Desensitization and endocytosis mechanisms of ghrelin-activated growth hormone secretagogue receptor 1a

In this study, a sequential analysis of pathways involved in the regulation of GH secretagogue receptor subtype 1a (GHSR-1a) signaling has been undertaken to characterize the process of rapid desensitization that is observed after ghrelin binding. This process was evaluated by studying the binding of [(125)I]ghrelin, measurement of intracellular calcium mobilization, and confocal microscopy. The results indicate that GHSR-1a is mainly localized at the plasma membrane under unstimulated conditions and rapidly desensitizes after stimulation. The agonist-dependent desensitization is not mediated by protein kinase C because phorbol ester, phorbol-12-myristate-13-acetate, failed to block the ghrelin-induced calcium response. The ghrelin/GHSR-1a complex progressively disappears from the plasma membrane after 20 min exposure to ghrelin and accumulates in the perinuclear region after 60 min. Colocalization of the internalized GHSR-1a with the early endosome marker (EEA1) after 20 min exposure to ghrelin suggests that endocytosis occurs via clathrin-coated pits, which is consistent with the lack of internalization of this receptor observed after potassium depletion. Different from other G protein-coupled receptors, GHSR-1a showed slow recycling. Surface binding slowly recovered after agonist treatment and returned to control levels within 360 min. Furthermore, inhibition of vacuolar H(+)-ATPases prevented recycling of the receptor, suggesting that the nondissociation of the ligand/receptor complex is responsible for this effect. The GHSR-1a internalization may explain the characteristic physiological responses mediated by this receptor.     

Age- and gender-related growth hormone responses to intravenous clonidine in healthy adults.

The alpha(2)-adrenoceptor agonist clonidine stimulates growth hormone (GH) release in both animals and humans. It has been used to test for GH deficiency in children, to assess central alpha(2)-adrenoceptor function in adults and to determine the pathophysiological basis and to confirm diagnosis in neurological diseases with autonomic failure. The dose and mode of administration, however, may be important, as in some studies in adults oral clonidine has minimal effects on GH. We report our experience following intravenous (i.v.) clonidine (2 microg/kg) in 98 normal adults on the neuroendocrine (GH, insulin, glucose and catecholamine) and cardiovascular (blood pressure) responses. In males between 25 and 89 years and females between 25 and 64 years there was a significant rise in GH secretion (P < 0.05) after clonidine. Males showed an age-sensitive secretory pattern, with the greatest response between 25 and 35 years (P < 0.02). Younger males (< 45 years) had significantly higher peak GH levels post-clonidine than younger females < 45 years (P < 0.03). No sex-related change was observed in older subjects (< 45 years). Clonidine caused a significant fall in plasma noradrenalin and adrenalin in all age-sex groups (P< 0.001). There were no significant changes in glucose or insulin. There were no effects of age on the fall in blood pressure induced by clonidine. In conclusion, i.v. clonidine stimulated GH in all age groups and there was a marked sexually dimorphic pattern in adults < 45 years. The results overall suggest that i.v. clonidine-GH testing provides a reliable method for investigation of central alpha(2)-adrenergic function in adult humans.     

Joint mechanisms of impaired growth-hormone pulse renewal in aging men

CONTEXT: Aging reduces the size (mass) of GH secretory bursts and thereby reduces total GH secretion. Experimental data indicate that high-amplitude GH pulses are evoked by reversible cycles of GH-induced negative feedback. Whether aging impairs autofeedback is unknown. OBJECTIVE: The objective of this study is to assess whether age attenuates and IGF-I potentiates negative feedback by a near-physiological pulse of GH. DESIGN/SETTING/SUBJECTS: In a university setting, 17 healthy men ages 19-71 yr each underwent four randomly ordered infusion studies on separate mornings fasting. INTERVENTION: Intravenous injection of a pulse of: 1) saline or 2) recombinant human (rh) GH to impose controlled negative feedback, followed in 2 h by a bolus of 3) saline or (iv) the ghrelin analog GHRP-2 to overcome feedback inhibition. OUTCOME MEASURES: The impact of age and IGF-I concentrations on GH autofeedback was assessed by regression analysis. RESULTS: Percentage feedback inhibition correlated negatively with: 1) age after consecutive rh GH/saline infusion (R(2) = 0.42, P = 0.005) at any IGF-I concentration; and 2) total IGF-I concentrations after rh GH/GHRP-2 infusion (R(2) = 0.40, P = 0.009) at any age. In contrast, sex-steroid concentrations and body mass index were unrelated to degree of autoinhibition. CONCLUSIONS: Increased age in healthy men predicts impaired GH autofeedback, which may contribute to attenuated renewal of high-amplitude GH pulses. Conversely, higher IGF-I concentrations in young men forecast accentuated GH autoinhibition, which may drive prominent GH pulses.     

