysmal dilation (100% of patients with this type of malformation) and in five of the six patients with the mural type of malformation (83%). Among patients with the choroidal type of malformation, complete obliteration of the shunt could be achieved in three patients. In three patients with high-flow choroidal malformations, embolization carried out in a single sitting resulted in shunt reduction of nearly 90%. These patients received clinical follow up.

CONCLUSIONS

The authors' experience in evaluation and management of VGMs reveals that in areas of the world where access to dedicated specialist care is limited, the clinical presentation of VGMs can differ appreciably from the classic descriptions in the literature. Endovascular management of these lesions results in excellent angiographic and clinical results.

Absence of the left common carotid artery with cervical origin of the right subclavian artery

We report the case of a 1 1/2-year-old female child, who developed symptomatic hemorrhage from major aorto-pulmonary collaterals after surgery for Tetralogy of Fallot. During the course of embolization of the aorto-pulmonary collaterals, we discovered the presence of direct origin of the left internal and external carotid arteries from the aortic arch. Further, there was cervical origin of right subclavian artery. We discuss the clinical significance and potential embryological mechanism in development of this anomaly.

Vein of Galen malformations: review

Vein of Galen malformations are unique congenital malformations of the cerebral vasculature that result in persistence and 'aneurysmal' dilatation of the venous structures. The varied clinical presentations and their distinctive and complex angioarchitecture make it important for the caring physician to understand their embryological and pathophysiological aspects. Management of these lesions--both in the neonatal period and at the time of definitive intervention, is challenging. Considering the rarity of these lesions, there are very few studies that have been able to compare the results of different techniques in the management. Continuing developments in the diagnostic as well as interventional aspects during the last two decades have radically changed the management of these lesions. Antenatal diagnosis and referral to a center with facilities for advanced neonatal cardiac care as well as for interventional neuroradiological therapy can go a long way in improving the prognosis in these children.

Chordoid meningioma: a report of two cases

Chordoid meningioma is an uncommon histopathological variant of meningioma. We report 2 cases of chordoid meningioma occurring in adult patients.

Cyclooxygenase-2 in human and experimental ischemic proliferative retinopathy

BACKGROUND

Intravitreal neovascular diseases, as in ischemic retinopathies, are a major cause of blindness. Because inflammatory mechanisms influence vitreal neovascularization and cyclooxygenase (COX)-2 promotes tumor angiogenesis, we investigated the role of COX-2 in ischemic proliferative retinopathy.

METHODS AND RESULTS

We describe here that COX-2 is induced in retinal astrocytes in human diabetic retinopathy, in the murine and rat model of ischemic proliferative retinopathy in vivo, and in hypoxic astrocytes in vitro. Specific COX-2 but not COX-1 inhibitors prevented intravitreal neovascularization, whereas prostaglandin E2, mainly via its prostaglandin E receptor 3 (EP3), exacerbated neovascularization. COX-2 inhibition induced an upregulation of thrombospondin-1 and its CD36 receptor, consistent with the observed antiangiogenic effects of COX-2 inhibition; EP3 stimulation reversed effects of COX-2 inhibitors on thrombospondin-1 and CD36.

CONCLUSIONS

These findings point to an important role for COX-2 in ischemic proliferative retinopathy, as in diabetes.

Prostanoid receptors: ontogeny and implications in vascular physiology

Prostanoids exert significant effects on circulatory beds. They play a role in the response of the vasculature to adjustments in perfusion pressure and oxygen and carbon dioxide tension, and they mediate the actions of numerous factors. The role of prostanoids in governing circulation of the perinate is suggested to surpass that in the adult. Prostanoids are abundantly generated in the perinate. They have been implicated in autoregulation of blood flow as studied in brain and eyes. Prostaglandins are also dominant regulators of ductus arteriosus tone. The effects of these autacoids are mediated through specific G protein-coupled receptors. In addition to the pharmacological characterization of the prostanoid receptors, important advances in understanding the biology of these receptors have been made in the last decade. Their cloning and the development of animals with disrupted genes of these receptors have been very informative. The involvement of prostanoid receptors in the developing subject, especially on brain and ocular vasculature and on ductus arteriosus, has also begun to be investigated; the expression of these receptors changes with development. Some but not all of the ontogenic changes in these receptors are attributed to homologous regulation. Interestingly, in the process of elucidating their effects, functional perinuclear prostaglandin E2 receptors have been uncovered. This article reviews prostanoid receptors and addresses implications on the developing subject with attention to vascular physiology.

Major role for neuronal NO synthase in curtailing choroidal blood flow autoregulation in newborn pig

We examined whether nitric oxide (NO) generated from neuronal NO synthase (nNOS) contributes to the reduced ability of the newborn to autoregulate retinal blood flow (RBF) and choroidal blood flow (ChBF) during acute rises in perfusion pressure. In newborn pigs (1-2 days old), RBF (measured by microsphere) is autoregulated over a narrow range of perfusion pressure, whereas ChBF is not autoregulated. N(G)-nitro-L-arginine methyl ester (L-NAME) or specific nNOS inhibitors 7-nitroindazole, 3-bromo-7-nitroindazole, and 1-(2-trifluoromethyl-phenyl)imidazole as well as ganglionic blocker hexamethonium, unveiled a ChBF autoregulation as observed in juvenile (4- to 6-wk old) animals, whereas autoregulation of RBF in the newborn was only enhanced by L-NAME. All NOS inhibitors and hexamethonium prevented the hypertension-induced increase in NO mediator cGMP in the choroid. nNOS mRNA expression and activity were three- to fourfold higher in the choroid of newborn pigs than in tissues of juvenile pigs. It is concluded that increased production of NO from nNOS curtails ChBF autoregulation in the newborn and suggests a role for the autonomic nervous system in this important hemodynamic function, whereas, for RBF autoregulation, endothelial NOS seems to exert a more important contribution in limiting autoregulation.

