Dissociation of effects of LH-RH analogs on pituitary regulation and reproductive behavior

Analogs of LH-RH were studied for their effect on lordosis in ovariectomized rats primed with estrogen. Classified by their gonadotropin-releasing activity, representatives of three types of analogs were tested for facilitation of lordotic (L) responses of preselected females to mounting (M) by male studs. Positive responses (L/M greater than 0.5) were found after SC administration of LH-RH peptides modified so as to be inhibitory, stimulatory, or inactive in releasing LH and FSH. The results further support the concept of a dissociation between the endocrine and extra-endocrine effects of peripherally injected hypothalamic peptides.