Effects of chloroquine on the pineal gland of postnatal rats.

1-day old postnatal rats were given daily intraperitoneal injections of chloroquine and sacrificed at various time intervals thereafter. In rats killed at 7 and 14 days of age a large number of cytoplasmic lamellar bodies were induced in the pinealocytes. The macrophages/microglia among the pinealocytes showed the presence of large dense bodies in their cytoplasm. In chloroquine injected rats killed at 21 days of age, the lamellar bodies had vanished. The macrophages/microglia were comparable to those in the control animals. Cytoplasmic lamellar bodies were not observed in the pinealocytes of the control rats in any age group and in rats killed at 2 and 4 days of age following chloroquine injections. The pineal macrophages/microglia in these rats showed the presence of only some small dense granules in their cytoplasm. The immunoreactivity of the macrophages/microglia with OX-42, OX-18, OX-6 and ED1 which detect the complement-type 3 receptors, major histocompatibility complex class I and class II antigens and monocyte/macrophage antigens respectively was comparable in chloroquine injected and control rats. The labelling of the macrophages/microglia with rhodamine isothiocyanate (RhIC) in 7 days old chloroquine injected rats was also comparable to the labelling of cells in the corresponding control rats. It is concluded from this study that although repeated chloroquine administration induces acute structural alteration of the pinealocytes and macrophages/microglia in the pineal gland, its effects are reversible since the cells regained their normal ultrastructural features following discontinuation of the drug. The immune functions and phagocytic activity of the macrophages/microglia shown by their immunoreactivity with various antibodies and RhIC labelling respectively are not altered by chloroquine.