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K L Kirk

Publications and source records attributed to K L Kirk.

At least 109 records · Page 6Linked to original sources
PubMed1986

Synthesis and adrenergic activity of ring-fluorinated phenylephrines.

2-Fluoro-, 4-fluoro-, and 6-fluorophenylephrine (6-FPE) were synthesized from the corresponding fluorinated 3-hydroxybenzaldehydes. New routes to 2-fluoro- and 6-fluoro-3-hydroxybenzaldehydes were developed based on regioselective lithiation of 2- and 4-[(dimethyl-tert-butylsilyl)oxy]fluorobenzene ortho to fluorine. As with norepinephrine and isoproterenol analogues, the adrenergic properties of phenylephrine were markedly altered by ring fluorination. The order of potency of the fluoro analogues as alpha 1-adrenergic agonists in the stimulation of contraction of aortic strips and of phosphatidylinositol turnover and potentiation of cyclic AMP accumulation in guinea pig synaptoneurosomes was 6-FPE greater than PE greater than 4-FPE greater than 2-FPE. The same pattern was observed for the displacement of radioligands specific for alpha 1- and alpha 2-adrenergic receptors on brain membranes. The order of potency for the displacement of [3H]dihydroalprenolol, a beta-specific adrenergic ligand from brain membranes, was 2-FPE greater than 4-FPE = PE much greater than 6-FPE. 6-FPE was much more selective for alpha-adrenergic receptors compared to beta-receptors than was phenylephrine. A rationale for the observed fluorine-induced alterations in potency and selectivity of the FPEs for alpha- and beta-adrenergic systems is presented based on fluorine-induced conformations due to electrostatic repulsion of fluorine and the benzyl hydroxyl group.

Animals↗
PubMed1986

[3H]xanthine amine congener of 1,3-dipropyl-8-phenylxanthine: an antagonist radioligand for adenosine receptors.

An amine-functionalized derivative of 1,3-dipropyl-8-phenylxanthine has been prepared in tritiated form as a xanthine amine congener ([3H]XAC) for use as an antagonist radioligand for adenosine receptors. [3H]XAC has higher receptor affinity, higher specific activity, lower nonspecific membrane binding, and more favorable hydrophilicity than 1,3-diethyl-8-[3H]phenylxanthine, the xanthine commonly used for adenosine receptor binding. In rat cerebral cortical membranes, [3H]XAC exhibits saturable, specific binding with a Kd of 1.23 nM and a Bmax of 580 fmol/mg of protein at 37 degrees C. N6-(R-Phenylisopropyl)adenosine is a more potent inhibitor of [3H]XAC binding than is 5'-N-ethylcarboxamidoadenosine, indicating that binding is to an A1-adenosine receptor. In the absence of GTP, the inhibition curves for adenosine agonists versus [3H]XAC binding are biphasic, indicating that [3H]XAC is binding to low- and high-affinity agonist states of the A1 receptor. In the presence of GTP, adenosine analogs exhibit monophasic, low-affinity inhibition of binding of [3H]XAC. Inhibition of [3H]XAC binding by theophylline or by various 8-phenylxanthines is monophasic, and the potencies are commensurate with the potencies of these xanthines as adenosine receptor antagonists. The receptor sites in calf brain membranes exhibit a higher affinity (Kd = 0.17 nM) for [3H]XAC, whereas sites in guinea pig exhibit a slightly lower affinity (Kd = 3.0 nM). Densities of [3H]XAC binding sites are similar in brain membranes from all species.

Animals↗
PubMed1986

A functionalized congener approach to adenosine receptor antagonists: amino acid conjugates of 1,3-dipropylxanthine.

