Soil greenhouse gas emissions from drained and rewetted agricultural bare peat mesocosms are linked to geochemistry.

In view of climate considerations regarding the management of peatlands, there is a need to assess whether rewetting can mitigate greenhouse gas (GHG) emissions, and notably how site-specific soil-geochemistry will influence differences in emission magnitudes. However, there are inconsistent results regarding the correlation of soil properties with heterotrophic respiration (Rh) of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from bare peat. In this study, we determined 1) soil-, and site-specific geochemical components as drivers for emissions from Rh on five Danish fens and bogs, and 2) emission magnitudes under drained and rewetted conditions. For this, a mesocosm experiment was performed under equal exposure to climatic conditions and water table depths controlled to either -40 cm, or -5 cm. For the drained soils, we found that annual cumulative emissions, accounting for all three gases, were dominated by CO2, contributing with, on average, 99 % to a varying global warming potential (GWP) of 12.2-16.9 t CO2eq ha-1 yr-1. Rewetting lowered annual cumulative emissions from Rh by 3.2-5.1 t CO2eq ha-1 yr-1 for fens and bogs, respectively, despite a high variability of site-specific CH4 emissions, contributing with 0.3-3.4 t CO2 ha-1 yr-1 to the GWP. Overall, analyses using generalized additive models (GAM) showed that emission magnitudes were well explained by geochemical variables. Under drained conditions, significant soil-specific predictor variables for CO2 flux magnitudes were pH, phosphorus (P), and the soil substrate's relative water holding capacity (WHC). When rewetted, CO2 and CH4 emissions from Rh were affected by pH, WHC, as well as contents of P, total carbon and nitrogen. In conclusion, our results found the highest GHG reduction on fen peatlands, further highlighting that peat nutrient status and acidity, and the potential availability of alternative electron acceptors, might be used as proxies for prioritising peatland areas for GHG mitigation efforts by rewetting.

Antibacterial isoeugenol coating on stainless steel and polyethylene surfaces prevents biofilm growth.

AIMS: Pathogenic bacteria can spread between individuals or between food items via the surfaces they share. Limiting the survival of pathogens on surfaces, therefore, presents an opportunity to limit at least one route of how pathogens spread. In this study, we propose that a simple coating with the essential oil isoeugenol can be used to circumvent the problem of bacterial transfer via surfaces. METHODS AND RESULTS: Two commonly used materials, stainless steel and polyethylene, were coated by physical adsorption, and the coatings were characterized by Raman spectroscopy, atomic force microscopy and water contact angle measurements. We quantified and visualized the colonization of coated and uncoated surfaces by three bacteria: Staphylococcus aureus, Listeria monocytogenes and Pseudomonas fluorescens. No viable cells were detected on surfaces coated with isoeugenol. CONCLUSIONS: The isoeugenol coating prepared with simple adsorption proved effective in preventing biofilm formation on stainless steel and polyethylene surfaces. The result was caused by the antibacterial effect of isoeugenol, as the coating did not diminish the adhesive properties of the surface. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study demonstrates that a simple isoeugenol coating can prevent biofilm formation of S. aureus, L. monocytogenes and P. fluorescens on two commonly used surfaces.

Ovarian features in white-tailed deer (Odocoileus virginianus) fawns and does.

The knowledge about ovarian reserve is essential to determine the reproductive potential and to improve the methods of fertility control for overpopulated species, such as white-tailed deer (Odocoileus virginianus). The goal of this study was to evaluate the effect of age on the female reproductive tract of white-tailed deer, focusing on ovarian features. Genital tracts from 8 prepubertal and 10 pubertal females were used to characterize the preantral follicle population and density, morphology, distribution of follicular classes; stromal cell density; and apoptosis in the ovary. In addition, uterus and ovary weights and dimensions were recorded; and the number and the size of antral follicles and corpus luteum in the ovary were quantified. Overall, fawns had a greater (P < 0.05) preantral follicle population, percentage of normal follicles, and preantral follicle density than does. The mean stromal cell density in ovaries of fawns and does differed among animals but not between age groups. The apoptotic signaling did not differ (P > 0.05) between the ovaries of fawns and does. However, apoptotic ovarian cells negatively (P < 0.001) affected the preantral follicle morphology and density, and conversely, a positive correlation was observed with stromal cell density. As expected, the uteri and ovaries were larger (P < 0.002) and heavier (P < 0.001) in does than in fawns. In conclusion, this study has shown, for the first time, the preantral follicle population and distribution of classes, rate of morphologically normal follicles, and density of preantral follicles and stromal cells in white- tailed deer. Therefore, the findings herein described lead to a better understanding of the white-tailed deer ovarian biology, facilitating the development of new methods of fertility control.

