Alpha 1-Adrenergic Receptors in the Neural Lobe of the Rat Pituitary: Autoradiographic Identification and Localization
α1-Adrenergic receptors were identified, characterized, and localized in rat pituitary gland by quantitative light microscopic autoradiography. Autoradiographic studies were carried out in slide-mounted rat pituitary sections using both [125I]2-[β-(4-hydroxy-3-iodophenyl)ethyl-aminomethyl]tetralone ([125I]HEAT) and [3H]prazosin to localize ai-adrenergic receptors. Data analysis by densitometry showed that [125I] HEAT binding in the rat neural lobe was saturable and of high affinity, with an apparent dissociation constant (Kd) of about 5 pM. Data from competition studies using a variety of compounds demonstrated an α-adrenergic receptor profile for [125I]HEATbinding sites in the rat pituitary. A high density of ai-adrenergic receptors (1 μM prazosin-displaceable [125I]HEAT binding or 10 fiM phentolamine-displaceable [3H]prazosin binding) was found present only in the neural lobe, with negligible concentrations in the anterior and intermediate lobes. The regulation of [126I] HEAT-binding sites in the neural lobe was examined in pituitary stalk-transected and superior cervical ganglionectomized rats. Significant increases in [125I]HEAT-binding sites were observed after superior cervical ganglionectomy, but no changes in [125I] HEAT binding were found in pituitary stalk-transected rats compared to that in sham-operated controls. These data provide the first identification of ai-adrenergic receptors in the neural lobe of the rat pituitary and suggest that these receptors may be localized primarily in blood vessels. In addition, a primary role for the peripheral sympathetic nervous system in regulating the neurohypophyseal vasculature is suggested. The precise function of ai-adrenergic receptors in the neural lobe in regulating posterior lobe hormone secretion remains to be demonstrated.
Autoradiography, adrenergic receptors, pituitary gland, rats, neural lobe, posterior lobe, hormone secretion
De Souza, E. B. and Kuyatt, Brian L., "Alpha 1-Adrenergic Receptors in the Neural Lobe of the Rat Pituitary: Autoradiographic Identification and Localization" (1987). Center for Teaching and Learning Publications. 20.