1,3-Dipropyl-8-phenylxanthine, a synthetic analog of theophylline and a potent antagonist of adenosine at A1 and A2-adenosine receptors, has been attached covalently through a functionalized chain to amino acids and oligopeptides. The xanthine conjugates have been studied as competitive inhibitors of the specific binding of [3H]N6-cyclohexyladenosine to A1-receptors of rat cerebral cortical membranes and for inhibition of cyclic AMP accumulation elicited by 2-chloroadenosine in guinea pig brain slices through A2-receptors. A free amino group on the extended chain generally resulted in high potency at A1-receptors. The potency (in some cases extending into the subnanomolar range) and selectivity for A1-receptors (up to 200-fold) suggest that this approach can yield a versatile class of "functionalized congeners" of adenosine receptor antagonists in which distal modifications of the attached moiety ("carrier") can serve also to improve pharmacodynamic and pharmacokinetic parameters. The water solubility in many of the more potent analogs has been enhanced by two orders of magnitude over that of simple, uncharged 8-phenyl xanthine derivatives. Analogs in which the carrier contains D-tyrosine have potential for development of iodinated radioligands for adenosine receptors. The functionalized congener approach is potentially applicable to other drugs and for development of prodrugs.

Adenosine↗
PubMed1986

Effect of repeated restraint stress, desmethylimipramine or adrenocorticotropin on the alpha and beta adrenergic components of the cyclic AMP response to norepinephrine in rat brain slices.

The cyclic AMP response to catecholamines in rat cortical slices is mediated by a beta adrenergic receptor which is coupled to adenylate cyclase and an alpha adrenergic receptor which potentiates the response to beta receptor stimulation. The present studies examined the effects of repeated restraint stress, adrenocorticotropin or desmethylimipramine administration on the beta and alpha adrenergic components of this response. Restraint was found to produce a small nonsignificant decrease of the beta receptor response accompanied by a significant reduction of the alpha receptor-induced potentiation of the beta response. Desmethylimipramine was found to lower the cyclic AMP response to beta receptor stimulation but not to alter the alpha-induced potentiation of the beta response. Adrenocorticotropin, like restraint stress, was found to reduce only the alpha-induced potentiation of the beta response. Experiments with adenosine and histamine showed that restraint stress lowered the alpha-induced potentiation of cyclic AMP responses to these neurohormones also. It is concluded that restraint stress acts primarily to reduce the response to stimulation of central alpha adrenergic receptors whereas desmethylimipramine acts primarily to reduce the response to stimulation of beta adrenergic receptors. Adrenocorticotropin has the same effect as restraint stress suggesting that pituitary adrenal hormones mediate the stress effect.

Adenosine↗
PubMed1985

Electrochemical detection of biogenic amines following acylation by N-hydroxysuccinimide esters.

A general methodology for the selective derivatization of amines, to enable quantitation by high pressure liquid chromatography with electrochemical detection, is presented. N-Hydroxysuccinimide active esters present in large excess are suitably mild acylating agents to derivatize selectively trace quantities of amines for electrochemical detection. The 2 separate problems of extraction yield and detectability can be solved by this derivatization method. Due to its lipophilicity the resulting N-acylated amine, as demonstrated with serotonin, is extracted efficiently into organic solvents during sample preparation for chromatography. Moreover, the acyl group introduced can be designed to be electroactive, thus extending the procedure to amines not readily oxidized, e.g., histamine and phenylethylamine.

Acylation↗
PubMed1985

The effect of ring-fluorination on the rate of O-methylation of dihydroxyphenylalanine (DOPA) by catechol-O-methyltransferase: significance in the development of 18F-PETT scanning agents.

The three ring-fluorinated analogs of dihydroxyphenylalanine (DOPA) were synthesized and the kinetics of their O-methylation catalyzed by catechol-O-methyltransferase compared to those of DOPA. The affinities (Km) of 2-FDOPA, 5-FDOPA, DOPA, and 6-FDOPA were 20, 23, 55, and 552 microM, respectively, whilst the Vmax values were 4.0, 4.4, 5.0 and 5.4 nmol per min per mg protein. The importance of the low affinity and decreased rate constant of 6-FDOPA for COMT are discussed with regard to the use of 6-FDOPA as an 18-fluorine labeled probe for positron emission transaxial tomography (PETT).

Animals↗
PubMed1985

Probing the adenosine receptor with adenosine and xanthine biotin conjugates.

