Type III cyclic nucleotide phosphodiesterases and insulin action

Citrullinated Histone H3: Early Biomarker of Neutrophil Extracellular Traps in Septic Liver Damage

BACKGROUND

Neutrophil extracellular traps (NETs) play a crucial role in host defense, but excess and prolonged interaction of NETs with platelets can cause severe inflammation and host organ damage. Modification of histone H3 by citrullination is involved in in vitro NET formation. The phosphodiesterase III inhibitor, cilostazol (Ciz), which has a protective effect on liver sinusoidal endothelial cells and inhibits platelet aggregation, may prevent organ damage caused by excess NETosis. In this study, we investigated whether citrullinated histone H3 (H3Cit) could serve as a biomarker for the detection of critical liver damage in sepsis and the efficacy of phosphodiesterase-III inhibition for preventing the liver dysfunction induced by NETosis.

MATERIALS AND METHODS

Mice injected with lipopolysaccharide (LPS; 1 mg/kg) were used as a sepsis model with or without treatment with Ciz (200 mg/kg). H3Cit, myeloperoxidase, and neutrophil elastase levels were measured by immunohistochemistry. We evaluated H3Cit-positive neutrophils in the peripheral blood by flow cytometry.

RESULTS

Immunohistochemistry revealed that H3Cit-, neutrophil elastase-, and myeloperoxidase-positive cell numbers in the livers peaked at 12 h after LPS administration. However, flow cytometry showed a significant increase in H3Cit-positive neutrophils in the peripheral blood only 4 h after LPS injection. Treatment with Ciz significantly ameliorated all parameters.

CONCLUSIONS

H3Cit is a useful biomarker for early detection of NETosis or liver dysfunction, and Ciz may be an effective treatment for septic liver damage.

Tryptophan depletion under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through reactive oxygen species-dependent and independent pathways

In atherosclerosis-associated pathologic entities characterized by malnutrition and inflammation, L-tryptophan (TRP) levels are low. Insulin resistance is an independent cardiovascular risk factor and induces endothelial dysfunction by increasing fatty acid oxidation. It is also associated with inflammation and low TRP levels. Low TRP levels have been related to worse cardiovascular outcome. This study evaluated the effect of TRP depletion on endothelial dysfunction under conditions that imitate insulin resistance. Fatty acid oxidation, harmful pathways due to increased fatty acid oxidation, and endothelial dysfunction were assessed in primary human aortic endothelial cells cultured under normal glucose, low insulin conditions in the presence or absence of TRP. TRP depletion activated general control non-derepressible 2 kinase and inhibited aryl hydrocarbon receptor. It increased fatty acid oxidation by increasing expression and activity of carnitine palmitoyltransferase 1. Elevated fatty acid oxidation increased the formation of reactive oxygen species (ROS) triggering the polyol and hexosamine pathways, and enhancing protein kinase C activity and methylglyoxal production. TRP absence inhibited nitric oxide synthase activity in a ROS-dependent way, whereas it increased the expression of ICAM-1 and VCAM-1 in a ROS independent and possibly p53-dependent manner. Thus, TRP depletion, an amino acid whose low levels have been related to worse cardiovascular outcome and to inflammatory atherosclerosis-associated pathologic entities, under conditions that imitate insulin resistance enhances fatty acid oxidation and induces endothelial dysfunction through ROS-dependent and independent pathways. These findings may offer new insights at the molecular mechanisms involved in accelerated atherosclerosis that frequently accompanies malnutrition and inflammation.

Anti-Obesity Effect of the CB2 Receptor Agonist JWH-015 in Diet-Induced Obese Mice

