Standards of care for medical management of acromegaly in pituitary tumor centers of excellence (PTCOE).

PURPOSE: A series of consensus guidelines on medical treatment of acromegaly have been produced in the last two decades. However, little information is available on their application in clinical practice. Furthermore, international standards of acromegaly care have not been published. The aim of our study was to report current standards of care for medical therapy of acromegaly, using results collected through an audit performed to validate criteria for definition of Pituitary Tumor Centers of Excellence (PTCOE). METHODS: Details of medical treatment approaches to acromegaly were voluntarily provided by nine renowned international centers that participated in this audit. For the period 2018-2020, we assessed overall number of acromegaly patients under medical treatment, distribution of patients on different treatment modalities, overall biochemical control rate with medical therapy, and specific control rates for different medical treatment options. RESULTS: Median number of total patients and median number of new patients with acromegaly managed annually in the endocrinology units of the centers were 206 and 16.3, respectively. Median percentage of acromegaly patients on medical treatment was 48.9%. Among the patients on medical treatment, first-generation somatostatin receptor ligand (SRL) monotherapy was used with a median rate of 48.7%, followed by combination therapies with a median rate of 29.3%. Cabergoline monotherapy was used in 6.9% of patients. Pegvisomant monotherapy was used in 7 centers and pasireotide monotherapy in 5 centers, with median rates of 7.9% and 6.3%, respectively. CONCLUSIONS: Current standards of care in PTCOEs include use of first-generation SRLs as the first medical option in about 50% of patients, as recommended by consensus guidelines. However, some patients are kept on this treatment despite inadequate control suggesting that cost-effectiveness, availability, patient preference, side effects, and therapeutic inertia may play a possible role also in PTCOE. Moreover, at odds with consensus guidelines, other monotherapies for acromegaly appear to have a marginal role as compared to combination therapies as extrapolated from PTCOE practice data. Presence of uncontrolled patients in each treatment category suggest that further optimization of medical therapy, as well as use of other therapeutic tools such as radiosurgery may be needed.

Pilot study to define criteria for Pituitary Tumors Centers of Excellence (PTCOE): results of an audit of leading international centers.

PURPOSE: The Pituitary Society established the concept and mostly qualitative parameters for defining uniform criteria for Pituitary Tumor Centers of Excellence (PTCOEs) based on expert consensus. Aim of the study was to validate those previously proposed criteria through collection and evaluation of self-reported activity of several internationally-recognized tertiary pituitary centers, thereby transforming the qualitative 2017 definition into a validated quantitative one, which could serve as the basis for future objective PTCOE accreditation. METHODS: An ad hoc prepared database was distributed to nine Pituitary Centers chosen by the Project Scientific Committee and comprising Centers of worldwide repute, which agreed to provide activity information derived from registries related to the years 2018-2020 and completing the database within 60 days. The database, provided by each center and composed of Excel® spreadsheets with requested specific information on leading and supporting teams, was reviewed by two blinded referees and all 9 candidate centers satisfied the overall PTCOE definition, according to referees' evaluations. To obtain objective numerical criteria, median values for each activity/parameter were considered as the preferred PTCOE definition target, whereas the low limit of the range was selected as the acceptable target for each respective parameter. RESULTS: Three dedicated pituitary neurosurgeons are preferred, whereas one dedicated surgeon is acceptable. Moreover, 100 surgical procedures per center per year are preferred, while the results indicated that 50 surgeries per year are acceptable. Acute post-surgery complications, including mortality and readmission rates, should preferably be negligible or nonexistent, but acceptable criterion is a rate lower than 10% of patients with complications requiring readmission within 30 days after surgery. Four endocrinologists devoted to pituitary diseases are requested in a PTCOE and the total population of patients followed in a PTCOE should not be less than 850. It appears acceptable that at least one dedicated/expert in pituitary diseases is present in neuroradiology, pathology, and ophthalmology groups, whereas at least two expert radiation oncologists are needed. CONCLUSION: This is, to our knowledge, the first study to survey and evaluate the activity of a relevant number of high-volume centers in the pituitary field. This effort, internally validated by ad hoc reviewers, allowed for transformation of previously formulated theoretical criteria for the definition of a PTCOE to precise numerical definitions based on real-life evidence. The application of a derived synopsis of criteria could be used by independent bodies for accreditation of pituitary centers as PTCOEs.

Role of pulsatile growth hormone (GH) secretion in the regulation of lipolysis in fasting humans.

