TOPOCHEMISTRY OF MEMBRANE PROTEASES IN VESSELS OF GUINEA-PIG SUBFORNICAL ORGAN

Localization of membrane-bound proteases, glutamyl aminopeptidase (EAP ), microsomal alanyl aminopeptidase (mAAP), dipeptidyl peptidase IV (D PP-IV), and gamma-glutamyl transpeptidase (gamma-GTP), which may parti cipate in the metabolism of various peptides, was studied in guinea pi g subfornical organ (SFO). The reaction products of these enzymes were localized in both small vessels located in the central part of SFO an d large vessels present in the peripheral part of SFO. The small vesse ls showed positive enzyme activity for mAAP and gamma-GTP, traces for EAP, but a negative reaction for DPP-IV. The large vessels showed posi tivity in various intensities for mAAP, EAP, and DPP-IV; however, gamm a-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 gamma-GTP activity was not clearly demonstrated. In ves sels of the choroid plexus in the vicinity of SFO, the reactions for m AAP and EAP were positive, but negative for DPP-IV and gamma-GTP. Epit helium of this part of the choroid plexus was positive for gamma-GTP b ut negative for mAAP, EPA, and DPP-IV. Differences in the location and enzyme activity of mAAP, EAP, DPP-IV, and gamma-GTP in different vasc ular compartments, ie., differences among small and large vessels of g uinea pig SFO, and vessels of choroid plexus in the vicinity of the SF O, suggest different roles for vascular endothelium in influencing the blood-borne peptides which would be dependent on the spectrum of memb rane-bound peptidases present on cells in these structures.