2,3-Dinor-5,6-dihydro-15-F(2t)-isoprostane: a bioactive prostanoid metabolite

15-F(2t)-isoprostane (15-F(2t)-IsoP), also termed 8-isoprostaglandin F(2alpha), is one of a series of prostanoids formed by free radical-mediated peroxidation of arachidonic acid and exerts potent biological actions such as vasoconstriction. We recently demonstrated that 15-F(2t)-IsoP is metabolized in humans to a major metabolite, 2,3-dinor-5,6-dihydro-15-F(2t)-IsoP (15-F(2t)-IsoP-M). 15-F(2t)-IsoP-M can also potentially be formed as a product of free radical-induced oxidation of the low abundance fatty acid gamma-linolenic acid. We confirmed that 15-F(2t)-IsoP-M is generated during oxidation of gamma-linolenic acid and explored whether it may exhibit biological activity. 15-F(2t)-IsoP-M caused marked constriction of porcine surface retinal and intraparenchymal brain microvessels, comparable to that observed with 15-F(2t)-IsoP. These effects were associated with increased thromboxane A(2) (TXA(2)) formation and were virtually abolished by TXA(2)-synthase and -receptor inhibitors (CGS-12970 and L-670596). Vasoconstriction induced by either 15-F(2t)-IsoP or 15-F(2t)-IsoP-M on perfused ocular choroid was also abrogated by TXA(2)-synthase inhibition as well as by removal of endothelium. Similar to 15-F(2t)-IsoP, 15-F(2t)-IsoP-M evoked vasoconstriction and TXA(2) generation by activating Ca(2+) influx from nonvoltage-gated channels (SK&F96365 sensitive) in the retina and from both nonvoltage- and N-type voltage-gated Ca(2+) channels (omega-conotoxin MVIIA sensitive), respectively, in brain endothelial and astroglial cells; smooth muscle cells were unresponsive to both agents. Cross-desensitization experiments further suggest that 15-F(2t)-IsoP and 15-F(2t)-IsoP-M act on the same receptor mechanism. Findings reveal a novel concept by which a beta-oxidation metabolite of 15-F(2t)-IsoP that can also be formed by nonenzymatic oxidation of gamma-linolenic acid is equivalently bioactive to 15-F(2t)-IsoP and may prolong the vascular actions of F(2)-IsoPs.

Role of thromboxane in retinal microvascular degeneration in oxygen-induced retinopathy

Microvascular degeneration is an important event in oxygen-induced retinopathy (OIR), a model of retinopathy of prematurity. Because oxidant stress abundantly generates thromboxane A2 (TxA2), we tested whether TxA2 plays a role in retinal vasoobliteration of OIR and contributes to such vascular degeneration by direct endothelial cytotoxicity. Hyperoxia-induced retinal vasoobliteration in rat pups (80% O2 exposure from postnatal days 5-14) was associated with increased TxB2 generation and was significantly prevented by TxA2 synthase inhibitor CGS-12970 (10 mg x kg(-1) x day(-1)) or TxA2-receptor antagonist CGS-22652 (10 mg x kg(-1) x day(-1)). TxA2 mimetics U-46619 (EC50 50 nM) and I-BOP (EC50 5 nM) caused a time- and concentration-dependent cell death of neuroretinovascular endothelial cells from rats as well as newborn pigs but not of smooth muscle and astroglial cells; other prostanoids did not cause cell death. The peroxidation product 8-iso-PGF2, which is generated in OIR, stimulated TxA2 formation by endothelial cells and triggered cell death; these effects were markedly diminished by CGS-12970. TxA2-dependent neuroretinovascular endothelial cell death was mostly by necrosis and to a lesser extent by apoptosis. The data identify an important role for TxA2 in vasoobliteration of OIR and unveil a so far unknown function for TxA2 in directly triggering neuroretinal microvascular endothelial cell death. These effects of TxA2 might participate in other ischemic neurovascular injuries.

Characterization of PGE2 receptors in fetal and newborn lamb ductus arteriosus

Although the role of PGE2 in maintaining ductus arteriosus (DA) patency is well established, the specific PGE2 receptor subtype(s) (EP) involved have not been clearly identified. We used late gestation fetal and neonatal lambs to study developmental regulation of EP receptors. In the fetal DA, radioligand binding and RT-PCR assays virtually failed to detect EP1 but detected EP2, EP3D, and EP4 receptors in equivalent proportions. In the newborn lamb, DA total density was one-third of that found in the fetus and only EP2 was detected. Stimulation of EP2 and EP4 increased cAMP formation and was associated with DA relaxation. Though stimulation of EP3 inhibited cAMP formation, it surprisingly relaxed the fetal DA both in vitro and in vivo. This EP3-induced relaxation was specifically diminished by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide. In conclusion, PGE2 dilates the late gestation fetal DA through pathways that involve either cAMP (EP2 and EP4) or K(ATP) channels (EP3). The loss of EP3 and EP4 receptors in the newborn DA is consistent with its decreased responsiveness to PGE2.

In utero remodeling of the fetal lamb ductus arteriosus: the role of antenatal indomethacin and avascular zone thickness on vasa vasorum proliferation, neointima formation, and cell death

BACKGROUND

The ductus arteriosus (DA) of newborn infants exposed in utero to indomethacin is resistant to postnatal indomethacin; we hypothesized that this is due to ductus constriction in utero, with subsequent remodeling of the vessel.

METHODS AND RESULTS

Infusion of fetal lambs with indomethacin for 48 hours constricted the DA and increased the thickness of the avascular zone of the DA, which in turn induced the expression of vascular endothelial growth factor, endothelial nitric oxide synthase (due to ingrowth of vasa vasorum), neointima formation, and loss of smooth muscle cells; moderate degrees of DA constriction in utero increased NO production, which inhibited DA contractility. Marked degrees of DA constriction decreased tissue distensibility and contractile capacity.

CONCLUSIONS

DA patency is no longer controlled primarily by prostaglandins once it has been exposed to indomethacin in utero.

Characterization of PGE2 receptors in fetal and newborn ductus arteriosus in the pig

We compared the total density and the relative expression of EP receptor (EP) subtypes in ductus arteriosus (DA) of the newborn with that of the fetal piglet. Saturation binding experiments showed 3-fold less PGE2 receptors in the newborn than in the fetus because of loss of EP3 and EP4 receptors thus explaining, at least partly, the reduced responsiveness to PGE2 of the newborn DA. Displacement experiments showed that the relative proportions of EP2, EP3, and EP4 were similar in the fetal DA but only EP2 was detected in the DA of the newborn pig. Hence, PGE2 effects in the newborn DA seem to be exclusively mediated by EP2 receptors both in vitro and in vivo. These findings may help to propose more specific therapies for regulation of DA's tone in certain newborns for whom conventional therapy is contraindicated.

Graded contribution of retinal maturation to the development of oxygen-induced retinopathy in rats

PURPOSE

Newborn rats exposed to hyperoxia during the first days of life have been shown to exhibit not only vasculopathy but also permanent changes in the structure and function of the retina. Given that the rat retina is immature at birth and that the maturation process continues until the opening of the eyes at 14 days of life, this study was conducted to investigate the susceptibility of the retina to oxygen toxicity as a function of the degree of retinal maturity reached at the time of oxygen exposure.

METHODS

Newborn rats were exposed to hyperoxia during selected postnatal day intervals. Scotopic electroretinograms were recorded at 30 and 60 days of age, and retinal histology was obtained at the end of the study.

