BIOASSAY OF THE PITUITARY GROWTH HORMONE. WIDTH OF THE PROXIMAL EPIPHYSIAL CARTILAE OF THE TIBIA IN HYPOPHYSECTOMI2ED RATS¹,²

Abstract

HYPOPHYSECTOMY causes regressive changes at the proximal end of the tibia in the immature rat, as described by various authors (1–4). Within a few days, the thickness of the cartilage plate decreases significantly, a consequence of a retardation or cessation of cartilage formation, and of an active destruction of cartilage. Administration of pituitary growth hormone reverses these regressive changes (1, 2, 4, 5). The initial effects of growthhormone treatment consist predominantly of chondrogenesis. Activation of osteogenesis follows later. The width of the cartilage disc increases during the first 6 to 8 days of treatment with growth hormone until the normal equilibrium between chondrogenesis and osteogenesis is reestablished. During this initial period of administration of growth hormone the resulting increase in width of the cartilage is, within certain limits of dosage, proportional to the quantity of growth hormone injected (5). Based on these phenomena, a new method was developed for the bioassay of the pituitary growth hormone.