The mean
prolactin concentration during sleep and the per cent change (increase) and increment in the nocturnal elevation of plasma
prolactin concentrations were significantly reduced (P less than .01, less than .01, and less than .001, respectively) in 6 untreated patients with clinically active
Cushing's disease, compared with concentrations seen in normal subjects. There was no significant difference between mean-awake and mean-sleep plasma
prolactin concentration in these patients, in contrast to that seen in normal subjects. In contrast, patients with
hypercorticism secondary to adrenal
adenoma (n = 2) or receiving long-term, high-dose
corticosteroid therapy (n = 6) did not differ significantly from normal subjects in the percentage change seen in the nocturnal elevation of their plasma
prolactin concentrations. Although mean
prolactin concentration during sleep was reduced in these two categories of
hypercorticism, a significant difference was still present between mean-awake and mean-sleep plasma
prolactin concentration. (The nocturnal increment in plasma
prolactin concentrations in these patients with
hypercorticism compared with that of normal subjects was reduced, P less than .02). The difference between the percentage change and nocturnal increment observed in patients with
Cushing's disease versus that seen in these two categories of
hypercorticism was significant at P less than .02 and P less than .01, respectively. Four untreated patients with localized
hypothalamic tumors also showed a significant reduction in the percentage change and increment in the nocturnal elevation of plasma
prolactin concentrations (P less than .05 and P less than .02). In contrast to these findings, the
prolactin responses to
thyrotropin-releasing hormone (indicative of pituitary responsiveness) in patients with
Cushing's disease, patients with adrenal
adenoma, or those receiving chronic
corticosteroid therapy, were all within the normal range seen in sex-matched control subjects. These findings provide additional evidence for the suggestion that there is altered hypothalamic function in patients with
Cushing's disease.