Degradation of 125I-labelled prolactin in the rabbit: effect of nephrectomy and prolactin infusion.

Hyperprolactinaemia in patients with chronic renal disease undergoing dialysis has prompted the investigation of the relative roles of liver and kidney in the degradation of prolactin. Male rabbits were acutely nephrectomized, and compared with intact animals with or without prolactin infusion. Prolactin degradation was followed after intravenous injection of 125I-labelled ovine prolactin. Measurements were made of peptide-bound 125I and 125I-labelled degradation products in plasma, liver, kidney, bile, urine and muscle and total thyroid radioactivity. A significant (P less than 0.01) reduction in the metabolic clearance rate of 125I-labelled prolactin was observed due to nephrectomy, with double the accumulation of 125I-labelled peptides in the livers in this group. Prolactin infusion of nephrectomized animals had a further and larger effect than nephrectomy alone on prolactin degradation. Metabolic clearance rate significantly (P less than 0.01) decreased from 5.5 ml/min per kg in nephrectomized rabbits to 0.8 ml/min per kg with prolactin infusion. The accumulation of 125I-labelled prolactin degradation products in the blood was significantly (P less than 0.01) lower in this group of animals and the amount of peptide-bound 125I in plasma at 60 min after 125I-labelled prolactin administration was significantly (P less than 0.01) higher. Liver degradation of prolactin in the absence of exogenous hormone appears to be sufficient to maintain an approximately normal half-life for prolactin in plasma (intact t 1/2 = 6.8 min; nephrectomized t 1/2 = 8.5 min).(ABSTRACT TRUNCATED AT 250 WORDS)