The cannabinoid receptor 2 (CB2) is well known for its immune modulatory role. However, recent localisation of CB2 receptors in metabolically active tissue suggests that the CB2 receptor plays a significant role in energy homeostasis. This study was designed to investigate the impact of chronic CB2 receptor stimulation on food intake, body weight and mood. Lean male C57BL/6 mice were injected i.p. with the selective CB2 receptor agonist, JWH-015 (0.0, 1.0, 5.0 and 10.0 mg kg-1) to establish dose response parameters. Mice made obese following exposure to a diet consisting of 19.4 MJ/kg (4641 Kcal/kg) of energy (19.0% protein, 21.0% total fat, 4.7% crude fiber, and 4.7% AD fiber were given either vehicle or 10 mg/kg JWH-015. Impact on mood, food intake, body weight, plasma metabolites, expression of key metabolic proteins in the brown adipose tissue (BAT) and white adipose tissue (WAT), and markers of inflammation were measured. High dose (10 mg/kg) JWH-015 reduced food intake after 1, 2, 4, and 24 h in lean mice. When given to diet induced obese (DIO) mice, a 10 mg/kg dose of JWH-015 significantly reduced body weight compared to vehicle. This dose led to a shift in markers of lipid metabolism and inflammation in WAT consistent with lipolysis and improved immune response. Furthermore, JWH-015 (10 mg/kg) produced a transient reduction in food intake and significant reduction in fat mass and adipocyte cell size. Importantly, JWH-015 produced an anxiolytic response in the elevated plus maze while having no effect on immobility time in the forced swim test. It should be noted that though the 10 mg/kg dose produced positive effects on the obese state, the possibility that these effects are mediated via non-CB2 receptor mechanisms cannot be ruled out. These results demonstrate a role for CB2 receptors in modulating energy homeostasis and obesity associated metabolic pathologies in the absence of any adverse impact on mood.

The effects of glucocorticoids on adipose tissue lipid metabolism

Glucocorticoids (GCs) have long been accepted as being catabolic in nature, liberating energy substrates during times of stress to supply the increased metabolic demand of the body. The effects of GCs on adipose tissue metabolism are conflicting, however, because patients with elevated GCs present with central adiposity. We performed an extensive literature review of the effects of GCs on adipose tissue metabolism. The contradictory effects of GCs on lipid metabolism occur through a number of different mechanisms, some of which are well defined and others remain to be elucidated. Firstly, through increases in caloric and dietary fat intake, along with increased hydrolysis of circulating triglycerides (chylomicrons, very low-density lipoproteins) by lipoprotein lipase activity, GCs increase the amount of fatty acids in circulation, which are then available for ectopic fat distribution (liver, muscle, and central adipocytes). Glucocorticoids also increase de novo lipid production in hepatocytes through increased expression of fatty acid synthase. There is some controversy as to whether these same mechanisms occur in adipocytes, thereby contributing to adipose hypertrophy. Glucocorticoids promote preadipocyte conversion to mature adipocytes, causing hyperplasia of the adipose tissue. Glucocorticoids also have acute antilipolytic effect on adipocytes, whereas their genomic actions facilitate increased lipolysis after about 48 hours of exposure. The acute and long-term effects of GCs on adipose tissue lipolysis remain unclear. Although considerable evidence supports the notion that GCs increase lipolysis through glucocorticoid-induced increases of lipase expression, they clearly have antilipolytic effects within these same tissues and cell line models.

Olprinone attenuates excessive shear stress through up-regulation of endothelial nitric oxide synthase in a rat excessive hepatectomy model

After extended hepatectomy, excessive shear stress in the remnant liver causes postoperative liver failure. Olprinone (OLP), a selective phosphodiesterase inhibitor, has been reported to improve microcirculation and attenuate inflammation. The aim of this study was to investigate the effects of OLP on shear stress in rats with an excessive hepatectomy (EHx) model. In this study, EHx comprised 90% hepatectomy with ligation of the left and right Glisson's sheaths in Lewis rats. OLP or saline was intraperitoneally administered with an osmotic pump 48 hours before EHx. To evaluate the shear stress, we measured the portal vein (PV) pressure. We also assessed sinusoidal endothelial cell injury by immunohistochemistry and electron microscopy. Furthermore, we assessed apoptosis in the liver with the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling method. Treatment with OLP up-regulated hepatic endothelial nitric oxide synthase (eNOS) expression. The increase in the PV pressure due to Glisson's sheath ligation was attenuated in OLP-treated rats during a 30-minute period after ligation. Treatment with OLP preserved sinusoidal endothelial cells and reduced apoptosis in the remnant liver. The probability of survival in the OLP-treated rats was significantly better than that in the controls (33.3% versus 13.3%). Furthermore, the postoperative eNOS activity in the OLP-treated rats was higher than that in the controls. The administration of Nω-nitro-l-arginine methyl ester to OLP-treated rats eliminated the effects of OLP on PV pressure and survival after EHx. Therefore, we concluded that OLP attenuates excessive shear stress through the up-regulation of eNOS and improves the survival rate after EHx.

Cellulite: Is there a role for injectables?

BACKGROUND

Cellulite describes the cutaneous dimpling of the thighs, buttocks, and hips that is seen predominately in women. Current evidence suggests that structural differences in fat architecture between the sexes account for its appearance. Mesotherapy, a method of delivering medication locally with the use of numerous cutaneous injections, has recently become a popular method to purportedly treat the condition.

METHODS

An overview of cellulite and adipocyte physiology, with a literature review and appraisal of compounds commonly used in mesotherapy.

RESULTS

Experimental studies using individual mesotherapy ingredients for other conditions suggest a number of mechanisms, including lipolysis, disrupting connective tissue and augmenting circulation, which may theoretically improve cellulite. Peer-reviewed studies have not evaluated whether these effects translate clinically.

CONCLUSIONS

Until further studies are performed, patients considering mesotherapy for cellulite must be aware that the substances currently being injected to treat this cosmetically disturbing, but medically benign, condition have not been thoroughly evaluated for safety or efficacy.

Insulin resistance reduces arterial prostacyclin synthase and eNOS activities by increasing endothelial fatty acid oxidation

Insulin resistance markedly increases cardiovascular disease risk in people with normal glucose tolerance, even after adjustment for known risk factors such as LDL, triglycerides, HDL, and systolic blood pressure. In this report, we show that increased oxidation of FFAs in aortic endothelial cells without added insulin causes increased production of superoxide by the mitochondrial electron transport chain. FFA-induced overproduction of superoxide activated a variety of proinflammatory signals previously implicated in hyperglycemia-induced vascular damage and inactivated 2 important antiatherogenic enzymes, prostacyclin synthase and eNOS. In 2 nondiabetic rodent models--insulin-resistant, obese Zucker (fa/fa) rats and high-fat diet-induced insulin-resistant mice--inactivation of prostacyclin synthase and eNOS was prevented by inhibition of FFA release from adipose tissue; by inhibition of the rate-limiting enzyme for fatty acid oxidation in mitochondria, carnitine palmitoyltransferase I; and by reduction of superoxide levels. These studies identify what we believe to be a novel mechanism contributing to the accelerated atherogenesis and increased cardiovascular disease risk occurring in people with insulin resistance.

An insulin-response element-binding protein that ameliorates hyperglycemia in diabetes

Insulin modulates glucose homeostasis, but the role of insulin-responsive transcription factors in such actions is not well understood. Recently, we have identified the insulin-response element-binding protein-1 (IRE-BP1) as a transcription factor that appears to mediate insulin action on multiple target genes. To examine the possibility that IRE-BP1 is an insulin-responsive glucoregulatory factor involved in the metabolic actions of insulin, we investigated the effect of adenoviral overexpression of hepatic IRE-BP1 on the glycemic control of insulin-resistant diabetic rats. Adenoviral IRE-BP1 lowered both fasting and postprandial glucose levels, and microarray of hepatic RNA revealed modulation of the expression of genes involved in gluconeogenesis, lipogenesis, and fatty acid oxidation. The insulin mimetic effects of IRE-BP1 were also confirmed in L6 myocytes; stable constitutive expressions of IRE-BP1 enhanced glucose transporter expression, glucose uptake, and glycogen accumulation in these cells. These findings showed physiologic sufficiency of IRE-BP1 as the transcriptional mediator of the metabolic action of insulin. Understanding IRE-BP1 action should constitute a useful probe into the mechanisms of metabolic regulation and an important target to develop therapeutic agents that mimic or enhance insulin action.

Leptin signaling in the hypothalamus: emphasis on energy homeostasis and leptin resistance