RESULTS

There was a strong correlation between the duration of the hyperoxic event and the structural and functional consequences in the retina. However, the repercussions were significantly more profound when the exposure to oxygen occurred within the second week of life (6-14 days), compared with earlier (0-6 days) or later periods (14-28 days).

CONCLUSIONS

The results strongly suggest that the structural and functional retinal changes secondary to postnatal hyperoxia are not only the direct consequence of exposure to high levels of oxygen (i.e., free radicals), but also are determined by the level of retinal maturity reached at the time of oxygen exposure. The results also indicate that the structural anomalies precede the functional impairments.

Prolonged hypercapnia-evoked cerebral hyperemia via K(+) channel- and prostaglandin E(2)-dependent endothelial nitric oxide synthase induction

Mechanisms for secondary sustained increase in cerebral blood flow (CBF) during prolonged hypercapnia are unknown. We show that induction of endothelial NO synthase (eNOS) by an increase in prostaglandins (PGs) contributes to the secondary CBF increase during hypercapnic acidosis. Ventilation of pigs with 6% CO(2) (PaCO(2 approximately)65 mm Hg; pH approximately 7.2) caused a approximately 2.5-fold increase in CBF at 30 minutes, which declined to basal values at 3 hours and gradually rose again at 6 and 8 hours; the latter increase was associated with PG elevation, nitrite formation, eNOS mRNA expression, and in situ NO synthase (NOS) reactivity (NADPH-diaphorase staining). Subjecting free-floating brain sections to acidotic conditions increased eNOS expression, the time course of which was similar to that of CBF increase. Treatment of pigs with the cyclooxygenase inhibitor diclofenac or the NOS inhibitor Nomega-nitro-L-arginine blunted the initial rise and prevented the secondary CBF increase during hypercapnic acidosis; neuronal NOS blockers 1-(2-trifluoromethylphenyl) imidazole and 3-bromo-7-nitroindazole were ineffective. Diclofenac abolished the hypercapnia-induced rise in cerebrovascular nitrite production, eNOS mRNA expression, and NADPH-diaphorase reactivity. Acidosis (pH approximately 7.15, PCO(2 approximately )40 mm Hg; 6 hours) produced similar increases in prostaglandin E(2) (PGE(2)) and eNOS mRNA levels in isolated brain microvessels and in NADPH-diaphorase reactivity of brain microvasculature; these changes were prevented by diclofenac, by the receptor-operated Ca(2+) channel blocker SK&F96365, and by the K(ATP) channel blocker glybenclamide. Acidosis increased Ca(2+) transients in brain endothelial cells, which were blocked by glybenclamide and SK&F96365 but not by diclofenac. Increased PG-related eNOS mRNA and NO-dependent vasorelaxation to substance P was detected as well in rat brain exposed to 6 hours of hypercapnia. PGE(2) was the only major prostanoid that modulated brain eNOS expression during acidosis. Thus, in prolonged hypercapnic acidosis, the secondary CBF rise is closely associated with induction of eNOS expression; this seems to be mediated by PGE(2) generated by a K(ATP) and Ca(2+) channel-dependent process.

Oxidants, nitric oxide and prostanoids in the developing ocular vasculature: a basis for ischemic retinopathy

The choroid is the main source of oxygen to the retina. In contrast to the adult, the absence of autoregulation of choroidal blood flow in the newborn leads to hyperoxygenation of the retina. In the immature retina which contains relatively low levels of antioxidants this hyperoxygenation favors peroxidation including the generation of biologically active isoprostanes, and results in vasoconstriction and vascular cytotoxicity leading to ischemia, which predisposes to the development of a vasoproliferative retinopathy, commonly termed retinopathy of prematurity. During frequently encountered oxidative stress to the perinate, the combined absence of vascular autoregulation and excessive oxygen delivery to the eyes of the developing subject is largely the result of a complex epigenetic and genetic interplay between prostanoids and nitric oxide (NO) systems on vasomotor regulation. The effects of certain prostaglandins are NO-dependent; conversely, those of NO have also been found to be largely prostaglandin I(2)-mediated in the eye; and NO synthase expression seems to be significantly regulated by other prostaglandins apparently through activation of functional perinuclear prostanoid receptors which affect gene transcription. The increased production of both prostaglandins and NO in the perinate augment ocular blood flow and as a result oxygen delivery to an immature retina partly devoid of antioxidant defenses. The ensuing peroxidation results in impaired circulation (partly thromboxane A(2)-dependent) and vascular integrity, leading to ischemia which predisposes to abnormal preretinal neovascularization, a major feature of ischemic retinopathy. Because tissue oxygenation is largely dependent upon circulation and critical in the generation of reactive oxygen species, and since the latter exert a major contribution in the pathogenesis of retinopathy of prematurity, it is important to understand the mechanisms that govern ocular blood flow. In this review we focus on the important and complex interaction between prostanoid, NO and peroxidation products on circulatory control of the immature retina.

Preservation of neural function in the perinate by high PGE(2) levels acting via EP(2) receptors

Despite increasingly frequent and longer lasting hypoxic episodes during progressive labor, the neonate is alert and vigorous at birth. We investigated whether high levels of PGs during the perinatal period assist in preserving neural function after such "stressful" hypoxic events. Visual evoked potentials (VEPs) and electroretinograms (ERGs) were recorded before and 45 min after mild moderate asphyxic hypoxia (two 4-min asphyxic-hypoxic periods induced by interrupting ventilation at 8-min intervals) in newborn piglets <12 h old treated or not treated with inhibitors of PG synthase (ibuprofen or diclofenac) with or without PG analogs. At 45 min after the hypoxic episode, P2 and b-wave amplitudes were slightly decreased and latencies were delayed. These changes in the VEP and ERG returned to near normal by 120 min. Ibuprofen and diclofenac decreased brain and retinal PG levels and markedly intensified 45 min after hypoxia-induced changes in VEP and ERG, but cerebral and retinal blood flows improved. Combined treatment with PG synthase inhibitor in combination with 16,16-dimethyl-PGE(2) (a PGE(2) analog), but not with PGI(2) and PGF(2alpha) analogs, and in combination with the EP(2) receptor agonist butaprost (but not EP(1) or EP(3) agonists), prevented ibuprofen- and diclofenac-aggravated postasphyxia electrophysiological changes. In conclusion, high levels of PGE(2) in nervous tissue, via actions on EP(2) receptors, seem to contribute to preservation of neural function in the perinate subjected to frequent hypoxic events.

