Atropine selectively blocks GHRH-induced GH secretion without altering LH, FSH, TSH, PRL and ACTH/cortisol secretion elicited by their specific hypothalamic releasing factors

Topical Atropine in Retarding Myopic Progression and Axial Length Growth in Children with Moderate to Severe Myopia: A Pilot Study

PURPOSE

To study the safety and efficacy of topical 1% atropine eye ointment in retarding myopic progression in children with moderate to severe myopia.

METHODS

This was an interventional control study. Children (aged 5-10 years) with myopia of -3.00 diopters (D) or more were treated with 1% atropine ointment once daily for 1 year. Baseline and regular assessments of refractive errors by cycloplegic autorefraction and of axial length were done by ultrasound biometry, and the results were compared with data of control subjects.

RESULTS

Twenty-three children (mean age: 7.4 +/- 1.6 years) with moderate to severe myopia, being treated in the Hong Kong Eye Hospital of the Chinese University of Hong Kong, were recruited into the atropine group, and 23 children from the same eye clinic were matched with the study subjects with respect to age, sex, and initial spherical equivalent refraction, as controls. The initial refractive errors were -5.18 +/- 2.05 D and -5.12 +/- 2.33 D in the atropine and the control groups, respectively (P = 0.934). Myopic progression was significantly less (P = 0.005) in the atropine group (+0.06 +/- 0.79 D) than in the control group (-1.19 +/- 2.48 D). Axial length increase was also significantly smaller in the atropine group (0.09 +/- 0.19 mm) than in the control group (0.70 +/- 0.63 mm) (P = 0.004). One child (4.3%) developed an allergic reaction. No other major adverse effects related to the treatment were noted.

CONCLUSION

Topical 1% atropine ointment is a safe and effective treatment for retarding myopic progression in moderate to severe myopia. Further large-scale randomised controlled study with longer follow-up seems warranted.

Acetylcholine does not play a major role in mediating the endocrine responses to ghrelin, a natural ligand of the GH secretagogue receptor, in humans

OBJECTIVE

Ghrelin is a 28 amino residue peptide produced predominantly by the stomach with substantially lower amounts deriving from other central and peripheral tissues. Ghrelin is a natural ligand of the GH secretagogue (GHS) receptor (GHS-R) and possesses a potent GH-releasing activity for which the acylation in serine 3 is essential. Ghrelin also possesses other endocrine and non-endocrine activities reflecting central and peripheral GHS-R distribution and stimulates PRL, ACTH and cortisol secretion, has been reported able to induce hyperglycaemia and to decrease insulin levels and has orexigenic activity. Moreover, ghrelin stimulates gastric motility and acid secretion and its action is mediated by acetylcholine which, in turn, is known to play a stimulatory influence on GH, ACTH and insulin secretion.

SUBJECTS AND METHODS

In order to clarify the influence, if any, of acetylcholine on the endocrine activities of ghrelin, we studied the effects of cholinergic enhancement by pyridostigmine (PD, 120 mg p.o. at -60 minutes) and blockade by pirenzepine (PIR, 100 mg p.o. at -60 minutes) on GH, PRL, cortisol, insulin and glucose responses to human acylated ghrelin (1.0 microg/kg i.v. at 0 minutes) in seven normal young volunteers [age (mean +/- SEM): 28.3 +/- 3.1 years; BMI: 21.9 +/- 0.9 kg/m2]. In the same subjects, the effects of PD and PIR on the GH response to GHRH (1.0 microg/kg i.v. at 0 minutes) have also been studied.

RESULTS

The administration of ghrelin induced a prompt increase in circulating GH levels (hAUC: 5452.4 +/- 904.9 microg*min/L) which was markedly higher (P < 0.01) than that elicited by GHRH (966.9 +/- 20.50 microg*min/L). Ghrelin also induced a significant increase in PRL (1273.5 +/- 199.7 microg*min/L) and cortisol levels (15505.1 +/- 796.3 microg*min/L) and a decrease in insulin levels (Delta hAUC: -198.1 +/- 39.2 mU*min/L) which was preceded by an increase in plasma glucose levels (8743.8 +/- 593.0 mg*min/dL). The GH response to GHRH was markedly potentiated by PD (4363.3 +/- 917.3 microg*min/L; P < 0.01 vs. GHRH alone). In turn, PD did not modify either the GH response to ghrelin (6564.2 +/- 1753.5 microg*min/L) or its stimulatory effect on PRL and cortisol as well as its effects on insulin and glucose levels. The GH response to GHRH was inhibited by PIR (171.5 +/- 34.7 microg*min/L, P < 0.01 vs. GHRH alone) which, in turn, did not significantly modify the GH response to ghrelin (4044.0 +/- 948.8 microg*min/L). PIR also did not modify the effects of ghrelin on PRL, cortisol, insulin and glucose levels.

CONCLUSIONS

The endocrine activities of ghrelin are not affected significantly by cholinergic enhancement and muscarinic blockade. Thus, acetylcholine does not play a major role in the endocrine actions of ghrelin. Moreover, as the cholinergic system influences GH secretion via modulation of somatostatin release, the present data agree with the assumption that ghrelin is partially refractory to the influence of somatostatin.

Myopia: attempts to arrest progression

Previous studies have evaluated the efficacy of several interventions to decrease the progression of myopia. These include devices that alter the perception of the visual environment and pharmacological treatments. There is no conclusive evidence thus far that alteration of the pattern of spectacle wear, bifocals, ocular hypotensives, or contact lenses retards the progression of myopia. Several randomised clinical trials have demonstrated that the rate of progression of myopia is lower in children given atropine eye drops than those given placebo. However, atropine is associated with short term side effects such as photophobia and possible long term adverse events including light induced retinal damage and cataract formation. Other more selective antimuscarinic agents such as pirenzipine are presently being evaluated. Further well conducted randomised clinical trials with large sample sizes and adequate follow up designed to evaluate treatments to retard the progression of myopia should be conducted, since the identification of an effective intervention may have a greater public health impact on the burden and morbidity from myopia than the few treatments currently available.

