Diurnal change and prolonged dark effect on myeloid bodies in the retinal pigment epithelium of the leopard frog.

Myeloid bodies (MBs) are multi-lamellar membrane structures which are widely distributed in the retinal pigment epithelium (RPE) of lower vertebrates. The functional significance of these organelles is not known, but they are believed to be associated with lipid processing in the retina. To determine the nature of the daily changes which occur in MBs, and to ascertain the best sampling time for MB isolation as a prelude to the biochemical characterization of these organelles, this study has assessed the occurrence and area density of MBs in the leopard frog (Rana pipiens) over a daily light-dark cycle. Eye tissues from light-entrained (12L:12D) frogs were sampled at 1, 4, 7, 10 hr after both lights-on and lights-off (n = 5). In addition, to determine whether MB formation is a circadian or light-driven event, the effect of a period of prolonged darkness on MB formation was also examined by maintaining frogs in the dark for an additional 1, 4, 7, and 10 hr at the end of a normal dark phase (n = 5). The number and area density as a percentage of total RPE cell area (area %) for phagosomes (PGs), oil droplets (ODs) and MBs were determined morphometrically using light and electron microscopy. Data were analyzed by a nested analysis of variance. Results indicated that: 1) PG numbers were elevated significantly following lights-on and were reduced almost to nil in the late dark period.(ABSTRACT TRUNCATED AT 250 WORDS)