SYNTHESIS, TURNOVER, AND RELEASE OF PEPTIDES FROM THE NEUROHYPOPHYSISOF THE JERBOA JACULUS-ORIENTALIS

Peptide contents of neural lobes from adult jerboas (Jaculus orientali s) under different states of hydration were determined by radioimmunoa ssay. The amounts of vasopressin, oxytocin, and their associated neuro physins in animals dehydrated for up to 4 weeks were not significantly different from those of controls. The different neurohypophyseal pept ides were separated on two different types of gradient using reverse-p hase high-performance liquid chromatography. The shape of the chromato grams suggests that, in contrast to the case of the rat, for which onl y three types of neurophysins have been shown, there are, in jerboa, m any subspecies of neurophysins. This was also shown using two-dimensio nal electrophoresis. Injection of [S-35]cysteine into the supraoptic n ucleus followed by HPLC of extracts from the neural lobes from animals under different states of dehydration showed that the labeled materia l is not released any faster in dehydrated animals than in controls. L abeled vasopressin, oxytocin, and neurophysins could still be detected by HPLC 4 weeks after injection. Neural lobes from animals injected w ith [S-35]cysteine were perfused in vitro and the release of neuropept ides was triggered by bursts of electrical pulses and also by K+-induc ed depolarization. The amplitude of the rate constant for release and the amounts of vasopressin and of radiolabeled material released were similar in animals dehydrated for up to 3 weeks and in controls. Under physiological conditions similar to those that would be expected to o ccur in their natural habitat, the jerboas appear to have a hypothalam oneurohypophyseal system which is down-regulated. (C) 1994 Academic Pr ess, Inc.