Subcellular localization of luteinizing hormone releasing hormone degrading activity in the hypothalamus

The in vitro degradation of endogenous as well as exogenous luteinizing hormone releasing hormone (LHRH) by subcellular fractions of rat hypothalamic tissue was studied. Endogenous LHRH, localized in isolated nerve terminals (synaptosomes), was found to be resistant to enzymatic degradation (60 min, 37 °C) as long as the synaptosomal membrane remained intact. Endogenous LHRH was rapidly degraded by the900 × gsupernatant fluid and cytosol by not myelin/microsomes, intact synaptosomes, or mitochondria. Lysed synaptosomes rapidly degraded exogenous LHRH. The LHRH degrading activity of synaptosomes was highly concentrated in the ‘synaptosomal’, i.e., the cytosol of the nerve terminal. These data suggest that the LHRH degrading activity of the rat hypothalamus is a readily solubilized component of neurons, and possibly of non-neuronal cells.