Low-Temperature Vacuum Drying on Broccoli: Enhanced Anti-Inflammatory and Anti-Proliferative Properties Regarding Other Drying Methods

Low-temperature vacuum drying (LTVD) has shown great potential for drying vegetables. It could avoid excessive degradations of active compounds with potential therapeutic agents. In this study, the effect on several relevant bioactive compounds, anti-inflammatory activity, and anti-proliferative activity of broccoli (Brassica oleracea var. italica) were evaluated. Effects of other drying methods, including vacuum drying (VD), convective drying (CD), infrared drying (IRD), and freeze drying (FD), were also comparatively evaluated. The results of all dried samples showed high polyunsaturated fatty acid contents (of up to 71.3%) and essential amino acid contents (of up to 8.63%). The LTVD method stands out above the other drying methods, since it obtained the highest content of total phenols, chlorogenic acid, and ferulic acid. Both the LTVD and CD samples demonstrated high anti-inflammatory and anti-proliferative activities. These CD and LTVD samples were also the most active against the breast carcinoma MDA-MB-23 cell line. Due to the good retention of bioactive compounds via LTVD, the obtained dried broccoli here can be used in a near time as an ingredient for the development of novel natural products with anti-inflammatory and anti-proliferative effects.

Comprehensive Evaluation of the Bioactive Composition and Neuroprotective and Antimicrobial Properties of Vacuum-Dried Broccoli (Brassica oleracea var. italica) Powder and Its Antioxidants

In this study, vacuum drying (VD) was employed as an approach to protect the bioactive components of and produce dried broccoli powders with a high biological activity. To achieve these goals, the effects of temperature (at the five levels of 50, 60, 70, 80 and 90 °C) and constant vacuum pressure (10 kPa) were evaluated. The results show that, with the increasing temperature, the drying time decreased. Based on the statistical tests, the Brunauer-Emmett-Teller (BET) model was found to fit well to sorption isotherms, whereas the Midilli and Kucuk model fit well to the drying kinetics. VD has a significant impact on several proximate composition values. As compared with the fresh sample, VD significantly reduced the total phenol, flavonoid and glucosinolate contents. However, it was shown that VD at higher temperatures (80 and 90 °C) contributed to a better antioxidant potential of broccoli powder. In contrast, 50 °C led to a better antimicrobial and neuroprotective effects, presumably due to the formation of isothiocyanate (ITC). Overall, this study demonstrates that VD is a promising technique for the development of extracts from broccoli powders that could be used as natural preservatives or as a neuroprotective agent.

Increased reversal and oscillatory shear stress cause smooth muscle contraction-dependent changes in sheep aortic dynamics: role in aortic balloon pump circulatory support

AIMS

The intra-aortic balloon pumping (IABP) changes pressure and increases the aorta shear stress reversal (SS(R)) and oscillatory (SS(O)) components. Hence, IABP-dependent changes in aortic biomechanics would be expected, because of vascular smooth muscle (VSM) tone (i.e. flow-induced endothelium-dependent response, related to SS(R) and SS(O) variations) and/or pressure changes. To characterize: (i) the IABP effects on the aortic and global (systemic circulation) biomechanics, analysing their dependence on pressure and VSM basic tone changes and (ii) the relation between the SS(R) and SS(O) and the aortic biomechanical changes associated with the VSM tone variations.

METHODS

Aortic flow, pressure and diameter were measured in eight sheep during basal, augmented and assisted beats (1 : 1 and 1 : 2 IABP modalities). Calculations: (i) aortic effective and isobaric elasticity, viscosity, circumferential stress, pulse wave velocity, shear stress and buffer and conduit functions, (ii) peripheral resistance, global compliance, reflection coefficient and wave propagation times and (iii) the relation between SS(R) and SS(O) and biomechanical changes associated with variations in the aortic VSM tone.

