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The receptor for vasoactive intestinal polypeptide (VIP) was characterized using rat dispersed pineal cells. 1251-VIP binding to the cells was saturable, reversible, and temperature-dependent. Scatchard analysis of "SI-VIP binding indicated the presence of two classes of binding sites: a. high aflinity-low capacity site and a low affinityhigh capacity site. Each cell possessed 42,000 high aflinity binding sites with a dissociation constant (Kd) of 0.8 >< l0'9M, and 780,000 low afiinity binding sites with a K, of 32>< l0"9M, respectively. Norepinephrine did not inhibit 1251-VIP binding to the pineal cells. 1251-VIP binding was displaced by natural secretin with 1/ l00 the potency of unlabeled VIP. The potency of displacement of C-terminal and Nterminal fragments was lower than that of natural secretin. VIP stimulated cyclic AMP production of the pineal cells with dose-dependency. Half-maximal stimulation was detected at a concentration of l0'9M. This stimulatory efiect closely corresponded with the manner of binding by VIP to the pineal cells. These results clearly demonstrate that the functions of the pineal gland are regulated through a.
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Kaku et al. (1983) studied this question.
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