Leptin, the long-sought satiety factor of adipocytes origin, has emerged as one of the major signals that relay the status of fat stores to the hypothalamus and plays a significant role in energy homeostasis. Understanding the mechanisms of leptin signaling in the hypothalamus during normal and pathological conditions, such as obesity, has been the subject of intensive research during the last decade. It is now established that leptin action in the hypothalamus in regulation of food intake and body weight is mediated by a neural circuitry comprising of orexigenic and anorectic signals, including NPY, MCH, galanin, orexin, GALP, alpha-MSH, NT, and CRH. In addition to the conventional JAK2-STAT3 pathway, it has become evident that PI3K-PDE3B-cAMP pathway plays a critical role in leptin signaling in the hypothalamus. It is now established that central leptin resistance contributes to the development of diet-induced obesity and ageing associated obesity. Central leptin resistance also occurs due to hyperleptinimia produced by exogenous leptin infusion. A defective nutritional regulation of leptin receptor gene expression and reduced STAT3 signaling may be involved in the development of leptin resistance in DIO. However, leptin resistance in the hypothalamic neurons may occur despite an intact JAK2-STAT3 pathway of leptin signaling. Thus, in addition to defective JAK2-STAT3 pathway, defects in other leptin signaling pathways may be involved in leptin resistance. We hypothesize that defective regulation of PI3K-PDE3B-cAMP pathway may be one of the mechanisms behind the development of central leptin resistance seen in obesity.

Phosphodiesterase 3B gene expression is enhanced in the liver but reduced in the adipose tissue of obese insulin resistant db/db mouse

Phosphodiesterase (PDE) 3B, when activated by insulin, causes a decrease in intracellular cAMP concentration. The activation of this enzyme results in the reduced output of free fatty acids (FFA) from adipocytes, and an increased lipogenesis in liver. We have recently shown that PDE3B gene expression is reduced in adipose tissues of KKAy mice. We intend to further elucidate the regulation of PDE3B in liver as well as adipose tissues in relation to the insulin resistant state. We examined PDE3B gene expression in liver and adipose tissues of obese, insulin-resistant diabetic db/db mice and also checked the effect of an insulin-sensitizing drug, troglitazone, on this gene expression. In the liver of db/db mice, PDE3B mRNA, its corresponding protein, and the associated catalytic activity were all increased by 2.1, 1.9 and 1.6-fold, respectively, over those in db/+ control mice. Histological examination revealed substantial triglyceride storage in the liver of db/db mice. Conversely, in the adipose tissue of db/db mice, PDE3B mRNA, protein, and its associated activity were all decreased by 0.38, 0.33 and 0.36-fold, respectively. Troglitazone, which has no effect on PDE3B in liver, increased the expression of this gene in adipocytes. This increase is associated with a reduction in the elevated levels of serum insulin, glucose, FFA and triglycerides. The reduced PDE3B gene expression in adipose tissues, which results in the elevation of serum FFA, could be the primary event in the development of insulin resistance in db/db mice. The enhanced PDE3B gene expression may correlate with changes in triglyceride storage in the liver of these mice.

Hepatothermic therapy of obesity: rationale and an inventory of resources

Hepatothermic therapy (HT) of obesity is rooted in the observation that the liver has substantial capacities for both fatty acid oxidation and for thermogenesis. When hepatic fatty acid oxidation is optimized, the newly available free energy may be able to drive hepatic thermogenesis, such that respiratory quotient declines while basal metabolic rate increases, a circumstance evidently favorable for fat loss. Effective implementation of HT may require activation of carnitine palmitoyl transferase-1 (rate-limiting for fatty acid beta-oxidation), an increase in mitochondrial oxaloacetate production (required for optimal Krebs cycle activity), and up-regulation of hepatic thermogenic pathways. The possible utility of various natural agents and drugs for achieving these objectives is discussed. Potential components of HT regimens include EPA-rich fish oil, sesamin, hydroxycitrate, pantethine, L-carnitine, pyruvate, aspartate, chromium, coenzyme Q10, green tea polyphenols, conjugated linoleic acids, DHEA derivatives, cilostazol, diazoxide, and fibrate drugs. Aerobic exercise training and very-low-fat, low-glycemic-index, high-protein or vegan food choices may help to establish the hormonal environment conducive to effective HT. High-dose biotin and/or metformin may help to prevent an excessive increase in hepatic glucose output. Since many of the agents contemplated as components of HT regimens are nutritional or food-derived compounds likely to be health protective, HT is envisioned as an on-going lifestyle rather than as a temporary 'quick fix'. Initial clinical efforts to evaluate the potential of HT are now in progress.