RESULTS

Augmented and assisted beats showed: global VSM relaxation pattern (reduced peripheral resistance and reflection coefficient; increased propagation times) and local VSM contraction pattern (increased viscosity; reduced diameter, elasticity and circumferential stress), associated with SS(R) and SS(O), levels and changes. The vascular changes reduced the ventricle afterload determinants, increased the vascular buffer performance and kept the conduit capability.

CONCLUSION

In addition to pressure-dependent changes, IABP determined biomechanical changes related to variations in the VSM tone. The increased SS(R) and SS(O) were associated with the aortic VSM contraction pattern and biomechanical changes.

Binding and functional properties of hexocyclium and sila-hexocyclium derivatives to muscarinic receptor subtypes

1. We have compared the binding properties of several hexocyclium and sila-hexocyclium derivatives to muscarinic M1 receptors (in rat brain, human neuroblastoma (NB-OK 1) cells and calf superior cervical ganglia), rat heart M2 receptors, rat pancreas M3 receptors and M4 receptors in rat striatum, with their functional antimuscarinic properties in rabbit vas deferens (M1/M4-like), guinea-pig atria (M2), and guinea-pig ileum (M3) muscarinic receptors. 2. Sila-substitution (C/Si exchange) of hexocyclium (-->sila-hexocyclium) and demethyl-hexocyclium (-->demethyl-sila-hexocyclium) did not significantly affect their affinities for muscarinic receptors. By contrast, sila-substitution of o-methoxy-hexocyclium increased its affinity 2 to 3 fold for all the muscarinic receptor subtypes studied. 3. The p-fluoro- and p-chloro-derivatives of sila-hexocyclium had lower affinities than the parent compound at the four receptor subtypes, in binding and pharmacological studies. 4. In binding studies, o-methoxy-sila-hexocyclium (M1 = M4 > or = M3 > or = M2) had a much lower affinity than sila-hexocyclium for the four receptor subtypes, and discriminated the receptor subtypes more poorly than sila-hexocyclium (M1 = M3 > M4 > M2). This is in marked contrast with the very clear selectivity of o-methoxy-sila-hexocyclium for the prejunctional M1/M4-like heteroreceptors in rabbit vas deferens. 5. The tertiary amines demethyl-hexocyclium, demethyl-sila-hexocyclium and demethyl-o-methoxy-sila-hexocyclium had 10 to 30 fold lower affinities than the corresponding quaternary ammonium derivatives.

Thermodynamics of antagonist binding to rat muscarinic M2 receptors: antimuscarinics of the pridinol, sila-pridinol, diphenidol and sila-diphenidol type

1. We studied the effect of temperature on the binding to rat heart M2 muscarinic receptors of antagonists related to the carbon/silicon pairs pridinol/sila-pridinol and diphenidol/sila-diphenidol (including three germanium compounds) and six structurally related pairs of enantiomers [(R)- and (S)-procyclidine, (R)- and (S)-trihexyphenidyl, (R)- and (S)-tricyclamol, (R)- and (S)-trihexyphenidyl methiodide, (R)- and (S)-hexahydro-diphenidol and (R)- and (S)-hexbutinol]. Binding affinities were determined in competition experiments using [3H]-N-methyl-scopolamine chloride as radioligand. The reference drugs were scopolamine and N-methyl-scopolamine bromide. 2. The affinity of the antagonists either increased or decreased with temperature. van't Hoff plots were linear in the 278-310 degrees K temperature range. Binding of all antagonists was entropy driven. Enthalpy changes varied from large negative values (down to -29 kJ mol-1) to large positive values (up to +30 kJ mol-1). 3. (R)-configurated drugs had a 10 to 100 fold greater affinity for M2 receptors than the corresponding (S)-enantiomers. Enthalpy and entropy changes of the respective enantiomers were different but no consistent pattern was observed. 4. When silanols (R3SiOH) were compared to carbinols (R3COH), the affinity increase caused by C/Si exchange varied between 3 and 10 fold for achiral drugs but was negligible in the case of chiral drugs. Silanols induced more favourable enthalpy and less favourable entropy changes than the corresponding carbinols when binding. Organogermanium compounds (R4Ge) when compared to their silicon counterparts (R4Si) showed no significant difference in affinity as well as in enthalpy and entropy changes. 5. Exchange of a cyclohexyl by a phenyl moiety was associated with an increase or a decrease in drug affinity (depending on the absolute configuration in the case of chiral drugs) and generally also with a more favourable enthalpy change and a less favourable entropy change of drug binding. 6. Replacement of a pyrrolidino by a piperidino group and increasing the length of the alkylene chain bridging the amino group and the central carbon or silicon atom were associated with either an increase or a decrease of entropy and enthalpy changes of drug binding. However, there was no clear correlation between these structural variations and the thermodynamic effects. 7. Taken together, these results suggest that hydrogen bond-forming OH groups and, to a lesser extent, polarizable phenyl groups contribute significantly to the thermodynamics of interactions between these classes of muscarinic antagonists and M2 muscarinic receptors.

