A single growth hormone determination 30 minutes after the administration of the GHRH plus GHRP-6 test is sufficient for the diagnosis of somatotrope dysfunction in patients who have suffered traumatic brain injury

As hypopituitarism is frequent in patients who have suffered a traumatic brain injury (TBI) a hormonal check-up is necessary. However, the prevalence of TBI is so large that the number of potential candidates to be tested is difficult to manage, in particular for GH deficiency diagnosis that requires cumbersome and expensive dynamic tests. GHRH plus GH-releasing hexapeptide (GHRP-6) is a safe and effective test capable of segregating normal subjects from GH deficient patients. As the GHRH+GHRP-6 test induces GH peaks consistently in the first 30 min, the working hypothesis assessed in this study was whether a single determination of GH 30 min after stimulus could provide the same biochemical classification as the whole secretory curve. A total of 83 subjects who suffered TBI at least one year before the study were administered GHRH 1 mug/kg iv plus GHRP-6 1 mug/kg iv at 0 min, and blood samples were obtained at regular intervals. GH was determined in all samples. An excellent correlation was observed between GH values at 30 min and GH peaks (r=0.972, p<0.0001). When comparing the 30-min GH values against the peaks, the biochemical classification changed only in 5 out of 83 subjects from normal GH secretion to uncertain.

CONCLUSIONS

The GHRH+GHRP-6 test is convenient, safe and in patients with TBI can be reduced to a single fixed GH determination 30 min after stimulus without losing diagnostic power.

Can treatment with somatostatin analogs replace neurosurgery?

There is an ongoing controversy on first-line treatment in acromegaly. Although transsphenoidal surgery has always traditionally been considered the first option, the evolution of new medical treatments is now challenging the clinical paradigm. In fact, somatostatin analogs are highly effective, convenient, avoid the growth of tumors or even shrink them, and also have the advantage of preserving normal pituitary function. On the other hand, when successful, neurosurgery has the advantage of eliminating long-term medical treatment and is less expensive. This manuscript discusses the pros and cons of both treatments.

TSH stimulates leptin secretion by a direct effect on adipocytes

Leptin is a circulating hormone secreted by adipose tIssue which acts as a signal to the central nervous system where it regulates energy homeostasis and neuroendocrine processes. Although leptin modulates the secretion of several pituitary hormones, no information is available regarding a direct action of pituitary products on leptin release. However, it has been pointed out that leptin and TSH have a coordinated pulsatility in plasma. In order to test a direct action of TSH on in vitro leptin secretion, a systematic study of organ cultures of human omental adipose tIssue was performed in samples obtained at surgery from 34 patients of both sexes during elective abdominal surgery. TSH powerfully stimulated leptin secretion by human adipose tIssue in vitro. In contrast, prolactin, ACTH, FSH and LH were devoid of action. These results suggest that leptin and the thyroid axis maintain a complex and dual relationship and open the possibility that plasmatic changes in TSH may contribute to the regulation of leptin pulses.

Retinoic acid and vitamin D(3) powerfully inhibit in vitro leptin secretion by human adipose tissue

Leptin, the product of the ob gene, is secreted into the circulation by white adipose tissue; its major role being to participate in the regulation of energy homeostasis. Plasma leptin levels are mainly determined by the relative adiposity of the subject; however, the great dispersion of values for any given body mass index and the noteworthy gender-based differences indicate that other factors are operating. Steroid hormones actively participate in the regulation of leptin secretion; however, non-steroid nuclear hormones have either not been studied or have provided contradictory results. In order to understand the role of hormones of the non-steroid superfamily such as 3,5,3'-tri-iodothyronine (T(3)), vitamin D(3) and retinoic acid (RA) in the control of leptin secretion, in the present work doses of 10(-9), 10(-8) and 10(-7) M of these compounds have been studied on in vitro leptin secretion. The organ culture was performed with omental adipose tissue samples from healthy donors (n=28). T(3) was devoid of effect at any dose studied, while an inhibition of leptin secretion was observed with 9-cis-RA (slight) and all-trans-RA (potent). Interestingly, vitamin D(3) exerted a powerfully inhibitory role at the doses studied, and its action was synergistic with all-trans-RA. In conclusion, in vitro leptin secretion by human adipose tissue is negatively controlled by either RA or vitamin D(3). The clinical significance of leptin regulation by this superfamily of nuclear receptors remains to be ascertained.

