The addition of colchicine (10-5M) to adenohypophyses incubated in Krebs-Ringer bicarbonate suppressed the augmented release of ACTH induced by a 5-fold increase in K+ concentration. However, this concentration of colchicine was without effect on the augmented release induced by the addition of a crude acid extract of rat hypothalamus-stalk-median eminence (HSME). Since colchicine binds to and blocks the contractile microtubular system which might be involved in the translocation of hormone-containing granules within the cell, these findings suggest (a) that this system does not mediate the augmented release of ACTH induced by releasing factor activity and (b) that the mechanism of augmented release of ACTH induced by high K+ differs from that governing the release induced by the HSME extract. (Endocrinology89:408,1971)
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Kraicer et al. (1971) studied this question.