Differences In Relative Potency Research Articles

Effects of the K + channel blockers paspalitrem-C and paxilline on mammalian smooth muscle

The tremorgenic alkaloids, paxilline and paspalitrem-C (0.1–10 μM), increased the spontaneous contractility of guinea-pig and rat urinary bladder, and rat duodenum, and induced tension in guinea-pig trachea. These effects are ascribed to blockade of high-conductance, Ca 2+-activated K + (BK Ca) channels. Paxilline potentiated the charybdotoxin-induced stimulation of guinea-pig detrusor muscle; this is consistent with the alkaloid's ability to allosterically enhance the binding of charybdotoxin to smooth muscle membranes (Knaus et al., 1994). Paspalitrem-C and paxilline did not affect the myogenic activity of isolated portal vein from guinea-pig, which is insensitive to charybdotoxin, or of that from rat which is stimulated by charybdotoxin. Paxilline and paspalitrem-C also differed from charybdotoxin in that the alkaloids did not consistently elicit tension in guinea-pig aortic rings. These discrepancies are attributed to differences in relative potency, sites and/or mechanisms of action of the indole alkaloids vs. peptidyl blockers of the BK Ca channel.

Determination of the stability of diluted allergen extracts using a concentration step prior to EAST inhibition

Generally the stability of diluted allergen extracts, as used for skin testing, provocation testing and immunotherapy can not be measured using a normal enzyme allergosorbent test (EAST) inhibition method. The aim of this study was to determine the stability of diluted allergen extracts using an ultrafiltration step prior to the standard EAST inhibition procedure, in which the allergen extract was concentrated 100-fold. This concentration procedure was validated for Dermatophagoides pteronyssinus, timothy pollen, birch pollen and cat dander extracts and used in a stability study in which three batches were stored for 1 year at 6 degrees C and 25 degrees C. There was no difference in relative potency before and after concentration of birch and timothy pollen extracts. D. pteronyssinus and cat dander extracts showed a significant decrease of 25% and 35% of the relative potency after concentration. The mean coefficient of variation of 12 determinations of the stability study was 11.8%. For all allergens the 30 BU/mL or approximately 0.00025 mg/mL solution was stable for 12 months at both temperatures, except for D. pteronyssinus which declined rapidly at 25 degrees C.

Biologic activities of iodinated analogues of Tyr 0-bradykinin and bradykinin-Ile 10-Tyr 11 assessed in the rat uterus and the guinea pig ileum

1. 1. The biological activity of bradykinin (BK) and analogues containing Tyr in extended N- or C-terminal portions of the molecule, as well as that of their iodinated products, was compared in isolated rat uterus and guinea pig ileum preparations. 2. 2. BK-Tyr 10 and BK-Ile 10-Tyr 11 were obtained by solid phase synthesis employing fmoc chemistry. 3. 3. Iodination of BK-Ile 10-Tyr 11 and Tyr 10-BK was performed using iodobeads R, and the products were purified by reverse-phase HPLC. 4. 4. The relative potency (RP) of noniodinated analogues in the uterus was: Tyr 0-BK (1.3)=BK (1.0)>BK-Ile 10-Tyr 11(0.45)>>BK-Tyr 10 (0.02) and BK (1.0)>BK-Ile 10-Tyr 11 (0.25)=Tyr 0-BK (0.22)>>BK-Tyr 10(0.002). The RP of mono-iodo (MI) and di-iodo (Dl) products was: BK (1.0)>IBK-Ile 11-Tyr 11 (0.63)=DI-Tyr 0-BK (0.63)>MI-Tyr 0-BK (0.46)=MI-BK-Ile 10-Tyr 10 (0.40). 5. 5. The RP of noniodinated analogues in the guinea pig ileum was: BK (1.0)>MI-Tyr 0-BK (0.39)>MI-BK-Ile 10-Tyr 11 (0.17)=DI-Tyr 0-BK (0.16)=DI-BK-Ile 10-Tyr 11(0.13). 6. 6. Differences in RP of 8–10 fold for Tyr 0-BK or BK-Tyr 10 and 2-fold for BK-Ile 10-Tyr 11 were observed between the two preparations used, indicating possible receptor differences. 7. 7. Iodination caused a reduction in the RP of the analogues in both preparations. 8. 8. In the rat uterus, the changes in the RP of the Tyr 0-BK analogues were more evident than those observed with the iodinated analogues of BK-Ile 10-Tyr 11, indicating that iodination causes different changes in RP, according to the localization of the Tyr in the molecule. 9. 9. The data support the idea that iodinated analogues of BK-Ile 10-Tyr 11, with intact N-terminal portion, may be as useful as iodinated analogues of Tyr- 0-BK for the study of BK receptors.

