Progestin And adipoQ Receptor Research Articles

Non-genomic rapid responses via progesterone in human peripheral T cells are not indirectly mimicked by sphingosine 1-phosphate

Progesterone is an endogenous immunomodulator that suppresses T cell activation during pregnancy. Progesterone has been shown to induce rapid responses that cause intracellular calcium ([Ca2+]i) elevation and acidification followed by inhibition of phytohemagglutinin (PHA)-stimulated proliferation. These rapid responses involve T cell plasma membrane sites, but the mechanisms remain unclear. Three new membrane progesterone receptors (mPRα/mPRβ/mPRγ) have been identified as expressed in T cells. These proteins have been identified as G-protein-coupled receptors. Recently, mPRs have been classified as progestin and adipoQ receptors (PAQRs). Furthermore, they have been suggested to be alkaline ceramidases, possibly involved in mediating sphingolipid signaling. Alkaline ceramidases are capable of converting ceramide to sphingosine, which might then be further phosphorylated sphingosine via sphingosine kinase to sphingosine 1-phosphate (S1P). This pathway could result in progesterone acting indirectly via S1P on membrane sphingosine 1-phosphate receptors (S1PRs) in T cells to induce rapid responses. Therefore, our aim was to investigate whether progesterone rapid responses occur indirectly in T cells via S1P. We found that S1P induces [Ca2+]i elevation however there was no change in intracellular pH. This is different from the situation with progesterone: S1P alone does not suppress PHA-stimulated cell proliferation and does not act synergistically with progesterone on the inhibition of PHA-induced cell proliferation. In contrast, S1P at 1μM is able to antagonize the proliferation inhibitory effect of progesterone. Thus the rapid responses that are induced by progesterone in human peripheral T cells probably do not involve indirect signaling via S1P and S1PRs.

Nonclassical Progesterone Signalling Molecules in the Nervous System

Progesterone (P4) regulates a wide range of cognitive, neuroendocrine, neuroimmune and neuroprotective functions. Therefore, it is not surprising that this ovarian hormone acts through multiple receptors. Ever since the 1980s, studies investigating the neural effects of P4 have focused mainly on genomic and nongenomic actions of the classical progestin receptor (PGR). More recently, two groups of nonclassical P4 signalling molecules have been identified: (i) the class II progestin and adipoQ receptor (PAQR) family, which includes PAQR 5, 6, 7, 8 and 9, also called membrane progestin receptor α (mPRα; PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6) and mPRε (PAQR9), and (ii) the b5-like haeme/steroid-binding protein family, which includes progesterone receptor membrane component 1 (Pgrmc1), Pgrmc2, neudesin and neuferricin. In this review, we describe the structures, neuroanatomical localisation and signalling mechanisms of these molecules. We also discuss gonadotrophin-releasing hormone regulation as an example of a physiological function regulated by multiple progesterone receptors but through different mechanisms.

Membrane progestin receptors in the midbrain ventral tegmental area are required for progesterone-facilitated lordosis of rats

Progesterone (P4) and its metabolites, rapidly facilitate lordosis of rats partly through actions in the ventral tegmental area (VTA). The study of membrane progestin receptors (mPRs), of the Progestin and AdipoQ Receptor (PAQR) superfamily, has been limited to expression and regulation, instead of function. We hypothesized that if mPRs are required for progestin-facilitated lordosis in the VTA, then mPRs will be expressed in this region and knockdown will attenuate lordosis. First, expression of mPR was examined by reverse-transcriptase polymerase chain reaction (RT-PCR) in brain and peripheral tissues of proestrous Long–Evans rats. Expression of mPRα (paqr7) was observed in peripheral tissues and brain areas, including hypothalamus and midbrain. Expression of mPRβ (paqr8) was observed in brain tissues and was abundant in the midbrain and hypothalamus. Second, ovariectomized rats were estrogen (E2; 0.09mg/kg, SC), and P4 (4mg/kg, SC) or vehicle-primed, and infused with antisense oligodeoxynucleotides (AS-ODNs) targeted against mPRα and/or mPRβ intracerebroventricularly or to the VTA. Rats were assessed for motor (open field), anxiety (elevated plus maze), social (social interaction), and sexual (lordosis) behavior. P4-facilitated lordosis was significantly reduced with administration of AS-ODNs for mPRα, mPRβ, or co-administration of mPRα and mPRβ to the lateral ventricle, compared to vehicle. P4-facilitated lordosis was reduced, compared to vehicle, by administration of mPRβ AS-ODNs, or co-administration of mPRα and mPRβ AS-ODNs, but not mPRα AS-ODNs alone, to the VTA. No differences were observed for motor, anxiety, or social behaviors. Thus, mPRs in the VTA are targets of progestin-facilitated lordosis of rats.