Oral administration of the growth hormone secretagogue NN703 in adult patients with growth hormone deficiency

OBJECTIVE: Little is known of the usefulness of GH secretagogues (GHSs) in GH-deficient (GHD) adults. The objective of this study was to determine the number of responders to treatment with NN703 in GHD adults. DESIGN: A multicentre, randomized, double-blind, and placebo-controlled study. PATIENTS: Ninety-seven GHD adults were included. MEASUREMENTS: The GH response before and after 1 week of oral treatment with NN703 (n = 83) or placebo (n = 14) was determined. The first and last dose of NN703 was 3 mg/kg, whereas the dose of NN703 was 1.5 mg/kg/day during the 6 days between the first and last doses. Furthermore, all 97 patients received 1 micro g/kg GH-releasing hormone (GHRH) 3 weeks after the last dose of NN703. RESULTS: Serum GH peak and area under curve (AUC) values after the first NN703 administration were greater than those after placebo administration (P < 0.05). However, after correction for the lower body mass index (BMI) in the NN703 group, this difference lost statistical significance. After 1 week of therapy, GH peak and AUC values were similar following the final doses of NN703 and placebo. Serum peak and AUC values of other anterior pituitary hormones were similar between the NN703 and placebo groups both after the first and last administration of study drug. Nine of the 83 patients (11%) responded with a serum peak GH concentration >or= 5 micro g/l after the first and/or last NN703 administration, whereas no patient responded after placebo administration. Serum IGF-I was unaffected by 1-week NN703 treatment, whereas serum IGFBP-3 was increased (P < 0.05 vs. placebo) also after correction for BMI. Mean serum peak GH concentration after GHRH administration was 2.1 micro g/l (+/-0.3, SEM), which was higher than that after the first NN703 administration (1.32 +/- 0.3, P < 0.05). CONCLUSION: NN703 administration was generally well tolerated. Eleven per cent of the GHD adult patients responded with a peak GH response >or= 5 micro g/l after the first and/or last administration of oral NN703. Although a majority of GHD adults will not respond to NN703, the present results suggest that oral NN703 treatment could be useful in some adult patients with moderately severe GHD. These patients may be identified by a test dose of GHS.     

Changes in skeletal muscle and body composition after discontinuation of growth hormone treatment in growth hormone deficient young adults

OBJECTIVES: The aim of this study was to determine whether there are any changes in skeletal muscle strength and size and body composition following growth hormone (GH) withdrawal in GH deficient young adults. DESIGN: A longitudinal, 1-year, open, uncontrolled study of the changes in skeletal muscle and body composition following GH withdrawal was performed. Endocrine status was reassessed at the end of the study period during an insulin tolerance test. Some measurements were repeated after 2 years of treatment. PATIENTS: Twelve (11 male, one female; age range 14-21) patients who had been diagnosed during childhood as growth hormone deficient took part in the study. Four of the 12 patients were found to have a normal GH response on retesting at the end of the study and their results were analysed as a separate group. MEASUREMENTS: Quadriceps and forearm flexor maximum voluntary isometric strength, body fat content and serum IGF-1 were measured at 3-monthly intervals over 1 year. Every 6 months muscle size was measured from computerized tomography scans and fibre area from quadriceps needle biopsy samples. RESULTS: For the growth hormone deficient group the 12 month quadriceps strength, size and fibre areas were 94.0% +/- 8.5 (mean +/- SD), 94.5% +/- 6.3 and 85.6% +/- 17.7 respectively of control (baseline) values. Forearm flexor strength and size were 101.4% +/- 7.9 and 92.0% +/- 9.2 of control. Body fat percentage had increased from 19.5% +/- 8.6 to 24.1% +/- 9.5. No change was seen in the non-growth hormone deficient group. CONCLUSIONS: Although the changes measured were relatively small they suggest a role for GH in the maintenance of muscle integrity and body composition in the young adult with growth hormone deficiency.     

