Treatment of adrenocorticotropin-dependent Cushing's syndrome: a consensus statement.

OBJECTIVE: Our objective was to evaluate the published literature and reach a consensus on the treatment of patients with ACTH-dependent Cushing's syndrome, because there is no recent consensus on the management of this rare disorder. PARTICIPANTS: Thirty-two leading endocrinologists, clinicians, and neurosurgeons with specific expertise in the management of ACTH-dependent Cushing's syndrome representing nine countries were chosen to address 1) criteria for cure and remission of this disorder, 2) surgical treatment of Cushing's disease, 3) therapeutic options in the event of persistent disease after transsphenoidal surgery, 4) medical therapy of Cushing's disease, and 5) management of ectopic ACTH syndrome, Nelson's syndrome, and special patient populations. EVIDENCE: Participants presented published scientific data, which formed the basis of the recommendations. Opinion shared by a majority of experts was used where strong evidence was lacking. CONSENSUS PROCESS: Participants met for 2 d, during which there were four chaired sessions of presentations, followed by general discussion where a consensus was reached. The consensus statement was prepared by a steering committee and was then reviewed by all authors, with suggestions incorporated if agreed upon by the majority. CONCLUSIONS: ACTH-dependent Cushing's syndrome is a heterogeneous disorder requiring a multidisciplinary and individualized approach to patient management. Generally, the treatment of choice for ACTH-dependent Cushing's syndrome is curative surgery with selective pituitary or ectopic corticotroph tumor resection. Second-line treatments include more radical surgery, radiation therapy (for Cushing's disease), medical therapy, and bilateral adrenalectomy. Because of the significant morbidity of Cushing's syndrome, early diagnosis and prompt therapy are warranted.

Pulsatile growth hormone secretion in normal man during a continuous 24-hour infusion of human growth hormone releasing factor (1-40). Evidence for intermittent somatostatin secretion.

Growth hormone (GH) secretory patterns were studied in a patient with ectopic growth hormone releasing factor (GRF) secretion and in normal men given continuous infusions of human growth hormone releasing factor (1-40)-OH (hGRF-40). In the patient with ectopic GRF secretion, GH secretion was pulsatile despite continuously elevated immunoreactive GRF levels. To determine if pulsatile GH secretion is maintained in normal subjects, we administered to six healthy young men vehicle or hGRF-40, 2 ng/kg per min, for 24 h and gave a supramaximal intravenous bolus dose of hGRF-40, 3.3 micrograms/kg, after 23.5 h of infusion. hGRF-40 infusion resulted in greater GH secretion than did vehicle infusion and pulsatile GH secretion was maintained throughout hGRF-40 infusion. During the 23.5 h of vehicle infusion, total GH secretion (microgram; mean +/- SEM) was 634 +/- 151 compared with 1,576 +/- 284 during hGRF-40 infusion (P = 0.042). The GH response to the intravenous bolus of hGRF-40 was greater after vehicle infusion than after hGRF-40 infusion; 877 +/- 170 and 386 +/- 125 micrograms of GH was secreted after the bolus on vehicle and hGRF-40 days, respectively (P = 0.015). The total amount of GH secreted during the 25.5 h of the two study days was not different; 1,504 +/- 260 and 1,952 +/- 383 micrograms were secreted during vehicle and hGRF-40 days, respectively (P = 0.36). Not only was pulsatile GH secretion maintained during hGRF-40 infusion, but there was augmentation of naturally occurring GH pulses, which is in contrast to the effect of gonadotropin-releasing hormone on gonadotropin secretion. We suggest that GH pulses are a result of GRF secretion that is associated with a diminution or withdrawal of somatostatin secretion.

Enhanced basal and disorderly growth hormone secretion distinguish acromegalic from normal pulsatile growth hormone release.

