Persistent GHRH-induced PRL secretion in Cushing's syndrome, obesity and exogenous hypercortisolism

Endogenous Cushing's syndrome, obesity and chronic glucocorticod treatment are characterized by blunted GH secretion. The administration of GHRH is capable of stimulating a small but significant PRL increase in normal subjects. The current study was designed to determine plasma PRL levels in response to GHRH, studied in three different situations characterized by a blunted GH secretion. Obese patients (n = 6) with a weight over 30% of ideal body weight, patients with active Cushing's syndrome, and normal volunteers treated with dexamethasone 22 mg per os over two days before the pituitary challenge were studied. As a control group 18 normal subjects of similar age and sex were studied. GH and PRL was determined at intervals after GHRH (1 microgram/kg). GHRH-induced GH secretion was markedly reduced in patients with obesity, patients with endogenous Cushing's syndrome and volunteers treated with dexamethasone. In contrast, GHRH-induced PRL secretion was not affected in these three clinical situations. In summary, in three situations characterized for an impairment of the somatotroph cell, due to a primary intrinsic defect or to a functional hypothalamic alteration, there is a persistent GHRH-induced PRL secretion, suggesting that prolactin could be released by mammosomatotrophs that function normally in spite of hyposomatotropism.