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Clinical Studies |
Departments of Endocrinology (J.N.-P., J.M., M.S., M.B., A.G.) and Chemical Endocrinology (L.P., S.M.), St. Bartholomews Hospital, West Smithfield, London, United Kingdom EC1A 7BE
Address all correspondence and requests for reprints to: Dr. Ashley Grossman, Department of Endocrinology, St. Bartholomews Hospital, West Smithfield, London, United Kingdom EC1A 7BE. E-mail: a.b.grossman{at}mds.qmw.ac.uk
| Abstract |
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Each patient was studied on three occasions, in random order, separated by at least 48 h. At 0900 h, via an indwelling forearm cannula, 10 µg desmopressin, 100 µg CRH, or a combination of the two were given as an iv bolus; thereafter, blood was drawn every 15 min for 2 h. The responses to the individual agents were determined according to the timing and calculation criteria suggested by Nieman et al. (1993). A total of 25 patients with Cushings syndrome were studied: 17 patients with pituitary-dependent Cushings syndrome, Cushings disease (CD); 5 patients with occult ectopic ACTH secretion (EC); and 3 patients with primary adrenal (ACTH-independent) Cushings syndrome.
In this series, the best discrimination among ACTH-dependent patient groups was achieved using the combined test. Using the responses of plasma cortisol, all 17 patients with CD showed a rise greater than any of the 5 patients with EC, whereas 1 patient with CD showed a plasma ACTH response within the range seen in the patients with EC. Plasma cortisol responses to desmopressin alone were seen in 14 of 17 patients with CD and 1 of 5 patients with EC and, after CRH alone, in 15 of 17 patients with CD but in no patient with EC. In contrast, plasma ACTH responses after CRH alone were seen in 14 of 17 patients with CD and 2 of 5 patients with EC and, after desmopressin alone, in 12 of 17 with CD and 3 of 5 with EC, thus indicating overlapping responses between the groups and poorer discrimination. No responses were seen in the ACTH-independent group.
These data indicate that desmopressin causes the secretion of ACTH and cortisol in patients with ACTH-dependent Cushings syndrome, and that in combination with CRH, it may provide an improvement over the standard CRH test in the differential diagnosis of ACTH-dependent Cushings syndrome. Furthermore, these data suggest that there may be abnormalities in vasopressin receptor function or number in ACTH-secreting tumors.
| Introduction |
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Desmopressin, a long acting analog of vasopressin (15), has relative specificity for the renal V2 receptor, with little V1-mediated pressor activity (16). Although its specific V1b receptor activity is uncertain, it has been shown previously to have no intrinsic in vivo ACTH-releasing characteristics when given as an infusion in man (17). Desmopressin has, however, been shown to cause a significant release of cortisol and ACTH in the majority of patients with CD when given as bolus, but not in one patient with EC, and it has, therefore, been suggested that it may be used to aid the differential diagnosis of the causes of ACTH-dependent Cushings syndrome (18). However, previous studies have not explored whether the combination test of desmopressin and CRH would be better than either peptide alone in the differential diagnosis.
The present study, therefore, was designed to assess the effects of desmopressin on the release of ACTH and cortisol when given as an iv bolus dose, alone or in combination with CRH, to patients with Cushings syndrome and thus to compare the clinical utility of desmopressin and CRH as diagnostic tests. Human sequence CRH was used instead of the ovine sequence (19), as it is currently more widely available internationally.
| Subjects and Methods |
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After an overnight fast, an in-dwelling forearm cannula was inserted at 0830 h; the subject remained supine for the remainder of that days study. At 0900 h (0 min), 10 µg desmopressin (DDAVP, Ferring, Malmo, Sweden) and saline placebo for CRH, 100 µg human sequence CRH (Ferring, Malmo, Sweden) and saline placebo for desmopressin, or a combination of these peptides were injected sequentially over periods of 15 s each. Blood was taken for estimation of plasma ACTH and cortisol at -15, 0, 15, 30, 45, 60, 90, and 120 min. Blood pressure and pulse rate were recorded by automated means (Dinamapp, Tampa, FL) at each sampling point. After testing, each subject was advised to restrict fluid intake to 2 L for the remainder of the day. The order of all investigations was randomized and run in a single blind manner.
Calculation of response criteria
Following the suggested criteria of Nieman et al. (20) using the ovine CRH test, we calculated in each patient group the percent rise in the mean circulating plasma ACTH values at 15 and 30 min and circulating plasma cortisol values at 30 and 45 min above the mean basal values at -15 and 0 min, after the administration of human CRH, desmopressin, or a combination of the two. The response criteria documented by Nieman et al. (20) that best discriminated Cushings disease from the ectopic ACTH syndrome were a 20% rise in circulating plasma cortisol and a 35% rise in circulating plasma ACTH; these criteria were assessed in this study.
Assays
Plasma cortisol was measured by an in-house unextracted nonchromatographic RIA; the coefficient of variation at 100 and 1000 nmol/L was 6% (21). Plasma ACTH was measured by our routine in-house Vycor (Societe-A.T.A. Geneva, Switzerland) glass-extracted RIA originally developed in 1971, which has subsequently been validated using a range of chromatographic procedures in human studies (22).
| Results |
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Differential effects of CRH or desmopressin given alone. Using
the response criterion of at least a 20% rise in the circulating
plasma cortisol level, calculated from the ratio of the mean values at
30 and 45 min over the mean basal value (21), 15 of 17 patients with CD
responded positively to CRH, but no responses were seen in the patients
with EC. Using the same response criterion, 14 of 17 patients with CD
responded to desmopressin, as did patient 21 with an ACTH-secreting
medullary carcinoma of the thyroid. Patients 1, 2, 5, and 17 with CD
showed discordant responses to CRH and desmopressin; patients 1 and 17
responded only to desmopressin, whereas patients 2 and 5 responded only
to CRH (Table 1
). No responses to either treatment were seen in the
patients with ACTH-independent Cushings syndrome.