Stereoselective interaction of procyclidine, hexahydro-difenidol, hexbutinol and oxyphencyclimine, and of related antagonists, with four muscarinic receptors

We investigated the binding properties of the (R)- and (S)-enantiomers of the muscarinic antagonists trihexyphenidyl, procyclidine, hexahydro-difenidol, p-fluoro-hexahydro-difenidol, hexbutinol, p-fluoro-hexbutinol, and their corresponding methiodides at muscarinic M1, M2, M3 and M4 receptor subtypes. In addition, binding properties of the (R)- and (S)-enantiomers of oxyphencyclimine were studied. The (R)- enantiomers (eutomers) of all the compounds had a greater affinity than the (S)-isomers for the four muscarinic receptor subtypes. The binding patterns of the (R)- and (S)-enantiomers were generally different. We did not observe any general correlation between the potency of the high-affinity enantiomer and the affinity ratio (eudismic ratio) of the two enantiomers. The results are discussed in terms of a 'four subsites' binding model.

Binding properties of nine 4-diphenyl-acetoxy-N-methyl-piperidine (4-DAMP) analogues to M1, M2, M3 and putative M4 muscarinic receptor subtypes

1. We compared the binding properties of 4-diphenyl-acetoxy-N-methyl-piperidine methiodide (4-DAMP) and nine analogues of this compound on muscarinic receptors of human neuroblastoma NB-OK1 cells (M1 subtype), rat heart (M2 subtype), rat pancreas (M3 subtype) and to the putative M4 subtype in striatum. 2. The requirements for high affinity binding were somewhat different for the four receptor subtypes. In general, the requirements of M3 receptors were more stringent than for M1, M2 or putative M4 receptors. 3. The abilities of the compounds to discriminate muscarinic receptor subtypes were not correlated with their affinities at any subtype. 4. The temperature-dependence of binding of 4-DAMP analogues to M2 receptors varied with the drug structure. In particular, the increased affinity of the alpha-methyl derivative of 4-DAMP could be ascribed to van der Waals interactions. 5. The affinities of most 4-DAMP analogues for M2 and M3 receptors were similar to their pharmacological potencies on atrial and ileum preparations, respectively. 6. At concentrations above 1 microM, all 4-DAMP analogues as well as atropine, reduced the [3H]-N-methyl scopolamine ([3H]-NMS) dissociation rate from cardiac muscarinic receptors, with no obvious structure-activity relationship.

