Prolactin cells and plasma prolactin levels in the aging male Wistar rat: an immunocytochemical and biochemical study.

Non-neoplastic pituitary glands of 12 age-groups of 10 male Wistar rats (subpopulation 1) and of 228 rats with age-related disorders (population 2) were studied. For subpopulation 1 a positive correlation was found between body weight, pars distalis volume and total prolactin (PRL)-cell volume. These values increased during the first half of the life span and decreased to values similar to that found in young rats, after the 50% survival age was reached. Age-related changes were found with respect to the distribution of the PRL cells (from homogeneous into non-homogeneous) and to their ultrastructural features (PRL cells with polymorphic granules were substituted by cells with round granules). Pituitary glands of disordered aged rats (subpopulation 2) showed a similar non-homogeneous distribution of PRL cells. Plasma PRL levels of both subpopulations were similar. No age-related increase of plasma PRL level was found in rats with non-neoplastic pituitary glands.