The RAS Guanyl Nucleotide-releasing Protein RasGRP1 Is Involved in Lymphatic Development in Zebrafish

The molecular basis of the lymphatic development remains largely unknown. Using zebrafish as a model, we discovered a novel role for the Ras guanine-releasing protein 1 (RasGRP1), a protein involved in Ras activation in lymphangiogenesis. Secondary lymphatic sprouts from the posterior cardinal vein give rise to thoracic duct which is the first lymphatic vessel in zebrafish. Knockdown of rasgrp1 by injecting morpholino in zebrafish embryos impaired formation of thoracic duct accompanied by pericardial and truck edema, whereas blood vessel development of the embryos was largely unaffected. In rasgrp1-knockdown embryos, the number of sprouts producing the string of parachordal lymphangioblast cells was reduced. Meanwhile the total number of the secondary sprouts was not changed. As a result, the number of venous intersegmental vessels was increased, whereas the number of lymphatic vessel was reduced at a later stage. The lymphatic developmental defects caused by rasgrp1 knockdown could be rescued by ectopic expression of a constitutively active HRas. Further analysis revealed that RasGRP1 knockdown could synergize with flt4/vegfr3 knockdown to induce defects in lymphangiogenesis. Taken together, this finding demonstrates a critical role for RasGRP1 in lymphatic development in zebrafish.

Novel progesterone receptors: neural localization and possible functions

Progesterone (P4) regulates a wide range of neural functions and likely acts through multiple receptors. Over the past 30 years, most studies investigating neural effects of P4 focused on genomic and non-genomic actions of the classical progestin receptor (PGR). More recently the focus has widened to include two groups of non-classical P4 signaling molecules. Members of the Class II progestin and adipoQ receptor (PAQR) family are called membrane progestin receptors (mPRs) and include: mPRα (PAQR7), mPRβ (PAQR8), mPRγ (PAQR5), mPRδ (PAQR6), and mPRε (PAQR9). Members of the b5-like heme/steroid-binding protein family include progesterone receptor membrane component 1 (PGRMC1), PGRMC2, neudesin, and neuferricin. Results of our recent mapping studies show that members of the PGRMC1/S2R family, but not mPRs, are quite abundant in forebrain structures important for neuroendocrine regulation and other non-genomic effects of P4. Herein we describe the structures, neuroanatomical localization, and signaling mechanisms of these molecules. We also discuss possible roles for Pgrmc1/S2R in gonadotropin release, feminine sexual behaviors, fluid balance and neuroprotection, as well as catamenial epilepsy.