Defining the role of corticotropin releasing factor binding protein in alcohol consumption.

The corticotropin releasing factor (CRF) exerts its effects by acting on its receptors and on the binding protein (CRFBP), and has been implicated in alcohol use disorder (AUD). Therefore, identification of the exact contribution of each protein that mediates CRF effects is necessary to design effective therapeutic strategies for AUD. A series of in vitro/in vivo experiments across different species were performed to define the biological discrete role of CRFBP in AUD. First, to establish the CRFBP role in receptor signaling, we developed a novel chimeric cell-based assay and showed that CFRBP full length can stably be expressed on the plasma membrane. We discovered that only CRFBP(10 kD) fragment is able to potentiate CRF-intracellular Ca2+ release. We provide evidence that CRHBP gene loss increased ethanol consumption in mice. Then, we demonstrate that selective reduction of CRHBP expression in the center nucleus of the amygdala (CeA) decreases ethanol consumption in ethanol-dependent rats. CRFBP amygdalar downregulation, however, does not attenuate yohimbine-induced ethanol self-administration. This effect was associated with decreased hemodynamic brain activity in the CRFBP-downregulated CeA and increased hemodynamic activity in the caudate putamen during yohimbine administration. Finally, in alcohol-dependent patients, genetic variants related to the CRFBP(10 kD) fragment were associated with greater risk for alcoholism and anxiety, while other genetic variants were associated with reduced risk for anxiety. Taken together, our data provide evidence that CRFBP may possess both inhibitory and excitatory roles and may represent a novel pharmacological target for the treatment of AUD.

A 158 fs 5.3 nJ fiber-laser system at 1 microm using photonic bandgap fibers for dispersion control and pulse compression.

We demonstrate a 158 fs 5.3 nJ mode-locked laser system based on a fiber oscillator, fiber amplifier and fiber compressor. Dispersion compensation in the fiber oscillator was obtained with a solid-core photonic bandgap (SC-PBG) fiber spliced to standard fibers, and external compression is obtained with a hollow-core photonic bandgap (HC-PBG) fiber.

The epsilon isoform of protein kinase C is involved in regulation of the LTD(4)-induced calcium signal in human intestinal epithelial cells.

We investigated the potential roles of specific isoforms of protein kinase C (PKC) in the regulation of leukotriene D(4)-induced Ca(2+) signaling in the intestinal epithelial cell line Int 407. RT-PCR and Western blot analysis revealed that these cells express the PKC isoforms alpha, betaII, delta, epsilon, zeta, and mu, but not betaI, gamma, eta, or theta;. The inflammatory mediator leukotriene D(4) (LTD(4)) caused the TPA-sensitive PKC isoforms alpha, delta, and epsilon, but not betaII, to rapidly translocate to a membrane-enriched fraction. The PKC inhibitor GF109203X at 30 microM but not 2 microM significantly impaired the LTD(4)-induced Ca(2+) signal, indicating that the response involves a novel PKC isoform, such as delta or epsilon, but not alpha. LTD(4)-induced Ca(2+) signaling was significantly suppressed in cells pretreated with TPA for 15 min and was abolished when the pretreatment was prolonged to 2 h. Immunoblot analysis revealed that the reduction in the LTD(4)-induced calcium signal coincided with a reduction in the cellular content of PKCepsilon and, to a limited extent, PKCdelta. LTD(4)-induced Ca(2+) signaling was also markedly suppressed by microinjection of antibodies against PKCepsilon but not PKCdelta. These data suggest that PKCepsilon plays a unique role in regulation of the LTD(4)-dependent Ca(2+) signal in intestinal epithelial cells.

Incomplete, asymmetric, and route-dependent cross-tolerance between oxycodone and morphine in the Dark Agouti rat.

