Comparative metabolic clearance rate, volume of distribution and plasma half-life of human β-lipotropin and acth

An antiserum to βh-lipotropin (LPH) which does not cross react with βh-endorphin has been obtained utilizing two different methods of affinity chromatography. This was employed in studies of three normal human subjects in whom the metabolic clearance rate (MCR) apparent volume of distribution (Vd) and fractional rate of disappearance (Kd) of ACTH and βh-LPH were determined following bolus simultaneous injection of 270 μg highly purified βh-LPH and 230 μg of synthetic human ACTH. A biphasic disappearance curve was noted for both hormones. β h -LPH : MCR-0.571, 0.519, and 0.461 L/minute; Vd-30.7, 27.7, 25.0 liters, representing 49, 46 and 35% of body weight; Kd-0.0186, 0.0187, 0.0185 min−1. ACTH : MCR-0.274, 0.266, and 0.332 L/minute; Vd-6.5, 6.5, 14.5 liters, representing 10.4, 10.8 and 20.4% of body weight; Kd-0.0418, 0.0409, 0.0229 min−1. The observed larger MCR of βh-LPH can account for previous observations of basal plasma ACTH/LPH ratios greater than unity, even though these peptides are present in the pituitary in equimolar concentrations.