Alpha 1-adrenergic receptors in the neural lobe of the rat pituitary: autoradiographic identification and localization.
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.
D000818:Animals; D001345:Autoradiography; D005728:Ganglia, Sympathetic / Q000502:physiology; D008297:Male; D010627:Phenethylamines / Q000378:metabolism; D010902:Pituitary Gland / Q000502:physiology; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D013562:Sympathectomy; D044024:Tetralones
D010627:Phenethylamines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; C048008:2-(beta-(3-iodo-4-hydroxyphenyl)ethylaminomethyl)tetralone; D011224:Prazosin