Modifications in the Release of Rat Growth Hormone in vitro and the Morphology of Rat Anterior Pituitaries Incubated in Various Ionophores

Abstract

The ionophore A23187 increased the release of rat growth hormone [GH] in the presence of a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine; a 2nd ionophore X537A inhibited GH release induced by the methylxanthine. A23187 did not alter rat GH release in the absence of 3-isobutyl-1-methylxanthine, but X537A enhanced hormone release in the absence of Ca or in the presence or somatostatin. Both Ca and cyclic AMP are important in the regulation of GH release. Tissue incubated in X537A contained electron-lucent vesicles apparently derived from the Golgi apparatus, swollen granules and mitochondria with dense matrices. Tissue incubated in the presence of valinomycin or A23187 did not show altered morphology of either secretory granules or the Golgi complex. Possible mechanisms of these changes are discussed.