Biotin-containing analogs of a potent agonist (N6-phenyladenosine) and a potent antagonist (1,3-dipropyl-8-phenylxanthine) of adenosine receptor activity have been synthesized. A spacer chain to the biotin moiety is attached in both cases to the para-position of the phenyl ring. Two biotin conjugates of N6-phenyladenosine differing only in the length of the spacer chain bind to the adenosine receptor and to avidin simultaneously. The shorter-chain derivative was more potent in inhibiting binding of N6-[3H]cyclohexyladenosine to rat cerebral cortical membranes (Ki of 11 nM in the absence of avidin, 36 nM for the avidin complex). Three biotin conjugates of 1,3-dipropyl-8-phenylxanthine bound competitively to the adenosine receptor, but only in the absence of avidin. The results are interpreted in terms of the possible orientation of the ligands at the receptor binding site.

Adenosine↗
PubMed1985

Passive cation permeability of turtle colon: evidence for a negative interaction between intracellular sodium and apical sodium permeability.

The role of intracellular sodium in the regulation of apical sodium permeability was investigated in an electrically "tight" epithelium, the turtle colon. In the presence of low mucosal sodium (3 mM) and serosal ouabain, an inhibitor of the basolateral sodium pump, the apical membrane retained a substantial amiloride-sensitive, sodium conductance and the basolateral membrane exhibited a barium-sensitive potassium conductance in parallel with a significant sodium (and lithium) conductance. In the presence of a high mucosal sodium concentration (114 mM), however, inhibition of active sodium absorption by ouabain led to a disappearance of the amiloride-sensitive, transepithelial conductance that was due, at least in part, to a virtual abolition of the apical sodium permeability. Two lines of evidence indicate that this permeability decrease was dependent upon an increase in intracellular sodium content. First, raising the mucosal sodium concentration from 3-114 mM in the presence of ouabain reversibly inhibited the amiloride-sensitive conductance. The time course of the decline in conductance paralleled the apparent intracellular accumulation of sodium in exchange for potassium, which was monitored as a transient deflection in the amiloride-sensitive, short-circuit current. Second, the inhibitory effect of mucosal sodium-addition was markedly attenuated by serosal barium, which prevented the accumulation of sodium by blocking the electrically coupled, basolateral potassium exit. These results support the notion of a "negative feedback" effect of intracellular sodium on the apical sodium permeability.

Amiloride↗
PubMed1985

Functionalized congeners of 1,3-dialkylxanthines: preparation of analogues with high affinity for adenosine receptors.

A series of functionalized congeners of 1,3-dialkylxanthines has been prepared as adenosine receptor antagonists. On the basis of the high potency of 8-(p-hydroxyphenyl)-1,3-dialkylxanthines, the parent compounds were 8-[4-[(carboxymethyl)oxy]phenyl] derivatives of theophylline and 1,3-dipropylxanthine. A series of analogues including esters of ethanol and N-hydroxysuccinimide, amides, a hydrazide, an acylurea, and anilides were prepared. The potency in blocking A1-adenosine receptors (inhibition of binding of N6-[3H]cyclohexyladenosine to brain membranes) and A2-adenosine receptors (inhibition of 2-chloroadenosine-elicited accumulations of cyclic AMP in brain slices) was markedly affected by structural changes distal to the primary pharmacophore (8-phenyl-1,3-dialkylxanthine). Potencies in the dipropyl series at the A1 receptor ranged from Ki values of 1.2 nM for a congener with a terminal amidoethyleneamine moiety to a Ki value of 58 nM for the parent carboxylic acid to a Ki of 96 nM for the bulky ureido congener. Certain congeners were up to 145-fold more active at A1 receptors than at A2 receptors. Various derivatives of the congeners should be useful as receptor probes and for radioiodination, avidin binding, and preparation of affinity columns.

Adenosine↗
PubMed1985

Functionalized congeners of adenosine: preparation of analogues with high affinity for A1-adenosine receptors.