Ghrelin-induced growth hormone secretion in humans

Ghrelin is a novel growth hormone (GH) releaser acylated peptide that has recently been purified from stomach, and which potently binds to the GH secretagogue receptor. Ghrelin releases GH in vitro and in vivo in animal models, however its actions, potency and specificity in humans are unknown. In the present study, 12 healthy subjects were studied: 6 underwent four tests with ghrelin administered i.v. at the dose of 0 (placebo), 0.25, 0.5 and 1 microg/kg which corresponds to 0, 18, 37 and 75 microg total dose. A further 6 volunteers underwent two tests on different days with ghrelin at the dose of 3.3 or 6.6 microg/kg which corresponds to 250 microg and 500 microg total dose. Ghrelin-mediated GH secretion showed a dose-response curve, in which 1 microg/kg was the minimally effective dose in some individuals, but not as a group. On the contrary, the total doses of 250 microg and 500 microg elicited a powerful GH secretion, with a mean peak of 69.8+/-9.2 microg/l and 90.9+/-16.9 microg/l respectively, and areas under the curve of 4435+/-608 and 6125+/-1008 microg/l per 120 min respectively. All of them statistically significant vs placebo and vs the 1 microg/kg dose. Ghrelin administration also elicited a relevant dose-response mediated prolactin secretion suggesting no specificity of its actions. No relevant side effects were observed with ghrelin apart from a hyperhydrosis episode in two individuals tested with the higher ghrelin doses. In conclusion, ghrelin is a potent releaser of GH in normal individuals, with a dose-response pattern of operation. No saturating dose was observed.

Effect of resistance exercise (body building) training on serum leptin levels in young men. Implications for relationship between body mass index and serum leptin

Available data about the influence of exercise on leptin level are controversial, and there are no studies concerning leptin levels in trained men with low fat mass plus large increase of muscle. 65 healthy young male matched for age were separated in three groups. 1) 25 non-professional body builders; 2) 21 mild overweight sedentary subjects; 3) 19 normal weight sedentary controls. Body composition was determined by bioelectrical impedance. Serum leptin was measured in duplicate by RIA.

STATISTICS

Student's t and Pearson's test. Athletes showed similar BMI than overweight subjects: 26.98+/-0.49 vs 27.12+/-0.41 but lower fat mass: 12.53+/-0.96 vs 16.16+/-1.01 % (p=0.0064) and lower leptin: 4.66+/-0.51 vs 7.31+/-0.76 microg/l (p=0.014). Athletes showed higher BMI than controls: 26.98+/-0.49 vs 23.08+/-0.30 (p<0.0001) but similar fat mass: 12.53+/-0.96 vs 12.48+/-0.73% and leptin: 4.66+/-0.51 vs 4.79+0.58 microg/l. Overweight subjects showed higher BMI than controls: 27.12+/-0.41 vs 23.08+/-0.30 (p<0.0001), higher fat mass: 16.16+/-1.01 vs 12.48+/-0.73% (p=0.0064) and higher leptin: 7.31+/-0.76 vs 4.79+/-0.589 microg/l (p=0.014). When leptin was calculated by fat mass no differences were observed between the three groups. There was a significant correlation between leptin and fat mass in all groups. Leptin correlated with BMI in overweight subjects (r=0.438, p=0.0463), but this correlation was not observed either in athletes or in controls. In conclusion 1) regardless of the high BMI characteristic of body builders, no correlation was observed with leptin; 2) trained state induced by resistance exercise does not influence leptin production independently of variations in body composition.

Serum leptin levels in male marathon athletes before and after the marathon run

Leptin is a hormone produced by the adipocytes to regulate food intake and energy expenditure at the hypothalamic level. It is commonly accepted that the main determinants of leptin secretion are the net amount of body fat and the mean size of adipocytes. On the contrary, important vectors of energy flux in the organism, such as food intake and energy expended on exercise, are not thought to be regulators of that secretion. To understand whether leptin is regulated by an acute energy expenditure such as strenuous exercise, 29 male athletes who had trained for marathon running were studied before and after a marathon run and compared with 22 nonobese, age-, sex-, and body mass index (BMI)-matched sedentary controls. Controls and marathon athletes showed no differences in BMI or fat-free mass. Marathon runners showed a strong reduction in total fat mass (6.2 +/- 0.4 kg; 9.1 +/- 0.5% of body fat) compared with controls (12.3 +/- 0.5 kg; 16.1 +/- 0.5% of body fat; P < 0.05). This difference in body composition was paralleled by a mean serum leptin level that in marathonians (2.9 +/- 0.2 micrograms/L) was significantly (P < 0.05) reduced compared with that in controls (5.1 +/- 0.6 micrograms/L). It is remarkable that the ratio of leptin per kg body fat, showed a very good agreement between the two groups, 0.40 +/- 0.04 microgram/L.kg for controls and 0.46 +/- 0.03 microgram/L.kg for marathonians. In the two groups, leptin was correlated with both body weight, BMI, and fat mass (P < 0.001). The marathon trajectory was the standard 42.195 km accomplished in an average time of 3 h, 17 min, 7 s, with a calculated energy expenditure of over 2800 Cal. After the marathon run, a water imbalance occurred, with a significant decrease in body weight and an increase in serum albumin. A significant (P < 0.05) reduction in leptin values was observed after the run (2.6 +/- 0.2 micrograms/L) compared with before (2.9 +/- 0.2 micrograms/L), which was more relevant considering the relative hemoconcentration. In conclusion, 1) compared with sedentary subjects, leptin levels are reduced in male marathon runners in parallel with the relevant reduction in total body fat; 2) expressed as a ratio of leptin per kg body fat, no differences were observed between marathonians and controls; and 3) after an energy expenditure of 2800 Cal in the marathon run, a reduction in leptin levels occurred. Strong changes in energy expenditure may regulate serum leptin levels in man.

