Binding of (3H)dihydroergocryptine to an alpha-adrenergic site in the stalk median eminence of the steer
Dihydroergocryptine (DHE), a potent dopamine agonist and alpha-adrenergic antagonist, has been used as a radioligand to characterize both dopamine and alpha-adrenergic receptors. In the present study, the binding of (3H)DHE to particulate fractions of the steer stalk median eminence was characterized using a filtration assay. Specific binding was defined by the presence of 10 microM phentolamine or by an iterative nonlinear hyperbolic curve-fitting program. Scatchard analysis of equilibrium isotherms of specific binding defined a single high affinity (Kd . 1.78 +/- 0.22 nM), saturable (maximum binding, 481 +/- 39 fmol/mg protein), stereoselective binding site. The Kd, calculated from the ratio of the rate constants k2 and k1, was 2.8 +/- 0.14 nM. The rank order of potency of agonists to compete for (3H)DHE binding (l-epinephrine greater than l-norepinephrine greater than dopamine greater than l-isoproterenol) was consistent with interactions at an alpha-adrenergic site. The rank order of potency of alpha-antagonists (phentolamine greater than yohimbine greater than prazosin) suggested that this was an alpha 2-adrenergic receptor. The affinity of dopamine agonists for the (3H)DHE-binding site was 10-fold lower relative to their potency at known dopamine receptors, while the affinity of dopaminergic antagonists was 100-fold lower. Furthermore, Scatchard analysis of specific (3H)DHE binding in the presence of a concentration of spiperone which should saturate dopamine receptors, only decreased the number of binding sites by 9%. These data demonstrate the presence of large numbers of alpha-adrenergic receptors in the stalk median eminence of the steer. Only a small number of dopaminergic binding sites for (3H)DHE appeared to be present.
- Research Organization:
- Department of Obstetrics, Gynecology, University of California, San Francisco, School of Medicine
- OSTI ID:
- 5464355
- Journal Information:
- Endocrinology; (United States), Vol. 109:6
- Country of Publication:
- United States
- Language:
- English
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ADRENALINE
RECEPTORS
DOPAMINE
SYMPATHOMIMETICS
AUGMENTATION
BRAIN
CATTLE
INHIBITION
NORADRENALINE
SPECIFICITY
TRITIUM COMPOUNDS
ADRENAL HORMONES
AMINES
ANIMALS
AROMATICS
AUTONOMIC NERVOUS SYSTEM AGENTS
BODY
CARDIOTONICS
CARDIOVASCULAR AGENTS
CENTRAL NERVOUS SYSTEM
DOMESTIC ANIMALS
DRUGS
HORMONES
HYDROXY COMPOUNDS
LABELLED COMPOUNDS
MAMMALS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANS
PHENOLS
POLYPHENOLS
RUMINANTS
STEROID HORMONES
VERTEBRATES
551001* - Physiological Systems- Tracer Techniques