Cardiovascular alpha1-adrenoceptor subtypes: functions and signaling

alpha-Adrenoceptors (alpha1AR) are G protein-coupled receptors and include alpha1A, alpha1B, and alpha1D subtypes corresponding to cloned alpha1a, alpha1b, and alpha1d, respectively. alpha1AR mediate several cardiovascular actions of sympathomimetic amines such as vasoconstriction and cardiac inotropy, hypertrophy, metabolism, and remodeling. alpha1AR subtypes are products of separate genes and differ in structure, G protein-coupling, tissue distribution, signaling, regulation, and functions. Both alpha(1A)AR and alpha(1B)AR mediate positive inotropic responses. On the other hand, cardiac hypertrophy is primarily mediated by alpha(1A)AR. The only demonstrated major function of alpha(1D)AR is vasoconstriction. alpha1AR are coupled to phospholipase C, phospholipase D, and phospholipase A2; they increase intracellular Ca2+ and myofibrillar sensitivity to Ca2+ and cause translocation of specific phosphokinase C isoforms to the particulate fraction. Cardiac hypertrophic responses to alpha1AR agonists might involve activation of phosphokinase C and mitogen-activated protein kinase via Gq x alpha1AR subtypes might interact with each other and with other receptors and signaling mechanisms.

Distribution of alpha1-adrenoceptor subtype proteins in different tissues of neonatal and adult rats

Distribution of alpha(1)-adrenoceptor (alpha(1)AR) subtype (alpha(1A), alpha(1B), alpha(1D)) proteins in brain, heart, kidney, and liver of 1-week-old rats and in brain, heart, aorta, kidney, liver, vas deferens, prostate, and adrenal glands of adult rats was investigated by Western analysis, using receptor subtype specific polyclonal antibodies. High levels of immunoreactive alpha(1A)AR and alpha(1D)AR in brain and heart and of alpha(1B)AR in liver and heart of neonatal rats were detected. In adult rat tissues, the abundance of alpha(1A)AR protein was most marked in the brain, intermediate in heart, aorta, liver, vas deferens, and adrenals, and minimal in the kidney and prostate; relative to other tissues, the expression of alpha(1B)AR was higher in brain and heart and that of alpha(1D)AR in brain. All the three receptor subtypes increased with age in the brain cortex, whereas the abundance of alpha(1B)AR increased in the heart but decreased in the liver; alpha(1A)AR and alpha(1D)AR in liver, kidney, and heart were not affected by age. It is concluded that alpha(1)AR subtypes are widely expressed in different neonatal and adult rat tissues.

Augmented vasoconstriction and thromboxane formation by 15-F(2t)-isoprostane (8-iso-prostaglandin F(2alpha)) in immature pig periventricular brain microvessels

BACKGROUND AND PURPOSE

Oxidant stress, especially in the premature, plays a major role in the pathogenesis of hypoxic-ischemic encephalopathies mostly manifested in the periventricular region. We studied the vasomotor mode of actions of the peroxidation product 15-F(2t)-isoprostane (15-F(2t)-IsoP) (8-iso-prostaglandin F(2alpha)) on periventricular region during development.

METHODS

Effects of 15-F(2t)-IsoP on periventricular microvessels of fetal, newborn, and juvenile pigs were studied by video imaging and digital analysis techniques. Thromboxane formation and intracellular Ca(2+) were measured by radioimmunoassay and by using the fluorescent indicator fura 2-AM.

RESULTS

15-F(2t)-IsoP-mediated constriction of periventricular microvessels decreased as a function of age such that in the fetus it was approximately 2.5-fold greater than in juvenile pigs. 15-F(2t)-IsoP evoked more thromboxane formation in the fetus than in the newborn, which was greater than that in the juvenile periventricular region; this was associated with immunoreactive thromboxane A(2) (TXA(2)) synthase expression in the fetus that was greater than that in newborn pigs, which was greater than that in juvenile pigs. 15-F(2t)-IsoP-induced vasoconstriction was markedly inhibited by TXA(2) synthase and receptor blockers (CGS12970 and L670596). Vasoconstrictor effects of the TXA(2) mimetic U46619 on fetal, neonatal, and juvenile periventricular microvessels did not differ. 15-F(2t)-IsoP increased TXA(2) synthesis by activating Ca(2+) influx through non-voltage-gated channels in endothelial cells (SK&F96365 sensitive) and N-type voltage-gated channels (omega-conotoxin sensitive) in astrocytes; smooth muscle cells were not responsive to 15-F(2t)-IsoP but generated Ca(2+) transients to U46619 via L-type voltage-sensitive channels.

CONCLUSIONS

15-F(2t)-IsoP causes periventricular brain region vasoconstriction in the fetus that is greater than that in the newborn, which in turn is greater than that in the juvenile due to greater TXA(2) formation generated through distinct stimulatory pathways, including from endothelial and astroglial cells. The resulting hemodynamic compromise may contribute to the increased vulnerability of the periventricular brain areas to oxidant stress-induced injury in immature subjects.

Regulation of endothelial nitric oxide synthase by PGD(2) in the developing choroid

We investigated if prostaglandins might regulate the increased choroidal endothelial (e) nitric oxide synthase (NOS) expression in the perinate. Prostaglandins, eNOS mRNA, immunoreactive protein and activity, and nitrite [stable metabolite of nitric oxide (NO)] production were markedly higher in newborn (1 day old) than juvenile (6-8 wk old) pig choroid. Treatment of isolated newborn choroids with the prostaglandin synthase inhibitor ibuprofen for 24 h reduced eNOS mRNA and nitrite production to values in juveniles. This effect was equally observed with the PGD(2) receptor (DP) blocker BW A868C and was prevented by cotreatment with PGD(2) but not other prostaglandins; similar observations were made on NOS activity in vivo. PGD(2) also increased eNOS expression on choroids of juveniles, and this effect was blocked by BW A868C. The manifestation of this upregulation of eNOS by PGD(2) on the control of choroidal vasomotor response was tested by using NO-dependent vasorelaxants, ACh, bradykinin (Bk), and substance P (SP). ACh-, Bk-, and SP-elicited choroidal vasorelaxation was greater in saline-treated newborn than juvenile pigs. Ibuprofen (24 h) decreased ACh-, Bk-, and SP-evoked vasorelaxation in newborns, whereas PGD(2) increased that in juveniles and prevented the ibuprofen-induced attenuated relaxation in newborns; infusion of N(omega)-monomethyl-L-arginine in choroids of those animals treated with PGD(2) reversed the augmented vasorelaxation to ACh, Bk, and SP. Finally, PGD(2)-induced upregulation of NOS in the perinate was also reflected by curtailed choroidal blood flow autoregulatory response to increased perfusion pressure. In conclusion, PGD(2) exhibits a major role in upregulating eNOS expression and activity in the choroid, which in turn results in greater NO-mediated vasorelaxation; a new mechanism for eNOS regulation via DP is hereby disclosed. The relationship between PGD(2) and eNOS in the developing subject provides an explanation for the interactive role of these two factors in the absent choroidal blood flow autoregulation in the perinate.

