Relationship between myometrial cyclic nucleotide phosphodiesterase (PDE) activity and the RNA/DNA ratio at various stages of gestation in primates.

Cyclic AMP and cGMP PDE activities were assayed in crude homogenates prepared from biopsies excised between day 39-162 of gestation (normal length of gestation, 165 days) in outer and inner layers of the macaque myometrium. In both layers, kinetic analysis of PDE indicated high (app Km approximately equal to 2 X 10(-6)M) and low (app Km approximately equal to 2 X 10(-5)M) affinity component for each substrate. Measured in high affinity conditions, specific activities were increased around day 40 and beyond day 130 of gestation. By contrast, low values were observed between days 50 and 100. No significant differences were observed between outer and inner layers. In both layers, the RNA/DNA ratio, which presumably reflects the rate of protein synthesis, culminated at the same time as the PDE activity. These variations were observed in the myometrium at specific stages of gestation. In late pregnancy, the human myometrium also displayed biphasic kinetics for cAMP and cGMP PDE activities. Non-human primates may be a partially representative model of what happens in the human myometrium.