Gender differences in both spontaneous and stimulated leptin secretion by human omental adipose tissue in vitro: dexamethasone and estradiol stimulate leptin release in women, but not in men

Leptin is a hormone secreted by the adipocytes to serve as a signal to the central nervous system to regulate energy homeostasis. Circulating leptin mainly reflects both total fat mass and the size of constituent adipocytes, although other ancillary hormonal factors may contribute to its blood concentration. Relevant gender differences in leptin concentrations have been reported, but it is not clear whether the elevated leptin levels in women are an intrinsic property of their adipocytes or merely reflect a greater amount of fat reserves. To clarify these points, a systematic study with organ culture from human omental adipose tissue either stimulated or not with steroid hormones was undertaken in samples obtained at surgery from 67 nonobese donors (33 women and 34 men). The assay was standardized in periods of 24 h ending at 96 h, with no apparent tissue damage. Each adipose tissue sample from a single donor was incubated in triplicate, and leptin results are expressed as the mean +/- SEM of the integrated secretion to the medium (area under the curve; nanograms of leptin per g tissue/48 h). Control nonstimulated samples showed a steady leptin secretion along the 96 h studied, with the peak of secretory activity reached at 48 h; afterward, the in vitro secretion reached a plateau state. Spontaneous leptin secretion in samples from 33 women (3904 +/- 347) was significantly higher (P < 0.05) than that in samples from 34 men (2940 +/- 323). Coincubation of adipose tissue with 1 mumol/L dexamethasone induced a clear-cut leptin increase (P < 0.05) in samples from women (5848 +/- 624; n = 12), but did not change the spontaneous release of leptin in samples from men (3353 +/- 741; n = 6). Similarly, coincubation of adipose tissue with 1 mumol/L estradiol induced a notable leptin increase (P < 0.05) in samples from women (5698 +/- 688; n = 9), whereas it did not alter the secretion in the male samples (3373 +/- 444; n = 6). In samples from both sexes, coincubation with 1 mumol/L estrone or progesterone had no effect, whereas 1 mumol/L forskolin significantly (P < 0.05) reduced leptin release. In conclusion, leptin secretion from omental adipose tissue in vitro 1) is significantly higher in samples from women than in samples from men, 2) is stimulated by dexamethasone and estradiol in women but not in men, 3) is not modified by progesterone or estrone in both sexes, and 4) is inhibited by forskolin in both genders. This different response to the stimulation of adipose tissue may be the biological basis for the gender differences observed in circulating levels of human leptin.

Neuropharmacological assessment of growth hormone secretion

The biochemical diagnosis of individuals who are either deficient in growth hormone (GH) or who have alterations in the normal pattern of GH secretion is difficult. The uncertainty surrounding diagnosis reflects the lack of a thorough understanding of the physiology of GH secretion and of the hypothalamic hormones involved. At least three hormones are implicated: GH-releasing hormone (GHRH), somatostatin and the endogenous ligand of the GH secretagogue receptor, although the role that each plays in the release of GH is not clear from the available experimental evidence. In such a situation, most of the dynamic tests of GH secretory capacity in humans need to undergo a 'trial and error' process before being validated. The search for the 'gold standard' test of GH secretion is ongoing, and the combination of GHRH plus GH secretagogues will probably play an important role in future clinical diagnosis.

Influence of thyroid status on serum immunoreactive leptin levels

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Serum leptin concentrations increase in correlation with the percentage of body fat, but besides that, little is known about the physiological actions of leptin in humans. The aim of this study was to assess the influence of hypo- and hyperthyroidism on serum leptin levels. Thirty-two patients (16 with hypothyroidism and 16 with hyperthyroidism) were studied before and after treatment with replacement doses of T4 (hypothyroid patients) or methimazole (hyperthyroid), when thyroid function was normal. Control serum for each group was obtained from healthy age-, sex-, and body mass index-matched subjects. Plasma leptin levels were measured by specific RIA. The mean leptin level in the hypothyroid patients was lower before treatment (4.7 +/- 0.7 microg/L) than that in the controls (8.6 +/- 1.4 microg/L; P < 0.02) and was lower than that during treatment with T4 and normalization of thyroid function in the same group of patients (6.3 +/- 0.8 microg/L; P < 0.05). Leptin levels in the hyperthyroid patients were similar before (7.2 +.0 1.1 microg/L) and after normalization of thyroid function following treatment with methimazole (6.2 +/- 1.1 microg/L) and were similar to the control value (8.8 +/- 1.4 microg/L). In conclusion, leptin levels are decreased in the hypothyroid patients and unchanged in hyperthyroidism. Whether decreased leptin levels may contribute to the decreased energy expenditure in patients with hypothyroidism merits further investigation.