Binding kinetics of quinuclidinyl benzilate and methyl-quinuclidinyl benzilate enantiomers at neuronal (M1), cardiac (M2), and pancreatic (M3) muscarinic receptors

We analyzed the competition kinetics of quinuclidinyl benzilate (QNB) and QNB methiodide enantiomers on human NB-OK1 neuroblastoma (M1), rat cardiac (M2), and rat pancreas (M3) muscarinic binding sites. The association rate constants of the four drugs depended on the receptor subtype studied and were lower with pancreas (M3) (1-9 x 10(5) M-1 sec-1) than with cardiac (M2) (1-5 x 10(6) M-1 sec-1) and NB-OK1 (M1) (1-5 x 10(6) M-1 sec-1) binding sites. At each receptor subtype, we observed no significant difference between the association rate constants of the R- and S-enantiomers of either QNB or QNB methiodide. Receptor stereoselectivity, when present, was associated with differences in unlabeled drug dissociation rate constants. The dissociation rate constant varied much more than the association rate constant, when either (R)-QNB dissociation from the three subtypes (half-life, 77 min to greater than 340 min; best fit, 40 days) or dissociation of the four drugs from each receptor subtype (half-lives varying from 1.4 min to 4 hr at M1 receptors, 1.1 to 77 min at M2 receptors, and 3.5 min to greater than 340 min at M3 receptors were obtained by competition kinetics analysis) was compared.

Binding affinities of hexahydro-difenidol and hexahydro-sila-difenidol analogues at four muscarinic receptor subtypes: constitutional and stereochemical aspects

Hexahydro-sila-difenidol and eight analogues behaved as simple competitive inhibitors of [3H]N-methyl-scopolamine binding to homogenates from human neuroblastoma NB-OK 1 cells (M1 sites), rat heart (M2 sites), rat pancreas (M3 sites), and rat striatum 'B' sites (M4 sites). Pyrrolidino- and hexamethyleneimino analogues showed the same selectivity profile as the parent compound. Hexahydro-sila-difenidol methiodide and the methiodide of p-fluoro-hexahydro-sila-difenidol had a higher affinity but a lower selectivity than the tertiary amines. Compounds containing a p-methoxy, p-chloro or p-fluoro substituent in the phenyl ring of hexahydro-sila-difenidol showed a qualitatively similar selectivity profile as the parent compound (i.e., M1 = M3 = M4 greater than M2), but up to 16-fold lower affinities. o-Methoxy-hexahydro-sila-difenidol has a lower affinity than hexahydro-sila-difenidol at the four binding sites. Its selectivity profile (M4 greater than M1, M3 greater than M2) was different from hexahydro-sila-difenidol. Replacement of the central silicon atom of hexahydro-sila-difenidol, p-fluoro-hexahydro-sila-difenidol and their quaternary (N-methylated) analogues by a carbon atom did not change their binding affinities significantly. The four muscarinic receptors showed a higher affinity for the (R)- than for the (S)-enantiomers of hexahydro-difenidol, p-fluorohexahydro-difenidol and their methiodides. The stereoselectivity varied depending on the receptor subtype and drug considered.

Stereoselectivity of (R)- and (S)-hexahydro-difenidol binding to neuroblastoma M1, cardiac M2, pancreatic M3, and striatum M4 muscarinic receptors

(R)-Hexahydro-difenidol has a higher affinity for M1 receptors in NB-OK 1 cells, pancreas M3 and striatum M4 receptors (pKi 7.9 to 8.3) than for cardiac M2 receptors (pKi 7.0). (S)-Hexahydro-difenidol, by contrast, is nonselective (pKi 5.8 to 6.1). Our goal in the present study was to evaluate the importance of the hydrophobic phenyl, and cyclohexyl rings of hexahydro-difenidol for the stereoselectivity and receptor selectivity of hexahydro-difenidol binding to the four muscarinic receptors. Our results indicated that replacement of the phenyl ring of hexahydro-difenidol by a cyclohexyl group (----dicyclidol) and of the cyclohexyl ring by a phenyl moiety (----difenidol) induced a large (4- to 80-fold) decrease in binding affinity for all muscarinic receptors. Difenidol had a significant preference for M1, M3, and M4 over M2 receptors; dicyclidol, by contrast, had a greater affinity for M1 and M4 than for M2 and M3 receptors. The binding free energy decrease due to replacement of the phenyl and the cyclohexyl groups of (R)-hexahydro-difenidol by, respectively, a cyclohexyl and a phenyl moiety was almost additive in the case of M4 (striatum) binding sites. In the case of the cardiac M2, pancreatic M3, or NB-OK 1 M1 receptors the respective binding free energies were not completely additive. These results suggest that the four (R)-hexahydro-difenidol "binding moieties" (phenyl, cyclohexyl, hydroxy, and protonated amino group) cannot simultaneously form optimal interactions with the M1, M2, and M3 muscarinic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselectivity of procyclidine binding to muscarinic receptor subtypes M1, M2 and M4