Characterization, Neurosteroid Binding and Brain Distribution of Human Membrane Progesterone Receptors δ and ϵ (mPRδ and mPRϵ) and mPRδ Involvement in Neurosteroid Inhibition of Apoptosis

Three members of the progestin and adipoQ receptor (PAQR) family, PAQR-7, PAQR-8, and PAQR-5 [membrane progesterone (P4) receptor (PR) (mPR)α, mPRβ, and mPRγ], function as plasma mPRs coupled to G proteins in mammalian cells, but the characteristics of two other members, PAQR6 and PAQR9 (mPRδ and mPRε), remain unclear, because they have only been investigated in yeast expression systems. Here, we show that recombinant human mPRδ and mPRε expressed in MDA-MB-231 breast cancer cells display specific, saturable, high-affinity [(3)H]-P4 binding on the plasma membranes of transfected cells with equilibrium dissociation constants (K(d)s) of 2.71 and 2.85 nm, respectively, and low affinity for R5020, characteristics typical of mPRs. P4 treatment increased cAMP production as well as [(35)S]-guanosine 5'-triphosphate (GTP)γS binding to transfected cell membranes, which was immunoprecipitated with a stimulatory G protein antibody, suggesting both mPRδ and mPRε activate a stimulatory G protein (Gs), unlike other mPRs, which activate an inhibitory G protein (Gi). All five mPR mRNAs were detected in different regions of the human brain, but mPRδ showed greatest expression in many regions, including the forebrain, hypothalamus, amygdala, corpus callosum, and spinal cord, whereas mPRε was abundant in the pituitary gland and hypothalamus. Allopregnanolone and other neurosteroids bound to mPRδ and other mPRs and acted as agonists, activating second messengers and decreased starvation-induced cell death and apoptosis in mPRδ-transfected cells and in hippocampal neuronal cells at low nanomolar concentrations. The results suggest that mPRδ and mPRε function as mPRs coupled to G proteins and are potential intermediaries of nonclassical antiapoptotic actions of neurosteroids in the central nervous system.

PAQR3 Plays a Suppressive Role in the Tumorigenesis of Colorectal Cancers

PAQR3 is a member of the progestin and adipoQ receptor (PAQR) family and was recently characterized as a spatial regulator that negatively modulates Ras/Raf/MEK/ERK signaling cascade. However, little is known about the physiological functions of PAQR3 in the tumorigenesis of colorectal cancers. The function of PAQR3 in colorectal cancer development in mice was analyzed by crossing Paqr3-depleted mice with Apc(Min/+) mice that have a germline mutation of the gene-encoding tumor suppressor adenomatous polyposis coli (APC). The survival time and tumor area in the small intestine of the Apc(Min/+) mice was significantly aggravated by Paqr3 deletion. The cell proliferation rate, anchorage-independent growth, EGF-stimulated ERK phosphorylation and EGF-induced nuclear accumulation of β-catenin were inhibited by PAQR3 overexpression and enhanced by PAQR3 knockdown in SW-480 colorectal cancer cells. In humans, the expression level of PAQR3 was significantly decreased in colorectal cancer samples in comparison with adjacent normal tissues. In addition, the expression level of PAQR3 was inversely associated with tumor grade in the colorectal cancer samples. Collectively, our data reveal for the first time that PAQR3 has a tumor suppressor activity in the development of colorectal cancers.

Non-genomic progesterone signalling and its non-canonical receptor

The steroid hormone progesterone regulates many critical aspects of vertebrate physiology. The nuclear receptor for progesterone functions as a ligand-activated transcription factor, directly regulating gene expression. This type of signalling is referred to as the 'genomic' pathway. Nevertheless, progesterone also stimulates rapid physiological effects that are independent of transcription. This pathway, termed 'non-genomic', is mediated by the mPRs (membrane progesterone receptors). These mPRs belong to a larger class of membrane receptors called PAQRs (progestin and adipoQ receptors), which include receptors for adiponectin in vertebrates and osmotin in fungi. mPRs have been shown to activate inhibitory G-proteins, suggesting that they act as GPCRs (G-protein-coupled receptors). However, PAQRs do not resemble GPCRs with respect to topology or conserved sequence motifs. Instead, they more closely resemble proteins in the alkaline ceramidase family and they may possess enzymatic activity. In the present paper, we highlight the evidence in support of each model and what is currently known for PAQR signal transduction of this non-canonical receptor.