Ligand-independent negative chronotropic responses of rat and mouse right atria to beta-adrenoceptor antagonists

Negative chronotropic effects of beta-adrenoceptor (betaAR) antagonists on right atria from reserpine-treated rats and mice were determined as a test of their inverse agonist activities. BetaAR antagonist ICI-118,551 and nonselective betaAR antagonists alprenolol, propranolol, and timolol produced negative chronotropic effects. In contrast, nonselective betaAR antagonists pindolol and nadolol as well as beta1AR-selective antagonists atenolol, acebutolol, and metoprolol did not cause a significant decrease in atrial rates. The neutral antagonist pindolol but not the inverse agonist alprenolol inhibited the negative chronotropic activities of ICI-118,551. Isoprenaline, salbutamol, and noradrenaline produced positive chronotropic effects; the chronotropic effects of isoprenaline and salbutamol but not of noradrenaline were antagonized by ICI-118,551. It is concluded that both beta1AR and beta2AR mediate positive chronotropic effects of catecholamines on rat and mouse atria but only beta2AR are constitutively active.

Developmental regulation of endothelial nitric oxide synthase in cerebral vessels of newborn pig by prostaglandin E(2)

We investigated whether prostaglandins regulate endothelial nitric oxide synthase (eNOS) in the pig cerebral vasculature during the neonatal period. Prostaglandins, eNOS mRNA, eNOS protein, and NO production were higher in cerebral microvessels of newborn (1 day old) than in those of adult (6- to 8-month-old) pigs. The treatment of isolated cerebral microvessels of newborn animals with ibuprofen for 24 h reduced eNOS mRNA and nitrite production to levels in the adult; this effect of ibuprofen was prevented by concurrent treatment with prostaglandin (PG)E(2) analog 16,16-dimethyl-PGE(2), nonselective PGE(2) receptor analog 11-deoxy PGE(1), and prostaglandin EP(3) receptor agonists sulprostone and M&B 28,767 but was not modified by PGI(2) analog carbaprostacyclin, PGD(2), and EP(1) receptor agonist 17-phenyl trinor PGE(2). Correspondingly, 16, 16-dimethyl-PGE(2) and M&B 28,767 increased eNOS mRNA expression of adult microvessels to values in the newborn. Data similar to those with isolated cerebral vessels were obtained through histochemical analysis (NADPH-diaphorase positivity) of brain from newborn animals treated in vivo with ibuprofen in combination or not with sulprostone. Furthermore, substance P-induced NO-mediated cerebral vasorelaxation was decreased to adult values through the treatment of newborn pigs with ibuprofen; this effect was prevented by concomitant treatment with sulprostone. It is concluded that PGE(2) regulates eNOS in newborn pig cerebral microvessels via EP(3) receptors; this may be physiologically required during normal neurovascular development.

Developmental changes in prostaglandin E(2) receptor subtypes in porcine ductus arteriosus. Possible contribution in altered responsiveness to prostaglandin E(2)

BACKGROUND

Prostaglandin E(2) (PGE(2)) is important in ductus arteriosus (DA) patency, but the types of functional PGE(2) receptors (EP) in the developing DA are not known. We postulated that age-dependent alterations in EP and/or their subtypes may possibly contribute to the reduced responsiveness of the newborn DA to PGE(2).

METHODS AND RESULTS

We determined PGE(2) receptor subtypes by competition binding and immunoblot studies on the DA of fetal ( approximately 75% and 90% gestation) and newborn (<45 minutes old) pigs. We studied the effects of EP receptor stimulation on cAMP signaling in vitro and on term newborn (<3 hours old) DA patency in vivo. Fetal pig DA expressed EP(2), EP(3), and EP(4) receptors equivalently, but not EP(1). In neonatal DA, EP(1), EP(3), and EP(4) were undetectable, whereas EP(2) density was similar in fetus and newborn. Prostaglandin-induced changes in cAMP mirrored binding data. 16,16-Dimethyl PGE(2) and 11-deoxy PGE(1) (EP(2)/EP(3)/EP(4) agonist) produced more cAMP in fetus than newborn, but butaprost (selective EP(2) agonist) caused similar cAMP increases in both; EP(3) and EP(4) ligands (M&B28767 and AH23848B, respectively) affected cAMP production only in fetus. After birth, administration of butaprost alone was as effective as 11-deoxy PGE(1) and 16,16-dimethyl PGE(2) in dilating DA in vivo.

CONCLUSIONS

The data reveal fewer PGE(2) receptors in the DA of the newborn than in that of the fetus; this may contribute to the decreased responsiveness of the DA to PGE(2) in newborn. Because EP(2) receptors seem to mediate the effects of PGE(2) on the newborn DA, one may propose that a selective EP(2) agonist may be preferred as a pharmacological agent to maintain DA patency in infants with certain congenital heart diseases.

Developmentally increased cerebrovascular NO in newborn pigs curtails cerebral blood flow autoregulation

We tested the hypothesis that a reduced ability of the newborn (1-2 d old) to autoregulate cerebral blood flow (CBF) during acute hypertension is contributed by an increased synthesis of nitric oxide (NO) from endothelial (e) and neuronal NO synthase (nNOS). As previously reported, CBF (measured by radiolabeled microsphere technique) in newborn pigs remained constant only between 50 and 90 mm Hg of mean arterial blood pressure. Treatment of newborn pigs with Nomega-monomethyl-L-arginine or specific nNOS inhibitors 7-nitroindazole monosodium, 3-bromo-7-nitroindazole, and 1-(2-trifluoromethylphenyl) imidazole extended the upper limit of CBF autoregulation as seen in saline-treated (control) juvenile (4-6-wk-old) animals. Cerebrovascular production of nitrite (stable NO oxidation product) in vivo was markedly increased during hypertension (mean arterial blood pressure > 90 mm Hg) in newborn but not in the juvenile pigs. Inhibition of NOS with Nomega-monomethyl-L-arginine, 7-nitroindazole monosodium, 3-bromo-7-nitroindazole, or 1-(2-trifluoromethylphenyl) imidazole prevented the hypertension-induced increase in nitrite levels. In addition, eNOS and nNOS protein expression and activity were 2- to 3-fold higher (p < 0.05) in the cerebral microvasculature of newborn than in the tissues of juvenile pigs. It is concluded that during acute hypertension, excess production of NO associated with increased activity of NOS curtails the upper limit of CBF autoregulation in the newborn subject; in addition, nNOS seems to serve a significant role in this important physiologic function.

