LACK OF A DIRECT EFFECT OF SYNTHETIC SALMON CALCITONIN ON LUTEINIZING HORMONE AND THYROTROPHIN RELEASE IN ANTERIOR PITUITARY CELL CULTURES

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Abstract
To test the hypothesis of a direct action of calcitonin on pituitary cells, the effect of synthetic salmon calcitonin on HL [luteinizing hormone] and TSH [thyrotropin] release in unstimulated, and LH-RH [luteinizing hormone-releasing hormone] and TRH [thyrotropin-releasing hormone]-stimulated [rat] anterior pituitary cell cultures was examined. LH-RH (10-9 M) significantly stimulated LH release, and TRH (10-7 M) significantly enhanced TSH release. LH-RH did not affect TSH release, and TRH did not alter LH release, demonstrating the hormonal specificity of these responses. In order to determine whether calcitonin influenced LH or TSH release, the appropriate control group and hormone-treated groups were compared by 1-way analysis of variance. There was no statistically significant effect of calcitonin on basal LH or TSH release. No differences in LH release were noted when the LH-RH (10-9 M) control was compared with the calcitonin + LH-RH groups or in TSH release when the TRH (10-7 M) control was compared with the calcitonin + TRH groups. A control experiment performed to assess the mechanical loss of salmon calcitonin in the handling procedures revealed that about 75% of the biological activity of the peptide was lost during conduction of the experiments. Synthetic salmon calcitonin at concentrations as high as 2.5 .times. 10-7 M does not act directly on gonadotrophs or thyrotrophs in cell culture to alter basal, or LH-RH- or TRH-stimulated LH and TSH release, respectively.
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