The goals of the present study were: (1) to investigate the binding properties of (R)- and (S)-procyclidine and two achiral derivatives of muscarinic M1, M2 and M4 receptor subtypes and (2) to identify the interactions which allow these receptors to discriminate between the two stereoisomers. (R)-Procyclidine showed a higher affinity for human neuroblastoma NB-OK 1 muscarinic M1 and rat striatum muscarinic M4 receptors, as compared to rat cardiac M2 receptors. (S)-Procyclidine had a 130-fold lower affinity than (R)-procyclidine for M1 and M4 receptors, and a 40-fold lower affinity for M2 receptors. Pyrrinol, the achiral diphenyl derivative with the cyclohexyl group of (S)-procyclidine replaced by a phenyl group, has an eight-fold lower affinity for M1 and M4 receptors, as compared to (R)-procyclidine, and a three-fold lower affinity for M2 receptors. Hexahydro-procyclidine, the corresponding achiral dicyclohexyl compound, had a 10- to 20-fold lower affinity than (R)-procyclidine for the three receptors. The increase in binding free energy, which is observed when the phenyl and cyclohexyl groups of procyclidine are separately replaced by cyclohexyl and phenyl groups, respectively, was additive in the case of M1, M2 and M4 receptors. This indicates that the muscarinic receptor stereoselectivity was based on the coexistence of two binding sites, one preferring a phenyl rather than cyclohexyl group and the second preferring a cyclohexyl rather than a phenyl group. In addition, there were also binding sites for the hydroxy moiety and the protonated amino group of the ligands. The greater affinity and stereoselectivity of M1 and M4 muscarinic receptors for (R)-procyclidine reflected the better fit of the cyclohexyl group of (R)-procyclidine to the subsite of M1 and M4 as compared to M2 receptors.

Binding of selective antagonists to four muscarinic receptors (M1 to M4) in rat forebrain

To compare the proportions of four muscarinic receptors in different rat brain regions, we used competition curves with four selective antagonists, at 1-[N-methyl-3H]scopolamine methyl chloride [( 3H]NMS) binding equilibrium and after allowing [3H]NMS dissociation for 35 min. Himbacine and methoctramine were shown to discriminate two muscarinic receptor subtypes having a high affinity for 4-diphenylacetoxy-N-methylpiperidine methiodide and hexahydrosiladifenidol, intermediate affinity for pirenzepine, and low affinity for AF-DX 116. One M4 subtype had a high affinity for himbacine and methoctramine; it was found predominantly in homogenates from rat striatum (46% of total [3H]NMS receptors) and in lower proportion in cortex (33% of [3H]NMS receptors) and hippocampus (16% of [3H]NMS receptors). Its binding properties were identical to those of muscarinic receptors in the neuroblastoma x glioma NG 108-15 hybrid, suggesting that it was encoded by m4 mRNA. The M3 subtype (typically found in rat pancreas, a tissue expressing the m3 mRNA) had a low affinity for himbacine and methoctramine and represented about 10% of all [3H]NMS receptors in rat brain cortex, hippocampus, striatum, and cerebellum. M1 and M2 receptors were identified in rat brain by their high affinity for pirenzepine and AF-DX 116, respectively.