Characterization and Transcriptional Regulation Analysis of the Porcine PAQR6 Gene

Progestin and adipoQ receptor family member VI (PAQR6) is a new member of the Progestin and adipoQ receptors (PAQRs) family that functions as an important factor in the nongenomic actions of rapid steroid response. Considering the important role of PAQR6 in these nongenomic actions, we determined porcine PAQR6 expression and regulation. We cloned the cDNA of porcine PAQR6 and analyzed its genomic structure. Subcellular localization analysis showed that PAQR6-green fluorescent protein fusion protein was distributed in cytoplasm. Spatial expression patterns analysis revealed that porcine PAQR6 was more highly expressed in small intestinal than in other tissues. To investigate the regulatory mechanism of porcine PAQR6, we cloned approximately 1.5 kb of porcine PAQR6 5'-regulatory region and generated sequential deletion constructs and evaluated their activity in a dual-luciferase reporter assay. The results suggested that the core promoter region of this gene is located in the first exon region from +90 to +241. Site-directed mutagenesis indicated that adiponectin receptor protein 1, E2F transcription factor 1, and Sp1 transcription factor might be important transcription factors for porcine PAQR6. This study is the first attempt to elucidate the transcriptional regulation of porcine PAQR6, which established a foundation for further study and contributed to the deeper investigation of the regulation and function of PAQR6.

Phylogenetic and Preliminary Phenotypic Analysis of Yeast PAQR Receptors: Potential Antifungal Targets

Proteins belonging to the Progestin and AdipoQ Receptor (PAQR) superfamily of membrane bound receptors are ubiquitously found in fungi. Nearly, all fungi possess two evolutionarily distinct paralogs of PAQR protein, which we have called the PQRA and PQRB subtypes. In the model fungus Saccharomyces cerevisiae, these subtypes are represented by the Izh2p and Izh3p proteins, respectively. S. cerevisiae also possesses two additional PQRA-type receptors called Izh1p and Izh4p that are restricted to other species within the “Saccharomyces complex”. Izh2p has been the subject of several recent investigations and is of particular interest because it regulates fungal growth in response to proteins produced by plants and, as such, represents a new paradigm for interspecies communication. We demonstrate that IZH2 and IZH3 gene dosage affects resistance to polyene antifungal drugs. Moreover, we provide additional evidence that Izh2p and Izh3p negatively regulate fungal filamentation. These data suggest that agonists of these receptors might make antifungal therapeutics, either by inhibiting fungal development or by sensitizing fungi to the toxic effects of current antifungal therapies. This is particularly relevant for pathogenic fungi such as Candida glabrata that are closely related to S. cerevisiae and contain the same complement of PAQR receptors.Electronic supplementary materialThe online version of this article (doi:10.1007/s00239-011-9462-3) contains supplementary material, which is available to authorized users.

Effect of adiponectin on human colorectal‐cancer cell proliferation

Adiponectin (Acrp30) is a protein hormone released from adipocytes that has been shown to have an anti‐proliferative effect on cancer cells. Three cellular receptors from the progestin and AdipoQ Receptor (PAQR) family have been identified that can actively bind Acrp30: AdipoR1 and AdipoR2, located on the cell membrane; and AdipoR3 in the Golgi body. Currently, it is known that AdipoR1 and R2 allow Acrp30 to regulate fatty acid and glucose metabolism as well as cell growth and proliferation. Prior research has indicated that AdipoR1 and AdipoR2 may be involved in the Acrp30 anti‐proliferative effect but there has been minimal research on if or how AdipoR3 (PAQR3) may be involved. To determine a possible relationship between Acrp30, AdipoR3, and cell proliferation, the production of mRNA in HT‐29 human colo‐rectal cancer cells in the presence or absence of Acrp30 was quantified using quantitative real‐time PCR (qRT‐PCR). These mRNA levels were also compared to the levels of AdipoR1 and R2. Briefly, the mRNA of the cell was extracted, converted to cDNA, and evaluated by qRT‐PCR using fluorescent probe primers. Following this study, RNAi knockdown experiments of AdipoR3 will be performed after which the anti‐proliferative effect of Acrp30 on HT‐29 cells will be reanalyzed. Preliminary results confirm the anti‐proliferative nature of Acrp30 and also indicate altered AdipoR3 mRNA abundance in adiponectin treated colo‐rectal cancer cells. This work was supported by the Henson School of Science and Technology, Salisbury University, and the Cort Scholarship.