Inverse agonist activities of beta-adrenoceptor antagonists in rat myocardium

1. Negative inotropic effects of several beta-adrenoceptor (betaAR) antagonists on electrically-stimulated right atria, left atria, right ventricles and left ventricular papillary muscles from reserpine-treated rats were used as a measure of their inverse agonist activities. 2. Beta1AR antagonists acebutolol, atenolol and metoprolol, beta2AR antagonist ICI-181,551 and nonselective betaAR antagonists alprenolol, nadolol, propranolol and timolol produced negative inotropic effects, which were most marked on the right atria. 3. The nonselective betaAR antagonist pindolol did not exhibit inverse agonist activity but inhibited the negative inotropic activities of ICI-118,551, atenolol and propranolol. 4. The negative inotropic effects of lidocaine, nifedipine and pentobarbitone were similar on all the four myocardial preparations. 5. The positive inotropic efficacy of salbutamol on right and left atria but not on right ventricles and papillary muscles was comparable to that of isoprenaline. The antagonist activity of ICI-118,551 against isoprenaline was greater on right atria than on other cardiac regions. 6. Beta1AR proteins were expressed in all regions of the heart but of beta2AR were primarily localized in the right atrium. 7. It is concluded that beta2AR play a greater role in right atria than in other cardiac regions and almost all betaAR antagonists behave as inverse agonists.

Localization of functional prostaglandin E2 receptors EP3 and EP4 in the nuclear envelope

The effects of prostaglandin E2 are thought to be mediated via G protein-coupled plasma membrane receptors, termed EP. However recent data implied that prostanoids may also act intracellularly. We investigated if the ubiquitous EP3 and the EP4 receptors are localized in nuclear membranes. Radioligand binding studies on isolated nuclear membrane fractions of neonatal porcine brain and adult rat liver revealed the presence of EP3 and EP4. A perinuclear localization of EP3alpha and EP4 receptors was visualized by indirect immunocytofluorescence and confocal microscopy in porcine cerebral microvascular endothelial cells and in transfected HEK 293 cells that stably overexpress these receptors. Immunoelectron microscopy clearly revealed EP3alpha and EP4 receptors localization in the nuclear envelope of endothelial cells; this is the first demonstration of the nuclear localization of these receptors. Data also reveal that nuclear EP receptors are functional as they affect transcription of genes such as inducible nitric-oxide synthase and intranuclear calcium transients; this appears to involve pertussis toxin-sensitive G proteins. These results define a possible molecular mechanism of action of nuclear EP3 receptors.

Augmentation of diabetes-associated renal hyperfiltration and nitric oxide production by pregnancy in rats

We tested the hypothesis that pregnancy might increase diabetes-associated nitric oxide (NO) production and renal hyperfiltration. Two weeks following i.v. streptozotocin (40 mg/kg), mean arterial pressure (MAP) was not modified by diabetes; glomerular filtration rate (GFR), renal plasma flow (RPF) and filtration fraction (FF) were higher in pregnant than in virgin controls and increased by diabetes to a greater extent in pregnant than in virgin rats. Urinary volume (UV), creatinine, albumin and sodium (UNaV) were significantly increased by diabetes. Diabetes led to an increase in renal, cardiac, aortic and uterine but not in placental NO synthase activities. Infusion of NG-nitro-l-arginine (l-NA) caused a dose-dependent reduction in GFR, RPF, plasma NO2-/NO3-, UV and UNaV; in general, diabetes increased these effects to a greater extent in pregnant than in virgin rats. l-NA increased MAP in all groups of rats but did not alter FF. Diabetes did not alter responses of thoracic aorta rings to vasoconstrictor effects of phenylephrine and the vasorelaxant effects of sodium nitroprusside but increased endothelium-dependent relaxant effects of acetylcholine. In general the effects of diabetes of 7 days duration were similar to those described above for diabetes of 14 days duration. These data suggest that diabetes-associated renal hyperfiltration and NO production are augmented by pregnancy.

Nuclear localization of prostaglandin E2 receptors

Prostaglandin E2 receptors (EP) were detected by radioligand binding in nuclear fractions isolated from porcine brain and myometrium. Intracellular localization by immunocytofluorescence revealed perinuclear localization of EPs in porcine cerebral microvascular endothelial cells. Nuclear association of EP1 was also found in fibroblast Swiss 3T3 cells stably overexpressing EP1 and in human embryonic kidney 293 (Epstein-Barr virus-encoded nuclear antigen) cells expressing EP1 fused to green fluorescent protein. High-resolution immunostaining of EP1 revealed their presence in the nuclear envelope of isolated (cultured) endothelial cells and in situ in brain (cortex) endothelial cells and neurons. Stimulation of these nuclear receptors modulate nuclear calcium and gene transcription.

PGE2, via EP3 receptors, regulates brain nitric oxide synthase in the perinatal period

We tested the hypothesis that high prostaglandin levels during the perinatal period might regulate brain nitric oxide synthase (nNOS) expression. nNOS and cyclooxygenase (COX)-2 mRNAs were higher in brain cortex and the periventricular area of newborn rats and pigs compared with adult brain. Nitric oxide synthase activity was also 2. 5- to 4-fold higher in newborn than in adult brain. Administration of nonselective COX inhibitor ibuprofen or COX-2 inhibitor nimesulide every 8 h for 24 h to newborn rats and pigs reduced prostaglandin levels and caused comparable reductions in nNOS mRNA, protein, and activity to levels of adults; COX inhibitor-induced changes were prevented by cotreatment with PGE2 analog, 16, 16-dimethyl-PGE2, and agonist for the EP3 receptor of PGE2, sulprostone, but not by PGI2 analog carbaprostacyclin, PGD2, EP1 receptor agonist 17-phenyl trinor-PGE2, and EP2 agonist butaprost. Concordant observations were made in vitro and revealed that nNOS expression (detected by NADPH diaphorase reactivity) mostly present in neurons of the deeper cortical layers was reduced by COX inhibitor, and this effect was prevented by EP3 agonist. In conclusion, high levels of PGE2 in neonatal brain contribute to the increased expression of nNOS by acting on EP3 receptors; this positive interaction between PGE2 and nNOS might be required physiologically for normal brain development.

