TOPOCHEMISTRY OF MEMBRANE PROTEASES IN VESSELS OF GUINEA PIG SUBFORNICAL ORGAN

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Localization of membrane-bound proteases, glutamyl aminopeptidase (EAP), microsomal alanyl aminopeptidase (mAAP), dipeptidyl peptidase IV (DPP-IV), and γ-glutamyl transpeptidase (γ-GTP), which may participate in the metabolism of various peptides, was studied in guinea pig subfornical organ (SFO). The reaction products of these enzymes were localized in both small vessels located in the central part of SFO and large vessels present in the peripheral part of SFO. The small vessels showed positive enzyme activity for mAAP and γ-GTP, traces for EAP, but a negative reaction for DPP-IV. The large vessels showed positivity in various intensities for mAAP, EAP, and DPP-IV; however, γ-GTP enzyme activity was not present. In the ependyma which cover the SFO, the enzyme-histochemical reactions for mAAP, EAP and DPP-IV were negative, and γ-GTP activity was not clearly demonstrated. In vessels of the choroid plexus in the vicinity of SFO, the reactions for mAAP and EAP were positive, but negative for DPP-IV and γ-GTP. Epithelium of this part of the choroid plexus was positive for γ-GTP but negative for mAAP, EPA, and DPP-IV. Differences in the location and enzyme activity of mAAP, EAP, DPP-IV, and γ-GTP in different vascular compartments, ie., differences among small and large vessels of guinea pig SFO, and vessels of choroid plexus in the vicinity of the SFO, suggest different roles for vascular endothelium in influencing the blood-borne peptides which would be dependent on the spectrum of membrane-bound peptidases present on cells in these structures.