The Interactions Between Vitamin A,Vinblastine,and Cytochalasin B in Parathyroid Hormone Secretion 1

Abstract

Summary

The role of, and interrelationships between, microtubules, microfilaments, and membrane active agents in the secretion of parathyroid hormone were determined utilizing VB, a microtubule disrupter, CB, a microfilament disrupter, and Vit A, an agent known to interact with membranes.

Parathyroid tissue pieces were incubated for 180 min in the presence of VB, CB, and Vit A, alone or in combination. VB alone consistently inhibited parathyroid hormone secretion. While Vit A alone stimulated the mean parathyroid hormone secretion rate, VB markedly inhibited this effect. CB alone did not change secretion in the first 30 min of incubation but thereafter stimulated secretion. In contrast to the delayed effect of CB alone, Vit A plus CB together increased the PTH secretion rate during the first 30 min, and their effects were at least additive at 120 and 180 min of incubation.

Assuming that the actions of the agents tested are reasonably specific and that immunoreactive PTH in media appropriately reflects secretion of intact hormone, our results suggest that: (a) Vit A increases PTH secretion perhaps through an interaction with the cell or secretion granule membrane; (b) microtubules or microtubular-like proteins facilitate PTH secretion; (c) microfilaments may retard the release of PTH; (d) there is a close interrelationship between membrane, microtubular protein, and microfilament function.