A major role for prostacyclin in nitric oxide-induced ocular vasorelaxation in the piglet

We studied the mechanisms of retinal and choroidal vasorelaxation elicited by nitric oxide (NO) using piglet eyes. The NO donors sodium nitroprusside (SNP) and diethylamine-NONOate caused comparable concentration-dependent relaxation that was partially (approximately 40%) attenuated by the guanylate cyclase inhibitors methylene blue and LY83583 and reduced to a lesser extent (approximately 25%) by the inhibitor of cGMP-dependent kinase, KT 5823. In contrast, NO-induced dilatation (by NO donors and endogenous NO after stimulation with bradykinin) was substantially (approximately 70%) diminished by the KCa channel blockers tetraethylammonium (TEA), charybdotoxin, and iberiotoxin; by the cyclooxygenase inhibitors indomethacin and ibuprofen; by the prostaglandin I (PGI2) synthase inhibitor trans-2-phenyl cyclopropylamine (TPC); and by the removal of endothelium; whereas relaxation of endothelium-denuded vasculature to SNP was unaltered by indomethacin, TPC, and charybdotoxin but was nearly nullified by methylene blue and the Kv channel blocker 4-aminopyridine. NO donors significantly increased PGI2 synthesis and the putative PGI2 receptor-coupled second messenger cAMP, from ocular vasculature (retinal microvessels and choroidal perfusate), and this increase in PGI2 formation was markedly reduced by TPC, tetraethylammonium, charybdotoxin, and/or the removal of endothelium, but it was only slightly reduced by methylene blue and LY83583. Also, SNP and KCa channel openers NS1619 and NS004 caused an increase in PGI2 synthesis in cultured endothelial cells, which was virtually abolished by KCa blockers. Finally, vasorelaxation to a cGMP analogue, 8-bromo cGMP, and protein kinase G stimulant beta-phenyl-1,N2-etheno-8-bromoguanosine 3':5'-cyclic monophosphate was mostly Kv dependent and, in contrast to NO, largely unrelated to PGI2 formation. In conclusion, data indicate that NO-induced ocular vasorelaxation is partly mediated by cGMP through its action on smooth muscle, and more importantly, by stimulating PGI2 formation of endothelial origin via a mechanism mostly independent of guanylate cyclase, which involves the opening of a KCa channel.

Increases in retinovascular prostaglandin receptor functions by cyclooxygenase-1 and -2 inhibition

PURPOSE

To determine the relative contribution of cyclooxygenase (COX)-1 and COX-2 in regulating prostaglandin (PG) E2 and PGF2alpha receptors (EP and FP, respectively) densities and their functions in retinal vasculature of neonatal pigs.

METHODS

Newborn pigs were treated intravenously every 8 hours for 48 hours with saline, 40 mg/kg nonselective COX inhibitor ibuprofen, 80 mg/kg COX-1 inhibitor valeryl salicylate, or 5 mg/kg DuP697 and 5 mg/kg NS398, COX-2 inhibitors. Retinal microvessel EP and FP receptor densities were measured by radioligand binding and receptor-coupled effects by determining second-messenger inositol 1,4,5-trisphosphate (IP3) and vasomotor responses. Retinal blood flow (RBF) response to incremental increases in blood pressure (BP) was measured by a microsphere technique.

RESULTS

Valeryl salicylate, DuP697, and NS398 reduced retinal PGE2 and PGF2alpha concentrations in the newborn by approximately half, whereas ibuprofen caused further reduction to levels observed in adults. Retinal vessel EP1, EP3, and FP receptor densities increased approximately threefold after treatments with COX-1 or COX-2 inhibitors, and five- to sixfold after ibuprofen treatment. EP and FP receptor upregulation was associated with corresponding increases in IP3 production and retinal vasoconstriction in response to PGF2alpha, fenprostalene (an FP agonist), PGE2, 17-phenyl trinor PGE2 (an EP1 agonist), and M&B28,767 (an EP3 agonist) and with enhanced RBF autoregulation of high BP (> or =125 mm Hg). Conversely, EP2 receptor density and coupled functions were minimally affected by COX inhibition.

CONCLUSIONS

Data suggest that increased COX-1- and COX-2-catalyzed prostaglandin synthesis contribute equivalently to the downregulation of retinovascular EP1, EP3, and FP receptors and their vasoconstrictor functions in newborn pigs; the EP2 receptor was not significantly influenced by ontogenic alterations in prostaglandin levels.

Crosstalk between alpha-1A and alpha-1B adrenoceptors in neonatal rat myocardium: implications in cardiac hypertrophy

The myocardial effect of alpha-1A adrenoceptor (alpha-1 AR) agonists in neonatal rats are mediated by alpha-1A AR and not by alpha-1B AR, although both receptor subtypes are equally expressed; the functions of alpha-1B AR are not known. Here, we report that alpha-1 B ARs inhibit the activities of alpha-1A ARs in neonatal rat myocardium so that the inactivation of alpha-1 B ARs by chloroethylclonidine (CEC) potentiated the effects of nonselective alpha-1 AR agonist phenylephrine (PE) on myocardial protein synthesis and early gene (c-fos and c-jun) expression. CEC did not modify the hypertrophic effect of angiotensin II. The potentiation of the effects of PE by CEC was associated with a translocation of Ca(++)-dependent protein kinase C (PKC)alpha, which did not occur in the absence of CEC. Alpha-1A AR-selective agonist A61603 was approximately 1000-fold more potent than PE as a positive inotropic agent; it caused the translocation of PKC alpha, which was not affected by CEC. 5-Methylurapidil antagonized the effects of PE and A61603, suggesting that these were mediated via alpha-1A ARs. Alpha-1D AR antagonist BMY 7378 did not modify PE-induced translocation of PKC. CEC potentiated the effects of PE on Ca++ transients in Fura 2-AM-loaded dispersed cardiomyocytes, and this potentiation was prevented by nifedipine. In whole-cell patch-clamp recordings of cultured cardiomyocytes, CEC potentiated the effect of norepinephrine on Ca++ channel currents, which was blocked by 5-methylurapidil. We conclude that alpha-1A ARs are positively and alpha-1B ARs are negatively coupled to nifedipine-sensitive Ca++ channels, possibly via Gi protein, and this antagonistic relationship between alpha-A AR and alpha-1B AR in the neonatal heart might be required physiologically for normal alpha-1 AR-mediated responses and myocardial development.