Our previous studies indicate that oxycodone is a putative kappa-opioid agonist, whereas morphine is a well documented micro-opioid agonist. Because there is limited information regarding the development of tolerance to oxycodone, this study was designed to 1) document the development of tolerance to the antinociceptive effects of chronically infused i.v. oxycodone relative to that for i. v. morphine and 2) quantify the degree of antinociceptive cross-tolerance between morphine and oxycodone in adult male Dark Agouti (DA) rats. Antinociceptive testing was performed using the tail-flick latency test. Complete antinociceptive tolerance was achieved in 48 to 84 h after chronic infusion of equi-antinociceptive doses of i.v. oxycodone (2.5 mg/24 h and 5 mg/24 h) and i.v. morphine (10 mg/24 h and 20 mg/24 h, respectively). Dose-response curves for bolus doses of i.v. and i.c.v. morphine and oxycodone were produced in naive, morphine-tolerant, and oxycodone-tolerant rats. Consistent with our previous findings that oxycodone and morphine produce their intrinsic antinociceptive effects through distinctly different opioid receptor populations, there was no discernible cross-tolerance when i.c.v. oxycodone was given to morphine-tolerant rats. Similarly, only a low degree of cross-tolerance (approximately 24%) was observed after i.v. oxycodone administration to morphine-tolerant rats. By contrast, both i.v. and i.c.v. morphine showed a high degree of cross-tolerance (approximately 71% and approximately 54%, respectively) in rats rendered tolerant to oxycodone. Taken together, these findings suggest that, after parenteral but not supraspinal administration, oxycodone is metabolized to a mu-opioid agonist metabolite, thereby explaining asymmetric and incomplete cross-tolerance between oxycodone and morphine.

Systemic coadministration of chloramphenicol with intravenous but not intracerebroventricular morphine markedly increases morphine antinociception and delays development of antinociceptive tolerance in rats.

Chloramphenicol, an in vitro inhibitor of the glucuronidation of morphine to its putative antianalgesic metabolite, morphine-3-glucuronide (M3G), was coadministered with morphine in adult male Sprague-Dawley rats to determine whether it inhibited the in vivo metabolism of morphine to M3G, thereby enhancing morphine antinociception and/or delaying the development of antinociceptive tolerance. Parenteral chloramphenicol was given acutely (3-h studies) or chronically (48-h studies). Morphine was administered by the i.v. or i.c.v. route. Control rats received chloramphenicol and/or vehicle. Antinociception was quantified using the hotplate latency test. Coadministration of chloramphenicol with i.v. but not i.cv. morphine increased the extent and duration of morphine antinociception by approximately 5.5-fold relative to rats that received i.v. morphine alone. Thus, the mechanism through which chloramphenicol enhances i.v. morphine antinociception in the rat does not directly involve supraspinal opioid receptors. Acutely, parenteral coadministration of chloramphenicol and morphine resulted in an approximately 75% increase in the mean area under the serum morphine concentration-time curve but for chronic dosing there was no significant change in this curve, indicating that factors other than morphine concentrations contribute significantly to antinociception. Antinociceptive tolerance to morphine developed more slowly in rats coadministered chloramphenicol, consistent with our proposal that in vivo inhibition of M3G formation would result in increased antinociception and delayed development of tolerance. However, our data also indicate that chloramphenicol inhibited the biliary secretion of M3G. Whether chloramphenicol altered the passage of M3G and morphine across the blood-brain barrier remains to be investigated.

Intracranial self-stimulation and sucrose intake differ as hedonic measures following chronic mild stress: interstrain and interindividual differences.

The present study was designed to assess the utility of sucrose intake and intracranial self-stimulation (ICSS) as hedonic measures for chronic mild stress (CMS) induced behavioural deficits. Wistar and PVG hooded rats were exposed to a variety of mild stressors, e.g. periods of food and/or water deprivation, soiled cage, light/dark reversal, confinement to small cages and pairing, during 6-9 weeks. The intake of 1% sucrose solution was significantly reduced in stressed PVG hooded rats compared to control animals. The sucrose intake in stressed Wistar rats remained unaltered, indicating that CMS-induced decreases in sucrose intake are strain dependent. However, sucrose intake has in our experience been shown to be unreliable as the observed decreases following CMS were inconsistent over time. ICSS behaviour was evaluated from rate/frequency functions by determining the frequency that supported 50% of maximal response rate. Neither the Wistar nor the PVG hooded rats showed an overall decrease in ICSS behaviour following CMS. However, the ICSS measures revealed interindividual differences in both rat strains. In the stress groups a subgroup (14 +/- 2.4%) of rats progressively exhibited an attenuated ICSS behaviour. These findings may reflect the interindividual variability observed in humans as stress does not invariably lead to depression. The model may in its present form be used to study the pathophysiology of depressive disorders. However, the utility of the CMS model to study antidepressant drug actions has to be questioned. Our results show there is a need for rat strains in which there is a greater sensitivity for detecting stress effects. It emphasises the fact that replication of CMS-induced decreases in ICSS behaviour can be as problematic as inducing decreases in sucrose intake.