Betidamino acids: versatile and constrained scaffolds for drug discovery.

Betidamino acids (a contraction of "beta" position and "amide") are N'-monoacylated (optionally, N'-monoacylated and N-mono- or N,N'-dialkylated) aminoglycine derivatives in which each N'acyl/alkyl group may mimic naturally occurring amino acid side chains or introduce novel functionalities. Betidamino acids are most conveniently generated on solid supports used for the synthesis of peptides by selective acylation of one of the two amino functions of orthogonally protected aminoglycine(s) to generate the side chain either prior to or after the elongation of the main chain. We have used unresolved Nalpha-tert-butyloxycarbonyl-N'alpha-fluorenylmethoxycarbonyl++ + aminoglycine, and Nalpha-(Nalpha-methyl)-tert-butyloxycarbonyl-N'alpha-fluo renylmethoxycarbonyl aminoglycine as the templates for the introduction of betidamino acids in Acyline [Ac-D2Nal-D4Cpa-D3Pal-Ser-4Aph(Ac)-D4Aph(A c)-Leu-Ilys-Pro-DAla-NH2, where 2Nal is 2-naphthylalanine, 4Cpa is 4-chlorophenylalanine, 3Pal is 3-pyridylalanine, Aph is 4-aminophenylalanine, and Ilys is Nepsilon-isopropyllysine], a potent gonadotropin-releasing hormone antagonist, in order to test biocompatibility of these derivatives. Diasteremneric peptides could be separated in most cases by reverse-phase HPLC. Biological results indicated small differences in relative potencies (<5-fold) between the D and L nonalkylated betidamino acid-containing Acyline derivatives. Importantly, most betide diastereomers were equipotent with Acyline. In an attempt to correlate structure and observed potency, Ramachandran-type plots were calculated for a series of betidamino acids and their methylated homologs. According to these calculations, betidamino acids have access to a more limited and distinct number of conformational states (including those associated with alpha-helices, beta-sheets, or turn structures), with deeper minima than those observed for natural amino acids.

An Overview of the Further Evaluation of Penciclovir against Herpes Simplex Virus and Varicella-Zoster Virus in Cell Culture Highlighting Contrasts with Acyclovir

The antiviral action of penciclovir against herpes simplex virus (HSV) and varicella-zoster virus (VZV) in cell culture is reviewed. Acyclovir was included for comparison in most of the experiments described. Whilst these two acyclic nucleoside derivatives share a mode of action which is qualitatively similar, quantitative differences were revealed in certain cell culture experiments, and the objective of subsequent biochemical studies was to account for these differences. Where possible, the conditions selected for the cell culture experiments were clinically relevant. The relative antiviral activities of penciclovir and acyclovir were compared using four distinct assays against a single strain of HSV-1 in MRC-5 cells. Some differences in relative potency were observed between the assays and possible reasons for this are discussed. In a subsequent study the initial multiplicity of infection (MOI) was shown to be inversely related to the potency of penciclovir against HSV-1 in both a virus-yield reduction...

Characterization of adenosine receptor-mediated generation of cyclic AMP in slices of rat cerebral cortex with chronic epileptic activity.