BACKGROUND: The increase in growth hormone (GH) secretion during a prolonged fast stimulates lipolytic rate, thereby augmenting the mobilization of endogenous energy at a time when fuel availability is very low. STUDY AIM: To identify the specific component of GH secretory pattern responsible for the stimulation of lipolytic rate during fasting in humans. STUDY PROTOCOL: We measured lipolytic rate (using stable isotope dilution technique) after an overnight fast in 15 young, healthy, non-obese subjects (11 men and 4 women), and again on four separate occasions after a 59 h fast. These four prolonged fasting trials differed only by the contents of an infusion solution provided throughout the 59 h fasting period. Subjects were infused either with normal saline ("Control"; n = 15) or with graded doses of a GH Releasing Hormone Receptor Antagonist (GHRHa):10 µg/kg/h ("High"; n = 15), 1 µg /kg/h ("Medium"; n = 8), or 0.5 µg /kg/h ("Low"; n = 6). RESULTS: As expected, the 59 h fast completely suppressed plasma insulin levels and markedly increased endogenous GH concentrations (12 h vs 59 h Fast; p = 0.0044). Administration of GHRHa induced dose-dependent reduction in GH concentrations in response to the 59 h fast (p < 0.05). We found a strong correlation between the rate of lipolysis and GH mean peak amplitude (R = 0.471; p = 0.0019), and total GH pulse area under the curve (AUC) (R = 0.49; p = 0.0015), but not the GH peak frequency (R = 0.044; p = 0.8) or interpulse GH concentrations (R = 0.25; p = 0.115). CONCLUSION: During prolonged fasting (i.e., 2-3 days), when insulin secretion is abolished, the pulsatile component of GH secretion becomes a key metabolic regulator of the increase in lipolytic rate.

[The role of glucose and insulin in the metabolic regulation of growth hormone secretion].

The exact physiological basis for the suppression of growth hormone secretion by oral glucose intake remains unknown, despite the widespread use of the oral glucose tolerance test in endocrinology. Lack of growth hormone suppression by glucose occurs in about a third of patients with acromegaly, as well as in other disorders. It is currently known that the secretion of growth hormone is affected by various factors, such as age, gender, body mass index, and the redistribution of adipose tissue. There is also evidence of the impact of overeating as well as being overweight on the secretion of growth hormone. It is known that both of these conditions are associated with hyperinsulinemia, which determines the possibility of its predominant role in suppressing the secretion of growth hormone. The purpose of this review is to discuss the accumulated data on the isolated effects of hyperglycemia and hyperinsulinemia on growth hormone secretion, as well as other metabolic regulators and conditions affecting its signaling. Understanding of the pathophysiological basis of these mechanisms is essential for further research of the role of glucose and insulin in the metabolic regulation of growth hormone secretion. However, the studies in animal models are complicated by interspecific differences in the response of growth hormone to glucose loading, and the only possible available model in healthy people may be the hyperinsulinemic euglycemic clamp.

Long-acting pasireotide improves clinical signs and quality of life in Cushing's disease: results from a phase III study.

PURPOSE: Cushing's disease (CD) is associated with significant clinical burden, increased mortality risk, and impaired health-related quality of life (HRQoL). This analysis explored the effect of long-acting pasireotide on clinical signs of hypercortisolism and HRQoL in a large subset of patients with CD. METHODS: In this phase III study (clinicaltrials.gov: NCT01374906), 150 adults with CD and a mean urinary free cortisol (mUFC) level between 1.5 and 5.0 times the upper limit of normal (ULN) started long-acting pasireotide 10 or 30 mg every 28 days with dose increases/decreases permitted based on mUFC levels/tolerability (minimum/maximum dose: 5/40 mg). Changes in clinical signs of hypercortisolism and HRQoL were assessed over 12 months of treatment and were stratified by degree of mUFC control for each patient. RESULTS: Patients with controlled mUFC at month 12 (n = 45) had the greatest improvements from baseline in mean systolic (- 8.4 mmHg [95% CI - 13.9, - 2.9]) and diastolic blood pressure (- 6.0 mmHg [- 10.0, - 2.0]). Mean BMI, weight, and waist circumference improved irrespective of mUFC control. Significant improvements in CushingQoL total score of 5.9-8.3 points were found at month 12 compared with baseline, irrespective of mUFC control; changes were driven by improvements in physical problem score, with smaller improvements in psychosocial score. CONCLUSIONS: Long-acting pasireotide provided significant improvements in clinical signs and HRQoL over 12 months of treatment, which, in some cases, occurred regardless of mUFC control. Long-acting pasireotide represents an effective treatment option and provides clinical benefit in patients with CD. CLINICAL TRIAL REGISTRATION NUMBER: NCT01374906.

