A novel method for localization of gonadotropin releasing hormone receptors

Two ¹²⁵I-labeled analogs of GnRH, [azidobenzoyl-D-Lys⁶]GnRH (I) and [D-Lys⁶]GnRH (II) were used for the localization of GnRH receptors in pituitary cells. The analogs exhibited high binding affinity to pituitary membrane preparations and after photoactivation (analog I) or cross-linking with glutaraldehyde (analog II), these analogs are bound covalently to pituitary cells. The distribution of the labeled hownones by light and electron microscopic autoradiography indicated that after exposure of pituitary cells to ¹²⁵ I-labeled hormones at 4 C (90 min), most of the labeled hormones were associated with the cell surface membrane, while at 37 C (30 min) most of the cell-bound labeled hormones were internalized.