CREST - a large and diverse superfamily of putative transmembrane hydrolases

BackgroundA number of membrane-spanning proteins possess enzymatic activity and catalyze important reactions involving proteins, lipids or other substrates located within or near lipid bilayers. Alkaline ceramidases are seven-transmembrane proteins that hydrolyze the amide bond in ceramide to form sphingosine. Recently, a group of putative transmembrane receptors called progestin and adipoQ receptors (PAQRs) were found to be distantly related to alkaline ceramidases, raising the possibility that they may also function as membrane enzymes.ResultsUsing sensitive similarity search methods, we identified statistically significant sequence similarities among several transmembrane protein families including alkaline ceramidases and PAQRs. They were unified into a large and diverse superfamily of putative membrane-bound hydrolases called CREST (alkaline ceramidase, PAQR receptor, Per1, SID-1 and TMEM8). The CREST superfamily embraces a plethora of cellular functions and biochemical activities, including putative lipid-modifying enzymes such as ceramidases and the Per1 family of putative phospholipases involved in lipid remodeling of GPI-anchored proteins, putative hormone receptors, bacterial hemolysins, the TMEM8 family of putative tumor suppressors, and the SID-1 family of putative double-stranded RNA transporters involved in RNA interference. Extensive similarity searches and clustering analysis also revealed several groups of proteins with unknown function in the CREST superfamily. Members of the CREST superfamily share seven predicted core transmembrane segments with several conserved sequence motifs.ConclusionsUniversal conservation of a set of histidine and aspartate residues across all groups in the CREST superfamily, coupled with independent discoveries of hydrolase activities in alkaline ceramidases and the Per1 family as well as results from previous mutational studies of Per1, suggests that the majority of CREST members are metal-dependent hydrolases.ReviewersThis article was reviewed by Kira S. Markarova, Igor B. Zhulin and Rob Knight.

Expression of Membrane Progesterone Receptors (mPR/PAQR) in Ovarian Cancer Cells: Implications for Progesterone-Induced Signaling Events

The high mortality rates associated with ovarian cancer are largely due to a lack of highly effective treatment options for advanced stage disease; a time when initial diagnosis most commonly occurs. Recent evidence suggests that the steroid hormone, progesterone, may possess anti-tumorigenic properties. With the discovery of a new class of membrane-bound progesterone receptors (mPRs) belonging to the progestin and adipoQ receptor (PAQR) gene family in the ovary, there are undefined mechanisms by which progesterone may inhibit tumor progression. Therefore, our goal was to define potential mPR-dependent signaling mechanisms operative in ovarian cancer cells. We detected abundant mPRα (PAQR7), mPRβ (PAQR8), and mPRγ (PAQR5), but not classical nuclear PR (A or B isoforms) mRNA expression and mPRα protein expression in a panel of commonly used ovarian cancer cell lines. In contrast to mPR action in breast cancer cells, progesterone alone failed to induce changes in cyclic adenosine monophosphate (cAMP) levels in ovarian cancer cells. However, progesterone enhanced cAMP production by β(1,2)-adrenergic receptors and increased isoproterenol-induced transcription from a cAMP response element (CRE)-driven reporter gene. Independently of β-adrenergic signaling, we additionally observed activation of both JNK1/2 and p38 MAPK in response to progesterone alone. This finding was supported by the results of a screen for potential mPR gene targets. Progesterone induced a significant increase in transcription of the pro-apoptotic marker BAX, whose activity and expression has been linked to JNK1/2 and p38 signaling. Inhibitors of JNK, but not p38, blocked progesterone-induced BAX expression. Taken together, these observations implicate at least two distinct signaling pathways that may be utilized by mPRs in ovarian cancer cells that exhibit regulatory genomic changes. These studies on mPR signaling in ovarian cancer lay the foundation for future work aimed at understanding how progesterone exerts its anti-tumorigenic effects in the ovary and suggest that pharmacologic activation of mPRs, abundantly expressed in ovarian cancers, may provide a new treatment option for patients with advanced stage disease.

