CONVERSION OF TRIGLYCYLVASOPRESSIN TO LYSINE-VASOPRESSIN IN MAN

The concentrations in plasma of triglycl-8-lysine-vasopressin (TGLVP), determined by radioimmunoassay, and lysine-vasopressin, determined by bioassay, have been monitored in five subjects after intravenous (7.5 micron/kg) or intranasal (5 mg) administration of TGLVP. The level of excretion in urine was also measured. The TGLVP concentration in plasma fell rapidly after the intravenous injection, the mean half-time of disappearance being 24.2 +/- 1.9 (S.E.M.) min (d.f. 4). Biologically active lysine-vasopressin reached a peak between 60 and 120 min. A similar pattern was seen following intranasal instillation but only a small proportion of the administered dose appeared in the plasma and the concentration of lysine-vasopressin was relatively higher. Less than 1% of the TGLVP injected appeared in the urine. Intravenous TGLVP had no effect on systolic blood pressure but produced an increase in diastolic blood pressure of 1.7 +/- 0.19 kPa (d.f. 4) and a fall in heart rate of 9 +/- 2.3 beats/min. Creatinine clearance and sodium excretion remained relatively constant in all subjects throughout the study but intravenous injection of TGLVP resulted in an antidiuresis which was evident within the first hour of observation and was maintained for a further 4 h. It was concluded that TGLVP is converted to lysine-vasopressin in man and after an intravenous injection of 7.5 micron/kg sufficiently high concentrations of lysine-vasopressin may be maintained for 2 h to produce sustained vasoconstriction. Tryglycylvasopressin may therefore be of value in controlling haemorrhage.