Serum immunoreactive leptin concentrations in patients with anorexia nervosa before and after partial weight recovery

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Serum leptin concentrations increase in correlation with the percentage of body fat, but besides that little is known about the physiological actions of leptin in humans. In order to understand the role of leptin in severe malnutrition, in the present work 10 patients recently diagnosed with anorexia nervosa were studied both before and 2 months later, after partial weight recovery, and were compared with 18 normal-weight women as controls. Leptin was measured by a newly developed radioimmunoassay and both IGF-I and IGFBP-3 were measured by commercial radioimmunoassays. The mean (+/-SE) serum leptin concentrations (in microgram/liter) were 18.1 +/- 2.0 in control women with BMI of 21.1 +/- 0.3, significantly higher (P < 0.01) than that in the anorexia nervosa patients at diagnosis (2.2 +/- 0.1, BMI 15.3 +/- 0.6). These differences were also observed in IGF-I values (microgram/liter) that were 228.0 +/- 14.6 in controls and 157.4 +/- 28.7 in anorexia nervosa patients (P < 0.02). No differences were observed in IGF-BP3. After treatment, patients with anorexia nervosa experienced an increase in BMI (17.1 +/- 0.5, P < 0.0001 vs before) although they were still underweight. The partial recovery in weight led to a complete normalization of IGF-I levels (214.0 +/- 21.0 micrograms/liter) and to an enhancement in leptin levels (3.3 +/- 0.5 micrograms/liter; P < 0.03 vs before treatment), though still lower than those in normal-weight women (P < 0.05). Individually analyzed, a large dispersion was observed in control subjects, with leptin levels ranging from 5.5 to 38.7 micrograms/liter, while in all anorexia nervosa patients leptin levels were under 3 micrograms/liter. A treatment-induced increase in body weight led to an increase in leptin levels in 7 out of the 10 anorexia nervosa patients studied and the 3 patients with no increase in leptin were all initially under the 14.5 BMI. In conclusion, leptin levels are severely reduced in anorexia nervosa patients with severe malnutrition, and a significant rise occurred after partial weight recovery. There seems to be a level of BMI below which leptin levels do not drop further but also do not increase despite weight gain. While IGF-I reflects the energy intake of the previous few weeks, the serum leptin concentration reflects the true status of the adipose stores, a fact that has useful clinical implications.

Serum leptin concentrations in patients with anorexia nervosa, bulimia nervosa and non-specific eating disorders correlate with the body mass index but are independent of the respective disease

OBJECTIVE

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Serum leptin concentrations increase in correlation with the percentage of body fat, but little else is known about the physiological actions of leptin in humans. The aim of this study was to determine the role of leptin in severe eating disorders, and whether its levels are correlated with the specific disease or exclusively with body weight.

TESTS

Serum concentrations of human leptin were analysed by specific radioimmunoassay and compared with the individual body mass indexes (BMI). The correlations between serum leptin concentrations and BMI, age and height were analysed.

PATIENTS

A total of 65 women were studied: 25 patients with anorexia nervosa, 20 women with bulimia nervosa, 6 women with a diagnosis of nonspecific eating disorder, and 14 normal-weight women who acted as controls. At the time of the study, the patients were non-cured, under treatment, and at different stages of therapeutic evolution.

MEASUREMENTS

Plasma leptin levels were measured by specific radioimmunoassay.

RESULTS

The mean serum leptin in the normal-weight women was 10.5 +/- 1.1 micrograms/l, compared with 7.6 +/- 1.1 micrograms/l in the anorexia nervosa patients (P < 0.05). This reduction in leptin levels was paralleled by the differences in BMI (21.4 +/- 0.4 vs 18.8 +/- 0.2) P < 0.05. These differences between the controls and anorexia nervosa patients were not observed in patients with bulimia nervosa who had a mean serum leptin level of 9.9 +/- 1.4 micrograms/l and BMI of 21.3 +/- 0.6, neither significantly different from controls. On the contrary, patients with non-specific eating disorders showed a large reduction in BMI (17.9 +/- 1.2, P < 0.05 vs control), and a parallel reduction in serum leptin levels, 4.5 +/- 1.0 (P < 0.05 vs controls). When individual values of leptin were plotted against BMI a wide range was observed in all groups; in the control subjects from 5.6 to 17.7 micrograms/l, in anorexia nervosa patients from 2.1 to 28.1 micrograms/l, in patients with bulimia nervosa between 2.6 and 25.9 micrograms/l, and in women with non-specific eating disorder from 2.0 to 8.9. No correlation was observed with the specific disease but in each group a significant correlation was observed only with BMI.

CONCLUSIONS

Serum leptin levels in three groups of patients affected by severe eating disorders are not related to the specific pathology but are correlated with the individual BMI. The analysis of leptin values may be a useful index of assessing the adipose tissue stores in the clinical setting, but will be of no help for diagnosis nor prognosis of severe eating disorders.

