Ontogeny of PHI in the rat brain.

The regional distribution of immunoreactive PHI (IR-PHI) was investigated in rat brain between postcoitum (pc) and day 60 postpartum (pp). IR-PHI was undetectable in all regions of the foetal brain, and only very small amounts were found at day 7 pp. However, there was a dramatic increase thereafter reaching a peak at day 20 pp (e.g. in the hippocampus there was a 12-fold increase in the PHI concentration). Highest concentrations were found in the cortex (40 +/- 5 pmol/g) and hippocampus (35 +/- 8 pmol/g), with lower concentrations in the diencephalon (11 +/- 4 pmol/g) and mesencephalon (10 +/- 3 pmol/g). The brainstem and cerebellum contained very low amounts of IR-PHI. Permeation analysis of brain extracts, on Sephadex G50-superfine, indicated the presence of one major form of IR-PHI which eluted in a similar position to pure intestinal porcine PHI and human intestinal PHI.