Enterolith ileus: liberated large jejunal diverticulum enterolith causing small bowel obstruction in the setting of jejunal diverticulitis.

We present an 80-year-old man with multiple medical problems, and acute abdominal pain with feculent emesis. An unenhanced CT examination of the abdomen and pelvis demonstrated jejunal diverticulitis and findings of high-grade small bowel obstruction caused by a large enterolith. Enterolith ileus has rarely been reported in the radiology literature. This phenomenon has occasionally been reported in the surgical and gastroenterology literature. We highlight the CT findings associated with enterolith ileus in the setting of jejunal diverticulitis, to alert radiologists to this unusual diagnosis.

Pasireotide (SOM230) demonstrates efficacy and safety in patients with acromegaly: a randomized, multicenter, phase II trial.

CONTEXT: Pasireotide (SOM230) is a novel multireceptor ligand somatostatin analog with affinity for somatostatin receptor subtypes sst(1-3) and sst(5). Because most GH-secreting pituitary adenomas express sst(2) and sst(5), pasireotide has the potential to be more effective than the sst(2)-preferential somatostatin analogs octreotide and lanreotide. OBJECTIVE: Our objective was to evaluate the efficacy and safety of three different doses of pasireotide in patients with acromegaly. DESIGN: We conducted a phase II, randomized, multicenter, open-label, three-way, crossover study. PATIENTS: Sixty patients with acromegaly, defined by a 2-h five-point mean GH level higher than 5 microg/liter, lack of suppression of GH to less than 1 microg/liter after oral glucose tolerance test, and elevated IGF-I for age- and sex-matched controls. Patients could have had previous surgery, radiotherapy, and/or medical therapy or no previous treatment. INTERVENTION: After treatment with octreotide 100 microg s.c. three times daily for 28 d, each patient received pasireotide 200, 400, and 600 microg s.c. twice daily in random order for 28 d. MAIN OUTCOME MEASURE: A biochemical response was defined as a reduction in GH to no more than 2.5 microg/liter and normalization of IGF-I to age- and sex-matched controls. RESULTS: After 4 wk of octreotide, 9% of patients achieved a biochemical response. After 4 wk of pasireotide 200-600 microg s.c. bid, 19% of patients achieved a biochemical response, which increased to 27% after 3 months of pasireotide; 39% of patients had a more than 20% reduction in pituitary tumor volume. Pasireotide was generally well tolerated. CONCLUSIONS: Pasireotide is a promising treatment for acromegaly. Larger studies of longer duration evaluating the efficacy and safety of pasireotide in patients with acromegaly are ongoing.

Guidelines for acromegaly management: an update.

OBJECTIVE: The Acromegaly Consensus Group reconvened in November 2007 to update guidelines for acromegaly management. PARTICIPANTS: The meeting participants comprised 68 pituitary specialists, including neurosurgeons and endocrinologists with extensive experience treating patients with acromegaly. EVIDENCE/CONSENSUS PROCESS: Goals of treatment and the appropriate imaging and biochemical and clinical monitoring of patients with acromegaly were enunciated, based on the available published evidence. CONCLUSIONS: The group developed a consensus on the approach to managing acromegaly including appropriate roles for neurosurgery, medical therapy, and radiation therapy in the management of these patients.

Guidelines for the treatment of growth hormone excess and growth hormone deficiency in adults.

The V Consensus Group Meeting on 'Guidelines for Treatment of GH Excess and GH Deficiency in the Adult' was an international workshop held on February 20-22, 2006 in Santa Monica, California, USA. The principal aim of this meeting was to provide guidelines for the evaluation and treatment of adults with either form of abnormal GH secretion: GH excess or GH deficiency. The workshop included debates as to the choice of primary treatment, discussions of the targets for adequate treatment, and concluded with presentations on open issues germane to adult GH treatment including the role of GH in malignancies, the impact of longterm treatment on bone, and a cost-benefit analysis. The meeting was comprised of 66 delegates representing 13 different countries.

Linewidth and tuning characteristics of terahertz quantum cascade lasers.

We have measured the spectral linewidths of three continuous-wave quantum cascade lasers operating at terahertz frequencies by heterodyning the free-running quantum cascade laser with two far-infrared gas lasers. Beat notes are detected with a GaAs diode mixer and a microwave spectrum analyzer, permitting very precise frequency measurements and giving instantaneous linewidths of less than -30 kHz. Characteristics are also reported for frequency tuning as the injection current is varied.