Serum immunoreactive-leptin levels are increased in patients with Cushing's syndrome

Leptin, the product of the ob gene, is a recently discovered hormone secreted by adipocytes. Cushing's syndrome is a disease state usually associated with weight gain due to the accumulation of adipose tissue. In order to study the effect of chronic glucocorticoid excess upon serum leptin levels; in the present work, four patients with recently diagnosed Cushing's syndrome and a group of control subjects matched for age, sex and body mass index (BMI) were studied. Serum leptin concentrations, measured by radioimmunoassay, were assessed in samples taken every 60 minutes over a 24 hour period. Assessment of leptin concentrations over 24 hours, by means of the area under curve showed a twofold increase in serum leptin levels in patients with Cushing's syndrome (mean+/-SEM 54.3+/-14) in comparison to control subjects (29.3+/-4.4; p<0.05). In conclusion, our data show that leptin levels are markedly increased in Cushing's syndrome patients. The relevance of this finding to the increased body fat present in patients with Cushing's syndrome merits further studies.

The sequential administration of growth hormone-releasing hormone followed 120 minutes later by hexarelin, as an effective test to assess the pituitary GH reserve in man

OBJECTIVE

GH deficiency, either in children or in adults, is a clinically relevant problem. The diagnosis is based on dynamic tests of GH secretion, which are clear cut on a group basis but highly problematic for individual diagnosis. The controversy surrounding the diagnosis of GH deficiency reflects the absence of a gold standard dynamic test. The synthetic hexapeptide hexarelin and GHRH stimulate GH secretion using different mechanisms. A sequential test has been devised using the administration of GHRH as first stimulus followed 120 minutes later by hexarelin. The two aims of the study were (a) to evaluate the interaction of GHRH and hexarelin, and (b) to devise a sequential test of GH reserve.

DESIGN

The GH stimuli used were GHRH (1 microgram/kg i.v.) as a pituitary stimulus, and hexarelin (1 microgram/kg i.v.) as a GH stimulus whose main action is hypothalamic. Each subject was tested twice in order to serve as his own control. Three different studies, each with two duplicate tests, were performed on separate groups of individuals: (a) GHRH followed 120 minutes later by hexarelin and on the second day hexarelin followed 120 minutes later by GHRH; (b) GHRH followed 120 minutes later by GHRH and on the other day hexarelin followed 120 minutes later by hexarelin; (c) GH 0.5 IU i.v. followed 120 minutes later by GHRH and on the other day, the same dose of GH followed 120 minutes later by hexarelin.

PATIENTS

Eighteen normal volunteers (12 women, 6 men) after giving informed consent.

MEASUREMENTS

Plasma GH levels were measured by time-resolved fluoroimmunoassay; each value shown is the mean +/- SEM of n = 6.

RESULTS

GHRH followed 120 minutes later by hexarelin induced two episodes of GH secretion (expressed as mean GH peak, mU/l). The GHRH-mediated GH release showed a mean GH peak of 38.2 +/- 13.6 mU/l and after hexarelin 120 minutes later of 56.7 +/- 18.0 mU/l. The contrary sequence blocked the second stimulus, i.e. the hexarelin-stimulated GH mean peak was 54.7 +/- 18.4, and the GH release 120 minutes later after GHRH was 4.8 +/- 1.9 (P < 0.05 vs GHRH used as first stimulus). In the two sequential tests using the same stimulus, the second GH peak was reduced. In fact, GHRH induced a GH mean peak of 63.8 +/- 21.1 mU/l as first stimulus, greater (P < 0.05) than when GHRH was administered again 120 minutes later (22.0 +/- 5.9 mU/l). Similar results were obtained with hexarelin, with a first mean peak of 70.6 +/- 10.3 mU/l, and a second one 120 minutes later of 13.4 +/- 4.6 mU/l (P < 0.05). The blockade of the second stimulus was not due to the feed-back action of the GH released by the first stimulus. In fact, the i.v. administration of exogenous GH induced a mean GH peak of 168.0 +/- 89.7 and reduced the action of GHRH administered 120 minutes later (26.1 +/- 8.1). The previous administration of GH (mean peak 115.5 +/- 42.0) did not alter the action of hexarelin injected 120 minutes later, showing a mean peak of 71.9 +/- 11.2. The large variability in the stimulatory action of GHRH contrasted vividly with the reproducibility of hexarelin. Furthermore, individually analysed, only one of the 12 subjects tested first with hexarelin, compared to 4 out of 12 tested with GHRH as first stimulus, presented a blunted response (< 13 mU/l). After the sequential stimulus there were no false negatives.

CONCLUSION

The sequential administration of GHRH in normal subjects and of hexarelin 120 minutes later provides separate information regarding pituitary GH reserve, of both secretagogues without mutual interference. There were not false negative results to the combined test. This sequentially delayed test may be of some value in the clinical setting for assessing pituitary GH reserve.

