Proiactin Binding in Rat Langerhans Islets

Abstract

Membrane preparations of collagenase-dispersed Langerhans islets of female Wistar rats exhibit specific binding sites for ¹²⁵I labelled ovine prolactin (¹²⁵I-oPrl). Almost negligible binding was detected in islets of male animals. The binding is a saturable and time-temperature dependent process, equilibrium being reached after 16 h incubation at 0°C. The bound oPrl is not displaceable by hFSH, hLH, bGH or hGH. In contrast with other cell fractions, the 12,000 g pellet accounts for more than 80% of the specific binding of ¹²⁵I-oPrl. Scatchard plots of data obtained in saturation studies indicate a single class of binding sites with K_a = 0.21 × 10¹⁰ M^-1. Protein and phospholipid moieties are essential for the receptor activity, since after trypsin or phospholipase C digestions marked loss of binding was verified. In islets of streptozotocin diabetic rats a marked reduction in the number of binding sites was observed. These findings may suggest that some of the actions of prolactin on endocrine pancreas could be explained by its specific interaction with islet cell membranes.