Ontogeny of thyrotropin-releasing hormone biosynthesis and release in hypothalamic neurons

Amidating processing enzyme complex for bioactive peptides (PAM) shows differences in specific activity and form in secretory granules isolated from the proximal and distal parts of the hypothalamo-neurohypophyseal tract in rats

In rats the PAM specific activity in hypothalamic and neurohypophyseal extracts was 0.58 +/- 0.8, respectively 1.78 +/- 0.6 nmol.mg prot.-1 x h-1 (n = 5). PHM specific activity in the soluble part of the granules was higher in the neurohypophyseal than in the hypothalamic granules, and the fraction of total PHM and PAL present in the soluble part increased with the distance from the hypothalamus from some 45% to approx. 85%. Western blots of membrane and soluble granule fractions showed prevalence of higher mol. wt. forms in hypothalamic granules. It would appear that higher mol. wt. forms of PAM are processed by proteolytic enzymes during transport in the neuron and that non-neural cells in the neurohypophysis have a considerable PAM activity.