Muscarinic receptors in the posterior pituitary gland.
The characteristics of atropine-sensitive binding of l-[3H]-quinuclidinyl benzilate ([3H]-QNB) to membrane suspensions of sheep posterior pituitary indicate that the binding sites represent muscarinic cholinergic receptors. Scatchard plots of 6 saturation experiments showed a single class of binding sites, with an equilibrium dissociation constant of 16 +/- 2 pM and a density equivalent to 1.8 +/- 0.2 pmol/g wet weight of tissue. Kinetic analysis of 2 association and 3 dissociation curves yielded mean association and dissociation rate constants of 3.9 x 10(8) M-1 min-1 and 4.3 x 10(-3) min-1, respectively. The binding had a detailed pharmacology for 12 drugs consistent with muscarinic receptor identification. In rat neurointermediate lobes, superior cervical ganglionectomy had no demonstrable effect on [3H]-QNB binding. The location(s) and functional role(s) of neurohypophyseal muscarinic receptors remain to be elucidated.
D000818:Animals; D005728:Ganglia, Sympathetic / Q000502:physiology; D007700:Kinetics; D010904:Pituitary Gland, Posterior / Q000032:analysis* / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000032:analysis*; D011954:Receptors, Dopamine / Q000032:analysis; D011976:Receptors, Muscarinic / Q000032:analysis* / Q000378:metabolism; D012756:Sheep; D013562:Sympathectomy
D011950:Receptors, Cholinergic; D011954:Receptors, Dopamine; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate