Day-night variability in acid phosphatase activity of pineal gland macrophages.

Acid phosphatase (ACP) activity was investigated in the photoreceptive pineal gland of the goldfish by both light and electron microscopy. Intraluminal macrophages exhibited the greatest ACP reactivity that was generally confined to lysosomal bodies containing membranous debris. Quantitative light microscopic evaluation revealed significantly higher ACP reactivity in animals collected at mid-light compared to those collected at mid-dark suggesting that functional activities of macrophages in this photoneuroendocrine organ are cyclical over the 24-h photoperiod. Day-night differences in macrophage ACP activity may reflect rhythmic renewal and shedding of photoreceptor outer segment membranes.