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Endocrinology, Vol 120, 2227-2233, Copyright © 1987 by Endocrine Society

ARTICLES

Alpha 1-adrenergic receptors in the neural lobe of the rat pituitary: autoradiographic identification and localization

EB De Souza and BL Kuyatt

alpha 1-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-[beta-(4-hydroxy-3- iodophenyl)ethyl-aminomethyl]tetralone ([125I]HEAT) and [3H]prazosin to localize alpha 1-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 alpha 1-adrenergic receptor profile for [125I]HEAT- binding sites in the rat pituitary. A high density of alpha 1- adrenergic receptors (1 microM prazosin-displaceable [125I]HEAT binding or 10 microM 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 [125I]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 alpha 1- 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 alpha 1-adrenergic receptors in the neural lobe in regulating posterior lobe hormone secretion remains to be demonstrated.




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Copyright © 1987 by The Endocrine Society