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Plasma ACTH responses (Table 2
and Fig. 2
)
Differential effects of CRH and desmopressin given alone. Using the response criterion of at least a 35% rise in plasma ACTH calculated from the ratio of the mean of the values at 15 and 30 min over the mean basal level (21), 14 of 17 patients with CD and 2 of 5 patients with EC (patients 18 and 22) responded to CRH alone. After the administration of desmopressin alone, 12 of 17 patients with CD and 3 patients with EC showed such a response (patients 19, 20, and 21). After CRH alone, 6 patients, and after desmopressin alone, 9 patients with CD responded within the range of responses seen in the patients with EC. Patients 1, 2, 5, and 17 had the same discordant responses to CRH and desmopressin using ACTH response criteria as they demonstrated using cortisol criteria (see above). Patient 4 showed a cortisol, but apparently not an ACTH, response to CRH. ACTH remained undetectable in all 3 patients with primary adrenal disease.
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Side-effects
After the administration of either peptide, adverse effects were limited to a short-lived flushing sensation (115 min), which was similar in nature to that after the combination treatment, but slightly longer in duration (220 min). After the combination treatment, three patients experienced a slight metallic taste in their throats, lasting 25 min. In no case was there evidence of water overload. There was no significant change in blood pressure in any patient; two patients experienced a transient (<5 min) sinus tachycardia after the combination treatment (maximum heart rates, 113 and 100 beats/min), with no symptomatic palpitations, chest pain, or fall in blood pressure.
| Discussion |
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Vasopressin has a well documented synergistic effect with CRH for ACTH release (9, 23, 24). Desmopressin has similar ACTH-releasing effects in rats in vitro (25), and this effect is not reversed by V2 receptor antagonists (26). Previous data in normal volunteers have not demonstrated either direct or potentiating effects of desmopressin for ACTH release when coadministered with CRH (17). Desmopressin is said to be a specific V2 receptor agonist, and this may explain the lack of response of ACTH secretion in the normal volunteers. Desmopressin does, however, as shown in this study and previously (18), cause significant release of ACTH and cortisol in ACTH-dependent Cushings syndrome. Glucocorticoids have recently been shown to up-regulate the expression of the V1b receptor in normal rat anterior pituitary glands and rescue the down-regulation seen after adrenalectomy, with similar effects reported in the vasopressin-deficient Brattleboro rat (27); thus, such up-regulation may be caused by hypercortisolemia rather than changes in vasopressin levels (27). Furthermore, the majority of human corticotroph adenomas and some ACTH-secreting bronchial carcinoids have been demonstrated to express high levels of the V1b receptor; in contrast, the CRH receptor is expressed in corticotroph adenomas, but far less commonly in bronchial carcinoid tumors (28, 29). Taken together, these studies suggest that the effect of desmopressin in these tumors may be mediated by up-regulation of the V1b receptor in neuroendocrine tissue, which, in turn, may reflect prevailing hypercortisolemia. It seems probable that desmopressin may show cross-affinity with the V1b receptor when it is present in high concentrations, although it is also possible that up-regulation or aberrant expression of the V2 receptor in ACTH-secreting cells may occur. Further, it is possible that the differentiating ability of the combined test may relate to a greater increase in the co-overexpression of the CRH and V1b receptors in many of the corticotroph adenomas than in ectopic tumors secreting ACTH and the higher response seen in CD.
A previous report has suggested that desmopressin is a readily available and cost-effective alternative to CRH in the investigation of Cushings syndrome (18). Certainly, in this study it seems to have a similar, but inferior, ability to differentiate between CD and EC when analyzing either plasma ACTH or cortisol responses. Clearly, three of our five patients with EC responded to desmopressin given alone.
In conclusion, desmopressin given alone appears to cause the release of ACTH and cortisol in ACTH-dependent Cushings syndrome. Such effects of desmopressin suggest abnormalities in receptor number or function in these neuroendocrine ACTH-secreting tumors that merit further study. As a diagnostic test, human sequence CRH alone appears to be better than desmopressin alone in discriminating between ACTH-dependent groups, whereas the combination of the two appears to produce better results than either alone. Occult ectopic ACTH-secreting tumors can be extremely small and may offer a considerable diagnostic challenge, behaving in many ways similarly to eutopic corticotroph tumors (30). Thus, the combined test may be of considerable diagnostic utility. This is, however, a relatively small series of patients, and the percent rise criterion that distinguishes pituitary from ectopic ACTH production may need alteration with the benefit of further experience. Although we do not suggest that this combination test replace the standard CRH test, it seems probable that testing with these agents in addition to conventional testing with the high dose dexamethasone suppression test or inferior petrosal catheter studies may be of considerable clinical benefit.
| Acknowledgments |
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| Footnotes |
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Received October 4, 1995.
Revised June 10, 1996.
Revised August 14, 1996.
Accepted September 14, 1996.
| References |
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