iodohydroxybenzylpindolol and zinterol

A nonfusing variant of L6 muscle cells was used to study the interactions of 16 agonists and 8 antagonists with beta-adrenergic receptors. Membranes prepared from L6 cells and intact cells in monolayer culture were used. Beta-adrenergic receptors on broken cells and on intact cells had the same affinities for all of the antagonists studied. Studies of the inhibition of the binding of [125I]iodohydroxybenzylpindolol by agonists indicated that two states of the receptor can exist on intact cells attached to the substratum. The form of the receptor normally present on intact cells appeared to have the same properties as receptors on membranes when assayed in the presence of GTP. Several full agonists converted this form of the receptor to a form which had a 40- to 50-fold lower affinity for agonists. This conversion appeared to occur during the first few minutes of exposure to an agonist. Four of the agonists tested did not convert any of the receptors on intact cells to a form with a low affinity for agonists. Included in this group of agents were two full agonists and two partial agonists. Therefore, interactions of these drugs with receptors on broken or intact cells were the same. Several other full and partial agonists converted some of the receptors on intact cells to a low-affinity form, and their interactions with receptors on intact cells were characterized by shallow inhibition curves. The conversion of beta-adrenergic receptors on intact cells to a low-affinity state did not appear to be a prerequisite for the decrease in the rate of agonist-stimulated cyclic AMP accumulation that occurs 1-2 min after exposure of L6 cells to agonists. Studies were also carried out on viable intact cells detached from plates following brief exposure to trypsin or EDTA. The properties of receptors on suspended cells were the same as those of receptors on broken cells when assayed in the presence of GTP, rather than being similar to the properties of receptors on attached cells. In summary, data are presented indicating that agonists with the same potency and intrinsic activity in membrane preparations (and intact cells in suspension) can interact very differently with beta-adrenergic receptors on intact cells attached to the substratum. Thus, certain agonists cause a rapid conversion of beta-adrenergic receptors to a form which has a low affinity for agonists. This effect is seen with some but not all agonists and is seen only in studies with attached cells.

Topics: Adrenergic beta-Agonists; Adrenergic beta-Antagonists; Animals; Binding, Competitive; Cell Line; Cyclic AMP; Ethanolamines; Isoproterenol; Muscles; Pindolol; Rats; Receptors, Adrenergic, beta

Topics: Adrenergic beta-Agonists; Androgens; Animals; Estrus; Ethanolamines; Female; Granulosa Cells; Isoproterenol; Kinetics; Ovary; Pindolol; Pregnancy; Progesterone; Propranolol; Rats; Rats, Inbred Strains; Receptors, Adrenergic; Receptors, Adrenergic, beta; Sexual Maturation

The subtype of the beta-adrenergic receptor expressed in 3T3-L1 preadipocytes and adipocytes differentiated with dexamethasone and methylisobutylxanthine was determined by comparing the affinity of the receptors for epinephrine, norepinephrine, and beta-1 and beta-2 selective antagonist, 8-fold more avidly than adipocyte receptors. In contrast, adipocyte beta-receptors had a 10-fold higher affinity for epinephrine than for norepinephrine and complexed the beta-2 selective agonist zinterol with a 20-fold higher affinity than preadipocyte receptors. Hofstee plots and computer analyses of the binding data revealed that the populations of beta-1 receptors in preadipocytes and beta-2 receptors in adipocytes were nearly homogeneous. Preliminary characterizations of the beta-receptor phenotype in (nondifferentiating) 3T3-C2 cells treated with dexamethasone and methylisobutylxanthine and 3T3-422A adipocytes differentiated with insulin indicated that the expression of beta-2 receptors was not correlated with differentiation, but rather with exposure of the cells to dexamethasone and methylisobutylxanthine. The regulator of beta-receptor subtype was identified as the glucocorticoid analog, dexamethasone, by employing 3T3-L1 adipocytes which were stimulated to differentiate with methylisobutylxanthine and insulin. Detailed binding studies showed that under these conditions the adipocyte receptors retain beta-1 character. Subsequent treatment with 0.5 microM dexamethasone promoted the loss of beta-1 receptors, the appearance of beta-2 receptors, and a net 2- to 3-fold increase in the number of beta-receptors. Dexamethasone effected a complete switch from beta-1 to beta-2 subtype at concentrations as low as 2.5 nM while other steroids were ineffective below a concentration of 10 microM.

Topics: Adipose Tissue; Adrenergic beta-Agonists; Animals; Binding, Competitive; Cell Differentiation; Cell Membrane; Cells, Cultured; Dexamethasone; Ethanolamines; Isoproterenol; Kinetics; Mice; Pindolol; Receptors, Adrenergic; Receptors, Adrenergic, beta

The 125I-labeled iodohydroxybenzylpindolol (IHYP) binding to beta-receptors on brain micro-vessels is inhibited by isoproterenol, epinephrine and norepinephrine, with Ki values of 2 X 10(-7) M, 2.5 X 10(-6) M and 1.2 X 10(-5) M, respectively. A modified Scatchard analysis of the inhibitory effects of practolol, metroprolol and zinterol on IHYP binding has shown that the proportion of beta 2-receptors in our preparation is about 80% of the total beta-adrenergic receptor population. Our data indicate that the beta-adrenergic receptors located on cerebral microvessels are of both beta 1 and beta 2 types, with a predominance of the beta 2 type.

Topics: Animals; Binding, Competitive; Cerebrovascular Circulation; Ethanolamines; Kinetics; Metoprolol; Pindolol; Practolol; Rats; Receptors, Adrenergic; Receptors, Adrenergic, beta