Bovine Pituitary Folliculo-Stellate Cells Have β-Adrenergic Receptors Positively Coupled to Adenosine 3′,5′-Cylic Monophosphate Production*

Publisher Website
Google Scholar
Abstract
The specific .beta.-adrenergic radioligand [125I]iodocyanopindolol (ICYP) was used to identify and characterize .beta.-adrenergic receptors in bovine pituitary folliculo-stellate cells (bFSC) grown in culture. Saturation analysis demonstrated the binding of ICYP to bFSC particulate fractions to be of high affinity (apparent Kd = 80 pM) and low capacity (Bmax = 37 fmol/mg protein). The specific .beta.-adrenergic radioligand [3H] dihydroalprenolol also bound to bFSC particulate preparations with parameters compatible with binding to the .beta.-adrenergic receptor (Kd = 3.0 nM; Bmax = 52 fmol/mg protein). No specific binding was observed with either the dopamine receptor radioligand [3H]spiperone or the .alpha.-adrenergic radioligand [3H]dihydro.alpha.-ergocryptine. The bFSC .beta.-adrenergic receptors were further characterized by computer modeling of competition studies with a variety of agonists and antagonists selective for .beta.-adrenergic subtypes. The pharmacological profiles of ICYP binding obtained from these studies indicated that approximately equal proportions of both .beta.1- and B2-adrenergic subtypes are expressed in cultured bFSC. Bovine FSC .beta.-adrenergic receptors are functionally coupled to activation of cAMP. The .beta.-adrenergic agonists isoproterenol, epinephrine, and norepinephrine provoked a rapid and marked stimulation of intracellular cAMP accumulation. The approximately equipotent effect of epinephrine and norepinephrine indicated that the .beta.-adrenergic effect on cAMP product is principally mediated via the .beta.1-adrenergic receptor. The identification of .beta.-adrenergic receptors on bFSC positively coupled to adenylate cyclase provides a possible regulatory control pathway for the proposed role of pituitary FSC in the modulation of anterior pituitary hormone secretion.