[Differentiated carcinoma of the thyroid gland in an area of endemic goiter. Clinical study and prognostic correlation]

OBJECTIVE

Differentiated thyroid Carcinoma is a relatively frequent malignant neoplasia with three histologic types: papillary, follicular, and Hürtle cell carcinoma. Although papillary is the most common type, in endemic goitre areas the frequency of follicular type increases. Up to now, the only European studies about clinical aspects of differentiated thyroid carcinoma in endemic goitre areas are those performed in the Bavarian region until 1983. As the province of Orense (assistance zone concerning to the Hospital Virgen del Cristal) is a zone of endemic goitre, we have analyzed clinical presentation features and prognostic correlation factors in patients with differentiated thyroid carcinoma living in this area.

DESIGN

Retrospective study. Variables analyzed: 1) Age. 2) Sex. 3) Histologic type. 4) Tumor size. 5) Stage. 6) Presence of multinodular goitre. 7) Posttherapeutic disease persistence. 8) Recurrence. 9) Distant metastases. 10) Death attributed to thyroid carcinoma.

PATIENTS

61 cases of differentiated thyroid carcinoma, detected from 1983 to 1993. Mean follow-up period: 5 years (minimum 1, maximum 21). All patients were treated with total thyroidectomy followed by radioiodine ablation.

RESULTS

67.2% of papillary, 31.2% of follicular and 1.6% of Hürtle cell carcinoma. Male/female ratio: 1/4. Mean age: 48.8 +/- 2.9 (M +/- ESM) in papillary and 55 +/- 3.2 in follicular. Tumor size was smaller in papillary: 2.2 +/- 0.2 vs 6.2 +/- 0.5 cm (p < 0.001). Papillary type was detected more frequently than follicular in stages I, II and III, whereas follicular prevailed in stage IV (p < 0.03). Positive correlation between age and size in papillary: r = 0.393 (p < 0.01) and similar tendency in follicular: r = 0.423 (p = 0.057). Multinodular goitre was more frequent in follicular: 47% vs 25% (p = 0.02). Free of disease cases after treatment: 81% of papillary (p < 0.05) and 42% of follicular. Stage correlated independently with disease persistence after treatment (p = 0.0006). Age was minor in free of disease group: 50.0 +/- 3.8 vs 65.3 +/- 3.8 (p = 0.01).

CONCLUSIONS

In our area, papillary is the most common type, but follicular proportion is higher than reported from non endemic goitre areas. PC is a small tumor detected in stage I, whereas FC is large and detected in stage IV. Tumor stage is an independent prognostic factor. Frequent presence of multinodular goitre in patients with differentiated thyroid carcinoma suggests that in zones of endemic goitre, clinical attitude in multinodular goitre and solitary nodule must be similar.

Growth hormone releasing hexapeptide-6 (GHRP-6) test in the diagnosis of GH-deficiency

Pituitary GH reserve can be assessed by substances that act directly at the somatotroph, such as GHRH, or by a variety of metabolic and neuropharmacological tests acting at the hypothalamic level, such as hypoglycemia, clonidine or L-Dopa. In order to evaluate GHRP-6 as a test of pituitary GH reserve, we studied GH responses of i.v. administered GHRP-6 in a group of short-statured children, as well as in a group of adults diagnosed with growth hormone deficiency (GHD) by conventional GH testing. Although we found that the GH response to GHRP-6 was lower in patients with GHD than in normal children, on an individual basis a considerable degree of overlap was observed between the two groups. In contrast, we found an almost complete blockade of GH response to either GHRP-6 or GHRH plus GHRP-6 in patients with pituitary stalk transection, suggesting that this could be a cost-effective test for the diagnosis of this condition. A similar finding was also obtained in GH response to the combined administration of GHRH plus GHRP-6 in patients with GHD of adult onset; this test may well prove valuable in the diagnosis of this clinical entity.

Acipimox-mediated plasma free fatty acid depression per se stimulates growth hormone (GH) secretion in normal subjects and potentiates the response to other GH-releasing stimuli