Pulses of growth hormone (GH) release in acromegaly may arise from hypothalamic regulation or from random events intrinsic to adenomatous tissue. To distinguish between these possibilities, serum GH concentrations were measured at 5-min intervals for 24 h in acromegalic men and women with active (n = 19) and inactive (n = 9) disease and in normal young adults in the fed (n = 20) and fasted (n = 16) states. Daily GH secretion rates, calculated by deconvolution analysis, were greater in patients with active acromegaly than in fed (P < 0.05) but not fasted normal subjects. Significant basal (nonpulsatile) GH secretion was present in virtually all active acromegalics but not those in remission or in fed and fasted normal subjects. A recently introduced scale- and model-independent statistic, approximate entropy (ApEn), was used to test for regularity (orderliness) in the GH data. All but one acromegalic had ApEn values greater than the absolute range in normal subjects, indicating reduced orderliness of GH release; ApEn distinguished acromegalic from normal GH secretion (fed, P < 10(-12); fasted, P < 10(-7)) with high sensitivity (95%) and specificity (100%). Acromegalics in remission had ApEn scores larger than those of normal subjects (P < 0.0001) but smaller than those of active acromegalics (P < 0.001). The coefficient of variation of successive incremental changes in GH concentrations was significantly lower in acromegalics than in normal subjects (P < 0.001). Fourier analysis in acromegalics revealed reduced fractional amplitudes compared to normal subjects (P < 0.05). We conclude that GH secretion in acromegaly is highly irregular with disorderly release accompanying significant basal secretion.

Plasma growth hormone responses to constant infusions of human pancreatic growth hormone releasing factor. Intermittent secretion or response attenuation.

Administration of human pancreatic tumor growth hormone (GH) releasing factor (hpGRF[1-40]) as a single injection to normal human subjects stimulates the secretion of GH in a dose-responsive manner. In the present studies, hpGRF(1-40) was infused in a graded stepwise manner over a 6-h period in order to determine whether the GH secretory response would be sustained. Normal adult males received four consecutive 90-min infusions of hpGRF(1-40) at doses of 1, 3.3, 10, and 33 ng/kg per min, preceded and followed by a 90-min saline infusion; and the plasma GH responses were compared with those during a separate control infusion. Plasma GH levels were significantly elevated by each hpGRF(1-40) infusion; and dose responsiveness was evident for the lowest three doses. Mean integrated GH secretory rates for the four doses were 1.95, 3.29, 4.29, and 3.65 times those of the respective control study. Plasma GH responses exhibited considerable variability, frequently decreasing during the latter part of each infusion; and at the highest dose, they decreased continuously beginning shortly after the onset of infusion. Episodic GH secretion occurred in individual subjects during each of the infusion periods. The possible contribution of hypothalamic somatostatin secretion to the diminished GH responsiveness was evaluated by determining plasma thyroid stimulating hormone (TSH) levels during the infusions and the TSH responses to thyrotropin-releasing hormone (500 micrograms i.v.) during a separate hpGRF(1-40) infusion of 2 ng/kg per min. Neither basal nor stimulated TSH levels differed between GRF-infused and control groups. The results indicate that GH secretion is dose responsive to hpGRF(1-40) infusions, though the response to hpGRF(1-40) infusions, though the response is complex. The absence of impaired TSH secretion provides evidence against a mediating role of somatostatin. The explanation for the loss of GH responsiveness remains undetermined but could include GRF-induced receptor down-regulation, a postreceptor effect, or, in spite of our negative results, a somatostatin-mediated inhibition.

Metabolic clearance and plasma disappearance rates of human pancreatic tumor growth hormone releasing factor in man.

The metabolic clearance rate (MCR) and plasma disappearance rate (t1/2) of human pancreatic tumor growth hormone releasing factor [hpGRF(1-40)] was determined in normal adult male subjects by single injection and constant infusion techniques. Single injections of 1, 3.3, and 10 micrograms/kg hpGRF(1-40) were administered intravenously, plasma immunoreactive (IR) GRF levels were measured during the subsequent 180 min, and biexponential curve analysis was performed. Graded, dose-constant infusions of hpGRF(1-40) at rates of 1, 3.3, 10, and 33 ng/kg per min were administered and the MCR was calculated from measurement of steady state plasma IR-GRF levels at each infusion rate. The postinfusion disappearance rate was determined by linear regression analysis of plasma IR-GRF levels during the 120-min period after cessation of the infusion. The calculated MCR during the single injection study was 194 +/- 17.5 liters/m2 per d and was not significantly different from the calculated value during the constant infusion study (202 +/- 16 liters/m2 per d). The disappearance rate during the single injection study was subdivided into two linear phases: an initial equilibration phase (7.6 +/- 1.2 min) and a subsequent elimination phase (51.8 +/- 5.4 min). The latter was similar to the linear disappearance rate observed (41.3 +/- 3.0 min) after cessation of the constant infusion. The chromatographic and biologic characteristics of plasma IR-GRF, 30 min after injection, were similar to those of synthetic hpGRF(1-40). The results have been discussed in relation to the MCR of other hypothalamic hormones and have been used to extrapolate secretion rates of GRF in patients with ectopic GRF production.

