Dihydroergocryptine binding sites in bovine and rat pineal glands

High affinity binding of [3H]dihydroergocryptine (DHE) to crude membrane preparations of bovine and rat pineal glands was examined by a rapid filtration procedure through Whatman GFB paper. Scatchard analysis of bovine pineal membranes revealed a single population of binding sites with Kd = (4.8 +/- 1.9) X 10(-8) M (mean +/- S.E.M., n = 3) and binding site concentration = 834 +/- 103 fmol/mg of protein. When various alpha- and beta-adrenergic agonists or antagonists were tested for their ability to inhibit [3H]DHE binding the following Ki values (microM) were obtained: DHE (0.039), phentolamine (0.102), phenoxybenzamine (0.262), methysergide (0.670), L-epinephrine (2.27), serotonin (3.09), L-norepinephrine (3.20), octopamine (30.3), L-propranolol (1710), L-isoproterenol (greater than 2000). In order to obtain information on the pre- or postsynaptic location of pineal DHE binding sites, pineal 900 g supernatants were prepared from rats subjected to bilateral superior cervical ganglionectomy or sham-operation 7 days earlier. Ganglionectomy caused a 53% increase in the number of binding sites without changing significantly their Kd (5.2 X 10(-8) M and 5.5 X 10(-8) M in ganglionectomized and control rats, respectively). These results are compatible with the view that postsynaptic alpha-adrenoceptors are present in the pineal gland.