The rate of disappearance from blood of injected bovine parathyroid hormone (PTH) was measured by radioimmunoassay in intact, nephrectomized and partially hepatectomized rats. Both bilateral nephrectomy and partial hepatectomy resulted in a significant decrease in the PTH disappearance rate. No change was observed after partial hemorrhage, adrenalectomy or splenectomy. The PTH disappearance rate was not altered by pretreatment of the rats with phenobarbital, 3-methylcholanthrene, SKF-525A, cortisol or Trasylol. Incubation in vitro of PTH with rat liver homogenate led to a rapid loss of the calcium-mobilizing, phosphaturic and immunological activities of the hormone. The factor in liver responsible for PTH inactivation is heat labile, and the extent of PTH inactivation is related to the amount of homogenate protein added to the incubation mixture. On the basis of tissue protein, kidney is about 5–6 times more active than liver in inactivating PTH; however, the mass of the liver is about 6 times that of kidneys. We conclude that the total PTH-inactivating capacity of rat liver is comparable to that of renal tissue and, therefore, must be considered in future studies of the peripheral metabolism of PTH. (Endocrinology90: 1177, 1972)
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Fang et al. (1972) studied this question.