Consensus statement: medical management of acromegaly.

In November 2003, the Pituitary Society and the European Neuroendocrine Association sponsored a consensus workshop in Seville to address challenging issues in the medical management of acromegaly. Participants comprised 70 endocrinologists and neurosurgeons with international expertise in managing patients with acromegaly. All participants participated in the workshop proceedings, and the final document written by the scientific committee reflects the consensus opinion of the interactive deliberations. The meeting was supported by an unrestricted educational grant from Ipsen. No pharmaceutical representatives participated in the program planning or in the scientific deliberations.

Long-term treatment of 189 acromegalic patients with the somatostatin analog octreotide. Results of the International Multicenter Acromegaly Study Group.

BACKGROUND: We wanted to determine the clinical and biochemical effects of long-term therapy with the somatostatin analog octreotide in 189 acromegalic patients. METHODS: Patients were treated at 23 medical centers for 6 days to 231 weeks (median, 24.2 weeks) with varying octreotide dosages (100 to 1500 micrograms/d; median, 300 micrograms/d). Serum growth hormone and insulin-like growth factor I (IGF-I) concentrations before and at the end of the study were compared, and correlations between the response to treatment with total daily dosage and duration of treatment were sought. RESULTS: The clinical response rate was 88%, irrespective of dosage or treatment duration. Serum growth hormone levels decreased in 172 (94%) of 182 patients and IGF-I levels decreased in 91 (92%) of 99. The mean pretreatment growth hormone level was 39.4 +/- 4.4 micrograms/L and decreased to 12.2 +/- 1.5 micrograms/L. Growth hormone levels decreased to less than 5 micrograms/L in 82 (45%) of 182 patients. The pretreatment IGF-I level was 5.62 +/- 0.41 U/mL and decreased to 2.64 +/- 0.19 U/mL; suppression to 2 U/mL or lower occurred in 46 (46%) of 99 patients. The degree of growth hormone suppression was associated with longer treatment duration but not with the total octreotide dosage per day. In 34 patients studied prospectively, pituitary tumor size decreased by greater than 20% in 15 (44%). Side effects occurred in 37% of patients and were most commonly transient loose alcoholic stools, pain at the injection site, and abdominal discomfort; severity was mild to moderate. Glucose tolerance was unchanged or improved in 52% and declined in 48% of 25 patients evaluated. CONCLUSIONS: Octreotide is an effective treatment for acromegaly that may be used as primary therapy or after surgery and/or pituitary irradiation.

Neuroendocrine regulation of growth hormone secretion.

Growth hormone (GH) secretion is controlled by many factors, including stage of development, age, gonadal steroids, body composition, nutritional state, time of day and whether the subject is asleep or awake. Understanding regulation of GH secretion is important since this hormone regulates not only growth, but also the partitioning of nutrients and body composition. There is increasing evidence that there is a basic ultradian rhythm of GH secretion. The NSF Center studies will be facilitated by 3 major efforts: (a) improvement of sensitivity of GH assays to permit accurate description of GH pulses; (b) use of biomathematical models to objectively determine GH pulse characteristics, as well as calculation of secretion rates to facilitate the study of the relationship between neural controls and GH secretion; and (c) use of the tau mutant hamster and the new mouse mutant animal models. By manipulation of the endogenous circadian clock in these animal models it will be possible to study the relationship between endogenous circadian systems and ultradian GH rhythms.

Fasting alters pulsatile and rhythmic cortisol release in normal man.

