The kinetics of 35S-labelled cysteine in the hypothalamic-neurohypophyseal neurosecretory system of the dehydrated rat

Abstract

Thirst stimulation of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) was induced in rats by withholding all fluids during three days. 35S-cysteine was then intraperitoneally administered and the rats were killed at predetermined times and examined by autoradiography, applying the authors' previously described method. This experimental series totalling 51 animals was compared with a control series of 70 rats, similarly treated, who had had free access to water. The kinetic phenomena in SON and PVN were analysed in terms of the two-compartment model previously used, which gives an estimate of the neurosecretory material (NSM) secretion parameters and of those of the lumped structural cell protein turnover in the nuclei. The kinetics of the precursor amino acids after administration of labelled cysteine were also assessed. Determinations of the label uptake at two specific times in the experiment, in the infundibular nucleus, ventromedial nucleus and optic nerve tissue in both series served as a check on the specifity of the structural protein turnover changes observed. Compared with the controls, the turnover rate of the slow compartment was more than tripled in the dehydrated rats, while that of the fast compartment had gone down to about one-third; both effects very nearly equal in SON and PVN. These results are compatible with the concept according to which thirst stimulates the SON and PVN equally. A distinct, and strikingly equal, hump was observed (2 hours after label administration) in all specific activity curves, also in the precursor serum concentration, and it is probably due to recycling of 35s from cysteine to methionine. This and other circumstances render the phenomena rather too complex for a straight-forward evaluation by the two-compartment model. Even so, the observations are believed to furnish good evidence of the biological verity of this model as well as the thirst-induced changes elicited.

Evolution of Vasopressin Levels in the Hypothalamo-Posthypophysial System of the Rat during Rehydration following Water Deprivation

“…The decrease of AVP in HHS parallels the increase of circulating AVP levels. This result is in good agreement with the general observation that protein synthesis in hypothalamic nuclei is enhanced during dehydration Talanti, 1971; Kekki et al, 1975;G ainer et al, 1977] and that the axonal transport of neuro secretory material from the cell bodies to the PLH increases [Norstrom and Sjostrand, 1972;G ainer et al, 1977], Rehydration A brief period of rehydration (1 min) results in a significant A VP increase of the PLH, which reaches a maximum after 15 min of free drinking. The AVP peak in the PLH at the 15th min parallels an increase in AVP content of the 3 hypothalamic nuclei, and may correspond to a decrease or even to a transient interruption (less than 30 min) of AVP release, most probably associated with a slowing of AVP axonal flow.…”

A freeze-fracture study of membrane events during neurohypophysial secretion.

“…After 2 days of water deprivation, the plasma hormone level has increased nearly 10-fold and can be sustained for several days before the neurohypophysis eventually becomes depleted (12,15). This is permitted by a continuous synthesis of hormone in the corresponding perikarya (11,16). The exocytotic figures described above represent a stage in exocytosis when fusion of the secretory granule and plasma membrane has already taken place.…”

Neuronal Uptake of Monoclonal Anti‐Vasopressin Antibodies in vivo and Relationship with the Physiological Status of Vasopressin Neurosecretory Cells

“…The withdrawal of drinking water induces an increase in plasma VP (12, 13) and a significant reduction in the neurohypophysial VP content (5, 13-15) by an osmotic stimulation. This is related to VP neuron stimulation as shown by the significant increase in radiolabelled cysteine incorporation (2,(16)(17)(18)(19), increased VP mRNA expression (20)(21)(22) and specific electrical activity (23). Moreover, during water deprivation, the VP turnover is stimulated (14,17).…”