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LIU, B AND J P H BURBACH Changes m vasopressm-converttng amlnopepttdase acttvtty tn the rat pmeal gland during summer Relationship to vasopressm contents PEPTIDES 9(6) [1235][1236][1237][1238][1239][1240] 1988--Vasopressln (VP)-convertmg amlnopeptldase (VP-AP) actlwty and VP contents were measured m smgle rat pineal glands dunng the summer of two successive years The peptldase activtty decreased slgntficantly m August The lowest activity (±SEM) of 0 18---0 02 pmol hour -1 was recorded on August 14, compared to the basal actlwty of 0 25±0 01 pmol.hour -1 in July and September of 1986 The change with slmdar percentage occurred m the same period of 1987 The specific act,wty of the enzyme m the crude homogenate, 15,000 g pellet and supernatant fract,on ol rat pineal glands, exhibited the same pattern of vanat~ons The decrease m pept,dase activity coincided with the previously reported dramatic rise in pineal VP content in early August which was confirmed m this series of experiments Another peptldase, the so-called y-endorphm generating endopeptldase (y-EGE) acUwty, and fl-endorphm-related peptldes m the pineal gland did not change m th,s period The results show that the vanat,ons of pineal VP contents and VP-AP act~vtty dunng summer are not general for other pept~des and pept,dases The comodence of opposite changes tn VP content and VP-AP actw,ty of the pineal gland may md,cate a role of the peptldase act~wty to regulate the VP content Vasopressm-convertlng ammopepttdase act~wty Pineal gland Summer Vasopressm content VASOPRESSIN (VP) has biological functions in the periphery and the central nervous system (9,11). In contrast to the periphery, central actions of VP are also exerted by fragments of VP (6, 9, 11). An amlnopeptidase activity with restricted specificity has been implicated in the formation of such active fragments (4,5). The functional role of this "VP-convertIng amlnopeptidase (VP-AP)" activity in the metabolism of VP, however, remains to be clarified. Both VP and VP-AP activity have been found in the rat pineal gland (7,16), an endocnne organ which is important in regulation of biological rhythms (1) Recent experiments in our laboratory mdlcated that a diurnal rhythm of VP-AP activity exists m the rat pineal gland which is inversely related to the pineal VP contents (15). The marked rise of pineal VP contents dunng summer (14) provides another physiological condition for evaluation of their relationship in the pineal gland. Therefore, VP-AP activity and VP contents were measured in the rat pineal gland dunng the period of summer in two successive years. The specificity of the changes was mvestlgated by comparison to another peptide system and its converting enzyme, i.e., fl-endorphln-related peptides and the so-called "y-endorphln-generatlng endopeptidase (y-EGE)," a Leu-Phe cleaving endopeptIdase which converts fl-endorphm into y-endorphln (12,13) The results indicate that VP-AP In the rat pineal gland may participate in the regulation of pineal VP contents. METHOD MaterialsRadioactive materials [a...