The effect of a 5-day fast on integrated, pulsatile, and periodic cortisol release was studied in 10 normal men by measuring serum cortisol concentrations every 20 min for 24 h before (day 0) and during the fifth day of fasting (day 5). Serum concentration profiles were analyzed for integrated cortisol release (area under the curve), pulsatile hormone release by an objective, statistically based pulse detection algorithm (cluster analysis), and periodic hormone release (circadian and ultradian rhythms) by Fourier expansion time series analysis. Urinary cortisol excretion per 24 h was measured in 5 men. The mean 24-h integrated serum cortisol concentration increased 1.7-fold during fasting (P = 0.0006). This increase resulted from a 2-fold increase in the serum cortisol concentrations between pulses (valley mean; P = 0.0004), an increase in the pulse height (P = 0.001), and an increase in pulse increment above baseline (P = 0.01). There were no changes in the number of pulses per 24 h, the interval between pulses, the width of the pulses, or the area of the pulses during fasting. Twenty-four-hour urinary cortisol excretion increased in all men, and the mean urinary cortisol (nanomoles per L)/creatinine clearance (milliliters per s) ratio increased from 119 on day 0 to 187 on day 5 (n = 5; P = 0.05). The pattern of periodic hormone release also changed during fasting; the mean (+/- SE) circadian rhythm (24-h) amplitude decreased from 160 +/- 14 nmol/L on day 0 to 102 +/- 105 nmol/L on day 5 (P = 0.06), and the amplitude of the 12-h rhythm increased from 68 +/- 11 to 99 +/- 11 nmol/L. There also were significant increases in the amplitudes of rhythms with periodicities of 8.1, 4.1, 2.4, 1.6, and 1.3 h (P = 0.02-0.008). Fasting in normal men results in distinct changes in the amount and pattern of pulsatile, circadian, and ultradian cortisol release.

Plasma transport of human growth hormone in vivo.

We have previously shown that a substantial part of human GH is complexed with GH-binding proteins (BPs) when GH is incubated with plasma in vitro. The proportion of GH bound in vivo, however, is unknown and may differ because of factors that cannot be assessed in vitro, such as binding to tissue receptors, distribution of GH outside the vascular compartment, and fluctuating GH and possibly BP levels. Accordingly, we studied the plasma transport characteristics of GH in vivo in six normal men. Monomeric, natural sequence human GH (Humatrope, Eli Lilly Co.) was injected iv in a dose designed to yield physiological plasma levels. Endogenous GH was suppressed before injection with oral glucose administration. Fifteen minutes after injection, plasma was obtained and immediately analyzed by zonal and frontal analysis in gel chromatography, followed by GH measurement in the fractions by RIA. The results obtained were very similar to those derived from in vitro studies, regardless of which analytical method was used. Frontal analysis at 37 C, which most directly reflects the true bound fraction, showed that 38.8 +/- 4.7% (mean +/- SD) of GH was bound to BPs at plasma GH levels ranging from 32-59 micrograms/L, indistinguishable from in vitro results. [When allowance was made for partial BP saturation, the fraction bound at low GH levels (greater than 7 micrograms/L) was calculated as 45.5 +/- 7.5%.] There was evidence for binding to both high and low affinity BPs in the expected proportions. In contrast to complex formation between GH and BPs, no evidence was obtained for conversion of the monomeric GH to oligomeric forms. We conclude that in vitro predictions about binding of GH to BPs in human plasma are representative of in vivo conditions. Shortly after a GH pulse, almost half of plasma GH circulates in complexed form, primarily bound to the high affinity (receptor-related) BP. Aggregation of GH in plasma does not occur (at least within a 15-min period), suggesting that the pituitary is the predominant, if not sole, source of circulating GH oligomers.

Surgical management of GH-secreting pituitary adenomas: an outcome study using modern remission criteria.

