Divergent influences of calcium ions on releasing factor-stimulated anterior pituitary hormone secretion in normal man

To investigate the influence of calcium ions on the secretion of anterior pituitary hormones in response to stimulation by exogenous hypothalamic releasing factors in man, we measured serum concentrations of pituitary hormones serially during a continuous infusion of combined TRH (2 μg/min) and GnRH (1 μg/min), with concomitant iv saline or calcium administration. Compared to saline, calcium administration was associated with a significant increase in GnRH-TRH-stimulated LH and FSH release and a corresponding rise in serum testosterone concentrations. The effect of calcium ions on gonadotropin secretion was specific, because releasing factor-stimulated secretion of TSH and PRL was suppressed by hypercalcemia. Serum concentrations of GH were not significantly altered under these conditions. In summary, the present results provide the first in vivo evidence that acute infusion of calcium ions augments GnRHTRH-stimulated secretion of LH and FSH, with an accompanying increase in serum testosterone levels. In contrast, hypercalcemia did not alter serum GH concentrations, and it suppressed GnRH-TRH-stimulated release of PRL and TSH. We conclude that calcium ions can selectively influence releasing factorstimulated secretion of certain anterior pituitary hormones in man.