Cyclic AMP accumulations elicited by adenosine analogues 2-chloroadenosine (2-CADO), R-N6-phenylisopropyladenosine (R-PIA), and N6-cyclohexyladenosine (CHA) were investigated in cortical slices of chronic iron-induced epileptic rats. Cyclic AMP accumulation was elicited 9- to 18-fold by 2-CADO and it was elicited 5- to 7-fold by either R-PIA or CHA; 2-CADO was more potent than R-PIA or CHA in eliciting cyclic AMP accumulation. The adenosine analogues elicited cyclic AMP accumulation in a dose-dependent manner, and the elicitation was inhibited by the adenosine antagonist 8-phenyltheophylline. The 2-CADO-elicited accumulation of cyclic AMP was greatly increased in the cortical region on the primary epileptic side, while the R-PIA- or CHA-elicited accumulation did not change in any cortical region. The deviation detected only in the 2-CADO-elicited accumulation of cyclic AMP may be due to the difference in relative potency for adenosine receptors of the adenosine analogues. The results suggest that adenosine receptor-mediated generation of cyclic AMP is altered in the primary region of iron-induced epileptic cortex, in which heterogeneous alterations in different adenosine receptor subtypes may occur in the epileptic process.

Growth regulation by transforming growth factor-beta.

The name transforming growth factor-ß (TGF-ß) has come to represent a family of highly homologous polypeptides with a wide range of biological activities. The first member of this gene family was identified nearly a decade ago as one of two essential factors, called TGF-α and TGF-ß present in the conditioned medium of a murine sarcoma virus-transformed cell line, which together stimulated the anchorage-independent growth of non-transformed fibroblast cell lines [1]. Several members of the TGF-ß family have since been identified, of which TGF-ßl, ß2, and ß3 are produced by mammalian cells. These three forms of TGF-ß have similar biological activities in the majority of assay systems, though differences in relative potency are sometimes evident. For simplicity, we will use the name TGF-ß to refer to the TGF-ß family as a whole, unless otherwise specified. It should, however, be pointed out that most studies have evaluated only the biological activities of TGF-ßl. Finally, a number of proteins have been identified that exhibit structural similarities to TGF-ß, though with a more distant relationship than the individual TGF-ß isoforms. Together with TGF-ß, they constitute the TGF-ß superfamily. As yet little is known about the effects of these factors on cell proliferation, and they will not be discussed here.KeywordsTransform Growth FactorChicken Chorioallantoic MembraneType Beta Transform Growth FactorMink Lung Epithelial CellChinese Hamster Lung Fibroblast CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The second international standard for anti-poliovirus sera types 1, 2 and 3

The Second International Standard for anti-poliovirus sera types 1, 2 and 3 was established by the WHO Expert Committee on Biological Standardization in 1991 on the basis of an extensive collaborative study. Nine laboratories from eight countries participated and all used neutralizing antibody assays. The standard is a human serum pool which contains antibodies to all three poliovirus types and replaces the three previously established monovalent standards which were all hyperimmune monkey sera. The standard was assigned an activity of 25 IU of anti-poliovirus serum (type 1) human; 50 IU of anti-poliovirus serum (type 2) human; and 5 IU of anti-poliovirus serum (type 3) human. The study also showed significant interlaboratory differences in relative potency are observed when human sera are compared to hyperimmune monkey sera. It was therefore recommended that National laboratory references are established from human sera.

The genetic toxicology of 2-amino- N6-hydroxyadenine in eukaryotic organisms: Significance for genetic risk assessment

A collaborative study was designed to assess the mutagenicity of 2-amino N 6-hydroxylaminopurine (AHA) in a wide variety of eukaryotic assays systems in terms of potency and specificity. Earlier studies in Salmonella and Neurospora had shown that AHA was an extremely potent mutagen which appeared to cause predominantly AT to GC base-pair transitions. This discovery was viewed as an unusual opportunity to explore the general utility of different eukaryotic assay systems for genetic risk assessment. The objective was to determine whether AHA would show comparable potency and specificity in those eukaryotic organisms used to evaluate mutagenic potential of environmental chemicals for the human population. The data presented in this report show that AHA was mutagenic in all the eukaryotic assays utilized; however, the level of effect was found to be assay system-dependent. In addition, in assays where other base analogs were used as positive controls, differences in relative potency were observed from those obtained in the earlier studies with Salmonella and Neurospora. When alkylating agents were used as positive controls in the higher eukaryotic assays, AHA was found to have a mutagenic potency comparable to ethylnitrosourea (ENU), ethyl methanesulfonate (EMS) or methyl methanesulfonate (MMS) for many of the assays. With regard to mutagenic specificity, AHA appears to induce gene/point mutations in eukaryotic organisms, resulting predominantly from base-pair substitutions, predominantly AT to GC base-pair transitions; however, there was some unexplained variation in the ratio of these base-pair transitions and other transitions and transversions as a function of assay system. In addition, studies on the induction of micronuclei have shown that AHA induces chromosomal damage at high concentrations and low levels of survival.