Distribution and regulation of chicken growth hormone secretagogue receptor isoforms

Chicken ghrelin has recently been isolated as a hormone which stimulates growth hormone and corticosterone secretion in chicken. Ghrelin mediates these actions in mammals by binding to the growth hormone secretagogue receptor (GHS-R). In this study, we describe the partial cloning of two chicken GHS-R (cGHS-R) isoforms: cGHS-R1a and cGHS-R1c. cGHS-R1a and cGHS-R1c cDNA show, respectively, 81 and 78% homology with the corresponding parts of the human GHS-R1a cDNA. In contrast to the human GHS-R1b isoform, which is truncated after transmembrane domain 5 (TM-5), the chicken GHS-R1c isoform lacks 16 amino acids in TM-6 suggesting that this isoform is not active in ghrelin signal transduction. The cystein residues, N-linked glycosylation sites and potential phosphorylation sites, found in the human GHS-R1a, were also conserved in both chicken isoforms. RT-PCR analysis demonstrated cGHS-R1a and cGHS-R1c mRNA expression in all tissues tested, except liver and pancreas, with highest levels in the pituitary and the hypothalamus. Intermediate levels of expression were detected, in descending order, in the ovary, telencephalon, heart, adrenal gland, cerebellum, and optic lobes whereas low expression was detected in the brainstem, lung, kidney, proventriculus, duodenum, and colon. Very low expression was found in skin, stomach, and muscle. cGHS-R1c was expressed in lower amounts than cGHS-R1a in all analysed tissues. Administration of 1 microM chicken ghrelin to pituitaries in vitro resulted in a down-regulation of both cGHS-R isoforms within 15 min, whereas after 1h levels returned to control values. Growth hormone and corticosterone down-regulated cGHS-R1a and cGHS-R1c mRNA expression within 60 min of exposure, whereas growth hormone-releasing factor 1-29 (1 microM) only reduced cGHS-R1a mRNA expression after 60min. Thyrotropin-releasing hormone (1 microM) did not alter cGHS-R expression.     

Adenosine is an agonist of the growth hormone secretagogue receptor

Growth hormone secretagogues (GHSs) are synthetic compounds that induce GH release in several species, including man. The aim of the current study was to identify hypothalamic GHS receptor (GHS-R) agonists. This led to the discovery of adenosine as a GHS-R agonist. We demonstrate that adenosine as well as the A1 adenosine receptor agonist N6-R-phenylisopropyladenosine (R-PIA) induce calcium responses, with EC50 values of 50 nM and 0.5 nM, respectively, in cells which express recombinant human GHS-R. However, neither compound induces a calcium response in nontransfected cells. Binding experiments show that adenosine and the GHS compound MK-0677 bind to membranes from GHS-R expressing cells with nearly identical Bmax values (2.6 +/- 0.1 x 10(-10) mol/mg protein for adenosine and 2.0 +/- 0.3 x 10(-10) mol/mg protein for MK-0677). However, no binding to membranes from nontransfected cells could be detected. Furthermore, we show that the IC50 values for inhibition of the adenosine, R-PIA, and GHS induced calcium responses by the GHS-R antagonist [D-Arg1, D-Phe5, D-Trp7,9, D-Leu11]-substance P are similar. These findings strongly suggest that adenosine and R-PIA are agonists of the GHS-R. Interestingly, neither adenosine nor R-PIA were able to induce GH release from rat pituitary cells in vitro. The implications of the latter finding is discussed.     

Central actions of the nonpeptide growth hormone secretagogue GHS-25

Growth hormone secretagogues (GHSs) increase the activity of hypothalamic arcuate nucleus neurons thought to be involved in controlling the release of growth hormone (GH). The GHS receptor is also found in hypothalamic regions not associated with the release of GH, suggesting that GHSs may influence other hypothalamic systems. This study utilized double-labeling immunocytochemical techniques to examine the hypothalamic actions of a novel nonpeptide GHS, GHS-25. In common with other GHSs, GHS-25 induced significant amounts of Fos immunoreactivity in the arcuate nucleus of conscious male rats. However, unlike other GHSs, GHS-25 also induced Fos immunoreactivity in the supraoptic nucleus. Double labeling revealed that approx 66% of supraoptic nucleus cells that were Fos positive after the administration of GHS-25 were also immunoreactive for oxytocin. Thus, in addition to its actions on the GH axis, GHS-25 may influence the release of neurohypophyseal hormone.     