A series of functionalized congeners of adenosine based on N6-phenyladenosine, a potent A1-adenosine receptor against, was synthesized. Derivatives of the various congeners should be useful as receptor and histochemical probes and for the preparation of radioligands and affinity columns or as targeted drugs. N6-[4-(Carboxymethyl)phenyl]adenosine served as the starting point for synthesis of the methyl ester, the methyl amide, the ethyl glycinate, and various substituted anilides. One of the latter, N6-[4-[[[4-(carbomethoxymethyl)anilino]carbonyl]methyl]phenyl] adenosine, served as the starting point for the synthesis of another series of congeners including the methyl amide, the hydrazide, and the aminoethyl amide. The terminal amino function of the last congener was acylated to provide further analogues. The various congeners were potent competitive antagonists of binding of N6-[3H]cyclohexyladenosine to A1-adenosine receptors in rat cerebral cortical membranes. The affinity of the congener for the A1 receptor was highly dependent on the nature of the spacer group and the terminal moiety with Ki values ranging 1-100 nM. A biotinylated analogue had a Ki value of 11 nM. A conjugate derived from the Bolton-Hunter reagent had a Ki value of 4.5 nM. The most potent congener contained a terminal [(aminoethyl)amino]carbonyl function and had a Ki value of less than 1 nM.

Adenosine↗
PubMed1985

Direct visualization of the isolated and perfused macula densa.

Direct examination of the structure and function of the macula densa is compromised by the relative inaccessibility and small size of this cell plaque. We report the isolation and perfusion of rabbit nephron segments with attached glomeruli and the direct visualization of the macula densa with differential interference-contrast microscopy. We used this technique to examine the structural sensitivity of the macula densa to perturbations in luminal osmolality and NaCl concentration. Reducing luminal osmolality from 290 to 70 mosmol/kg by removing NaCl resulted in a dilation of the lateral intercellular spaces that was both reversible and specific to the region of the macula densa. Associated with the dilation of the intercellular spaces was a small (congruent to 10%), but statistically significant, increase in the height of the macula densa cells. These structural events were related to the reduction in luminal osmolality, since isosmotic replacement of NaCl with mannitol resulted in no detectable structural changes. Thus, the macula densa may represent a small water-permeable plaque of cells within the remaining water-impermeable thick ascending limb of Henle's loop.

Animals↗
PubMed1985

Microscopic investigation of structure and function in living epithelial tissues.

In this paper we shall illustrate the utility of direct microscopic methods for studying living epithelia. Beginning with an exposition on the available strategies for visualization of unstained biological materials, the rationale that leads to the choice of differential interference-contrast optics for examination of epithelia is illustrated. Findings from toad urinary bladder, Necturus gallbladder, and rabbit cortical collecting tubule are reviewed. Emphasis on renal structures is provided with a report on work in progress on proximal tubule volume regulation and on structural examination of the isolated perfused macula densa. Conclusions are drawn with respect to the advantages and shortcomings of discussed optical methods and with respect to the choice of model epithelia.

Animals↗
PubMed1984

Alpha-adrenergic potentiation of beta-adrenergic stimulation of rat pineal N-acetyltransferase. Studies using cirazoline and fluorine analogs of norepinephrine.

Recent evidence indicates that melatonin production is controlled by norepinephrine acting via alpha 1-and beta 1-adrenoceptors on pinealocytes; activation of alpha 1-adrenoceptors appears to potentiate the effects of beta 1-adrenoceptor activation. However, alpha-adrenergic potentiation of beta 1-adrenergic activation has been demonstrated with only one alpha-adrenergic agonist. For this reason, this issue was reinvestigated using two other alpha-adrenergic agonists, 6-fluoronorepinephrine and cirazoline. Both compounds, which were found to have a high affinity for pineal alpha 1-adrenoceptors, potentiated the stimulatory effects of isoproterenol on pineal N-acetyltransferase. 6-Fluoronorepinephrine also potentiated the stimulation of N-acetyltransferase activity produced by another beta-adrenergic agonist, 2-fluoronorepinephrine. These findings support the hypothesis that pineal N-acetyltransferase activity is regulated by norepinephrine acting through both alpha 1- and beta 1-adrenoceptors.

Acetyltransferases↗
PubMed1984

Determination of urinary 4-hydroxy-3-methoxyphenylethylene glycol in man by high performance liquid chromatography with electrochemical detection.