Structure activity relationship for mitomycin C and mitomycin A analogs

A set of 30 mitomycin C and mitomycin A analogues, including five new compounds, was screened against three different solid human tumor cell lines using the MTT tetrazolium dye assay. A statistically significant correlation among antitumor activity, quinone reduction potential (E1/2), and the logarithm of the partition coefficient (log P) was obtained, with the most easily reduced and the most lipophilic compounds being the most potent. When these analogues were separated into mitomycin C and mitomycin A subsets, the former gave a correlation only with E1/2, whereas the latter (which differ little in their E1/2 values) gave a correlation only with log P. These correlations are in contrast to those made in the P388 leukemia assay in mice wherein the most active mitomycin C and mitomycin A analogues were the most hydrophilic ones. When the same compounds were tested against P388 leukemia cells in the MTT assay, the results were the same as those of the solid tumor assays. Thus, the substantial differences in relative potencies of mitomycins are related not to the kind of tumor cell, but to the type of assay performed, cell culture versus whole animal. No correlation was found between antitumor potency in the cell culture systems and calculated relative DNA binding strengths, probably because the limiting factors in antitumor potency of mitomycins appear to be tumor cell uptake (log P) and/or bioreductive activation (E1/2).

Nicotinic receptor-elicited sodium flux in rat pheochromocytoma PC12 cells: Effects of agonists, antagonists, and noncompetitive blockers

Nicotinic agonists stimulate 22Na flux in rat pheochromocytoma PC12 cells. The stimulatory effect of carbamylcholine is maximal at 1 mM, while the stimulatory effect of nicotine and anatoxin maximize at the same level at 100 microM and 10 microM, respectively. The tertiary amines arecolone and isoarecolone have no effect on flux at 100 microM, while the methiodides at 100 microM stimulate flux to an extent similar to 1 mM carbamylcholine. Dihydro and alcohol analogues of isoarecolone methiodide have markedly smaller effects on flux. A preincubation for 2 to 20 min with carbamylcholine (2 mM), nicotine (300 microM), anatoxin (30 microM) or isoarecolone methiodide (100 microM) causes marked desensitization to a subsequent carbamylcholine-elicited stimulation of flux. d-Tubocurarine, mecamylamine, hexamethonium, and chlorisondamine inhibit carbamylcholine-elicited flux with IC50 values of 1.0, 0.8, 43, and 0.020 microM, respectively. Atropine has no effect at 1 microM, but reduces the response to carbamylcholine by 50% at 8.6 microM, presumably as a noncompetitive blocker. Other noncompetitive blockers of nicotinic acetylcholine-receptors, such as histrionicotoxins, gephyrotoxin, pumiliotoxin C, phencyclidine, bupivacaine and piperocaine, inhibit carbamylcholine-elicited stimulation of 22Na flux with IC50 values from 0.3 to 1.8 microM. In contrast to d-tubocurarine, which inhibits carbamylcholine-elicited desensitization, and mecamylamine, which has no apparent effect on desensitization, chlorisondamine and certain noncompetitive blockers appear to enhance desensitization. The effects of agonists, antagonists and noncompetitive blockers at the neuronal nicotinic acetylcholine receptor-channel of PC12 cells are compared to their effects on binding of [125I]alpha-bungarotoxin to agonist-recognition sites and of [3H]perhydrohistrionicotoxin to noncompetitive blocker sites of the nicotinic acetylcholine receptor-channel of electric ray (Torpedo) electroplax membranes. There are marked differences in relative potencies for the two types of nicotinic acetylcholine receptor-channel.