Insulin and heregulin-beta1 upregulate guanylyl cyclase C expression in rat hepatocytes: reversal by phosphodiesterase-3 inhibition

Guanylyl cyclase C (GC-C) is the receptor for the hormones guanylin and uroguanylin. Although primarily expressed in the rat intestine, GC-C is also expressed in the liver during neonatal or regenerative growth or during the acute phase response. Little is known about the hepatic regulation of GC-C expression. The influence of various hepatic growth or acute phase regulators on GC-C expression was evaluated by immunoblot analysis of protein from primary rat hepatocytes grown in a serum-free medium. Insulin and heregulin-beta1 strongly stimulated GC-C expression by 24 h of cell culture. Several different hormones and agents suppressed this action, including transforming growth factor beta (TGF-beta), as well as inhibitors of phosphatidylinositol 3-kinase (PI-3-kinase) and phosphodiesterase 3 (PDE-3, an insulin- and PI-3-kinase-dependent enzyme). The compartmental downregulation of cAMP levels by PDE-3 may be a critical step in the hormonal action that culminates in GC-C synthesis.

Antiplatelet agent cilostazol potentiates adipocyte differentiation of 3T3-L1 cells

Cilostazol is an antiplatelet drug, which has beneficial effects in treatment of intermittent claudication and decreases serum triacyiglycerol level in these patients. In this study, we examined adipogenic potency of cilostazol using 3T3-L1 preadipocyte cell line because cilostazol is one of the tissue specific phosphodiesterase (PDE) inhibitors. Addition of cilostazol into the differentiation medium including insulin and dexamethasone, induced the adipocyte differentiation without isobutyl methylxanthine (IBMX). Compared with the cells incubated with vehicle, the cells treated with cilostazol contain much more lipid droplets in the cells 6 days after induction of differentiation. Adipocyte specific gene like stearoyl-CoA desaturase was strongly induced after addition of cilostazol. C/EBPbeta, which is induced by IBMX was also induced by cilostazol. These findings suggest a possibility that adipogenic effect of cilostazol is one of the mechanisms, by which this agent decreases blood triacylglycerol level in the intermittent claudication patients.

Molecular pathways of cyclic nucleotide-induced inhibition of arterial smooth muscle cell proliferation

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are second messengers involved in the intracellular signal transduction of a wide variety of extracellular stimuli. These signals regulate many biological processes including cell proliferation, differentiation, migration, and apoptosis. Recently, significant progress has been achieved in the molecular basis underlying cyclic nucleotide regulation of cell proliferation. This review summarizes our knowledge of the signaling pathways regulated by cyclic nucleotides in arterial smooth muscle cells.

Cyclic nucleotide phosphodiesterases: relating structure and function

Cyclic nucleotide phosphodiesterases (PDEs) comprise a superfamily of metallophosphohydrolases that specifically cleave the 3',5'-cyclic phosphate moiety of cAMP and/or cGMP to produce the corresponding 5'-nucleotide. PDEs are critical determinants for modulation of cellular levels of cAMP and/or cGMP by many stimuli. Eleven families of PDEs with varying selectivities for cAMP or cGMP have been identified in mammalian tissues. Within these families, multiple isoforms are expressed either as products of different genes or as products of the same gene through alternative splicing. Regulation of PDEs is important for controlling myriad physiological functions, including the visual response, smooth muscle relaxation, platelet aggregation, fluid homeostasis, immune responses, and cardiac contractility. PDEs are critically involved in feedback control of cellular cAMP and cGMP levels. Activities of the various PDEs are highly regulated by a panoply of processes, including phosphorylation events, interaction with small molecules such as cGMP or phosphatidic acid, subcellular localization, and association with specific protein partners. The PDE superfamily continues to be a major target for pharmacological intervention in a number of medically important maladies.

Leptin induces insulin-like signaling that antagonizes cAMP elevation by glucagon in hepatocytes

Although many effects of leptin are mediated through the central nervous system, leptin can regulate metabolism through a direct action on peripheral tissues, such as fat and liver. We show here that leptin, at physiological concentrations, acts through an intracellular signaling pathway similar to that activated by insulin in isolated primary rat hepatocytes. This pathway involves stimulation of phosphatidylinositol 3-kinase (PI3K) binding to insulin receptor substrate-1 and insulin receptor substrate-2, activation of PI3K and protein kinase B (AKT), and PI3K-dependent activation of cyclic nucleotide phosphodiesterase 3B, a cAMP-degrading enzyme. One important function of this signaling pathway is to reduce levels of cAMP, because leptin-mediated activation of both protein kinase B and phosphodiesterase 3B is most marked following elevation of cAMP by glucagon, and because leptin suppresses glucagon-induced cAMP elevation in a PI3K-dependent manner. There is little or no expression of the long form leptin receptor in primary rat hepatocytes, and these signaling events are probably mediated through the short forms of the leptin receptor. Thus, leptin, like insulin, induces an intracellular signaling pathway in hepatocytes that culminates in cAMP degradation and an antagonism of the actions of glucagon.

