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Abstract Purified parathyroid hormone (PTH) strongly stimulates the initiation of deoxyribonucleic acid (DNA) synthesis and thereby raises the flow of cells into mitosis in rat thymic lymphocyte populations maintained in vitro . These actions of PTH are potentiated by caffeine and inhibited by imidazole which indicates that the hormonal action is mediated by cyclic adenosine 3′,5′,‐monophosphate (cyclic AMP). The feasibility of cyclic AMP being the mediator of PTH action is established by the observation that a low concentration (10 −7 M ) of dibutyryl cyclic AMP precisely mimics the stimulatory action of the hormone on DNA synthesis and cell proliferation.
Whitfield et al. (Wed,) studied this question.