Abstract
The membrane fraction of anterior pituitary in laying hens was found to possess a vasoactive intestinal polypeptide (VIP)-binding component having the properties of a receptor. Scatchard analysis of saturation studies revealed that the binding component had a single class of binding site with an equilibrium dissociation constant (Kd) of 0.092 ± 0.008 (mean ± SEM; n=5) nM and the maximum binding capacity (Bmax) of 631 ± 41 fmol/mg protein. The Kd value determined from kinetic analysis (0.091 ± 0.002 nM; n=3) was very similar to that obtained from Scatchard analysis. The Kd value obtained from Scatchard analysis was not significantly different between the laying and nonlaying hens. The Bmax in laying hens was greater than that in nonlaying hens. The administration of chicken VIP to nonlaying hens caused a marked decrease in the VIP receptor binding in the anterior pituitary with a concomitant increase in the blood serum concentrations of prolactin. The results may provide an evidence for a direct action of VIP on the anterior pituitary of female chickens.
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