Effect of thyroid status on alpha- and beta-catecholamine responsiveness of hamster adipocytes.

It has been suggested that part of the increased beta-catecholamine responsiveness in hyperthyroid animals is due to a decrease in alpha-catecholamine action. The present results indicate that neither hyperthyroidism nor hypothyroidism altered the alpha 2-adrenergic inhibition of adenylate cyclase or the alpha 1-adrenergic stimulation of phosphatidylinositol turnover in adipocytes from the white adipose tissue of hamsters. No effect of hyperthyroidism was found on the Kd for binding of [3H]dihydroergocryptine or the number of binding sites in membranes prepared from hamster adipocyte tissue.

Hypothyroidism modulates beta adrenergic receptor adenylate cyclase interactions in rat reticulocytes.

We have investigated alterations in beta adrenergic receptor binding sites of rat reticulocytes occurring in animals rendered hypothyroid by thyroidectomy. Beta adrenergic receptor interactions were assessed by measuring the number of (-)[3H]-dihydroalprenolol binding sites and the ability of an agonist to compete for occupancy of the receptors. The number of receptors was significantly reduced in cells from the hypothyroid animals.

Photoaffinity labeling of the beta-adrenergic receptor.

A new photoactive beta-adrenergic antagonist, p-azidobenzylcarazolol (pABC) has been synthesized by combining a carbazole moiety with a p-azido-benzyl substituent. The compound has been labeled with tritium to a specific activity of 26 Ci/mmol. In frog erythrocyte membranes, [3H]p-azido-benzylcarazolol binds to the beta-adrenergic receptor with the expected beta 2 specificity and with high affinity (KD congruent to 100 +/- 10 pM).

Agonist-promoted high affinity state of the beta-adrenergic receptor in human neutrophils: modulation by corticosteroids.

beta-Adrenergic agonists form high affinity complexes with receptors, resulting in activation of the associated adenylate cyclase. To examine the formation of the high affinity state of the receptor, curves were constructed for the competition of the full beta-adrenergic agonist isoproterenol, partial agonists cobefrin and soterenol, and the antagonist propranolol for [3H]dihydroalprenolol binding to beta-adrenergic receptors on human neutrophil membranes. Curve modeling by computer yielded a two-state binding model for the agonists, with distinct dissociation constants for the high (KH) and low (KL) affinity states.

Evidence that a beta-adrenergic receptor-associated guanine nucleotide regulatory protein conveys guanosine 5'-O-(3-thiotriphosphate)- dependent adenylate cyclase activity.

The guanine nucleotide regulatory protein component (N) of the frog erythrocyte membrane adenylate cyclase system appears to form a stable complex with the beta-adrenergic receptor (R) in the presence of agonist (H). This agonist-promoted ternary complex HRN can be solubilized with Lubrol. The guanine nucleotide regulatory protein associated with the solubilized complex can be adsorbed either to GTP-Sepharose directly or to wheat germ lectin-Sepharose via its interaction with the receptor which is a glycoprotein.

Subtype specificity of alpha-adrenergic receptors in rat heart.

Recent studies suggest that two subtypes of alpha-adrenergic receptors (alpha 1 and alpha 2) can be distinguished on the basis of the differential affinities of certain adrenergic ligands for each subtype. We have investigated the binding characteristics of several such ligands for alpha-adrenergic receptors in membrane preparations derived from rat heart. alpha-Adrenergic antagonists competed for binding sites identified by the nonsubtype selective alpha-adrenergic ligand [3H]dihydroergocryptine (DHE) in the order of potency expected for alpha 1-receptors, namely, prazosin (EC50 = 0.

alpha-Adrenergic receptors in human adipocyte membranes: direct determination by [3H]yohimbine binding.

The presence of alpha 2-adrenergic receptors in membranes derived from human sc adipose tissue was directly demonstrated with a new alpha 2-selective ligand, [3H]yohimbine. Binding of this radiolabeled antagonist to adipocyte membranes was of high affinity (Kd = 3.9 +/- 2.

Pharmacological characterizations of adrenergic receptors in human adipocytes.

Three types of adrenergic receptors, beta, alpha-1, and alpha-2, were identified in human adipocytes, isolated from properitoneal adipose tissue, using both the binding of radioactive ligands and the effects of adrenergic agents on receptor-specific biochemical responses. Adrenergic binding studies showed the following results: [(3)H]dihydroalprenolol binding (beta adrenergic) B(max) 280 fmol/mg protein, K(D) 0.38 nM; [(3)H]para-aminoclonidine binding (alpha-2 adrenergic) B(max) 166 fmol/mg protein, K(D) 0.

Myocardial beta-adrenergic receptors from adrenalectomized rats: impaired formation of high-affinity agonist-receptor complexes.

Adrenal steroid hormones potentiate beta-adrenergic actions on the heart. Accordingly, we investigated the effects of adrenalectomy on agonist and antagonist interactions with myocardial beta-adrenergic receptors and adenylate cyclase. The affinity and number of beta-adrenergic receptor sites, both defined by the antagonist (-) [3H]dihydroalprenolol, did not change after adrenalectomy.

Catecholamine-induced desensitization in turkey erythrocytes: cAMP mediated impairment of high affinity agonist binding without alteration in receptor number.

Desensitization of turkey erythrocyte adenylate cyclase by exposure of these cells to the beta-adrenergic agonist isoproterenol leads to a decrease in subsequent adenylate cyclase stimulation by isoproterenol, F-, or Gpp(NH)p without any apparent loss or down regulation of receptors (B.B. Hoffman et al.

Differential effects of cholera toxin on guanine nucleotide regulation of beta-adrenergic agonist high affinity binding and adenylate cyclase activation in frog erythrocyte membranes.

The guanine nucleotide regulatory protein(s) regulates both adenylate cyclase activity and the affinity of adenylate cyclase-coupled receptors for hormones or agonist drugs. Cholera toxin catalyzes the covalent modification of the nucleotide regulatory protein of adenylate cyclase systems. Incubation of frog erythrocyte membranes with cholera toxin and NAD+ did not substantially alter the dose dependency for guanine nucleotide activation of adenylate cyclase activity.

Differential regulation of the alpha 2-adrenergic receptor by Na+ and guanine nucleotides.

Many hormones interact with receptors which stimulate the enzyme adenylate cyclase. Less well characterized ar those receptors which mediate an inhibition of adenylate cyclase activity. However, guanine nucleotides are clearly important in the regulation of both stimulatory and inhibitory receptors.