Characterization of β‐Adrenergic Receptors in Dispersed Rat Testicular Interstitial Cells

Recent studies have shown that β‐adrenergic agents stimulate steroidogenesis and cyclic AMP formation in mouse Leydig cells in culture. To obtain information about the possible presence and the characteristics of a β‐adrenergic receptor in rat testicular interstitial cells, the potent β‐adrenergic antagonist [125I]cyanopindolol (CYP) was used as ligand. Interstitial cells prepared by collagenase dispersion from rat testis were incubated with the ligand for 2 h at room temperature. [125I]cyanopindolol binds to a single class of high affinity sites at an apparent KDvalue of 15 pM. A number of sites of 6,600 sites/cell is measured when 0.1 μM (‐) propranolol is used to determine non‐specific binding. The order of potency of a series of agonists competing for [125I]cyanopindolol binding is consistent with the interaction of a β2‐subtype receptor: zinterol > (‐) isoproterenol > (‐) epinephrine = salbutamol >> (‐) norepinephrine. In addition, it was observed that the potency of a large series of specific β1and β2synthetic compounds for displacing [125I]cyanopindolol in rat interstitial cells is similar to the potency observed for these compounds in a typical β2‐adrenergic tissue, the rat lung. For example, the potency of zinterol, a specific β2‐adrenergic agonist, is 10 times higher in interstitial cells and lung than in rat heart, a typical β1‐adrenergic tissue. Inversely, practolol, a typical β1‐antagonist, is about 50 times more potent in rat heart than in interstitial cells and lung. The binding of [125I]cyanopindolol to interstitial cells shows a marked stereoselectivity, the agonist (‐) isoproterenol and the antagonist (‐) propranolol being 500 and 300 times more potent than their respective (+) enantiomers. The high selectivity and density of β2‐adrenergic receptors in rat testicular interstitial cells suggest a role of circulating and/or locally secreted physiologic epinephrine in the control of testicular function.