Clearance from the circulation of the rat and whole-body autoradiography in the mouse of 125I-labelled neurophysins.

Abstract

1. The rate of clearance of 125I-labelled porcine neurophysins I and II from the circulation of the rat has an initial fast component followed by a slower component. 2. In the initial phase of clearance the half-life of neurophysin I was 1.50 min (s.e.m. = 0.03) and for neurophysin II was 1.74 min (s.e.m. = 0.05). In the slower phase of clearance the half-life of neurophysin I was 22.6 min (s.e.m. = 2.2) and for neurophysin II was 27.3 min (s.e.m. = 5.8). 3. The first component had a volume of distribution similar to the blood volume and the second component had a volume of distribution similar to the volume of extracellular fuid of the rat. 4. The metabolic clearance rates per 200 g of body weight were 1.94 ml/min (s.e.m. = 0.12) for neurophysin I and 1.29 ml/min (s.e.m. = 0.15) for neurophysin II. 5. Using whole-body autoradiography, the kidney was shown to be the major site of uptake of radioactivity in both virgin female and lactating mice.