The results of transsphenoidal surgery as initial therapy for GH-secreting pituitary adenomas in 57 acromegalic patients were analyzed retrospectively. Patients with prior surgery or radiation therapy were excluded from the study. Three different criteria were used to define remission: glucose-suppressed (nadir) GH less than 1.0 microg/liter, a normal sex- and age-adjusted IGF-I level, and postoperative random GH levels of 2.5 microg/liter or less. Additionally, we analyzed the neuropathological data, including immunohistochemistry and ultrastructural categorization, and the surgical complications. The short-term remission rate (6-wk postoperative follow-up visit), as determined by a random GH measurement of 2.5 microg/liter or less, was 48.8%; the remission rate, as determined by nadir GH, was 51.4%. For 57 patients followed for 12 months or more after surgery (mean, 37.7 months), surgical remission was achieved in 70.2%, 66.7%, and 61.1%, respectively, for patients assessed by normal IGF-I, random GH, and nadir GH. One patient (1.1%) developed recurrence of active acromegaly 81 months after initially successful surgical therapy. Extrasellar growth of the tumor (P = 0.04) and dural invasion by the adenoma (P = 0.008) were significant univariate predictors of a poor outcome. Tumor size was significantly greater in patients with persistent or recurrent acromegaly (P = 0.02). Patients with tumors of the ultrastructural categories of mixed GH/PRL cell and mammosomatotroph adenomas had the lowest remission rates (50% and 42.9%, respectively). There were no perioperative deaths, and there was no serious morbidity. The permanent complication rate was 3.3% (1 permanent DI and 2 nasal septal perforations). Surgical management of acromegaly currently provides prompt, effective, and satisfactory initial treatment for the majority of patients. Using stringent criteria for remission, primary transsphenoidal surgery for GH-secreting pituitary adenomas is effective and often definitive therapy for acromegaly. These results provide a benchmark for the contemporary results of surgical management as assessed by modern outcome criteria.

Follicle-stimulating hormone- and alpha-subunit-secreting pituitary tumor treated with bromocriptine.

Glycoprotein-secreting pituitary tumors are uncommon. With increased awareness that pituitary tumors may secrete FSH, LH, TSH, and the alpha-subunit, either as a sole product or in any combination, these tumors are more likely to be recognized. The standard therapy is surgical resection and, possibly, postoperative radiotherapy for residual tumor mass or persistent hormonal secretion. We report a patient with a FSH- and alpha-subunit-secreting tumor who refused surgery and was treated with the dopamine agonist bromocriptine as primary therapy. Bromocriptine treatment resulted in reduction of serum FSH and alpha-subunit levels to normal, improvement of visual field defects, and improvement in hypogonadism despite lack of demonstrable change in tumor size, as assessed by computed tomographic scan. Chromatographic analysis of the serum revealed distinct peaks corresponding to those of labeled FSH and alpha-subunit. The clinical and biochemical responses in this patient suggest that some glycoprotein-secreting tumors may be responsive to dopamine agonist therapy.

Circulating growth hormone forms after stimulation of pituitary secretion with growth hormone-releasing factor in man.

Human GH (hGH) in the circulation of acromegalic patients and pharmacologically stimulated normal subjects consists of several monomeric and oligomeric molecular forms. However, little is known about the nature of plasma hGH under physiological conditions. We examined the molecular composition of plasma hGH secreted in response to synthetic human pancreatic tumor GRF-(1-40) (hpGRF-40), a peptide closely resembling or identical to hypothalamic GRF. The peptide (10 micrograms/kg) was injected iv into six normal men, and blood was obtained 30 min later. Plasma hGH was characterized by gel filtration and by polyacrylamide gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and isoelectric focusing after extraction from plasma by immunoadsorbent chromatography. At least 53% of hGH eluted as little (monomeric) hGH, 27% as big (dimeric) hGH, and 20% or less as big-big (oligomeric and spurious) hGH during gel filtration. Among the monomeric forms, the 22,000-dalton form was predominant (83%), with smaller quantities of the 20,000-dalton variant (11%), and one or more unidentified acidic forms (N alpha-acetylated, deamidated, or cleaved hGH) (6%) also present. The molecular composition of plasma hGH secreted in response to hpGRF-40 is similar to that released after pharmacological stimuli or that circulating in acromegaly.

Dual effects of growth hormone (GH)-releasing hormone infusion in normal men: somatotroph desensitization and increase in releasable GH.