Pharmacology of hexahydro-difenidol, hexahydro-sila-difenidol and related selective muscarinic antagonists

A series of hexahydro-difenidol (HHD) and hexahydro-sila-difenidol (HHSiD) analogues modified in the amino group, the phenyl ring and in the alkylene chain were investigated for their binding and functional properties at muscarinic M1, M2 and M3 receptors. Novel muscarinic receptor antagonists were obtained which exhibited different receptor selectivity profiles from the parent compounds HHD and HHSiD (M1 congruent to M3 greater than M2), e.g. HHD and HHSiD methiodides, M1 greater than M2 congruent to M3; p-fluoro-HHSiD, M3 greater than M1 greater than M2; trans-hexbutenol, M1 greater than M3 greater than M2; and (s)-p-fluoro-hexbutinol, M3 greater than M2 congruent to M1. Stereoselectivity ratios [(R)/(S)] for the enantiomers of HHD, hexbutinol and p-fluoro-hexbutinol were highest at M1, intermediate at M3 and lowest at M2 receptors.

Stereoselectivity of the interaction of muscarinic antagonists with their receptors

The stereoselectivity of the interaction with muscarinic receptors of enantiomers of a series of chiral antagonists is receptor subtype dependent. There is no overall relationship between stereoselectivity and receptor affinity. Depending on the antagonist studied, receptor stereoselectivity may indeed reflect: (1) the weakening or loss of a single interaction involving one of the four groups bound to the asymmetric carbon; (2) steric hindrance preventing optimum interaction of the low affinity steroisomer with the receptor; and/or (3) the inversion of the relative positions of two moieties of the ligand with similar structural and electronic properties i.e. comparable affinities for the two corresponding subsites in the receptor.

Determination of the association and dissociation rate constants of muscarinic antagonists on rat pancreas: rank order of potency varies with time

Antagonist binding to rat pancreatic muscarinic receptors was relatively slow at 25 degrees (tracer dissociation half-life, 50 to 60 min). We, therefore, chose this system to investigate the errors induced by nonequilibrium incubations on the estimates of receptor capacity and selectivity, in binding studies. We took advantage of the fact that muscarinic antagonists recognize only one receptor subtype in rat pancreatic homogenates and that association and dissociation kinetics conform to the law of mass action to analyze quantitatively the binding kinetics of [3H]N-methylscopolamine and of several unlabeled progressive to these receptors. We observed no correlation between the affinities of drugs for muscarinic receptors and their dissociation rate constants. As a result, the apparent receptor specificity (based on relative affinities for different antagonists) varied markedly with the incubation period. We, therefore, strongly recommend that in general competition curves established for receptor classification should be compared at different incubation periods to ensure that equilibrium is attained. The association rate constants of muscarinic antagonists for rat pancreas receptors were remarkably low, when compared with other ligand-receptor systems. This suggests that the antagonist-pancreatic muscarinic receptor association reaction included a rate-limiting conformational change of the drug-receptor complex. This isomerization step was not directly detectable in our kinetic studies, due to the very low affinity and rapid dissociation rate of the initial nonisomerized complex.

Binding and functional properties of antimuscarinics of the hexocyclium/sila-hexocyclium and hexahydro-diphenidol/hexahydro-sila-diphenidol type to muscarinic receptor subtypes