A reverse phase high performance liquid chromatographic method for determining levels of 4-hydroxy-3- methoxyphenylethylene glycol (MHPG) in human urine that is virtually free of all interfering peaks has been developed. After addition of a homologous internal standard, enzymatic hydrolysis is performed. Samples are then placed onto columns containing AG1-X8, and the MHPG is collected in a phosphate buffer wash of the column. After ethyl acetate extraction and evaporation of the organic solvent, the dry residue is redissolved in mobile phase, and injected onto a reverse phase column. Results obtained with this assay were almost identical (101+/-5.6%, mean+/-SD, n=6) with those obtained using a gas chromatography - mass spectrometry (GCMS) assay.

Chromatography, High Pressure Liquid↗
PubMed1984

Morphologic response of the rabbit cortical collecting tubule to peritubular hypotonicity: quantitative examination with differential interference contrast microscopy.

The isolated and perfused cortical collecting tubule of the rabbit was examined by differential interference contrast microscopy in order to characterize the morphologic response of this nephron segment to peritubular hypotonicity. Computer-assisted, morphometric procedures were developed to obtain measurements of cell volume and lateral intercellular space geometry from interference contrast images of perfused nephron segments. Following dilution of the bath from 290 to 190 mOsm in the absence of antidiuretic hormone (T = 25 degrees C), the cells swelled rapidly to a new steady-state volume which was maintained for at least 20 to 30 min and which was about 90% of that predicted for ideal osmometric behavior. The increase in cell volume was accomplished entirely by bulging of the cells into the lumen; lateral space width and outside tubule diameter were unaffected by peritubular hypotonicity. In addition, the swelling of the cells was associated with an apparent swelling of intracellular organelles, e.g., nuclei and mitochondria. Our results indicate that cells of the mammalian collecting tubule swell without the capacity for significant volume regulation at 25 degrees C and without the cytoplasmic vacuolation and dilation of the lateral intercellular spaces observed following the onset of antidiuretic hormone-dependent volume reabsorption (E. Ganote , J. Grantham , H. Moses, M. Burg and J. Orloff , J. Cell Biol. 36:355, 1968).

Animals↗
PubMed1984

Quantitative analysis of the structural events associated with antidiuretic hormone-induced volume reabsorption in the rabbit cortical collecting tubule.

We quantitatively examined the influence of antidiuretic hormone (ADH)-dependent volume reabsorption on the morphology of the rabbit cortical collecting tubule. Estimates of cell volume and the geometry of the lateral intercellular spaces were extracted from differential interference contrast images of perfused nephron segments using the morphometric procedures described in the preceding paper (K.L. Kirk , D.R. DiBona and J.A. Schafer, J. Membrane Biol. 79:53-64, 1984). The results indicate that ADH addition in the presence, but not absence, of a lumen-to-bath osmotic gradient (130 to 290 mOsm) stimulated transepithelial volume flow and simultaneously increased the volumes of both the cells (+28%) and the lateral intercellular spaces (+78%). In addition, the formation of cytoplasmic vacuoles could be observed during the latter stages of the swelling response, and vacuole formation continued well after new steady-state values for transepithelial water flow and cell volume had been reached. Two main conclusions can be drawn from these results. First, the cytoplasmic vacuoles comprise a slowly filling compartment that lies in parallel to the transepithelial pathway for ADH-stimulated volume reabsorption. Second, from the magnitude of the cell volume increase, we estimate that the hydraulic conductivities of the opposing cell membranes are nearly equal during maximal ADH stimulation.

Absorption↗
PubMed1984

Differential effect of fluorinated analogs of TRH on the cardiovascular system and prolactin release.

The effects of thyrotropin-releasing hormone (TRH) and the TRH-analogs, 4-fluoro-Im-TRH (4-F-TRH) and 2-trifluoromethyl-Im-TRH (2-TFM-TRH), on the cardiovascular system and prolactin (PRL) release were examined in conscious rats. TRH (2.8 or 28 nmol) injected into the anterior hypothalamus produced dose-dependent increments in blood pressure and heart rate; plasma PRL was increased twofold after the higher dose of TRH. 4-F-TRH had effects similar to those of TRH on both the cardiovascular and PRL response. In contrast, the 2-TFM-TRH was significantly less active than TRH or 4-F-TRH in eliciting tachycardia, yet was noticeably more potent in affecting PRL release. These data suggest that the receptors for TRH-induced PRL release may be different from TRH-receptors which mediate central cardiovascular responses.

Animals↗