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The possible involvement of specific dopamine receptors in the relaxing effect of dopamine in the guinea-pig isolated jejunum has been investigated. The relaxing effect of dopamine does not show the tachyphylaxis phenomenon and it is present in preparations from guinea-pigs pretreated with reserpine. These results indicate that dopamine has a direct action. Comparison of the effect of dopamine with those of other dopamine receptor agonists, i.e. apomorphine, bromocriptine and the DA1 selective fenoldopam, were made to calculate potency ratios. Since apomorphine, bromocriptine and fenoldopam were shown to relax the guinea-pig jejunum, partly behaving as indirectly acting agents, comparisons were made on reserpine-pretreated guinea-pigs. It has been found that apomorphine is 2.5 times, fenoldopam 3 times and bromocriptine 20 times more active than dopamine in relaxing the guinea-pig jejunum. The order of potency is different from that found in other dopamine receptors containing tissues. The effects of the dopamine receptor blockers, haloperidol and cis-alpha-flupenthixol and the DA1 selective blocker SCH 23390 on the relaxing effect of dopamine were also studied. The relaxing effect of dopamine was not reduced by haloperidol, cis-alpha-flupenthixol and SCH 23390. It is concluded that specific postjunctional dopamine receptors are not involved in the relaxing action of dopamine. Since dopamine is known to interact with alpha- and beta-adrenoceptors in a variety of tissues, the effects of the alpha-adrenoceptor blocker phentolamine and the beta-adrenoceptor blocker propranolol on the relaxing effect of dopamine were also studied. Noradrenaline has been used to check the responsiveness of the tissue. Phentolamine did not block the responses to dopamine and propranolol was able only to partially reduce responses to dopamine, at concentrations higher than those at which it antagonized noradrenaline. Mechanisms other than dopamine, alpha- or beta-receptor activation should be involved in the relaxing effect of dopamine in the guinea-pig jejunum.

A murine monoclonal antibody, OKT16, specific for human lymphocytes of T lineage, was isolated by standard immunization and hybridization techniques. The distribution of the antigen defined by OKT16 was similar to the antigen reactive with monoclonal antibodies 3A1 and WT1. This identity of antigen targets was confirmed in an enzyme-linked immunosorbent assay system and by sequential immunoprecipitation. Under reducing conditions, OKT16 reacted with an antigen of 40K daltons; however, under nonreducing conditions this antigen appeared as an 84K-dalton molecule, which suggests that the p40 antigen exists as a disulfide-linked dimer. By indirect immunofluorescence, OKT16 reacted with a greater fraction of nonrosetting, non-B (null) lymphocytes than with antibodies to other T cell-specific proteins. Two-color immunofluorescence demonstrated the coexpression of the T16 antigen and the C3bi receptor on most null cells. The T10 antigen (found on cortical thymocytes and activated peripheral T cells) was restricted to most T16-bearing null cells and expression of the Fc receptor for aggregated IgG (defined by monoclonal antibody 73.1) was restricted to a major subset of T16-bearing null cells. The T cell-specific markers defined by OKT8, OKT11, and OKT17, as well as the monocyte marker defined by OKM5, were expressed by smaller subsets of OKT16-reactive null cells. These studies support by phenotypic analysis the functional heterogeneity ascribed to null cells. The 40K-dalton T16 antigen has the most extensive null cell representation of all the T lineage markers described to date.

The nicotinic activity of seven cholinergic agents endowed with a very high muscarinic activity (carbachol, methylfurtrethonium, cis-2-methyl-4-trimethylammoniummethyl-1,3-dioxolane, cis-2-methyl-5-trimethylammoniummethil-1,3-oxathiolane, muscarine, muscarone, oxotremorine) has been studied on the frog rectus abdominis. Carbachol is the most active compound with an EC50 value of 1.98 X 10(-6) M; the ratio between nicotinic and muscarinc activity is 67. Methylfurtrethonium and oxotremorine are the least potent and also behave as "partial agonists". Muscarine is devoid of activity. It is concluded that the nicotinic component does not interfere with the evaluation of the muscarinic potency of the compounds under investigation.

Dissociation constant and relative efficacy values of six cholinergic agents endowed with a high muscarinic activity (carbachol, methylfurtrethonium, cis-2-methyl-4-trimetylammoniummethyl-1,3-dioxolane, cis-2-methyl-5-trimethylammoniummethyl-1,3-oxathiolane, muscarone, oxotremorine) have been determined on the frog rectus abdominis nicotinic receptors. The results obtained point out that: a) the nicotinic receptor reserve of the frog rectus abdominis is very little if any, b) there are no appreciable variations in the relative efficacy values of all the compounds tested, c) it is instead possible to establish a rank order of affinity. The comparison of the affinity values towards nicotinic receptors, herewith reported, and those towards ileal muscarinic receptors, previously reported could be useful to shed some light on the differences between muscarinic and nicotinic receptors.

The present report attempts to determine if there are distinct epitopes on the T8 molecule that are involved in class I-restricted cytotoxic T lymphocyte (CTL) function. A panel of 9 monoclonal antibodies (OKT8A,B,C,E,F,G,H,I, and OKT5) was produced and all antibodies were shown to bind to the T8 molecule. This panel of antibodies was employed to characterize the distribution of distinct epitopes on the T8 molecule and to block the activity of class I-specific influenza virus-immune and allo-immune CTL effector function. Significant differences in the ability of the anti-T8 antibodies to block CTL function were observed: OKT8C and T8F blocked best (49 and 55% respectively); OKT8A,E,G,H,I, and OKT5 blocked less well (24-31%); and OKT8B blocked marginally (11%). There was no correlation between the capacity of the antibodies to block CTL function and their heavy chain isotype. Competitive binding of the different OKT8 antibodies to the cell surface and differential trypsin sensitivity of the epitopes recognized by the antibodies indicated that OKT8C and T8F were located on topographically distinct regions of the T8 molecule. These results indicate that specific epitopes on the T8 molecule are involved in CTL function, and that there could be more than one functional site on the molecule.

The relaxing effect of dopamine on the rat isolated jejunum has been studied. Dopamine was found 170 times less potent than noradrenaline and 3 times more potent than tyramine. The relaxing effect of dopamine does not show the tachyphylaxis phenomenon, is present in preparations from rats pretreated with reserpine and is not influenced by cocaine. These results indicate that dopamine has a direct action. To characterize the receptor(s) through which dopamine causes intestinal relaxation the alpha-blocker phentolamine, the beta-blocker propranolol and the dopamine receptor blockers haloperidol and cis-alpha-flupenthixol, alone or in combination have been tested. 40% of inhibition of the response to dopamine was obtained with phentolamine, 25% with propranolol and 30% with haloperidol or cis-alpha-flupenthixol. Combining together three antagonists acting on three different receptors it was possible to obtain 70% of inhibition of the responses to dopamine. It is concluded that alpha and beta adrenoceptors and specific dopamine receptors are involved in the direct relaxing action of dopamine.

This study was undertaken to determine dissociation constants (KA and relative efficacies (er) of seven muscarinic agonists (methylfurtrethonium; dioxolane, oxathiolane, carbachol, muscarine, muscarone and oxotremorine) in three isolated tissues (guinea-pig ileum and atria and rat urinary bladder). The rank order of affinities (-log KA) of the various compounds varied depending on the tissue used. er values for the different agonists did not differ significantly from each other in any of the three tissues, except that the er of muscarine in the guinea-pig ileum was higher than those of the other compounds and that of oxotremorine in the rat urinary bladder was lower than those of the other agonists. Comparisons among tissues show that KA and er values were the same in different tissues for some compounds (muscarone, muscarine and methylfurtrethonium), while significant differences were found for the other compounds. This suggests the existence of a discrete receptor population recognized by some but not all agonists. For oxotremorine er as well as -log KA, is greater in atria than in smooth muscle: these factors combine to determine the cardioselectivity of this compound which can now ascribed to receptor selectivity.

The antagonism of muscarinic receptor-mediated contraction of rat trachea by a range of muscarinic antagonists was quantified by Schild and resultant analysis. Dose-response curves to carbachol, muscarine and oxotremorine were shifted to the right by gallamine and pirenzepine in a parallel manner with no change in maximal response ostensibly indicating simple competitive inhibition. However, Schild analysis indicated differences in the blockade and estimated pKb values with each agonist for both gallamine and pirenzepine. This suggested either that the responses to these three agonists were mediated by a heterogeneous receptor population in this tissue or that the blockade produced by gallamine and by pirenzepine was not competitive. Further Schild analysis with the muscarinic antagonists scopolamine, atropine, 4-diphenylacetoxy-N-methyl piperidine methiodide and (11 [(2-[(diethylamino)methyl]-1-piperidinyl]acetyl)-5,11- dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine 6-one) with carbachol, muscarine and oxotremorine indicated simple competitive antagonism of a homogeneous population of muscarinic receptors. Therefore, the competitivity of binding of atropine, gallamine and pirenzepine with the scopolamine binding site was measured with the recently reported technique of resultant analysis. With this method the effect of various concentrations of the test antagonist on the antagonism produced by specified concentrations of the reference antagonist scopolamine was measured and the equilibrium dissociation constant of the test antagonist-receptor complex estimated. These data indicated that atropine and scopolamine bind to a common binding site on the muscarinic receptor, but that scopolamine and both gallamine and pirenzepine bind to mutually exclusive sites. This result is mine and pirenzepine are allosteric modulators of muscarinic receptors which bind at sites other than that utilized by agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

The frequency distributions of dissociation constant values of some muscarinic agonists (carbachol, muscarone and cis-2-methyl-5-trimethylammoniummethyl-1,3-oxathiolane) obtained on guinea-pig ileum and atria and rat urinary bladder have been examined to see if the means of the dissociation constant values and the statistical tests for their significance, should be based on geometric rather than on arithmetic means. For the three compounds the distributions on a logarithmic scale did not significantly deviate from normality while the distributions on an arithmetic scale tended to deviate from normality.