Specific binding of [3H]oxytocin in the female rat brain

Because of demonstrated effects of oxytocin on some limbic system mediated behaviours, the specific binding of [3H]oxytocin to a plasma membrane containing fraction of rat limbic tissue has been studied. The binding of the microsomal fraction of estrogenized, female rat tissue was time dependent and saturable, with a Bmax of 2.5 X 10(-13) moles per milligram of protein and an apparent KD of 3.53 X 10(-8)M, and appeared to show positive cooperativity. The pH optimum of the binding was 6.0, close to the pH optimum for oxytocin-neurophysin binding; however, other results show the two types of binding to be different. The microsomal fraction did not appreciably degrade oxytocin under the conditions used for [3H]oxytocin binding. The distribution in limbic tissue of oxytocin-degrading activity and of individual enzymes capable of degrading oxytocin has been examined and an interplay of enzymes concentrated in different cell types is proposed.