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The progesterone receptor (PR) in the oviducts of aged, nonlaying hens was compared to that in laying hens. The PRs in the mature oviducts of chicks that were diethylstilbestrol (DES) primed and of chicks with DES withdrawn were similarly analyzed for comparative purposes. The oviducts from the DES-withdrawn chicks and from aged nonlaying hens showed marked atrophy. The PR concentrations in the oviducts of DES-withdrawn chicks and of aged nonlaying hens were reduced to one half and one fourth those of controls, respectively. The oviduct atrophy and reduced PR concentrations in the nonlaying hen were not caused by decreased plasma estrogen since estrogen concentrations were similar in aged nonlaying hen and in the laying hens. The stabilities of the PR from laying and nonlaying hen oviducts were identical. However, analysis in vivo and in vitro revealed that the PR from the oviducts of DES-withdrawn chicks and of aged, nonlaying hens had lost the capacity for nuclear translocation and binding. This was accompanied in the DES-withdrawn chick by the inability of progesterone to alter RNA synthesis in the oviduct in vivo. This loss in nuclear binding capacity of PR in both animal models was accompanied by a loss of one of the molecular species of the PR (the B species). The loss of the B species differs from the loss of the A species that occurs during the winter in the domestic fowl. Thus, two types of regulation of the receptor may exist. The results suggest that biologically inactive receptors may explain the cessation of reproductive function in these aged animals.

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