Multihormonal regulation of ornithine decarboxylase activity in highly differentiated porcine granulosa cells in vitro

Purified luteinizing hormone, but not follicle‐stimulating hormone, elicited time‐ and dose‐dependent stimulation of the cytosolic enzyme, ornithine decarboxylase, in highly differentiated, porcine granulosa cells maintained in vitro in chemically defined medium. Enzymic induction was susceptible to inhibitors of protein and RNA synthesis, and was suppressed by selective direct and indirect inhibitors of ornithine decarboxylase. Physiologic concentrations of prostaglandin E₂ and L‐epinephrine also enhanced enzymic activity in a dose‐dependent and saturable manner. Systematic comparison of the hormonal induction of ornithine decarboxylase in highly differentiated versus poorly differentiated granulosa cells revealed distinctive patterns of enzymic responsivity in relation to the degree of cytodifferentiation attained in vivo. This in vitro model is likely to permit further detailed examination of the molecular mechanisms subserving the hormonal control of ovarian ornithine decarboxylase activity in spontaneously differentiated granulosa cells maintained under chemically defined conditions in vitro.