Cardiac type cGMP-inhibited phosphodiesterase (PDE3A) gene structure: similarity and difference to adipocyte type PDE3B gene

Phosphodiesterase type 3 isoforms, PDE3A and 3B, are expressed primarily in cardiovascular and adipose tissues, respectively. We previously reported a shorter transcript of 4.4-kb PDE3A which is predominantly transcribed in human placenta, whereas a full-length 7. 6-kb transcript corresponding to the cardiac PDE3A cDNA has not been characterized. Due to unfortunate circumstances created by changes in PDE3 nomenclature, PDE3B gene structure previously reported used PDE3A in its title. Here, we describe PDE3A gene structure, which comprises 16 exons spanning over 130 kb on chromosome 12p12. Two PDE3 isoforms share similar gene organization, but localize to different chromosomes. The most distal transcription initiation site of the PDE3A gene is approximately 1071 bases upstream of the ATG site, suggesting that exon 1 consists of 1071 and 960 bp of untranslated and translated sequences, respectively. The proximal 5'-flanking region, which does not contain TATA-like sequences, exhibited weak but significant promoter activity. Results suggest potential involvement of distal promoter/enhancer and translational regulation for expression of the 7.6-kb transcript.

On the control of lipolysis in adipocytes

The lipolytic reaction in adipocytes is one of the most important reactions in the management of bodily energy reserves, and dysregulation of this reaction may contribute to the symptoms of Type 2 diabetes mellitus. Yet, progress on resolving the molecular details of this reaction has been relatively slow. However, recent developments at the molecular level begin to paint a clearer picture of lipolysis and point to a number of unanswered questions. While HSL has long been known to be the rate-limiting enzyme of lipolysis, the mechanism by which HSL attacks the droplet lipids is not yet firmly established. Certainly, the immunocytochemical evidence showing the movement of HSL to the lipid droplet upon stimulation leaves little doubt that this translocation is a key aspect of the lipolytic reaction, but whether or not HSL phosphorylation contributes to the translocation, and at which site(s), is as yet unresolved. It will be important to establish whether there is an activation step in addition to the translocation reaction. The participation of perilipin A is indicated by the findings that this protein can protect neutral lipids within droplets from hydrolysis, but active participation in the lipolytic reaction is yet to be proved. Again, it will be important to determine whether mutations of serine residues of PKA phosphorylation sites of perilipins prevent lipolysis, and whether such modifications abolish the physical changes in the droplet surfaces that accompany lipolysis.

Cyclic nucleotide PDE-3. Quantitation of PDE-3A and -3B mRNAs in rat tissues by RNase protection assay

Type 3 cyclic nucleotide phosphodiesterase (PDE-3) isoforms exhibit a high affinity ("low K(m)") for cAMP and are specifically inhibited by cGMP and a number of pharmacological agents, which increase myocardial contractility, inhibit platelet aggregation, and increase smooth muscle relaxation. The PDE-3 family consists of at least two isozymes, PDE-3A (cardiac type) and PDE-3B (adipocyte type), with distinct tissue-specific distributions. PDE-3A mRNA is highly expressed in the cardiovascular system, whereas PDE-3B mRNA is primarily expressed in adipocytes and hepatocytes. Toward understanding potential roles of PDE-3 in diabetes mellitus, we have established a specific and sensitive RNase protection assay (RPA) for quantitating PDE-3A and PDE-3B mRNA in rat diabetic models. In fatty Zucker diabetic (ZDF) rats, PDE-3A mRNA, but not PDE-3B mRNA, was expressed in heart, whereas liver and white and brown fat tissues predominantly expressed PDE-3B mRNA. Unexpectedly, PDE-3B mRNA expression was approximately 2.5 times higher than PDE-3A mRNA in aorta from both ZDF and Sprague-Dawley (SD) rats. In contrast, expression levels of PDE-3A mRNA in heart were similar in both species. With this RPA, we were thus able to compare PDE-3A and -3B mRNA levels in different tissues as well as in different rat species.