Antagonism of Human Adiponectin Receptors and Their Membrane Progesterone Receptor Paralogs by TNFα and a Ceramidase Inhibitor

The progestin and AdipoQ receptor (PAQR) family of proteins comprises three distinct structural classes, each with seemingly different agonist specificities. For example, Class I receptors, like the human adiponectin receptors (AdipoR1 and AdipoR2), sense proteins with a particular three-dimensional fold, while Class II receptors are nonclassical membrane receptors for the steroid hormone progesterone. Using a previously developed heterologous expression system to study PAQR receptor activity, we demonstrate that human PAQRs from all three classes are antagonized by both 1(S),2(R)-d-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol, a ceramidase inhibitor, and TNFalpha, a homologue of adiponectin that functions antagonistically to both adiponectin and progesterone in human cells.

Sphingolipids Function as Downstream Effectors of a Fungal PAQR

The Izh2p protein from Saccharomyces cerevisiae belongs to the newly characterized progestin and adipoQ receptor (PAQR) superfamily of receptors whose mechanism of signal transduction is still unknown. Izh2p functions as a receptor for the plant PR-5 defensin osmotin and has pleiotropic effects on cellular biochemistry. One example of this pleiotropy is the Izh2p-dependent repression of FET3, a gene involved in iron-uptake. Although the physiological purpose of FET3 repression by Izh2p is a matter of speculation, it provides a reporter with which to probe the mechanism of signal transduction by this novel class of receptor. Receptors in the PAQR family share sequence similarity with enzymes involved in ceramide metabolism, which led to the hypothesis that sphingolipids are involved in Izh2p-dependent signaling. In this study, we demonstrate that drugs affecting sphingolipid metabolism, such as d-erythro-MAPP and myriocin, inhibit the effect of Izh2p on FET3. We also show that Izh2p causes an increase in steady-state levels of sphingoid base. Moreover, we show that Izh2p-independent increases in sphingoid bases recapitulate the effect of Izh2p on FET3. Finally, our data indicate that the Pkh1p and Pkh2p sphingoid base-sensing kinases are essential components of the Izh2p-dependent signaling pathway. In conclusion, our data indicate that Izh2p produces sphingoid bases and that these bioactive lipids probably function as the second messenger responsible for the effect of Izh2p on FET3.

Pancreatic Expression and Mitochondrial Localization of the Progestin-AdipoQ Receptor PAQR10

Steroid hormones induce changes in gene expression by binding to intracellular receptors that then translocate to the nucleus. Steroids have also been shown to rapidly modify cell function by binding to surface membrane receptors. We identified a candidate steroid membrane receptor, the progestin and adipoQ receptor (PAQR) 10, a member of the PAQR family, in a screen for genes differentially expressed in mouse pancreatic beta-cells. PAQR10 gene expression was tissue restricted compared with other PAQRs. In the mouse embryonic pancreas, PAQR10 expression mirrored development of the endocrine lineage, with PAQR10 protein expression confined to endocrine islet-duct structures in the late embryo and neonate. In the adult mouse pancreas, PAQR10 was expressed exclusively in islet cells except for its reappearance in ducts of maternal islets during pregnancy. PAQR10 has a predicted molecular mass of 29 kDa, comprises seven transmembrane domains, and, like other PAQRs, is predicted to have an intracellular N-terminus and an extracellular C-terminus. In silico analysis indicated that three members of the PAQR family, PAQRs 9, 10, and 11, have a candidate mitochondrial localization signal (MLS) at the N-terminus. We showed that PAQR10 has a functional N-terminal MLS and that the native protein localizes to mitochondria. PAQR10 is structurally related to some bacterial hemolysins, pore-forming virulence factors that target mitochondria and regulate apoptosis. We propose that PAQR10 may act at the level of the mitochondrion to regulate pancreatic endocrine cell development/survival.