Increases in plasma free fatty acids (FFA) inhibit the GH response to a variety of stimuli; however, the role of FFA depression in GH control is far from understood. In the present work, FFA reduction was obtained by the administration to normal subjects of acipimox, a lipid-lowering drug devoid of side-effects. Each subject tested underwent two paired tests. In one, acipimox was administered orally at a dose of 250 mg at -270 min and at a dose of 250 mg at -60 min; in the matched test, placebo was given at similar intervals. To induce GH release, four stimuli acting through different mechanisms were used: pyridostigmine (120 mg, orally) at -60 min, GHRH (1 microgram/kg, iv) at 0 min, GH-releasing peptide (GHRP-6; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2; 1 microgram/kg, iv) at 0 min, and finally, GHRH plus GHRP-6 at the same doses at 0 min. GH secretion was analyzed as the area under the secretory curve (AUC; mean +/- SE, micrograms per L/120 min). Acipimox pretreatment alone (n = 6) induced a reduction in FFA levels compared with placebo treatment. The FFA reduction led to a sustained GH secretion that increased from 2.4 +/- 1.8 micrograms/L at -120 min to 14.2 +/- 4.0 at 120 min. The GH AUC for placebo was 266 +/- 100, and that for acipimox was 1781 +/- 408 (P < 0.05). In the pyridostigmine-treated group (n = 6), the acipimox-pyridostigmine AUC (2046 +/- 323) was higher (P < 0.05) than the placebo-pyridostigmine AUC (764 +/- 101), but was not different from the AUC of acipimox alone. Previous FFA reduction nearly doubled the GHRH-mediated GH secretion (n = 6; placebo-GHRH AUC, 1817 +/- 365; acipimox-GHRH test, 3228 +/- 876; P < 0.05). A similar enhancement was observed when the stimulus employed was GHRP-6 (n = 6; placebo-GHRP-6 AUC, 2034 +/- 295; acipimox-GHRP-6, 4827 +/- 703; P < 0.05). Furthermore, even the most potent GH stimulus known to date, i.e. GHRH plus GHRP-6, was enhanced by the FFA suppression (placebo-GHRH-GHRP-6 AUC, 2034 +/- 277; acipimox-GHRH-GHRP-6, 5809 +/- 758; P < 0.05). The enhancing effect of lowering FFA levels was additive regardless of the stimulus employed. These results indicate that 1) FFA reduction per se stimulates GH secretion with a delayed time of action; 2) FFA reduction enhanced in an additive manner the GH secretion elicited by such different stimuli as pyridostigmine, GHRH, and GHRP-6; and 3) the observation that FFA reduction enhanced the response to the most potent GH stimulus, GHRH plus GHRP-6, suggests that FFA suppression acts by a separate mechanism. FFA reduction may have value in the clinical setting for assessing GH reserve.

Impaired growth hormone secretion in obese subjects is partially reversed by acipimox-mediated plasma free fatty acid depression

GH secretion in response to provocative stimuli is blunted in obese patients. On the other hand, increases in plasma free fatty acids (FFA) inhibit the GH response to a variety of stimuli, and FFA levels in plasma are increased with obesity. To ascertain whether FFA might be responsible for the GH secretory alterations of obesity, we studied spontaneous and stimulated GH secretion in 31 obese patients after FFA reduction by acipimox, a lipid-lowering drug devoid of serious side-effects. Each subject underwent two paired tests. In one, acipimox was administered orally at a dose of 250 mg at -270 min and at a dose of 250 mg at -60 min; in the matched test, placebo was given at similar intervals. To induce GH release, three stimuli acting through different mechanisms were used: pyridostigmine (60 mg, orally, at -60 min), GHRH (100 micrograms, iv, at 0 min), and GHRH plus GH-releasing peptide (GHRP-6; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2; both at a dose of 100 micrograms, iv, at 0 min). GH secretion was analyzed as the area under the secretory curve (AUC; mean +/- SE; micrograms per L/60 min). Acipimox pretreatment alone (n = 13) induced a large reduction in FFA levels compared with placebo treatment. The FFA reduction led to a slight GH rise (AUC, 123 +/- 47), not different from that in the placebo group (61 +/- 15). In the pyridostigmine-treated group (n = 6), the acipimox-pyridostigmine AUC (408 +/- 107) was significantly higher (P < 0.05) than that in the placebo-pyridostigmine group (191 +/- 25). Furthermore, the GHRH-mediated (n = 6) AUC of GH secretion in the placebo test (221 +/- 55) was tripled by FFA reduction due to acipimox, with an AUC of (691 +/- 134; P < 0.05). Even the most potent GH stimulus known to date, i.e. GHRH plus GHRP-6, was enhanced by FFA suppression. In fact, the placebo-GHRH-GHRP-6 AUC was 1591 +/- 349, lower (P < 0.05) than that in the acipimox-GHRH-GHRP-6 test (2373 +/- 242). The enhancing effects of FFA lowering on GHRH-mediated and GHRH- plus GHRP-6-mediated GH release were synergistic. These results indicate that in obese subjects, unlike normal weight subjects. FFA reduction per se does not stimulate GH secretion. A reduction in FFA with acipimox, however, increased pyridostigmine-. GHRH-, and even GHRH- plus GHRP-6-mediated GH release, suggesting that FFA reduction operates through a different mechanism from that of these three stimuli. The abnormally high FFA levels may be a contributing factor for the disrupted GH secretory mechanisms in obesity.

Absence of growth hormone (GH) secretion after the administration of either GH-releasing hormone (GHRH), GH-releasing peptide (GHRP-6), or GHRH plus GHRP-6 in children with neonatal pituitary stalk transection