Head and whole-body jerking in guinea pigs are differentially modulated by 5-HT1A, 5-HT1B/1D and 5-HT2A receptor antagonists.

The present study examined the role of 5-hydroxytryptamine 5-HT receptor subtypes on 5-hydroxytryptamine- (5-HT-) mediated myoclonus in guinea pigs, evaluating head and whole-body jerking as two distinct behavioural responses. Myoclonus was induced by the 5-HT precursor L-5-hydroxytryptophan (L-5-HTP) and the non-selective 5-HT1A/1B/5-HT2 receptor agonist 5-methoxy-N,N-dimethyl-tryptamine (5-MeODMT). The selective 5-HT1A receptor antagonist WAY100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cycloh exanecarboxamide trihydrochloride) inhibited both head and whole-body jerking. The selective 5-HT1B/1D receptor antagonist GR127935 (N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1 ,2,4-oxadiazol-3-yl)[1,1'-biphenyl]-4-carboxamide hemifumarate) only inhibited whole-body jerking, which resulted in unmasked head jerking. Co-administration of GR127935 and the selective 5-HT2A receptor antagonist MDL100.151 ((+/-)-alpha-(2,3-dimethoxyphenyl)-1-[-2-(4-fluorphenyl)ethyl]-4-+ ++piperidinmethanol) caused a complete inhibition of whole-body as well as head jerking. MDL100.151 had only limited effect on myoclonic jerking when given alone. The inhibitory effects of the 5-HT receptor antagonists on either L-5-HTP- or 5-MeODMT-induced myoclonus were found to be very similar. These data confirm a role for the 5-HT1A and 5-HT1B/1D receptors and suggest a role for 5-HT2A receptors in mediating myoclonus in guinea pigs. Moreover, the study shows that by considering head and whole-body jerking as two pharmacologically distinct behavioural responses, subtype specific 5-HT1A, 5-HT1B/1D and 5-HT2A receptor antagonists can be distinguished.

Discovery of OT4003, a novel, potent, and orally active cys-LT1 receptor antagonist.

The present paper describes the structural modifications leading to the discovery of a new series of quinoline-containing cys-LT1 receptor (LTD4 receptor) antagonists. A structural optimization with respect to the in vitro receptor binding, the in vivo brochoconstriction, and the toxicological effect in the form of peroxisomal proliferation was performed in order to achieve the target compound OT4003. OT4003 ((S)-(+)-E-2-(3-(2-(7- chloroquinolin-2-yl)ethenyl)phenylaminomethyl)-phenoxyl++ +-hexanoic acid) was found to be a potent and selective inhibitor of [3H]LTD4 specific binding to guinea pig lung membranes (IC50 2.4 +/- 1.0 nM), and also a potent, orally active, antagonist of LTD4 induced bronchoconstriction in guinea pigs [ED50 0.14 (ED16 0.1-ED84 0.4) mg/kg; 4 h pretreatment]. The enantiomerically pure OT4003 was prepared using a short convergent synthesis, including an enzymatic resolution step.

Detection of infectious bursal disease viruses in commercially reared chickens using the reverse transcriptase/polymerase chain reaction-restriction endonuclease assay.

Bursa samples from the United States, Mexico, and Puerto Rico were tested for the presence of infectious bursal disease virus (IBDV) using the reverse transcriptase/polymerase chain reaction-restriction endonuclease (RT/PCR-RE) assay. This assay amplifies a 394-bp fragment of the IBDV VP2 gene. A total of 151 samples were tested. Each was from a different physical location or farm. Forty-eight of the samples were determined to contain IBDV using RT/PCR. The RE profiles on 44 of these positive samples were determined using the enzymes BstNI or EcoRII, StyI, DraI, SacI, Sau3AI or MboI, and TaqI. A majority of the samples (34) had RE profiles typical of variant IBDV strains. One of six samples from Mexico was positive for IBDV. This virus had an RE profile typical of variant strains of IBDV. Three of seven samples from Puerto Rico had RE profiles characteristic of variant viruses. Two samples from the United States had RE profiles characteristic of classic vaccine IBDV strains and nine samples had new RE profiles. Five of these new profiles were BstNI- and StyI-negative, indicating that these viruses may be antigenically related to variant types. Although the new RE pattern observed in the other four samples was BstNI- and StyI-positive, it was not typical of classic vaccine IBDV strains. One flock from the United States had a mixture of two RE profiles, a typical variant type profile and an unknown variant RE profile. Two-thirds of the positive samples from flocks where the age of the birds was reported were observed between 21 and 28 days of age. The results of these studies demonstrate that the RT/PCR-RE assay can be used to diagnose IBDV in chickens and that IBDV strains exist in commercially reared chickens that have RE patterns different than known IBDV strains. The molecular differences observed using the RT/PCR-RE test were in a region of the VP2 gene, which is known to code for important neutralizing epitopes and to be highly variable among IBDV strains. Although the results demonstrate RE patterns different than those observed in known classic and variant IBDV strains, the influence of these molecular differences on biological properties of the viruses requires further investigation.

