Synchronous activation of DNA synthesis in hypophysectomized rat cartilage by growth hormone.

Abstract

Abstract The influence of growth hormone on cartilage cell multiplication was investigated. Costal cartilage from hypophysectomized rats incorporated much less thymidine- 3 H (THY- 3 H) than did cartilage from normal rats during 4 hours' in vitro incubation (1,481 ± 137 vs. 4,356 ± 435 c.p.m. per milligram cartilage protein). The hypophysectomized rats were injected with 200 μg bovine growth hormone daily. No increase in THY- 3 H uptake in vitro was noted in cartilage removed after 3, 6, and 12 hours. A marked increase in incorporation occurred with a peak at 48 hours when THY- 3 H was 17 to 26 times that of untreated hypophysectomized rats. The degree of stimulation of THY- 3 H uptake was markedly lower at 60 hours (8x) and 72 hours (5x). Insignificant stimulation of THY- 3 H uptake was observed when bovine growth hormone (50 μg per milliliter) was added in vitro during 24 hours' incubations of hypophysectomized rat cartilage. However, a fourfold stimulation of THY- 3 H uptake resulted when normal rat serum was added in vitro. Hypophysectomized rat serum proved slightly inhibitory. It is concluded that bovine growth hormone induces a synchronous wave of DNA synthesis which reaches a peak at 48 hours. The growth hormone does not act directly on cartilage cells but stimulates cell division indirectly by a circulating serum component which may be identical to sulfation factor.