Diurnal Variation of Cation Pump Enzyme Activity in Pineal and Seven Other Rat Brain Regions

Adult female Long‐Evans rats were maintained on an automatically regulated artificial lighting schedule of light:dark (L:D) 14.5:9.5 for 12 wk. After sacrifice at 0630, 1130, 1600, 1800, 2000, 2200, 0230, or 0400, the pineals were removed, weighed, and assayed for N‐acetyltransferase (NAT), melatonin, Mg⁺⁺‐paranitrophenylphosphatase (pNPPase), and K‐pNPPase activity. The brains were quickly dissected into the following areas: cerebellum, superior colliculi, inferior colliculi, visual cortex, auditory cortex, sensorimotor cortex, and the hypothalamic area around the suprachiasmatic nucleus. These regions were weighed and 10% sucrose homogenates were prepared for determinations of protein, Mg⁺⁺ ‐pNPPase, and K⁺‐pNPPase activity. Pineal melatonin rose over six‐fold from 144 ± 70 pg/gland at 1130 to 981 ± 173 pg/gland at 0230. Similarly, pineal NAT activity rose over 11‐fold, from 119 ± 12 pmol/gland/h to 1315 ± 232 pmol/gland/h at the same times. K ⁺ ‐pNPPase activity rose by about two‐thirds, from 133 ± 12.8 nmol/gland/h to 224 ± 22.3 nmol/gland/h from 1600 to 0230. However, when expressed per mg protein, these differences in pNPPase activity were not significant. There were no significant daily rhythms discernible in any of the seven other brain regions across these times. We conclude that cation pump enzyme activity varies only slightly with time in the rat brain and pineal gland, in spite of definite daily rhythms of pineal melatonin and NAT activity.