Five years of growth hormone replacement therapy in adults: age- and gender-related changes in isometric and isokinetic muscle strength

GH replacement therapy in adults with adult-onset GH deficiency (GHD) has been shown to increase isometric and isokinetic muscle strength in a few trials with limited numbers of patients. In this single center, prospective, open-label study, the effects of 5-yr GH replacement therapy on muscle function were determined in 109 consecutive adults (61 men and 48 women) with adult-onset GHD. The mean initial GH dose was 0.88 mg/d. The dose was gradually lowered, and after 5 yr the mean dose was 0.46 mg/d. The mean IGF-I SD score increased from -1.54 at baseline to 1.53 at study end. A sustained increase in lean body mass and decrease in body fat was observed. The GH treatment induced persistent increases in isometric knee flexor strength, concentric knee flexor strength at an angular velocity of 60 degrees/sec, and right-hand peak grip strength. After correction for age and gender using observed/predicted value ratios, a sustained increase was also observed in isometric (60 degrees) and concentric (180 degrees/sec) knee extensor strength, average right-hand grip strength for 10 sec, and left-hand grip strength. At study end, knee flexor and extensor strength was 96-104% of predicted and hand grip strength was 84-90% of predicted values. The local muscle endurance was transiently decreased after correction for age and gender. No gender difference was found in the treatment responses in muscle strength. However, muscle strength (also after correction for age and gender) was lower in women than men throughout the study period. In conclusion, GH replacement therapy in adults with adult-onset GHD normalized isometric and isokinetic knee flexor and extensor strength. Hand grip strength increased but was not fully normalized.     

Ghrelin stimulation of growth hormone release and appetite is mediated through the growth hormone secretagogue receptor

Synthetic agonists of the growth hormone secretagogue receptor (GHSR) rejuvenate the pulsatile pattern of GH-release in the elderly, and increase lean but not fat mass in obese subjects. Screening of tissue extracts in a cell line engineered to overexpress the GHSR led to the identification of a natural agonist called ghrelin. Paradoxically, this hormone was linked to obesity. However, it had not been directly shown that the GHSR is a physiologically relevant ghrelin receptor. Furthermore, ghrelin's structure is significantly different from the synthetic agonist (MK-0677) used to expression-clone the GHSR. To address whether the GHSR mediates ghrelin's stimulatory effects on GH release and appetite, we generated Ghsr-null mice. In contrast to wild-type mice, acute treatment of Ghsr-null mice with ghrelin stimulated neither GH release nor food intake, showing that the GHSR is a biologically relevant ghrelin receptor. Nevertheless, Ghsr-null mice are not dwarfs; their appetite and body composition are comparable to that of wild-type littermates. Furthermore, in contrast to suggestions that ghrelin regulates leptin and insulin secretion, fasting-induced changes in serum levels of leptin and insulin are identical in wild-type and null mice. Serum insulin-like growth factor 1 levels and body weights of mature Ghsr-null mice are modestly reduced compared to wild-type littermates, which is consistent with ghrelin's property as an amplifier of GH pulsatility and its speculated role in establishing an insulin-like growth factor 1 set-point for maintaining anabolic metabolism. Our results suggest that chronic treatment with ghrelin antagonists will have little effect on growth or appetite.     

Ghrelin and growth hormone secretagogue receptor expression in mice during aging

In well-nourished humans, GH and IGF-I decline during aging, and the responsiveness of the GH axis to exogenous ghrelin is attenuated with age. Intriguingly, the GH/IGF-I axis is rejuvenated by chronic treatment with the ghrelin mimetic MK-0677, resulting in improvements in body composition, suggesting that frail elderly subjects might benefit from treatment with ghrelin and ghrelin mimetics. Mouse models are widely used to study the effects of ghrelin, but the impact of age on the ghrelin pathway is unclear. In this study, total and active ghrelin peptides were measured in plasma, and ghrelin mRNA was quantitated in brain tissue from different aged C57BL/6J mice. Surprisingly, plasma levels of ghrelin peptide slightly increased with age; ghrelin mRNA levels were similar in brains from mice aged 2, 6, 12, and 28 months but higher in mice aged 18 and 24 months. The tissue distribution of Ghsr1a mRNA (ghrelin receptor) was also characterized, and pituitary and brain exhibited the highest levels of expression. In the pituitary gland, the highest concentration of Ghsr1a mRNA was observed at age 1-2 months, it was lower at 6 months, and remained unchanged for up to 30 months of age. This result is consistent with the finding that GH release in response to exogenous ghrelin was not significantly different in mice aged 7-30 months. In the brain, Ghsr1a mRNA levels remained stable during aging. Hence, in C57BL/6J male mice, aging is not associated with changes in circulating ghrelin levels or changes in ghrelin receptor expression in the pituitary gland and brain.     

