Pertussis Toxin Blocks the Somatostatin-Induced Inhibition of Growth Hormone Release and Adenosine 3′,5′ -Monophosphate Accumulation*

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Abstract
A protein toxin synthesized by the bacterium Bordetella pertussis had the unique property of blocking a number of receptor-mediated inhibitory systems which are linked to adenylate cyclase. Pertussis toxin (PT) eliminated the ability of somatostatin to reduce basal and GH[growth hormone]-releasing factor-stimulated GH release in primary cultures of rat pituitary cells. The ability of somatostatin to reduce GH-releasing factor-induced cAMP accumulation in the cells was significantly attenuated after PT treatment. The PT effect, which was dose dependent and prevented the pretreatment with anti-PT antibodies, represented an alteration in somatostatin efficacy rather than potency. The modification of somatostatin responsiveness persisted for at least 5 days after toxin removal. The PT actions on the somatotroph were similar to the effects on other eukaryotic cell types. Evidently, the toxin acts on a highly conserved component(s) that is obligatory for transducing the inhibitory hormone message into the cell.

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