Antigenicity, pathogenicity, and immunogenicity of small and large plaque infectious bursal disease virus clones.

A serotype 1 variant strain of infectious bursal disease virus designated IN was passaged 40 times in BGM-70 cell line. A small plaque (SP) clone and a large plaque (LP) clone were then isolated and plaque purified four times. The SP and LP viruses formed circular plaques about 0.5 mm and 6.0 mm in diameter, respectively. Both clones lost their pathogenicity for specific-pathogen-free (SPF) chickens and did not elicit significant levels of virus-neutralizing antibody titers. However, the SP and LP clones maintained their immunogenicity when used as inactivated vaccines in SPF chickens. The restriction enzyme profiles of both clones were similar. Back passage of the SP and LP clones in SPF chickens resulted in loss of their phenotypic characteristics.

Decreased hedonic responsiveness following chronic mild stress is not secondary to loss of body weight.

Chronic exposure to mild unpredictable stress (CMS) has previously been found to decrease hedonic responsiveness, as measured by the consumption of palatable sweet solutions or sensitivity to brain stimulation reward. These effects are reversed by chronic treatment with antidepressant drugs, and the CMS procedure has been proposed as a relatively valid animal model of depression. It has recently been suggested that the behavioural effects of CMS may be secondary to loss of body weight. This article collates data from five laboratories using the CMS procedure. Data are presented from seven studies using five different rat strains, as well as CD1 mice. Three-week exposure to CMS significantly decreased sucrose consumption by Lister hooded, PVG hooded, Wistar, and Wistar WU rats, and by CD1 mice, and sensitivity to brain stimulation reward in Ibm:Ro Ro rats. Weight loss in different experiments varied between 0 and 10%. Hedonic sensitivity relative to body weight (e.g., mg sucrose/g body weight) decreased significantly in all experiments. Animals maintained on a restricted feeding regime lost weight but did not show decreases in sucrose intake. It is concluded that decreased hedonic sensitivity following chronic mild stress cannot be attributed to loss of body weight.

Effect of chronic diazepam treatment on footshock-induced ultrasonic vocalization in adult male rats.

Rats were tested in the footshock-induced ultrasonic vocalization model of anxiety. The ultrasounds were recorded 1-11 min after 10 inescapable 0.6 mA footshocks each of 1 sec. duration. Repeated administration of benzodiazepines in the clinic has been reported to be accompanied by development of tolerance and withdrawal anxiety. The present study examined whether the ultrasonic vocalization model could reflect these two side effects. Diazepam 4.6 or 8.8 mumol/ kg (1.3 or 2.5 mg/kg, subcutaneously) administered twice a day (8 a.m. and 4 p.m.) abolished the vocalization after acute administration and after 3 weeks of treatment. Hence, no tolerance developed to the anxiolytic effect of diazepam. When the rats were tested 24 and 48 hr after the last doses of diazepam there were no significant differences from the control group, i.e. no apparent withdrawal anxiety. Instead, the control groups developed tolerance to the shock regimen during the chronic experiments. This was examined further by daily testing of a group of naive rats for 13 days. The findings indicated that there is a limitation in number of test sessions before tolerance to the model develops. In conclusion, the results of the present study contribute to the many contradictory and by no mean unequivocally findings in the literature. It indicates that substantial prediction of anxiolytic effects as well as unwanted side effects cannot be made from one single test model.

Derivatives of 2-methylenepropane-1,3-diol as new antagonists of platelet activating factor.