Heterologous expression of human mPRα, mPRβ and mPRγ in yeast confirms their ability to function as membrane progesterone receptors

The nuclear progesterone receptor (nPR) mediates many of the physiological effects of progesterone by regulating the expression of genes, however, progesterone also exerts non-transcriptional (non-genomic) effects that have been proposed to rely on a receptor that is distinct from nPR. Several members of the progestin and AdipoQ-Receptor (PAQR) family were recently identified as potential mediators of these non-genomic effects. Membranes from cells expressing these proteins, called mPRα, mPRβ and mPRγ, were shown to specifically bind progesterone and have G-protein coupled receptor (GPCR) characteristics, although other studies dispute these findings. To clarify the role of these mPRs in non-genomic progesterone signaling, we established an assay for PAQR functional evaluation using heterologous expression in Saccharomyces cerevisiae. Using this assay, we demonstrate unequivocally that mPRα, mPRβ and mPRγ can sense and respond to progesterone with EC 50 values that are physiologically relevant. Agonist profiles also show that mPRα, mPRβ and mPRγ are activated by ligands, such as 17α-hydroxyprogesterone, that are known to activate non-genomic pathways but not nPR. These results strongly suggest that these receptors may indeed function as the long-sought-after membrane progesterone receptors. Additionally, we show that two uncharacterized PAQRs, PAQR6 and PAQR9, are also capable of responding to progesterone. These mPR-like PAQRs have been renamed as mPRδ (PAQR6) and mPRɛ (PAQR9). Additional characterization of mPRγ and mPRα indicates that their progesterone-dependent signaling in yeast does not require heterotrimeric G-proteins, thus calling into question the characterization of the mPRs as a novel class of G-protein coupled receptor.

Laser catheter-induced atrioventricular nodal delays and atrioventricular block in dogs: Acute and chronic observations

Selective modification of atrioventricular (AV) nodal conduction, that is, induction of varying degrees of AV nodal delays or block (second or third degree), or both, was achieved with a pervenous laser catheter technique. In six adult mongrel dogs anesthetized with pentobarbital (Nembutal), 5F leads were placed through femoral and external jugular veins and placed into the right atrium and His bundle region. Through another femoral vein, a 200 micron optical fiber was inserted by way of a 7F catheter with a preformed curved tip. Guided by fluoroscopy and His bundle electrograms, the fiber's tip was positioned in the AV nodal region. After autonomic blockade was achieved with intravenous propranolol (5 mg) and atropine (1 mg), AV conduction was analyzed. An argon laser delivered 3 to 4 watts into the fiber in bursts of 10 seconds' duration until the desired degree of AV nodal delay or block (second or third degree) was manifested. Monitoring of His bundle electrograms was continued for 2 hours. Four weekly serial electrocardiograms were recorded, after which electrophysiologic studies were repeated. Acute post-lasing studies showed that: in all six dogs, the mean PR interval was prolonged from 116 ms (range 100 to 135) to 153 ms (range 120 to 185), with the prolongation being caused exclusively by AH lengthening from 68 ms (range 50 to 90) to 105 ms (range 65 to 140); the mean effective refractory period of the AV node increased from less than 185 ms (range less than 150 to less than 200) to 215 ms (range 190 to 280); and the mean atrial pacing cycle length, at which second degree AV nodal block was manifested, increased from 210 ms (range 160 to 260) to 261 ms (range 205 to 320).(ABSTRACT TRUNCATED AT 250 WORDS)