1. In an attempt to assess the structural requirements for the muscarinic receptor selectivity of hexahydro-diphenidol (hexahydro-difenidol) and hexahydro-sila-diphenidol (hexahydro-sila-difenidol), a series of structurally related C/Si pairs were investigated, along with atropine, pirenzepine and methoctramine, for their binding affinities in NB-OK 1 cells as well as in rat heart and pancreas. 2. The action of these antagonists at muscarinic receptors mediating negative inotropic responses in guinea-pig atria and ileal contractions has also been assessed. 3. Antagonist binding data indicated that NB-OK 1 cells (M1 type) as well as rat heart (cardiac type) and pancreas (glandular/smooth muscle type) possess different muscarinic receptor subtypes. 4. A highly significant correlation was found between the binding affinities of the antagonists to muscarinic receptors in rat heart and pancreas, respectively, and the affinities to muscarinic receptors in guinea-pig atria and ileum. This implies that the muscarinic binding sites in rat heart and the receptors in guinea-pig atria are essentially similar, but different from those in pancreas and ileum. 5. The antimuscarinic potency of hexahydro-diphenidol and hexahydro-sila-diphenidol at the three subtypes was influenced differently by structural modifications (e.g. quaternization). Different selectivity profiles for the antagonists were obtained, which makes these compounds useful tools to investigate further muscarinic receptor heterogeneity. Indeed, the tertiary analogues hexahydro-diphenidol (HHD) and hexahydro-sila-diphenidol (HHSiD) had an M1 = glandular/smooth muscle greater than cardiac selectivity profile, whereas the quaternary analogues HHD methiodide and HHSiD methiodide were M1 preferring (M1 greater than glandular/smooth muscle, cardiac).

Characterization of muscarinic receptors in human pancreatic membranes

Crude membranes (27,000 x g pellets) from three normal human pancreata were prepared. Muscarinic receptors were investigated by the ability of three antagonists (atropine, pirenzepine, and AF-DX 116) and three agonists (carbamylcholine, oxotremorine, and pilocarpine) to inhibit [3H]NMS binding. These receptors showed for pirenzepine and AF-DX 116 a M2 beta specificity, typical of secretory glands and smooth muscle, that was comparable to that of rat pancreatic membranes, i.e., a low affinity for the two antagonists (Ki of 0.4 and 0.2 microM, respectively). In addition, these receptors were predominantly in a low affinity state for the agonist carbamylcholine (Ki of 100 microM).

80% of muscarinic receptors expressed by the NB-OK 1 human neuroblastoma cell line show high affinity for pirenzepine and are comparable to rat hippocampus M1 receptors

The NB-OK 1 human neuroblastoma cell line expressed muscarinic cholinergic receptors that could be labeled with N-[3H]methylscopolamine (a nonselective antagonist). 80% of these receptors showed high affinity for pirenzepine, i.e. belonged to the M 1 subtype found in neuronal tissues. Their binding properties were identical to those of rat hippocampus M 1 receptors, and differed from those of rat pancreas and heart muscarinic receptors. The remaining (20%) muscarinic receptors showed low affinity for pirenzepine and AF-DX 116, being therefore of an M2 beta (or B) subtype, and were similar to rat pancreatic receptors.

Different antagonist binding properties of rat pancreatic and cardiac muscarinic receptors

The antagonist binding properties of rat pancreatic and cardiac muscarinic receptors were compared. In both tissues pirenzepine (PZ) had a low affinity for muscarinic receptors labelled by (3H)N-methylscopolamine [3)NMS) (KD values of 140 and 280 nM, respectively, in pancreatic and cardiac homogenates). The binding properties of pancreatic and cardiac receptors were, however, markedly different. This was indicated by different affinities for dicyclomine, (11-([(2-[diethylamino)-methyl)-1-piperidinyl] acetyl)-5, 11-dihydro-6H-pyrido(2,3-b)(1,4) benzodiazepin-6-on) (AFDX-116), 4-diphenylacetoxy-N-methyl-piperidine methobromide (4-DAMP) and hexahydrosiladifenidol (HHSiD). Pancreatic and cardiac muscarinic receptors also showed different (3H)NMS association and dissociation rates. These results support the concept of M2 receptor heterogeneity and confirm that M2 receptor subtypes have different binding kinetic properties.

