Radioimmunoassayable N-Tyr-MIF-1-like activity in rat brain is increased by pinealectomy

Levels of N-Tyr-MIF-1-like immunoreactivity were measured in rat brain by radioimmunoassay (RIA). Although the highest levels were found in the pineal and hypothalamus, the striatum and thalamus also contained significantly more immunoreactivity than the other parts of the brain. Since oxytocin cross-reacts 5.4% with the antibody for N-Tyr-MIF-1, oxytocin-like immunoreactivity was also measured by RIA, but could not account for the levels of radioimmunoassayable N-Tyr-MIF-1 found in these experiments. There was a significant increase in N-Tyr-MIF-1-like immunoreactivity after pinealectomy, a tendency for a decrease after stress, but essentially no change after hypophysectomy. A diurnal rhythm was observed with the highest levels at night and lowest levels during the day. The results demonstrate the presence in brain tissue of a novel immunoreactive peptide, the levels of which can be altered by neuroendocrine manipulations.