GH-releasing peptide (GHRP-6; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic compound that releases GH in a specific and dose-related manner through mechanisms and a point of action that are mostly unknown, but different from those of GHRH. In man, GHRP-6 is more efficacious than GHRH, and a striking synergistic action occurs when both compounds are administered together. To explain such a synergistic effect, it has been postulated, but not proven, that GHRP-6 acts through a double mechanism, with actions exerted at the pituitary and the hypothalamic level. On the other hand, patients with the syndrome of GH deficiency due to perinatal pituitary stalk transection have any hypothalamic factor nonoperandi. The aim of the present study was 3-fold: 1) to further understand how relevant, if at all, the hypothalamic action of GHRP-6 is for GH regulation; 2) to evaluate whether GHRP-6 plus GHRH could be a suitable diagnostic tool in children with pituitary stalk transection; and 3) to compare these results with similar published studies performed in patients with hypothalamo-pituitary disconnection, who developed the disease as adults. Seven patients with GH deficiency and different degrees of panhypopituitarism due to perinatal pituitary stalk transection and 7 age- and sex-matched normal controls were studied. The subjects underwent 3 different tests on separate occasions, being challenged with GHRH (1 microgram/kg, iv), GHRP-6 (1 microgram/kg, iv), or GHRH plus GHRP-6. GH was analyzed as the area under the curve (mean +/- SE; micrograms per L/90 min). In normal subjects, GH secretion was 1029 +/- 202 after GHRH treatment, 1221 +/- 345 after GHRP-6, and 3542 +/- 650 after GHRH plus GHRP-6; the latter value was significantly (P < 0.05) higher than the secretion elicited by GHRH or GHRP-6 alone. In the group of patients with perinatal pituitary stalk transection, the level of GH after GHRH treatment was 116 +/- 22 and was even more reduced (P < 0.05) after GHRP-6 treatment (37 +/- 8). After GHRH plus GHRP-6, GH secretion in those patients was 177 +/- 27, significantly higher (P < 0.05) than the secretion induced by either GHRH or GHRP-6 alone. Individually examined, none of the patients tested with the most potent stimulus known to date (GHRH plus GHRP-6) exhibited GH secretion greater than 5 micrograms/L.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of combined administration of growth hormone (GH)-releasing hormone, GH-releasing peptide-6, and pyridostigmine in normal and obese subjects

Growth hormone (GH) secretion in response to all provocative stimuli is decreased in patients with obesity. Recently, we found that the combined administration of GH-releasing hormone (GHRH) and the hexapeptide GH-releasing peptide-6 (GHRP-6) induced a large increase in plasma GH levels. To gain further insight into the disrupted mechanism of GH regulation in obesity, we investigated whether the inhibition of somatostatinergic tone with pyridostigmine could further increase the GH response to combined administration of GHRH and GHRP-6. In normal subjects, administration of GHRH plus GHRP-6 induced a marked increase in plasma GH with a peak at 30 minutes (mean +/- SEM, 76.7 +/- 9.7 micrograms/L), which was similar to that obtained after pretreatment with pyridostigmine (74.7 +/- 9.4 micrograms/L). In obese patients, combined administration of GHRH plus GHRP-6 induced a clear increase in GH secretion with a peak at 15 minutes of 42.2 +/- 10.0 micrograms/L, which was also unaffected after pretreatment with pyridostigmine (38.4 +/- 5.8 micrograms/L). The GH response was lower in obese patients than in controls as assessed by the area under the curve after administration of both GHRH plus GHRP-6 (1,846 +/- 396 v 4,773 +/- 653, P < .01) and pyridostigmine plus GHRH plus GHRP-6 (1,989 +/- 372 v 5,098 +/- 679, P < .005). In conclusion, these data suggest that GHRP-6 can behave as a functional somatostatin antagonist, and that somatotrope responsiveness to the combined administration of GHRH plus GHRP-6 is largely independent of somatostatinergic tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent GHRH-induced PRL secretion in Cushing's syndrome, obesity and exogenous hypercortisolism

Endogenous Cushing's syndrome, obesity and chronic glucocorticod treatment are characterized by blunted GH secretion. The administration of GHRH is capable of stimulating a small but significant PRL increase in normal subjects. The current study was designed to determine plasma PRL levels in response to GHRH, studied in three different situations characterized by a blunted GH secretion. Obese patients (n = 6) with a weight over 30% of ideal body weight, patients with active Cushing's syndrome, and normal volunteers treated with dexamethasone 22 mg per os over two days before the pituitary challenge were studied. As a control group 18 normal subjects of similar age and sex were studied. GH and PRL was determined at intervals after GHRH (1 microgram/kg). GHRH-induced GH secretion was markedly reduced in patients with obesity, patients with endogenous Cushing's syndrome and volunteers treated with dexamethasone. In contrast, GHRH-induced PRL secretion was not affected in these three clinical situations. In summary, in three situations characterized for an impairment of the somatotroph cell, due to a primary intrinsic defect or to a functional hypothalamic alteration, there is a persistent GHRH-induced PRL secretion, suggesting that prolactin could be released by mammosomatotrophs that function normally in spite of hyposomatotropism.

Regulation of growth hormone secretion by the growth hormone releasing hexapeptide (GHRP-6)

Growth hormone (GH) secretion is regulated by a complex system of central and peripheral signals. Recently, a new GH-releasing hexapeptide (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) called GHRP-6 which specifically releases GH has been studied. In the present work the mechanism of action of GHRP-6 has been addressed in experimental animal models as well as in obese subjects. GHRP-6 releases GH independently of the hypothalamic factors GHRH and somatostatin and is a powerful GH releaser in obesity.