Octimibate, a potent non‐prostanoid inhibitor of platelet aggregation, acts via the prostacyclin receptor

1. Octimibate, 8-[(1,4,5-triphenyl-1H-imidazol-2-yl)oxy]octanoic acid, is reported to have antithrombotic properties. This is in addition to its antihyperlipidaemic effects which are due to inhibition of acylCoA:cholesterol acyltransferase (ACAT). The aim of this study was to investigate the mechanism of the antithrombotic effect of octimibate, and to determine whether the effects of octimibate are mediated through prostacyclin receptors. 2. In suspensions of washed (plasma-free) human platelets, octimibate is a potent inhibitor of aggregation; its IC50 is approx. 10 nM for inhibition of aggregation stimulated by several different agonists, including U46619 and ADP. The inhibitory effects of octimibate on aggregation are not competitive with the stimulatory agonist; the maximal response is suppressed but there is no obvious shift in potency of the agonist. In platelet-rich plasma, octimibate inhibits agonist-stimulated aggregation with an IC50 of approx. 200 nM. 3. Octimibate also inhibits agonist-stimulated rises in the cytosolic free calcium concentration, [Ca2+]i, in platelets. Both Ca2+ influx and release from intracellular stores are inhibited. The effects of octimibate on aggregation and [Ca2+]i are typical of agents that act via elevation of adenosine 3':5'-cyclic monophosphate (cyclic AMP). Similar effects are seen with forskolin, prostacyclin (PGl2) and iloprost (a stable PGl2 mimetic). 4. Octimibate increases cyclic AMP concentrations in platelets and increases the cyclic AMP-dependent protein kinase activity ratio. Octimibate stimulates adenylyl cyclase activity in human platelet membranes, with an EC50 of 200 nM. The maximal achievable activation of adenylyl cyclase by octimibate is 60% of that obtainable with iloprost. Octimibate has no effect on the cyclic GMP-inhibited phosphodiesterase (phosphodiesterase-ITI), which is the major cyclic AMP-degrading enzyme in human platelets.5. Octimibate inhibits, apparently competitively, the binding of [3H]-iloprost (a stable PGl2 mimetic) to platelet membranes; the estimated Ki is 150 nm. 6. The platelets of different species show considerable differences in the apparent potency of their inhibition of aggregation by octimibate; platelets from cynomolgus monkeys are 3 fold more sensitive than those from humans, while rat, cat and cow platelets are 50, 100, and 250 fold less sensitive than human platelets. The sensitivity of these different species to iloprost, however, varies over a range of only 10 fold with no obvious difference between primates and non-primates. 7. Octimibate appears to be a potent agonist (aggregation), or partial agonist (adenylyl cyclase), at prostacyclin receptors and is the first non-prostanoid agent of this type to be identified. The species differences in relative potency of octimibate and iloprost may reflect the existence of receptor subtypes.

Effects of D 1 and D 2 dopamine receptor stimulation on the activity of substantia nigra pars reticulata neurons in 6-hydroxydopamine lesioned rats: D 1/D 2 coactivation induces potentiated responses

Extracellular single unit recording techniques were used to compare the effects of selective and non-selective dopamine agonists on substantia nigra pars reticulata activity in rats with 6-hydroxydopamine induced lesions of the nigrostriatal dopamine pathway. As previously shown, apomorphine (0.32 mg/kg), a dopamine agonist that interacts with both D 1 and D 2 dopamine receptor subtypes, produced consistent inhibitions of substantia nigra pars reticulata activity in these animals. The D 1-receptor agonist, SKF 38393 (RS-SKF 38393, 10 mg/kg), also induced significant inhibitions in the activity of these neurons in 6-hydroxydopamine lesioned rats, although less consistently than did apomorphine. The effects of SKF 38393 were reversed by the D 1-antagonist, SCH 23390. The D 2 selective agonist quinpirole was considerably less effective than apomorphine at inhibiting substantia nigra pars reticulata activity at doses up to 1 mg/kg. Since comparable experiments have shown that quinpirole is as effective as apomorphine at producing dopamine D 2-autoreceptor-mediated effects on dopamine neuron activity, quinpirole's lack of efficacy in the present study relative to that of apomorphine does not appear to be related to differences in relative potency for central D 2-receptors using this route of administration. Rather, the relative effectiveness of SKF 38393 on pars reticulata activity suggests that selective stimulation of D 1-receptors is at least, if not more, efficacious than selective stimulation of D 2-receptors at inducing alterations in the activity of substantia nigra pars reticulata neurons in 6-hydroxydopamine lesioned rats. The simultaneous stimulation of both receptors, however, was considerably more effective than selective stimulation of either receptor subtype: doses of SKF 38393 and quinpirole which had no significant effect on nigral activity when administered alone brought about marked inhibition of the firing of these cells when administered simultaneously. No such inhibition was seen when the inactive enantiomer, S-SKF 38393, was substituted for the racemic form of SKF 38393 in this protocol. These observations in 6-hydroxydopamine lesioned rats support other recent findings indicating that the two dopamine receptor sub-types can interact in a synergistic way to affect basal ganglia output.