儿童期起病的生长激素缺乏患者在青少年时期的生长激素水平——对胰岛素耐量试验的重新评价

一些研究发现许多儿童期起病的生长激素缺乏(COGHD)患儿在青春早期或晚期复查时,已不再缺乏生长激素.     

Long-term growth hormone treatment in growth hormone deficient adults.

Growth hormone treatment in GH-deficient adults has proved beneficial in recent short-term trials, but long-term results have not yet been reported. Thirteen GH-deficient adults (4 females, 9 males; mean (SEM) age 26.4 (1.7) years), who had completed 4 months of GH therapy in a double-blind placebo-controlled cross-over study were followed, for further 16.1 (0.8) months of uninterrupted GH therapy in an open design. A significant mean increase of 1.3 cm in linear height was recorded, whereas body mass index remained unchanged. Mean muscle volume of the thigh, estimated by computerised tomography, increased significantly compared with that of the initial placebo period (p = 0.01), and a slight decrease was recorded in adipose tissue volume of the thigh (p = 0.10) and subscapular skinfold thickness (p = 0.10). Still, the muscle to fat ratio of the thigh was significantly lower compared with that of normal subjects (72.6/27.4 vs 77.9/22.1) (p less than 0.01). The mean isometric strength of the quadriceps muscles increased significantly during long-term GH therapy (p less than 0.01), but remained lower compared with that of normal subjects (1.66 (0.10) vs 2.13 (0.11) Nm/kg body weight). Exercise capacity performed on a bicycle ergometer increased significantly after long-term therapy (p less than 0.05), but still did not reach the values seen in normal subjects (22.5 (3.4) vs 37.4 (4.2) watt.min.kg-1. No adverse reactions were recorded during long-term therapy and hemoglobin A1c remained unchanged. These data suggest that long-term GH replacement therapy in GH-deficient adults has beneficial effects on several physiological features which are subnormal in these patients.     

Effects of combined long-term treatment with a growth hormone-releasing hormone analogue and a growth hormone secretagogue in the growth hormone-releasing hormone knock out mouse

GH secretagogues (GHS) are synthetic ghrelin receptor agonists that stimulate GH secretion. It is not clear whether they act predominantly by stimulating the secretion of hypothalamic growth hormone-releasing hormone (GHRH), or directly on the somatotrope cells. In addition, it is not known whether combined treatment with GHRH and GHS has synergistic effects on growth. To address these questions, we used the GH-deficient GHRH knock out (GHRHKO) mouse model, which has severe somatotrope cell hypoplasia. We treated GHRHKO mice for 5 weeks (from week 1 to week 6 of age) with the GHRH analogue JI-38 alone, or in combination with a GHS (GHRP-2), and at the end of the treatment we examined their response to an acute stimulus with GHRP-2 or GHRP-2 plus JI-38. We used placebo-treated GHRHKO mice and animals heterozygous for the GHRHKO allele as controls. Animals treated with JI-38+GHRP-2 reached higher body length and weight than animals treated with JI-38 alone. All the animals receiving JI-38 (with or without GHRP-2) showed similar correction of somatotrope cell hypoplasia. None of the GHRHKO animals showed a serum GH response to the acute stimulation with GHRP-2 alone, while both treated groups responded to the combined test with JI-38 + GHRP-2. These data demonstrate that in GHRHKO mice, GHRP-2 has a growth-stimulating effect that augments the response induced by JI-38. In addition, the presence of GHRH seems necessary for the stimulation of GH secretion by GHRP-2.     