Long-term treatment of acromegaly with pegvisomant, a growth hormone receptor antagonist.

BACKGROUND: Pegvisomant is a new growth hormone receptor antagonist that improves symptoms and normalises insulin-like growth factor-1 (IGF-1) in a high proportion of patients with acromegaly treated for up to 12 weeks. We assessed the effects of pegvisomant in 160 patients with acromegaly treated for an average of 425 days. METHODS: Treatment efficacy was assessed by measuring changes in tumour volume by magnetic resonance imaging, and serum growth hormone and IGF-1 concentrations in 152 patients who received pegvisomant by daily subcutaneous injection for up to 18 months. The safety analysis included 160 patients some of whom received weekly injections and are excluded from the efficacy analysis. FINDINGS: Mean serum IGF-1 concentrations fell by at least 50%: 467 mg/L (SE 24), 526 mg/L (29), and 523 mg/L (40) in patients treated for 6, 12 and 18 months, respectively (p<0.001), whereas growth hormone increased by 12.5 mg/L (2.1), 12.5 mg/L (3.0), and 14.2 mg/L (5.7) (p<0.001). Of the patients treated for 12 months or more, 87 of 90 (97%) achieved a normal serum IGF-1 concentration. In patients withdrawn from pegvisomant (n=45), serum growth hormone concentrations were 8.0 mg/L (2.5) at baseline, rose to 15.2 mg/L (2.4) on drug, and fell back within 30 days of withdrawal to 8.3 mg/L (2.7). Antibodies to growth hormone were detected in 27 (16.9%) of patients, but no tachyphylaxis was seen. Serum insulin and glucose concentrations were significantly decreased (p<0.05). Two patients experienced progressive growth of their pituitary tumours, and two other patients had increased alanine and asparate aminotransferase concentrations requiring withdrawal from treatment. Mean pituitary tumour volume in 131 patients followed for a mean of 11.46 months (0.70) decreased by 0.033 cm(3) (0.057; p=0.353). INTERPRETATION: Pegvisomant is an effective medical treatment for acromegaly.

Semiquantification of hypothalamic GH-releasing hormone output in women: evidence for sexual dimorphism in the mechanism of the somatopause.

The neuroendocrine mechanisms underlying the decline of GH with aging (somatopause) are uncertain. We recently found that the age-dependent diminution of the hypothalamic GH-releasing hormone (GHRH) output contributes to the somatopause in men. As the regulatory mechanisms of GH secretion are sexually dimorphic, we assessed the suppressibility of spontaneous and GHRH-stimulated GH secretion by graded doses of a specific competitive GHRH receptor antagonist in nine young (20-27 yr old) and eight elderly (65-77 yr old) healthy nonobese women to semiquantify hypothalamic GHRH output. Nocturnal mean GH was lower in elderly women (2.2 +/- 0.4 vs. 0.9 +/- 0.2 microg/liter; P = 0.01). Graded boluses of GHRH-44 resulted in similar GH responses in both populations (P = 0.28). Graded infusions of GHRH antagonist inhibited in a dose-dependent manner the GH responses to GHRH in both groups (P = 0.0001-0.04). The dose-inhibition curve for the lowest GHRH bolus dose was shifted to the left compared with the highest one (P = 0.04). However, the dose-inhibition curves for spontaneous GH secretion were not different in young and elderly women (P = 0.50). Thus, the female somatopause is not associated with a measurable decrease in hypothalamic GHRH output. When the dose-inhibition curves for young men and young women were compared, the latter was shifted to the left (P = 0.009), suggesting that the somatotropic system in women operates with less GHRH. We conclude that the contribution of endogenous GHRH to the maintenance of GH secretion and the neuroendocrine mechanisms of somatopause in humans are sexually dimorphic.

Regulation of GH secretion in acromegaly: reproducibility of daily GH profiles and attenuated negative feedback by IGF-I.

