R. J. M. Croughs

Proliferation of the murine corticotropic tumour cell line AtT20 is affected by hypophysiotrophic hormones, growth factors and glucocorticoids

In pituitary-dependent hyperadrenocorticism (Cushings disease), the disturbed regulation of ACTH secretion is associated with neoplastic transformation of corticotropic cells. As these two phenomena are almost indissolubly connected, it is of prime importance to elucidate the factor(s) that induce corticotropic cell proliferation. Here we report on the effects of hypophysiotrophic hormones and intrapituitary growth factors on the proliferation and hormone secretion of the murine corticotropic tumour cell line AtT20/D16v, as measured by DNA content, and ACTH concentration in culture media. In addition, sensitivity to the inhibitory effect of cortisol was assessed under various conditions. Corticotropin releasing hormone (CRH) and vasopressin (AVP) induced proliferation of AtT20-cells. In contrast to that caused by AVP, the CRH-induced proliferation was associated with increased ACTH secretion, which could be inhibited by cortisol. Insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) also stimulated the proliferation of AtT20-cells. The proliferation of AtT20-cells was significantly inhibited by cortisol in all tests. The IGF-I-induced proliferation was the least sensitive to inhibition by cortisol. The growth factors did not stimulate ACTH secretion but IGF-I differed in that it prevented the inhibition of basal ACTH secretion by cortisol. Additional experiments (Western ligand blot analysis) concerning the relative insensitivity of IGF-I induced proliferation to inhibition by cortisol revealed that IGF-I increased the concentration of a 29 kDa IGF binding protein (IGFBP) in the culture medium. The concentration of the 29 kDa IGFBP was slightly decreased by cortisol.(ABSTRACT TRUNCATED AT 250 WORDS)

Response to neurotransmitter modulating drugs in patients with Cushing's disease

We designed a systematic study of patients with Cushings disease to compare the results of acute experiments with cyproheptadine, sodium valproate and bromocriptine with the results of chronic treatment with sodium valproate. In 13 patients the plasma Cortisol response to single doses of 2.5 mg bromocriptine, 6 mg cyproheptadine and 300 mg sodium valproate was assessed over 4.8 h. All patients were then treated with sodium valproate 200 mg three times a day for a period of 3 months. Subjects were classified as responders when there was a reduction in plasma Cortisol by at least 50% below the basal level in two consecutive plasma samples during one of these tests, and/or clinical remission and normalization of Cortisol production rate during sodium valproate treatment. Four patients responded significantly to at least one of the agents (group I) and 9 did not (group II). In group I three patients were bromocriptine responsive and one of these responded also to cyproheptadine; in this patient both sodium valproate and cyproheptadine were able to induce a remission during chronic treatment. In the one patient of the responder group who was bromocriptine insensitive, sodium valproate treatment also induced a remission. In two patients of the responder group sodium valproate treatment was ineffective. However, in both patients chronic treatment with bromocriptine induced a marked clinical improvement associated with a decrease of Cortisol production rate. There was no difference between the groups in sex, age, clinical presentation, duration or severity of hypercortisolism. In one patient in group I a macroadenoma with suprasellar extension was present, while a microadenoma was detected in four patients in group II. There was no difference in the sensitivity of Cortisol secretion to the suppressive effect of overnight or 5 h infusion of dexamethasone between the two groups, and PRL levels were normal in all. These data show that responsiveness of patients with Cushings disease to neurotransmitter modulating drugs is not associated by specific clinical or biochemical characteristics. Bromocriptine tests most reliably predict the chances for successful medical treatment. However, non‐responsiveness to acute administration of neurotransmitter modulating drugs does not exclude with certainty their usefulness during chronic treatment.

BROMOCRIPTINE THERAPY IN ACROMEGALY: EFFECTS ON PLASMA GH LEVELS, SOMATOMEDIN-C LEVELS AND CLINICAL ACTIVITY

Thirty‐one patients with active acromegaly were treated with 10–20 mg bromocriptine daily for a period of 6–9 months. The clinical response was evaluated both by a subjective ‘score of symptoms’, and by a combined subjective and objective ‘clinical and metabolic improvement score’(c‐m score). The biochemical response was evaluated both by measurement of the mean of four plasma growth hormone (GH) determinations during the day and by measurement of plasma somatomedin‐C (Sm‐C) concentration. The clinical response as assessed by both methods showed a better correlation with changes in plasma GH levels (respectively r= 0·33; r= 0·50) than with changes in Sm‐C levels (r= 0·20; r= 0·36). The study confirms that in some patients clinical improvement is not accompanied by a decrease of plasma GH concentration. However, it is not possible to identify a subgroup of patients who showed clinical improvement with a decrease of Sm‐C levels, but whose plasma GH levels remained constant. It is concluded that measurement of plasma GH levels still appears to be the most useful biochemical assessment of disease activity in bromocriptine‐treated acromegaly.

