A Multihormonal Response to Corticotropin-Releasing Hormone in Inferior Petrosal Sinus Blood of Patients with Cushing's Disease

Publisher Website
Google Scholar
Abstract
Bilateral, selective, and simultaneous catheterization of the inferior petrosal sinus is not only a valuable tool in the differential diagnosis of Cushing's syndrome, but may also provide new insights into paracrine interactions at the pituitary level. We have investigated whether CRH (1 μg/kg BW) has any effect on the release of PRL, GH, TSH, or the α-subunit of hCG during this procedure. Sixteen patients under evaluation for Cushing's syndrome (Cushing's disease, n = 12; ectopic ACTH syndrome, n = 2; glucocorticoid resistance, n = 1; hormonally inactive adenoma, n = 1) were catheterized. Two of the patients with Cushing's disease received 4.0 mg naloxone iv 15 min before stimulation with CRH. Patients with Cushing's disease demonstrated a central/peripheral gradient and an intersinus gradient not only for ACTH, but also for PRL, asubunit, GH, and TSH, provided that the latter two hormones were not completely suppressed by the glucocorticoid excess. Moreover, all hormones increased in response to CRH on the side with the highest ACTH concentration; PRL rose from 31.2 ± 6.4 to 61.6 ± 12.4 μg/L (P < 0.01), and α-subunit from 2.6 ± 0.6 to 6.4 ± 1.7 μg/L, (P < 0.01). Naloxone was unable to abolish the PRL or α-subunit increase in response to CRH. A multihormonal response to CRH in inferior petrosal sinus blood was also observed in the patient with glucocorticoid resistance and in the patient with the hormonally inactive tumor, but not in the patients with ectopic ACTH secretion. The multihormonal response to CRH could be explained by cosecretion of other hormones together with ACTH from corticotroph adenoma, by an effect of CRH on pituitary blood flow, or by a paracrine action of pituitary corticotrophs on adjacent normal pituitary cells. Our results do not support the concept that such a paracrine action is mediated by β- endorphin. However, a higher dose of naloxone may be required to antagonize the action of pituitary β-endorphin.