CHANGES IN BETA-ADRENERGIC RECEPTORS IN THE NEUROHYPOPHYSIS AND INTERMEDIATE LOBE OF RAT HYPOPHYSIS EXPOSED TO STRESS

Changes in beta-adrenergic receptors in the neurohypophysis and interm ediate lobe of the rat have been characterized under physiological and stress conditions. Classical immobilization stress (IMO) was also com bined with the immersion of rats into water (IMO + COLD stress). Both types of stress were applied for 30, 60 or 150 min. The intensity of s tress stimuli were controlled by measuring the level of plasma ACTH. C hanges in the level of plasma ACTH indicate that both types of experim ental protocol induced reliable and reproducible stress conditions. Bi nding studies dealing with beta-adrenergic receptors in the intermedia te lobe and neurohypophysis were performed in saturation binding studi es by using of I-125-iodopindolol. Binding parameters, maximal binding capacity (Bmax) and dissociation constant (Kd) were assessed by nonli near analysis with computer program Viewfit. in the neurohypophysis, n o changes of Kd were found in the stressed animals. However, maximal b inding capacity was decreased significantly with the increased exposur e to the stress. In the intermediate lobe Kd values were slightly decr eased and Bmax values decreased gradually with increasing duration of stress exposure. Our findings suggest that the process of receptor des ensitization of beta-adrenergic receptors can also be detected under s tress conditions in the neurohypophysis and intermediate lobe of the p ituitary gland where it could contribute to the mechanisms involved in stress reactions.