Testosterone inhibition of growth hormone release stimulated by a growth hormone secretagogue: studies in the rat and dog

Anabolic steroids are frequently taken by athletes and bodybuilders together with recombinant human GH (rhGH), though there is some scientific evidence that the use of anabolic steroids reverses the rhGH-induced effects. Recently, we have shown that treatment with rhGH (0.2 IU/kg s.c., daily x 12 days) in the dog markedly reduced the canine GH (cGH) responses stimulated by EP51216, a GH secretagogue (GHS), evaluated after 3 and 5 daily rhGH injections, and that the inhibition was still present a few days after rhGH discontinuation. The aim of the present study was to evaluate in the dog the GH response to EP51216 (125 mug/kg i.v.) in a condition of enhanced androgenic function (i.e. acute injection or 15-day treatment with testosterone at the dose of 2 mg/kg i.m. on alternate days), and in the hypophysectomized rat the hypothalamic and hippocampal expression of ghrelin, the receptor of GHSs (GHS-R), GH-releasing hormone (GHRH) and somatostatin (SS) after specific hormonal replacement therapies (testosterone, 1 mg/kg/day s.c.; hydrocortisone, 500 mug/kg/day s.c.; rhGH, 400 mug/kg/day s.c.; 0.9% saline 0.1 ml/kg/day s.c.; x11 days). In the dog experiments, under baseline conditions, a single injection of EP51216 elicited an abrupt rise of plasma cGH. Twenty-four hours from the acute bolus injection of testosterone, C(max) and AUC(0-90) of the GHS-stimulated cGH response were significantly lower than baseline cGH response; 5 days later, there was still a significant decrease of either parameter versus the original values. Short-term treatment with testosterone markedly reduced the GHS-stimulated cGH responses evaluated during (5th bolus) and at the end (8th bolus) of testosterone treatment. Four and 8 days after testosterone withdrawal, the EP51216-stimulated cGH response was still significantly reduced when compared with that under baseline conditions. Plasma concentrations of insulin-like growth factor 1 (IGF-1) were stable until the 5th bolus of testosterone and decreased progressively in the remaining time of the testosterone treatment; 4 and 8 days from treatment withdrawal, IGF-1 levels were still suppressed. In rat studies, hypothalamic mRNA levels of GHS-R were significantly reduced by treatments with testosterone and hydrocortisone, whereas hippocampal expressions of ghrelin, GHRH and SS were reduced by rhGH replacement therapy. In conclusion, these studies show that a single administration of testosterone can abrogate the cGH response ensuing acute stimulation by a GHS; the inhibitory effect of testosterone on the cGH response to GHS is present during and even 8 days after termination of a short-lived treatment with testosterone; these events occur via a Copyright (c) 2006 S. Karger AG, Basel.     

Cumulative adversity and drug dependence in young adults: racial/ethnic contrasts

Aims To study cumulative exposure to stressors as a risk factor for drug dependence, and evaluate whether group differences in exposure contribute to differences in prevalence. Design Cross‐sectional community survey of life‐time adverse experiences and substance and psychiatric disorders. Setting Data collected between 1997 and 2000 in Miami–Dade County, USA. Participants A total of 1803 former Miami–Dade public school students, 93% between ages 19 and 21 years when interviewed. Males and females of Cuban origin, other Caribbean basin Hispanics, African‐Americans and non‐Hispanic whites are represented equally. Measurements Drug dependence disorder assessed by DSM‐IV criteria using the Composite International Diagnostic Interview, and a 41‐item checklist of life‐time exposure to major and potentially traumatic experiences. Both measures include age at time of first occurrence. Findings Life‐time rate of drug dependence disorder (total 14.3%) did not vary significantly (P > 0.05) by socio‐economic group. Male rate (17.6%) was significantly greater than female rate (10.9%). The African‐American rate (6.5%) was dramatically lower than non‐Hispanic white (17.0%), Cuban (18.1%) and non‐Cuban Hispanic (16.0%) rates despite their dramatically higher exposure to adversity. Twenty‐eight of 33 individual adversities were associated with the subsequent onset of drug dependence (P < 0.05). Cumulative life‐time exposure was greatest for males and for African‐Americans, and was associated inversely with socio‐economic level. Multivariate discrete‐time event history analysis revealed significant independent effects of distal (>1 year earlier) and proximal (previous year) exposure to adverse events (P < 0.05), controlling for childhood conduct disorder, attention deficit hyperactive disorder and previous psychiatric disorder. Conclusions Life‐time cumulative exposure to distant as well as more recent adversity predicts risk of subsequent drug dependence, although it does not explain ethnic group differences in risk.