GH hypersecretion is a hallmark of acromegaly. It is unknown whether the secretory activity of somatotroph adenoma is autonomous or is still governed by central or peripheral mechanisms. In this study we investigated whether GH secretion in acromegaly 1) has a reproducible circadian pattern and 2) is inhibited by exogenous IGF-I. Eleven patients with newly diagnosed acromegaly were studied in 2 protocols. In protocol 1, peripheral blood was sampled every 10 min for 48 h in 6 patients for the determination of concordance between 24-h GH profiles. There was no significant day to day variability in mean 24-h output. There was, however, a significant time effect, and the 24-h GH secretion pattern was maintained between days. In protocol 2, 5 patients were sampled for GH every 10 min twice, once during infusion of normal saline and once during iv infusion of recombinant human IGF-I (10 microg/kg x h). The recombinant human IGF-I infusion increased plasma IGF-I to approximately 230% of the baseline concentration. This resulted in GH suppression (4220 +/- 1950 vs. 3223 +/- 1472 microg/liter.min; P = 0.001), but did not alter GH secretion pattern. There were highly significant cross-correlations for 10 of the 11 of the subjects in the two protocols when the lag was 0 min. By harmonic analysis, nocturnal augmentation of GH was maintained, and maximum daily GH occurred at approximately 2300 h. These data demonstrate that the pattern of GH secretion in acromegaly is not random, but is highly preserved with 24-h periodicity. In addition, negative feedback regulation by IGF-I is preserved, although the degree of negative feedback is grossly attenuated. Thus, secretory activity of somatotroph adenomas is not autonomous or haphazard, but is still subject to both feedback and feedforward regulatory mechanisms.

CRS1 is a novel group II intron splicing factor that was derived from a domain of ancient origin.

Protein-dependent group II intron splicing provides a forum for exploring the roles of proteins in facilitating RNA-catalyzed reactions. The maize nuclear gene crs1 is required for the splicing of the group II intron in the chloroplast atpF gene. Here we report the molecular cloning of the crs1 gene and an initial biochemical characterization of its gene product. Several observations support the notion that CRS1 is a bona fide group II intron splicing factor. First, CRS1 is found in a ribonucleoprotein complex in the chloroplast, and cofractionation data provide evidence that this complex includes atpF intron RNA. Second, CRS1 is highly basic and includes a repeated domain with features suggestive of a novel RNA-binding domain. This domain is related to a conserved free-standing open reading frame of unknown function found in both the eubacteria and archaea. crs1 is the founding member of a gene family in plants that was derived by duplication and divergence of this primitive gene. In addition to its previously established role in atpF intron splicing, new genetic data implicate crs1 in chloroplast translation. The chloroplast splicing and translation functions of crs1 may be mediated by the distinct protein products of two crs1 mRNA forms that result from alternative splicing of the crs1 pre-mRNA.

The "quality of life-assessment of growth hormone deficiency in adults" questionnaire: can it be used to assess quality of life in hypopituitarism?

Patients with hypopituitarism often have a multitude of physical and psychological complaints, collectively referred to as low quality of life (QoL). It has been asserted that GH deficiency (GHD) is the causative factor, and improved QoL scores have been reported during GH replacement. Qol-assessment of GHD (QoL-AGHDA) is the newest psychometric instrument with the purportedly high specificity for the issues encountered by patients with GHD. QoL-AGHDA was administered to 30 normal control subjects, 20 patients with severe GHD, and 22 patients with active acromegaly. QoL-AGHDA scores in controls (3.3 +/- 0.7) were significantly (P < 0.001) different from those in patients with hypopituitarism with unsubstituted GHD (10.6 +/- 1.5) and active acromegaly (11.6 +/- 1.6). However, QoL-AGHDA was unable to discriminate between the latter two groups, one with GHD and the other with GH excess. We conclude that as QoL-AGHDA cannot distinguish between the extremes of GH output, its ability to detect an improvement in QoL during GH replacement has to be viewed with skepticism. This can be dispelled only by double blind, placebo-controlled studies.

Recruitment of a peptidyl-tRNA hydrolase as a facilitator of group II intron splicing in chloroplasts.

Group II introns are catalytic RNAs that have been proposed to be the evolutionary precursors to the spliceosome. Most group II introns require accessory factors to splice efficiently in vivo, but few such factors have been identified. We have cloned the maize nuclear gene crs2, which is required for the splicing of nine group II introns in chloroplasts. CRS2 is related to peptidyl-tRNA hydrolase enzymes. However, CRS2 expression failed to rescue an Escherichia coli pth(ts) mutant and CRS2 lacks several conserved amino acids that are important for the activity of the E.coli enzyme, indicating that it may lack peptidyl-tRNA hydrolase activity. CRS2 is localized to the chloroplast stroma, where it is found in a large salt-stable complex that contains RNA. CRS2 co-sediments with group II intron RNA during centrifugation of stroma through sucrose gradients, suggesting that CRS2 facilitates splicing via direct interaction with intron RNA. Sequence comparisons indicate how evolutionary tinkering may have allowed an enzyme that interacts with peptidyl-tRNAs to acquire a function in group II intron splicing.

Aging-related growth hormone (GH) decrease is a selective hypothalamic GH-releasing hormone pulse amplitude mediated phenomenon.

BACKGROUND: Aging is accompanied by declining growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels. The neuroendocrine mechanisms of this decline have been studied previously, but the interpretation of the data was confounded by the imprecision in GH measurements and by the intervening variables of altered body composition and decreased gonadal steroid milieu in the elderly subjects of both sexes. METHODS: To study the contribution of aging per se, we evaluated discrete parameters of GH pulsatility in young (n = 8 women, n = 8 men) and elderly (n = 11 women, in 10 men) subjects closely matched for body mass index. Blood samples for GH were obtained every 10 minutes for 24 hours. Plasma GH was measured by a sensitive chemiluminescent assay. GH pulsatility was assessed using cluster analysis. RESULTS: The elderly subjects had plasma IGF-I levels and integrated GH concentrations that were 32% to -56% of their sex-matched younger counterparts. The age-associated attenuation in GH was due to a decrease in GH pulse amplitude, whereas pulse frequency and nadir levels were unchanged. The majority of the young subjects (81%) reached their peak GH during the "lights off" period, whereas the majority of the elderly subjects (62%) peaked during the "lights on" period (p = .01). CONCLUSIONS: We conclude that aging in both sexes is accompanied by profound decreases in GH output and in plasma IGF-I concentrations. This effect is separate from the alterations in body mass index that accompany the normal aging process. Attenuation of GH output associated with aging is related solely to the lower GH and, by inference, GH-releasing hormone (GHRH) pulse amplitude.

Generation of growth hormone pulsatility in women: evidence against somatostatin withdrawal as pulse initiator.

To test whether endogenous hypothalamic somatostatin (SRIH) fluctuations are playing a role in the generation of growth hormone (GH) pulses, continuous subcutaneous octreotide infusion (16 microg/h) was used to create constant supraphysiological somatostatinergic tone. Six healthy postmenopausal women (age 67 +/- 3 yr, body mass index 24.7 +/- 1.2 kg/m(2)) were studied during normal saline and octreotide infusion providing stable plasma octreotide levels of 2,567 +/- 37 pg/ml. Blood samples were obtained every 10 min for 24 h, and plasma GH was measured with a sensitive chemiluminometric assay. Octreotide infusion suppressed 24-h mean GH by 84 +/- 3% (P = 0.00026), GH pulse amplitude by 90 +/- 3% (P = 0.00031), and trough GH by 54 +/- 5% (P = 0.0012), whereas GH pulse frequency remained unchanged. The response of GH to GH-releasing hormone (GHRH) was not suppressed, and the GH response to GH-releasing peptide-6 (GHRP-6) was unaffected. We conclude that, in women, periodic declines in hypothalamic SRIH secretion are not the driving force of endogenous GH pulses, which are most likely due to episodic release of GHRH and/or the endogenous GHRP-like ligand.

Secretory process regularity monitors neuroendocrine feedback and feedforward signaling strength in humans.

The present experiments examine the neuroregulatory hypothesis that the degree of sample-by-sample regularity of hormone output by an interlinked hypothalamopituitary target-organ system monitors the strength of feedback and/or feedforward signaling. To test this postulate and assess its generality, we implemented a total of nine thematically complementary perturbation experiments. In particular, we altered feedback or feedforward signaling selectively in two distinct neuroendocrine systems; namely, the growth hormone (GH) insulin-like growth factor type I (IGF-I) and the luteinizing hormone-testosterone axes. Four experimental paradigms comprised preferential reduction vs. enhancement of IGF-I or testosterone feedback signal strength; and, conversely, five others entailed selective attenuation vs. augmentation of GH-releasing hormone and gonadotropin-releasing hormone feedforward signal intensity. In these independent interventions, quantitation of subordinate (nonpulsatile) secretory pattern reproducibility via the approximate entropy statistic unmasked salient changes (P values typically <10(-3)) in the conditional regularity of serial hormone output with high consistency (96-100%). In particular, approximate entropy quantified degradation of secretory subpattern orderliness under either muted feedback restraint or heightened feedforward drive. Assuming valid interpretation of the biological constraints imposed, these experimental observations coincide with earlier reductionist mathematical predictions, wherein increased irregularity of coupled parameter output mirrors attenuated feedback and/or augmented feedforward coupling within an integrative system.