Behavioural and convulsant actions of two methyl esters of β-carboline- 3-carboxylic acid in photosensitive baboons and in DBA/2 mice

The proconvulsant and convulsant actions of methyl 6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) and of methyl-β-carboline-3-carboxylate (β-CCM) have been evaluated in two animal models of reflex epilepsy, the photosensitive baboon, P ̄ apio papio, and the audiogenic seizure prone DBA/2 mouse. In baboons, myoclonic responses to photic stimulation are markedly enhanced 1 min after DMCM, 0.25 mg/kg i.v. In the absence of photic stimulation DMCM, 0.5 mg/kg i.v. induces a single brief tonic clonic seizure within 10–90 s. β-CCM, 0.025–0.05 mg/kg i.v. similarly enhances myoclonic responses to photic stimulation. Generalised seizures occur without photic stimulation 0.5–3 min after β-CCM, 0.1–0.2 mg/kg. Pretreatment with the excitatory amino acid antagonist, 2-amino- 7-phosphonoheptanoic acid (2-APH), 110 mg/kg i.v., prevents the generalised seizures induced by DMCM, 0.5 mg/kg, but not those induced by β-CCM, 0.1–0.2 mg/kg. In DBA/2 mice β-CCM and DMCM are indistinguishable in potency as convulsants (ED 50 values for clonic seizures: 4.4 and 4.6 mg/kg i.p. respectively) and as proconvulsants (ED 50 values for facilitation of clonic seizure responses to an 83 dB sound stimulus: 0.25 and 0.23 mg/kg). Pretreatment with 2-APH gives equipotent protection against audiogenic seizures induced by β-CCM, 1 mg/kg or DMCM, 1 mg/kg. The differences in relative potency of β-CCM and DMCM in the two species are probably accountable for in terms of differing metabolism. A differential action of two β-carbolines on receptor subtypes, with enhancement of excitatory amino acid release playing a more important role in epileptogenesis after DMCM, is proposed.

Assay methodology for urokinase: Its use in assessing the composition of mixtures of high- and low-molecular weight urokinase

Urokinase preparations of molecular weight 55,000 (high molecular weight urokinase, HMW-UK) and 33,000 (low molecular weight urokinase, LMW-UK) were assayed against the International Reference Preparation for Urokinase (IRP-UK) by three methods. Preparations of HMW-UK and LMW-UK which had the same potency when measured by use of S-2444 differed by a factor of 2–3 when measured by clot lysis. A formula is derived which allows these differences in relative potency to be used to calculate the molar ratios of the two forms of UK in a mixture. This method was tested on IRP-UK and on four mixtures of purified HMW-UK and LMW-UK. The results of the calculations for the four mixtures compare well with their composition as prepared. The result for IRP-UK is in approximate agreement with the ratio calculated by separating this material on a Sephadex G-75 column and assaying the two forms using S-2444. The difficulty caused by the different relative activities of the two forms of UK when compared by assay methods now in use is discussed.

