The effect of metyrapone on corticotrophin secretion

The plasma immunoreactive corticotrophin (ACTH) response to metyrapone (1 g orally at 08.00 h, and 6 hourly thereafter for 48 h) was analysed in 20 patients with a normal oxogenic steroid response. A greater than threefold rise in the mean plasma ACTH concentration was observed within 24 h. The mean plasma ACTH level at 08.00 h on the 2nd day of the test was significantly higher than the mean level at 16.00 h, indicating that the diurnal rhythm in ACTH release persists despite metyrapone administration. The degree of rhythmicity, as assessed by the ratio of the means of the 08.00 and 16.00 h ACTH values on the 2nd day of metyrapone administration, was comparable to, but slightly less than that observed in untreated normal controls.

The ACTH response to reduction of circulating cortisol levels was also studied by interrupting steroid replacement therapy for 24 h in eight patients with adrenal disease. The observed increase in plasma ACTH was more variable than that after metyrapone, the rapidity of the ACTH rise possibly being influenced by the details of previous replacement therapy and the severity of the adrenal disease.

There was no significant difference in the plasma ACTH response to metyrapone and insulin-induced hypoglycaemia in 13 patients whose pituitary function had been assessed by each of these procedures.

Influence of metyrapone on plasma concentrations of testosterone and androstenedione in man

Metyrapone was administered either orally, 750 mg every four h, in a total of six doses, or intravenously 30 mg per kg body weight as a four h infusion.

In three males with normal endocrine functions, metyrapone given orally or intravenously induced a fall in plasma testosterone and an elevation of androstenedione within 2–8 h. When metyrapone was administered to a patient given dexamethasone to suppress endogenous ACTH production, the androstenedione levels did not alter whereas the testosterone levels showed a slight, transient decrease.

In two normal females metyrapone administration was followed by a marked increase in plasma androstenedione whereas testosterone showed only a minor, gradual increase.

In one male patient with Addison's disease the basal plasma testosterone was normal whereas the level of androstenedione was low. Following metyrapone intravenously, there was a slight suppression of plasma testosterone but no change in the androstenedione concentration.

In one patient with primary hypogonadism, two with secondary hypogonadism and two with Klinefelter's syndrome the plasma testosterone was low under basal conditions and did not change following metyrapone. Basal plasma androstenedione was within the range for normal males and increased markedly following metyrapone in all the cases.

Immunoreactive corticotrophin levels in adrenocortical insufficiency

Plasma concentrations of immunoreactive corticotrophin (ACTH) have been determined in 14 patients with untreated Addison's disease and in 42 patients with secondary adrenocortical insufficiency. Basal morning plasma ACTH levels were markedly raised in those with Addison's disease but were either in the normal range or undetectable in the group with secondary adrenocortical insufficiency. In the group with Addison's disease circulating ACTH values showed a definite nyctohemeral rhythm, a pronounced rise in response to insulin-induced hypoglycaemia, and an immediate fall following the intravenous injection of corticosteroids, with a half-life of between 13.5 and 44.2 minutes. When assays were performed with antisera directed against the portion of the ACTH molecule responsible for corticosteroidogenesis (the N-terminal portion) the apparent ACTH concentrations were lower than with antisera directed against the non-steroidogenic (C-terminal) portion of the molecule. This emphasizes that different antisera may give different apparent hormone concentrations, and that the ranges of values obtained in normal and abnormal states must be established for each antiserum.

Normal and abnormal regulation of beta-msh in man

The regulation of plasma beta-melanocyte-stimulating hormone (beta-MSH) in man has been studied utilizing a radioimmunoassay previously described (1). In normal subjects plasma beta-MSH values ranged from 20 to 110 pg/ml. Metyrapone increased and dexamethasone decreased plasma beta-MSH levels. Surgical stress stimulated beta-MSH secretion. Plasma beta-MSH levels were elevated in patients with untreated Addison's disease and untreated congenital adrenal hyperplasia, and these levels fell to normal during glucocorticoid therapy. In patients with Cushing's syndrome due to pituitary adrenocorticotropic hormone (ACTH) excess, plasma beta-MSH was slightly elevated before treatment. In those patients who developed pituitary tumors and hyperpigmentation after bilateral adrenalectomy, plasma beta-MSH was greatly elevated. In patients with Cushing's syndrome due to adrenal tumor, plasma beta-MSH was subnormal. In patients with the ectopic ACTH syndrome, the levels of plasma beta-MSH were high. Plasma beta-MSH had a diurnal variation in normal subjects, patients with Addison's disease, and patients with congenital adrenal hyperplasia; but the normal diurnal variation was lost in patients with Cushing's disease. In patients with high plasma beta-MSH, simultaneous determinations of plasma ACTH showed close correlation between the degree of elevation of ACTH and that of beta-MSH. In extracts of tumors from patients with the ectopic ACTH-MSH syndrome the quantities of the two hormones were roughly equivalent. In patients with hyperpigmentation due to a variety of disorders other than pituitary-adrenal abnormalities, plasma beta-MSH was normal. It is concluded that the secretion of beta-MSH is regulated by the same factors that regulate ACTH.

Cortisol binding to plasma proteins in man in health, stress and at death

A method is described for determining the degree of binding by plasma proteins of cortisol by a technique of pressure ultrafiltration at 37° after addition of radioactively labelled cortisol.

In normal subjects, the mean concentration of transcortin binding sites was 5·82 × 10−7 moles/l. and the apparent association constant at 37° was 4·27 × 107 l./mole. Evidence of increased protein binding of cortisol was obtained in oestrogen-treated subjects and in women in the last 3 months of pregnancy. In the latter subjects normal levels of non-protein bound cortisol were found. The mean level of non-protein bound cortisol in eight men treated with stilboestrol was increased, but normal levels were present in four of these subjects.

The protein binding of cortisol in three patients with Cushing's syndrome and in three patients with Addison's disease was normal. Thirty-five% of cortisol in adrenal venous plasma was in the unbound state.

Increased levels of plasma 17-hydroxycorticosteroids (17-OHCS) were found in patients in stressful situations (post-operative states, infections and burns). There was no evidence of increased protein binding of cortisol.

Patients at death had increased levels of plasma 17-OHCS including three patients who had been on long-term steroid therapy. There was no evidence of increased protein binding of cortisol. On the contrary, there was some evidence of a decrease in transcortin binding sites.

It is concluded that stressful situations in man, regardless of the outcome, are associated with increased plasma levels of biologically active cortisol.