Glucocorticoid Suppression of Pancreatic and Pituitary Hormones: Pancreatic Polypeptide, Growth Hormone, and Prolactin*

The influence of short term, high dose glucocorticoids on pancreatic polypeptide (PP), GH, and PRL responses to insulin-induced hypoglycemia was studied in normal young men. Subjects underwent insulin tolerance tests before (ITTb) and on the fifth day (ITT5) of treatment with prednisone (25 mg orally twice daily) and again 2 (ITT7) and 5 (ITT10) days after termination of prednisone therapy. Eleven subjects completed ITTh, ITT7) and ITT10. Five of these underwent ITT5. Despite the more pronounced hypoglycemia associated with the higher insulin dose used during prednisone treatment, PP responses were significantly diminished. Basal PP was reduced from 92.7 ± 13 to 38.6 ± 5.7 pg/ml (P < 0.05) at the time of ITT5 and returned to pretreatment values at the time of ITT7. The peak pretreatment PP concentration of 1328 ± 203 pg/ml was reduced to 584 ± 118 (P < 0.05) during ITT5, and after discontinuation of prednisone returned progressively to pretreatment values. A more marked suppression was evident from comparison of the areas under the response curves. The control response of 64,926 ± 10,805 pg.min/ml was reduced to 18,782 ± 3,811 pg-min/ml on the fifth day of prednisone therapy (P < 0.01), returning to the control values subsequently. GH and PRL responses were suppressed during ITT5, and, as observed with PP, the responsiveness of both pituitary hormones to insulin had returned to baseline by ITT7. The ITTh GH peak of 61.4 ± 6.5 ng/ml was reduced to 19.2 ± 6.2 (P < 0.01), and the PRL peak of 21.9 ± 4.2 ng/ml was reduced to 5.5 ± 2.6 (P < 0.05) at ITT5, with a return by ITT7 to 56.9 ± 6.9 and 25.6 ± 5.4 ng/ml, respectively. Fasting PRL was suppressed from 9.35 ± 1.18 to 3.8 ± 0.77 ng/ml (P < 0.01). We conclude that short term, high dose glucocorticoid treatment suppresses basal and stimulated PP secretion, basal PRL, and stimulated PRL and GH secretion. These suppressive effects are evanescent, since secretory responses normalize within 48 h of cessation of prednisone therapy.