Molecular screening for somatic mutations in corticotropic adenomas of dogs with pituitary-dependent hyperadrenocorticism

Pituitary tumorigenesis is now generally regarded as a multistep process of genomic damage leading to uncoupling of interdependent systems that control cell proliferation and differentiation. The alterations include mutations in genes encoding for proteins involved in signal transduction pathways, such as G-proteins and the p21 protein encoded for by the ras genes. Apart from their excessive secretion of ACTH, corticotropic adenomas are characterized by decreased sensitivity to inhibition by glucocorticoids. Therefore, mutations in the glucocorticoid receptor leading to decreased sensitivity to glucocorticoids may contribute to corticotropic tumor formation. In this study, 16 corticotropic adenomas of dogs with pituitary-dependent hyperadrenocorticism were screened for mutations in the Gsα, H-, K-, N-ras genes and the coding region of the DNA-binding domain of the glucocorticoid receptor. The cDNA fragment of the Gsα gene encompassed codons 159–240. The K-, and N-ras fragments spanned codons 1–71. The H-ras gene was only screened for mutations in codons 12/13 by direct sequencing of the PCR product. The cDNA fragment of the DNA-binding domain of the glucocorticoid receptor encompassed codons 410–500. The Gsα, K-ras, N-ras genes and the DNA-binding domain of the glucocorticoid receptor were screened by single-strand conformation polymorphism analysis. No mutations were found in the Gsα gene, the ras genes and the DNA-binding domain of the glucocorticoid receptor. It is concluded that mutations in the Gsα gene (codons 159–240), the K- and N-ras genes (codons 1–71), the H-ras gene (codons 12/13) and mutations in the DNA-binding domain of the glucocorticoid receptor do not play a role in the tumorigenesis of canine corticotropic adenomas.

PLASMA GROWTH HORMONE SUPPRESSIVE EFFECT OF BROMOCRIPTINE IN ACROMEGALY. EVALUATION BY PLASMA GH DAY PROFILES AND PLASMA GH CONCENTRATIONS DURING ORAL GLUCOSE TOLERANCE TESTS

In most studies reporting favourable results of chronic bromocriptine treatment in acromegaly, plasma GH levels are measured at fixed intervals during the day. Negative results are reported in one major study measuring plasma GH levels during oral glucose tolerance tests (Lindholm et al., 1981). This study does not mention the time interval between the last dose of bromocriptine and the performance of an OGTT, but due to the short duration of action of bromocriptine this may be critical. Therefore, in the present report the plasma GH suppressive effect of bromocriptine in acromegaly is studied using plasma GH day‐profiles as well as OGTTs during continued bromocriptine administration and OGTTs at two different time intervals after the last dose of bromocriptine. Twelve patients with clinically active acromegaly were treated with 10–20 mg bromocriptine for 6–9 months. After 6–9 months during continued bromocriptine administration the plasma GH suppressive effect of bromocriptine was evaluated by the mean of four plasma GH determinations during the day and by the mean of seven plasma determinations during oral glucose tolerance tests (OGTTs) performed 1 h, 10 h and 34 h after the last dose. The percentage decrease of the mean plasma GH level during the day induced by chronic bromocriptine treatment showed a good correlation (r= 0·86, P< 0·001) with the percentage decrease of the mean plasma GH level during OGTT, if the post‐treatment test was carried out one hour after the last dose of bromocriptine. When OGTT was performed 10 h after the last dose no significant correlation (r= 0·17) was found and after 34 h a rebound of the mean plasma GH level occurred in eight patients. It is concluded that measurement of the mean plasma GH level during the day or during OGTT are equally effective indicators of the suppressive effect of bromocriptine treatment on GH secretion in acromegaly if the OGTT is performed 1 h after the last dose of bromocriptine.

Melatonin and jet lag

Jet lag is an ill-defined phenomenon resulting from rapid transmeridional flight and is considered to be due to desynchronization of circadian rhythms. The role of the pineal gland hormone, melatonin, in the synchronization of biological rhythms has raised interest in its use to alleviate jet lag. Indeed, recent studies support the use of this well-tolerated drug as a remedy for jet lag on long-haul flights.

No effect of treatment with sodium valproate on plasma growth hormone in bromocriptine unresponsive acromegaly

Administration of sodium valproate for 6 months at a dose of 300 mg three times daily to 7 bromocriptine unresponsive acromegalic patients who all but one had been treated with pituitary surgery and/or radiotherapy in the past did not result in a significant reduction of the plasma growth hormone (GH) level or in any clinical improvement. It is concluded that sodium valproate is not suitable for the treatment of acromegalic patients who do not show a favourable response to bromocriptine.