Comparison of the Effects of Insulin and Insulin-like Agents on Different Aspects of Adipocyte Metabolism

The effect of insulin, spermine, cysteine, and diamide on glucose transport, glucose oxidation, and lipolysis were compared using isolated rat adipocytes. Each agent exerted insulin-like effects on glucose transport and glucose oxidation, whereas spermine and cysteine, but not diamide, inhibited lipolysis. Furthermore, the relative potencies of these agents on the various insulin responsive processes were markedly different. Thus, although these agents have much in common with insulin, the differences in relative potencies suggest that at least some of the insulin-like properties of these compounds may not be exerted through the same mechanisms as insulin.

Effects of some autonomic drugs on duodenal smooth muscle.

Longitudinal muscle strips (LMS) and circular muscle strips (CMS), 2 mm wide and 1.5--2 cm long, from opossum duodenum were exposed to some autonomic agonists. The cholinergic agonists, acetylcholine, carbachol, methacholine, and bethanechol stimulated only tonic contractions in LMS and tonic followed by phasic contractions in CMS. These effects were abolished by atropine 10(-6) M. The ED50S of all cholinergic agonists for LMS were significantly lower than for CMS. Norepinephrine caused initial contraction (abolished by phenoxybenzamine, 10(-4) M), followed by relaxation (abolished by propranolol, 10(-5) M), and isopropylnorepinephrine caused relaxation (abolished by propranolol, 10(-5) M) in both layers. There were no differences in relative potencies for adrenergic agonists between the layers. Tetrodotoxin did not affect the response to adrenergic agonists. Thus, the potency of cholinergic agonists is greater in longitudinal than in circular muscle, and the layers respond differently to cholinergic agonists. The alpha-adrenergic receptors mediate contraction and beta-adrenergic receptors mediate relaxation on the duodenal smooth muscle.

Effect of 25-hydroxy-vitamin D 3 on intestinal absorption of calcium in normal man and patients with renal failure

The effects of short-term treatment with 25-hydroxy-vitamin D 3 (25(OH)D 3) on intestinal absorption of 47Ca were examined in 18 studies of normal subjects and 16 studies of patients with advanced renal failure. Doses of 25(OH)D 3 were 20, 100, 500, or 1000 μg/day given orally for 7–10 days. There was an increase in 47Ca absorption and urinary calcium in normal subjects receiving 20 μg/day, while doses of 500 or 1000 μg/day were required to augment 47Ca absorption in renal failure patients. During treatment, plasma levels of 25(OH) D increased to similar levels in both normal and uremic subjects. A comparison of the dose-response curves found 25(OH)D 3 to be 1 125 as potent as 1,25(OH) 2D 3 in the normal subjects and 1 400 as potent as 1,25(OH) 2D 3 in patients with chronic renal failure. Thus, pharmacologic doses of 25(OH)D 3 are active in both normal and uremic patients, although relatively greater quantities are necessary in uremia. This difference in relative potency of 1,25(OH) 2D 3 and 25(OH)D 3 may be explained by some conversion of 25(OH)D 3 to 1,25(OH) 2D 3 in normal compared to uremic subjects, while 25(OH)D 3 may act in large part via mass action in uremic patients.

Comparison of in vivo and in vitro responses to sulfated and non-sulfated ceruletide

Responses of guinea pig gall bladder to sulfated and non-sulfated ceruletide were compared in vitro and vivo. Tested in vivo, sulfated ceruletide was 75 times more potent than non-sulfated. In vitro, sulfated was 150 times more potent. Thus, differences in potency are substantially less when tested in vivo, and reported differences in relative potency reflect not only chemical structure but also the method used for testing.

Comparison of acetaldehyde and ethanol: Depression of motor activity in mice

The fine and gross motor activity of mice was measured at 1-minute intervals for 15 minutes after intravenous administration of ethanol or acetaldehyde. Acetaldehyde transiently reduced both types of motor activity whereas the effects of ethanol were more prolonged. The 1-minute ED 50 values for depression of fine and gross activity by acetaldehyde are 2.2. and 2.7 mg/kg, respectively. The corresponding values for ethanol are 740 and 516 mg/kg. The differences in relative potencies became smaller as the time interval over which activity was measured increased. Thus, the potency of acetaldehyde as a depressant of behavior relative to ethanol is considerably greater than has previously been reported if effects are determined immediately after drug administration.