Continuous infusion of human GH-releasing hormone (GHRH) stimulates GH secretion in normal subjects, but a single supramaximal iv dose of GHRH thereafter elicits a diminished serum GH response compared to that after a saline infusion; the response to the single dose challenge is inversely related to the dose of GHRH previously infused. To determine if this attenuated GH response is a result of depletion of available GH or desensitization of the somatotroph, a 6-h infusion of saline or GHRH (10 ng/kg . min) was administered to 10 normal men, and an iv bolus dose of either GHRH (3.3 micrograms/kg) or regular insulin (0.15 U/kg) was given after 5.5 h of infusion. On both days of GHRH infusion, there was significant stimulation of GH secretion compared to that after saline infusion. The GH response to the supramaximal dose of GHRH was greater after saline infusion than after GHRH infusion, and the GH response to insulin-induced hypoglycemia was significantly greater after GHRH infusion compared with the responses on the other 3 study days. The greatest GH secretion occurred during GHRH infusion followed by insulin administration; therefore, pituitary reserve was not decreased by prior exposure to GHRH. These studies suggest that somatotrophs become partially refractory to GHRH stimulation over time, but remain responsive to an alternate stimulus of GH secretion. We suggest that the hypoglycemia-induced GH response occurs via a reduction in hypothalamic somatostatin secretion, and the attenuated GH response to the supramaximal GHRH dose after GHRH infusion probably represents either partial desensitization or down-regulation of the GHRH receptor.

Octreotide suppresses both growth hormone (GH) and GH-releasing hormone (GHRH) in acromegaly due to ectopic GHRH secretion.

Two patients with acromegaly secondary to ectopic GHRH secretion by metastatic carcinoid tumors were studied before and during therapy with the somatostatin analog octreotide (SMS 201-995). GH and GHRH secretory patterns were assessed during intermittent sc administration, continuous sc infusion (CSI), and continuous iv infusion of octreotide. Octreotide reduced serum GH and plasma GHRH levels in the two patients, although there was differential sensitivity of GH and GHRH. Intermittent sc therapy transiently lowered serum GH in both patients. A higher iv dose was required to reduce plasma GHRH by 50% than to reduce serum GH by 50% (2.0 vs. 0.05 micrograms/kg.h, respectively; patient 1). A similar pattern was found during CSI octreotide administration in the same patient. Chronic therapy with intermittent sc and CSI octreotide was assessed by serial 24-h profiles of GH and GHRH secretion in patient 2. Mean hourly serum GH levels decreased from a pretreatment level of 31.5 +/- 3.5 (+/- SE) to 9.5 +/- 1.5 micrograms/L during CSI therapy (1000 micrograms/day or 0.40 micrograms/kg.h). In contrast, plasma GHRH levels were less effectively suppressed. The mean serum GH levels and the variation in hourly GH values were reduced to a greater extent with CSI than with intermittent sc therapy. Serum insulin-like growth factor I also declined from 5.9 x 10(3) to 2.5 x 10(3) U/L during chronic CSI therapy (patient 2). CSI therapy with octreotide can be more effective than intermittent sc therapy in controlling GH excess in the rare syndrome of ectopic GHRH secretion, although serum GH may not decline to normal.

Half-time of endogenous growth hormone (GH) disappearance in normal man after stimulation of GH secretion by GH-releasing hormone and suppression with somatostatin.

The half-life (t1/2) of disappearance of endogenous GH from serum was studied using physiological effectors to stimulate and then suppress GH release. GH secretion was stimulated by a single iv injection of GHRH, followed 45 min later by an iv bolus dose and then a 2.5-h infusion of somatostatin (SRIH) to suppress further release. The in vivo t1/2 of GH in seven men was calculated from serum GH concentrations measured at frequent intervals after beginning the SRIH infusion. The mean t1/2 of endogenous GH was 18.9 +/- 0.8 (+/- SE) min by monoexponential analysis and 3.5 +/- 0.7 and 20.7 +/- 0.7 min by biexponential fitting. In these normal men, the decline in GH concentrations after GHRH and SRIH administration was similar to that after the administration of GHRH alone, which yielded a t1/2 of 20.3 +/- 1.9 min. We conclude that the physiological kinetics of endogenous GH removal/disappearance can be estimated in vivo in man using GHRH with or without SRIH infusion.

Pheochromocytoma in von Hippel-Lindau disease: clinical presentation and mutation analysis in a large, multigenerational kindred.

The clinical presentation and characterization of the mutation in members of a large kindred with von Hippel-Lindau disease (VHLD) and pheochromocytoma were examined. Twenty-five proven cases of VHLD occurring in four generations of a large kindred have been followed since 1964, and pheochromocytoma has occurred in 17. Symptoms of pheochromocytoma developed at an early age, on average at 12.5 +/- 1.3 yr, and definitive diagnosis and treatment of pheochromocytoma occurred at 19.9 +/- 2.6 yr. Significantly higher urine catecholamine concentrations were observed in younger patients than in older ones. Mutation analysis was performed in 14 family members, and a new mutation in the VHLD gene was identified in 11; this mutation is a G to T change at nucleotide 658 that results in the substitution of a serine for an alanine residue at position 149 of the polypeptide chain. Seven of the 11 patients with the mutation have VHLD; four, all 10 yr old or less, are asymptomatic and have no evidence of disease, but are at high risk for developing VHLD. These children are being followed closely for clinical and biochemical manifestations. The characterization of this new mutation has permitted identification of family members who are likely to develop VHLD.

Fasting as a metabolic stress paradigm selectively amplifies cortisol secretory burst mass and delays the time of maximal nyctohemeral cortisol concentrations in healthy men.

Serum cortisol concentrations are increased in fasted or malnourished human subjects. The dynamic mechanisms underlying this adaptive response have been investigated in eight normal men by analyzing serum cortisol concentrations measured in blood obtained at 5-min intervals over 24 h on a control (fed) day and on the fifth day of a fast (water only) assigned in randomized order. A multiple parameter deconvolution method was used to simultaneously resolve endogenous cortisol secretion and half-life. Five days of fasting induced a 1.8-fold increase in the 24-h endogenous cortisol production rate (fed, 2504 +/- 308; fasted, 4528 +/- 488 nmol/L distribution volume; P < 0.006). This enhanced cortisol production rate was accounted for by a 1.6-fold increase in the mass of cortisol secreted per burst (fed, 115 +/- 12.1; fasted, 183 +/- 17.3 nmol/L; P < 0.02). Cortisol secretory event amplitudes (maximal rates of cortisol release attained within a burst) increased in seven of eight men, and mean secretory burst durations remained unchanged by fasting. Moreover, the number of computer-resolved cortisol secretory bursts per 24 h (fed, 22 +/- 1.4; fasted, 25 +/- 2.0; P = NS) and the interburst interval (fed, 65 +/- 4.0; fasted, 57 +/- 4.4 min) did not change significantly during a 5-day fast. The calculated half-life of endogenous cortisol was not significantly altered by fasting (fed, 108 +/- 9.7; fasted, 129 +/- 11 min). There was no significant change in the nyctohemeral pattern of varying adrenocortical secretory burst frequency in response to fasting. However, the mean (mesor) mass of glucocorticoid secreted per burst over 24 h rose significantly in response to fasting. In addition, by cosinor analysis, maximal serum cortisol concentrations occurred (95% confidence intervals) between 0930-1334 h in the fed state and between 1116-1612 h in the fasted state (P < 0.04). Fasting augmented the mesor (average value about which the diurnal rhythm oscillates; P < 0.0008 compared with fed state) and the amplitude (P < 0.04) of the 24-h serum cortisol concentration profile. Linear regression analysis disclosed a significant inverse relationship between mean serum cortisol and GH concentrations in fasted men (r = -0.76; P < 0.02). In conclusion, the present data indicate that starvation-induced enhancement of cortisol secretion in young healthy men is mediated by an increased glucocorticoid secretory burst mass, rather than changes in secretory burst frequency or duration or in cortisol half-life. In addition, fasting modifies the diurnal secretory pattern of cortisol by delaying maximal serum concentrations to the early afternoon. The inverse relationship between serum cortisol and GH responses to fasting suggests differential regulation of the corticotropic and somatotropic axis by the metabolic stress of fasting and/or feedback interactions between these two axes when they are both activated.

Amplitude suppression of the pulsatile mode of immunoradiometric luteinizing hormone release in fasting-induced hypoandrogenemia in normal men.

In the male rodent and primate, fasting or severe caloric restriction significantly decreases serum testosterone concentrations, putatively via inducing secondary hypogonadotrophism. To clarify this presumptive pathophysiology, we have used: 1) a high sensitivity immunoradiometric assay, which correlates well with an in vitro Leydig cell bioassay of LH; 2) blood sampling every 5 min for 24 h basally and every 10 min for 3 h after GnRH injection before and after a 5-day (water only) fast in eight healthy young men; and 3) deconvolution analysis to evaluate in vivo LH secretory burst frequency, amplitude, duration, and mass, and LH half-life simultaneously. We documented a 50% fall in serum total and free testosterone concentrations, and a 30% decrease in 24-h mean serum LH concentrations (viz., fed 3.0 +/- 0.47 vs. fasted 2.1 +/- 0.39 U/L, P = 0.043). Deconvolution analysis revealed preservation of LH secretory pulse frequency (fed 12.9 +/- 0.48 vs. fasted 12.6 +/- 0.78 secretory bursts/day, P = NS) during fasting-induced hypogonadotropism. The duration of computer-resolved LH secretory bursts, the interburst interval, and the calculated endogenous half-life of LH also did not change, whereas LH secretory burst mass declined significantly; viz. from 28 +/- 5 in the fed to 14 +/- 3.2 U/L of distribution volume/day in the fasted state (P = 0.034). In contrast, LH release after a 10 micrograms pulse of GnRH iv was enhanced during fasting in seven of the eight men. Fasting also decreased mean (24 h) serum TSH and PRL, increased cortisol, dehydroepiandrosterone sulfate and GH, and did not affect FSH concentrations or the radioiodinated albumen distribution space. In summary, in young men 5 days of nutrient deprivation selectively attenuates the mass of LH secreted per burst without altering LH secretory event frequency or LH half-life. We infer that decreased LH release per burst is due to decreased hypothalamic GnRH impulse strength, since LH release induced by a submaximally effective pulse of exogenous GnRH is amplified rather than attenuated.

Evidence for a limited growth hormone (GH)-releasing hormone (GHRH)-releasable quantity of GH: effects of 6-hour infusions of GHRH on GH secretion in normal man.

Human GH-releasing hormone [hGHRH-40 (GHRH)] stimulates GH release in a dose-dependent fashion when administered as single iv bolus doses or as continuous 90-min infusions. However, there has been variability in the GH responses, and it appears that there are waxing and waning effects of GHRH. To address whether these are a result of the dose of GHRH, time, or intermittent changes in sensitivity of the somatotrophs, we administered 6-h infusions of vehicle and different doses of GHRH to six normal men. In addition, an iv bolus injection of GHRH was given after 5.5 h of infusion to evaluate residual GH secretory capacity. The subjects were given infusions of either vehicle or GHRH (1, 3.3, and 10 ng/kg X min), followed by an iv bolus injection of 3.3 micrograms/kg on four separate occasions. GHRH infusions stimulated GH secretion compared to basal secretion. The changes from basal GH secretion (mean +/- SEM) were 2.0 +/- 1.6, 4.6 +/- 1.5, 12.7 +/- 5.1, and 8.2 +/- 1.8 ng/ml X h during the vehicle and GHRH (1, 3.3, and 10 ng/kg X min) infusions, respectively. The changes from basal GH secretion for 2 h after the iv bolus dose (after 5.5 h of infusion) were 33.3 +/- 8.7, 22.4 +/- 3.8, 14.0 +/- 3.6, and 10.5 +/- 2.0 ng/ml X h on the vehicle and GHRH (1, 3.3, and 10 ng/kg X min) infusion days, respectively. The magnitude of the GH response was inversely related to the GHRH infusion dose. The total amount of GH released during the 7.5-h study periods was not different among the vehicle and 3 GHRH infusion days. Thus, it appears that a finite amount of GH is released by GHRH. There was variability in the degree of responsiveness to the continuous infusions of GHRH. Surges of GH release occurred during the GHRH infusions, which may be attributed to intermittent secretion of a GH inhibitor, such a somatostatin.