The interaction of caerulein with the rat pancreas. 1. Specific binding of [3H]caerulein on plasma membranes and evidence for negative cooperativity

1. The binding of [3H]caerulein (a stable, biologically active labeled analog of cholecystokinin-pancreozymin) to semi-purified rat pancreatic plasma membranes was investigated. The binding was dependent on time and temperature, as well as saturable, specific and reversible. This process was pH-dependent and optimal at pH 7.0. Cysteine and serine residues in plasma membranes were of importance for binding. Mg2+ favored the binding. 2. The acceleration of the dissociation of [3H]caerulein in the presence of an excess of native caerulein suggests that binding was characterized by a negative cooperativity. The fast dissociation state evoked by a high degree of occupancy by caerulein was inhibited by lowering the temperature, by decreasing the pH, or by the presence of wheat germ agglutinin.

Association of binding sites for guanine nucleotides with adenylate cyclase activation in rat pancreatic plasma membranes. Interaction of gastrointestinal hormones

1. The activation of rat pancreatic adenylate cyclase by guanosine 5'-(beta-gamma-imido)triphosphate (p[NH]ppG) and GTP, and by the two gastrointestinal hormones pancreozymin (as C-terminal octapeptide) and secretin was correlated with the binding of [8-3H]guanosine 5'-(beta-gamma-imido)triphosphate to rat pancreatic plasma membranes. 2. The low basal adenylate cyclase activity was stimulated 17-fold by p[NH]ppG (after a 2 min lag period), 3,5-fold only by GTP, 21-fold by C-terminal octapeptide of pancreozymin, and 8-fold by secretin. GTP inhibited competitively the activation of adenylate cyclase by p[NH]ppG with a Ki,app almost identical with the Ka,app (0.3 micron). p[NH]ppG and GTP enhanced the stimulation by secretin more markedly than that by the C-terminal octapeptide of pancreozymin, leading to the same maximal activity. Both hormones suppressed the lag period of activation by p[NH]ppG. 3. The binding of [8-3H]p[NH]ppG was dependent on time, temperature and Mg2+ and it was also a saturable and reversible process. Scatchard plots with a concavity upward were linearized after co-addition of ATP, Mg2+ and an ATP-regenerating system that abolished low-affinity sites for p[NH]ppG without saturating higher affinity sites, GTP, ITP and UTP inhibited [8-3H]p[NH]ppG binding to the high-affinity sites in concentration ranges identical with those found for adenylate cyclase activation. Considerable binding of [8-3H]p[NH]ppG was still evident at 20 degrees C, but enzyme activation was not observed any more, except in the presence of hormones.

Subcellular distribution and response to gastroinetstinal hormones of adenylate cyclase in the rat pancreas. Partial purification of a stable plasma membrane preparation

1. The subcellular distribution of adenylate cyclase activity in rat pancreatic homogenates was examined after differential centrifugation. Divalent cations exerted significant effects on this distribution. In addition, the ratio of adenylate cyclase activities in the presence of the C-terminal octapeptide of cholecystokinin-pancreozymin and secretin was lower in the crude 'mitochondrial' fraction than in 'microsomal' fractions. This difference was due to the lability of cholecystokinin-pancreozymin receptors compared to secretin receptors. The Km,app of activation was affected more than the V by this lability. Such a degradation of cholecystokinin-pancreozymin receptors was markedly delayed by isolation and storage in the presence of a phospholipid mixture. 2. A simple, reasonably rapid (6 h), and easily reproducible method was developed to prepare a stable semi-purified plasma membrane fraction, characterized by a 10-fold increase in the specific activity of adenylate cyclase with respect to the whole homogenate. At variance with data obtained on crude subcellular fractions, the V of adenylate cyclase activity observed in this preparation, under maximal concentration of the C-terminal octapeptide of cholecystokinin-pancreozymin, was higher than that obtained with secretin or the vasoactive intestinal polypeptide.