A novel mechanism for vasoconstrictor action of 8-isoprostaglandin F2 alpha on retinal vessels

Using a video-imaging technique, we characterized the effects of 8-isoprostaglandin F2 alpha (8-iso-PGF2 alpha) on retinal vasculature from piglets. 8-Iso-PGF2 alpha potently contracted (EC50 = 5.9 +/- 0.5 nM) retinal vessels. These effects were completely antagonized by the cyclooxygenase inhibitor indomethacin, the thromboxane synthase blocker CGS-12970, the thromboxane receptor antagonist L-670596, and the putative inhibitor of the non-voltage-dependent receptor-operated Ca2+ pathway SKF-96365; constrictor effects of 8-iso-PGF2 alpha were also partly attenuated by the ETA-receptor blocker BQ-123 and an inhibitor of endothelin-converting enzyme, phosphoramidon, but was negligibly affected by the L-type voltage-gated Ca2+ channel blocker nifedipine. Correspondingly, 8-iso-PGF2 alpha elicited endothelin release from retinal preparations, which was markedly reduced by SKF-96365. 8-Iso-PGF2 alpha also increased thromboxane production in the retina and cultured endothelial cells, but not on retinovascular smooth muscle cells; these effects of 8-iso-PGF2 alpha were blocked by indomethacin, CGS-12970, SKF-96365, and EGTA, but not by nifedipine. 8-Iso-PGF2 alpha also increased Ca2+ transients in retinal endothelial cells, which were inhibited by SKF-96365 and EGTA, but not by nifedipine, whereas in smooth muscle cells U-46619, but not 8-iso-PGF2 alpha, stimulated a rise in Ca2+ transients. Finally, H2O2 + FeCl2 (in vitro) and anoxia followed by reoxygenation (in vivo) stimulated formation of 8-iso-PGF2 alpha in the retina. In conclusion, 8-iso-PGF2 alpha-induced retinal vasoconstriction is mediated by cyclooxygenase-generated formation of thromboxane and, to a lesser extent, by endothelin after Ca2+ entry into cells, possibly through receptor-operated channels. Retinal vasoconstriction to 8-isoprostanes might play a role in the genesis of ischemic retinopathies.

A role for protein kinase C alpha in stimulation of prostaglandin G/H synthase-2 transcription by 14,15-epoxyeicosatrienoic acid

Arachidonic acid, but not eicosapentaenoic acid, increased prostaglandin G/H endoperoxide synthase-2 transcription in cultured intestinal epithelial cells. This stimulatory effect on PGHS-2 synthesis was prevented by an AA utilization inhibitor, eicosatetraynoic acid. Specific inhibitors of the cyclooxygenase or the lipoxygenase pathways of AA metabolism did not prevent AA-mediated induction of PGHS-2 synthesis; however, the involvement of cytochrome P450 monoxygenases (CYP450) was indicated as several CYP450 blockers, ketoconazole, miconazole, and metyrapone, inhibited the induction of PGHS-2 mRNA synthesis by AA. This blockade by CYP450 inhibitors could be overcome by the addition of the AA epoxygenase metabolite 14,15-epoxyeicosatrienoic acid (14,15-EET); other EET regio-isomers were unable to elevate PGHS-2 mRNA level. Blockade of protein kinase C with a specific inhibitor, bisindolyl maleimide-1, or translational inhibition of protein kinase C alpha by antisense oligonucleotides reduced PGHS-2 transcription, suggesting the involvement of protein kinase C alpha in the signal transduction pathway.

Differential effects of rat pregnancy on uterine and lung atrial natriuretic factor receptors

We investigated if the refractoriness to the tocolytic effects of atrial natriuretic factor (ANF) during rat pregnancy is due to a downregulation of one or both guanylyl cyclase (GC)-coupled GC-A and GC-B ANF receptors; lungs were used as controls. Uteri and lungs of virgin, pregnant (days 7, 16, and 21), and day 2 postpartum rats expressed mRNAs for GC-A and GC-B as well as GC-uncoupled ANF-C receptors. GC-B receptor protein was more abundant than GC-A in uteri; the reverse was the case in lungs. Pregnancy decreased uterine mRNAs and proteins for GC-A and GC-B receptors as well as the effects of ANF and C-type natriuretic peptide (CNP) on uterine GC activity; lung ANF receptors and effects of ANF and CNP on lung GC activity were not modulated by pregnancy. It is concluded that pregnancy induces organ-specific modulation of ANF receptors and a downregulation of ANF-GC receptors would minimize interference with uterine motility during pregnancy.

Downregulation of adrenal atrial natriuretic peptide receptor mRNAs and proteins by pregnancy in rats

The main objective of this study was to find out if the reported changes in the aldosterone-suppressant activity of atrial natriuretic peptide (ANP) during different hormonal states in rats are due to a modulation of ANP receptors. In zona glomerulosa cells, ribonuclease protection assay detected mRNAs for guanylate cyclase (GC)-coupled ANP GC-A and GC-B receptors, and for ANP C receptors, which are not coupled to GC. Western analysis using polyclonal anti-GC-A and anti-GC-B receptor antibodies revealed the presence of GC-A but not GC-B receptor proteins in zona glomerulosa cells. Pregnancy (days 7, 16 and 21), oestradiol-17 beta and progesterone decreased mRNAs for all the three ANP receptors in zona glomerulosa cells. Pregnancy decreased GC-A receptor proteins in zona glomerulosa cells, but these recovered to virgin values on day 2 postpartum. ANP receptor mRNAs in zona glomerulosa cells increased by postpartum day 2, but did not reach the values found in virgin rats. Zona fasciculata mainly contained GC-A receptor mRNA. It is concluded that ANP receptors in rat adrenal zona glomerulosa are modulated by pregnancy, oestrogen and progesterone; a decrease in ANP GC-A receptors during pregnancy might explain the accompanying decrease in the aldosterone-suppressant effects of ANP.

Stimulation of prostaglandin G/H synthase-2 expression by arachidonic acid monoxygenase product, 14,15-epoxyeicosatrienoic acid

The relationship between arachidonic acid (AA) mobilization and transcription of immediate-early genes, particularly of prostaglandin G/H synthase-2 (PGHS-2), in intestinal crypt epithelial cells was analyzed. PGHS-2 mRNA and protein synthesis were stimulated by its own substrate, AA; actinomycin D, a transcription inhibitor, prevented the AA-induced increase in PGHS-2 mRNA. Eicosatetraynoic acid, an inhibitor of AA utilization, significantly reduced PGHS-2 mRNA synthesis elicited by AA. Inhibitors of cytochrome P450 monoxygenases, ketoconazole and miconazole, also prevented PGHS-2 mRNA synthesis in a dose-dependent manner. Phenyl chalcone oxide, an epoxide hydrolase inhibitor, potentiated AA-induced PGHS-2 mRNA synthesis. Of the four regioisomers of arachidonic acid epoxides, only 14,15-epoxyeicosatrienoic acid elicited the expression of PGHS-2 in intestinal crypt epithelial cells. This is the first direct evidence of stimulation of an immediate-early gene product, specifically PGHS-2, by an AA epoxygenase metabolite, 14,15-epoxyeicosatrienoic acid, as well as of a heterologous regulation of PGHS-2 synthesis by these monoxygenase products.