Two new achiral platelet activating factor (PAF) antagonists, N-[5-[[2-methylene-3- [[(octadecylamino)carbonyl]oxy]propoxy]carbonyl]pentyl]pyridinium bromide and 3-[6-[[2-methylene-3- [[(octadecylamino)carbonyl]oxy]propoxy]carbonyl]hexyl]thiazolium bromide were synthesized from 2-methylenepropane-1,3-diol. Platelet aggregation in platelet-rich plasma from rabbits, induced by racemic C16-PAF, was competitively antagonized by 9 or 10. At concentrations less than or equal to 10(-4) M, neither compound 9 nor compound 10 caused platelet aggregation, nor did they inhibit platelet aggregation induced by collagen or adenosine diphosphate. Bronchoconstriction in the guinea pig and hypotension in the rat, induced by racemic C16-PAF, were also effectively antagonized by 9 and 10. Both appear to be more potent as PAF antagonists than Takeda's CV-3988.

Effect of a new vasodilator, pinacidil (P 1134), on potassium, noradrenaline and serotonin induced contractions in rabbit vascular tissues.

Ring preparations of rabbit aorta were contracted by potassium (127 mM). Pinacidil (P 1134), a new vasodilator ( 2.3 x 10(-5) M), the calcium antagonists verapamil (3.4 x 10(-7) M), nifedipine (3.4 x 10(-9) M) and hydralazine (1.9 x 10(-4) M) relaxed the preparation by 50%. 50% relaxation of noradrenaline-contracted tissues was obtained with pinacidil, 6.8 x 10(-5) M, verapamil, 2.4 x 10(-3) M. At 2 x 10(-7) M concentration nifedipine was almost inactive. In ring preparations of rabbit aorta exposed to calcium-free medium and then depolarized with potassium (127 mM), pinacidil, 5 x 10(-5) M and nifedipine, 10(-8) M significantly inhibited the contractions by cumulative addition of calcium. Hydralazine, 10(-3) M had no effect. Noradrenaline-induced contractions in calcium-free medium or in presence of increasing amounts of calcium were significantly inhibited by nifedipine, 10(-8) M and hydralazine, 10(-3) M. Pinacidil, 10(-4) M had no effect. Pinacidil, 1.3 x 10(-5) M and verapamil, 2.0 x 10(-5) M inhibited by 50% the serotonin-induced increase of perfusion pressure of isolated rabbit ear artery. The noradrenaline effect in this preparation were 50% inhibited by pinacidil, 2.4 x 10(-4) M and by verapamil, 8.8 x 10(-5) M. Hydralazine, 10(-3) M exerted minor inhibitory effect. It is suggested that interference with calcium influx contributes to the vasodilator activity of pinacidil.

N''-cyano-N-4-pyridyl-N'-1,2,2-trimethylpropylguanidine, monohydrate (P 1134): a new, potent vasodilator.

N''-cyano-N-4-pyridyl-N'-1,2,2-trimethylpropylguanidine, monohydrate (P 1134) is a new agent which induces a marked and sustained hypotensive response in normotensive and renal, neurogenic, and spontaneously hypertensive rats, as well as in normotensive and renal hypertensive dogs. The overall potency of this compound is 2-3 times greater than that of hydralazine. The fall of blood pressure is accompanied by an increase in heart rate and cardiac output and a decrease in total peripheral resistance. The hypotensive effect appears to be due primarily to a direct relaxant effect on vascular smooth muscle.

Synthesis and hypotensive activity of N-alkyl-N"-cyano-N'-pyridylguanidines.

A variety of N-alkyl-N'-pyridyl-N"-cyanoguanidines III was prepared as potential bioisosteres of hypotensive N-alkyl-N'-pyridylthioureas Ia. Optimal activity of the N,N'-disubstituted cyanoguanidines III was assoicated with the presence of four to seven carbon branched alkyl and 3- or 4-pyridyl groups. Maximum potency was displayed by N-tert-pentyl-N'-3 pyridyl-N"-cyanoguanidine (20). This compound proved to be 200 times more potent than the corresponding thiourea in hypertensive rats and dogs. In comparison with guancydine, which is the de-3-pyridyl analogue of 20, a 150-fold increase of potency in spontaneously hypertensive rats was obtained with 20 and its tert-butyl analogue 19. The observed activity appears to be due to direct vascular relaxation. On a weight basis compounds 19, 20, 50, and 101 compared favorably with hydralazine.