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1. The systemic plasminogen activator response has been examined after intravenous infusion of the following peptides related to neurohypophyseal hormones in approximately equimolar dosages into informed, consenting human volunteer subjects: (a) the natural nonapeptides: lysine-and argininevasopressin, oxytocin and arginine-vasotocin, (b) the N-and C-terminal tripeptide fragments of vasopressin and (c) four vasopressin analogues without pressor activity, altered at the jV-terminus, the disulphide bridge and/or sequence position 8 in the C-terminal tripeptide. In addition, angiotensin II and adrenaline were infused.2. It was' observed that some of the cyclic nonapeptides resulted in high and prolonged increases in amounts of plasminogen activator in venous blood, in the following order, both for amplitude and duration: l-desamino-6-monocarba-[8-D-arginine]-vasopressin > l-desamino-[8-D-arginine]-vasopressin i> arginine-vasopressin = lysinevasopressin > JV a -glycyl-glycyl-glycyl-lysine-vasopressin.3. No plasminogen activator responses followed infusions of vasopressin tripeptide fragments, oxy tocin, angiotension II, l-desamino-[8-iV-MeArg]-vasopressin or 9-desglycineamide-lysinevasopressin octapeptide.4. Mole for mole, the four most active substances were approximately two orders of ten * Deceased 29 April, 1977. Correspondence: Dr J. D. Cash, Regional Blood Transfusion Centre, Royal Infirmary, Edinburgh EH3 9HB, Scotland, U.K. more potent than adrenaline by amplitude com parison alone.5. Intra-arterial adrenaline, in one-tenth the systemic dose, stimulated a release of plasminogen activator from the infused local vascular bed only, This did not occur with equivalent doses of arginine-vasopressin and l-desamino-[8-Dargininel-vasopressin.6. It is concluded that plasminogen activator release arising from catecholamine-responding and vasopressin-responding receptors are both molecule-specific and different in anatomical location. The molecular structural requirements for triggering the latter hypothetical receptor type and potential clinical applications are discussed.

Plasma natriuretic activity was evoked in cows and dogs by infusion of saline with or without dextran. Deproteinized samples were fractionated on both Sephadex and Bio-Gel columns; the activity was separated, the approximate molecular weight being in the region of 1000. Incubation with chymotrypsin destroyed the activity, suggesting that it might be a polypeptide. A similar activity in blood resulted from intracarotid injection of either oxytocin or either of two synthetic analogs. Possibly the latter are saluretic by virtue of a releasing action on some intracranial structure for another natriuretic peptide.