Radiation and neuroregulatory control of growth hormone secretion

OBJECTIVE

Cranial irradiation frequently results in growth hormone (GH) deficiency. Patients with radiation-induced GH deficiency usually remain responsive to exogenous growth hormone releasing hormone, implying radiation damages the hypothalamus rather than the pituitary. Little is known about the effect of cranial irradiation on the neuroendocrine control of GH secretion. This study was to determine the effect of cranial irradiation on somatostatin tone.

DESIGN

Somatostatin tone was examined by manipulating cholinergic tone in young adults with radiation-induced GH deficiency and a control population. Each individual underwent three separate studies: the GH response to 100 micrograms GHRH-(1-29)-NH2 was assessed alone, and 60 minutes after pyridostigmine or pirenzepine.

PATIENTS

Eight young male adults with radiation induced GH deficiency following treatment in childhood for a brain tumour or acute lymphoblastic leukaemia, and ten healthy adult men were studied.

MEASUREMENTS

Serum growth hormone was measured at 15-minute intervals throughout each of the three study periods.

RESULTS

One of 10 controls and four of eight irradiated subjects had a peak GH level to GHRH analogue of less than 20 mU/l. After pretreatment with pyridostigmine, all subjects except one irradiated subject had a peak GH level of greater than 20 mU/l. Pretreatment with pyridostigmine and pirenzepine significantly modified the GH response to GHRH analogue within both groups (P < 0.0005). Pretreatment with pyridostigmine significantly enhanced the GH response to GHRH analogue (median (range) area under the curve, 9029 (1956-20940) mU/l/min in controls vs 1970 (628-3608) mU/l/min in the irradiated group) compared with GHRH analogue alone (1953 (512-16140) mU/l/min in control group vs 997 (266-3488) mU/l/min in the irradiated group). Pretreatment with pirenzepine significantly attenuated the GH response to GHRH analogue (552 (64-1274) mU/l/min in controls vs 305 (134-2726) mU/l/min in irradiated group). Between the groups there was no significant difference in GH area under the curve (AUC) after GHRH analogue alone. There was a significantly (P = 0.0014) greater increment of GH secretion after pyridostigmine and GHRH analogue compared with GHRH analogue alone (difference in AUC of pyridostigmine+GHRH analogue and GHRH analogue alone 6348 (696-12856) mU/l controls vs 542 (120-1340) mU/l in the irradiated group) and significantly (P = 0.033) greater suppression of GH secretion after pirenzepine and GHRH analogue compared with GHRH analogue alone (difference in AUC of GHRH analogue alone and pirenzepine+GHRH analogue 1644 (222-15205) mU/l in controls vs 479 (469-1623) mU/l in the irradiated group) in the control population compared with those who had received cranial irradiation in childhood.

CONCLUSIONS

These data suggest that cranial irradiation reduces but does not abolish somatostatin (SRIH) tone and also reduces endogenous GHRH secretion. Although SRIH tone is reduced, it can be increased by cholinergic manipulation and is therefore not irreversibly fixed. This has possible implications if GHRH analogues were used to treat children with radiation induced GH deficiency.

Eptastigmine augments basal and GHRH-stimulated growth hormone release in young and old dogs

The aim of the present work was to evaluate the effect on the growth hormone (GH) secretion of eptastigmine, a new long-acting cholinesterase inhibitor, in unanesthetized beagle dogs. In a first study, 5 young dogs were given single doses (0.5, 1.0, and 2.0 mg/kg, i.m.) of the drug or saline in a randomized cross-over manner. Blood samples were collected immediately before and, at regular intervals, until 150 min after drug injection. GH plasma concentrations were determined by radioimmunoassay. Plasma cholinesterase activity was measured with a potentiometric method. There was a significant logistic relationship (r = 0.601, P < 0.01) between the administered dose of eptastigmine and the log-transformed areas under the GH plasma concentration-time curve (AUC) with a calculated ED50 for eptastigmine of 0.63 +/- 0.36 mg/kg. There was also a significant linear relationship (r = 0.630, P < 0.01) between log-transformed AUC of GH levels and AUC of plasma cholinesterase activity. In a second study we evaluate the ability of eptastigmine (2.0 mg/kg, i.m.) to potentiate the GH-releasing effect of the GH-releasing hormone (GHRH, 2.0 micrograms/kg, i.v.) in young and old dogs. Eptastigmine was administered 45 min before GHRH and blood collected every 15 min until 90 min after GHRH injection. In young dogs, maximum GH plasma levels (Cmax) were 6.1 +/- 1.0 ng/ml after GHRH compared to 22.5 +/- 2.3 ng/ml after GHRH preceded by eptastigmine (P < 0.01). In old animals, Cmax were 4.6 +/- 1.4 ng/ml after GHRH vs 13.2 +/- 7.4 ng/ml after combined administration of GHRH and eptastigmine (P < 0.05). These data indicate that eptastigmine is very effective in augmenting basal and stimulated GH secretion in old dog. The good activity also shown in old animals suggests a potential use of this drug to reverse the age-dependent decline in GH secretion responsible for many involutional changes of aging.

Pyridostigmine fails to increase either spontaneous or GHRH-stimulated GH secretion during day or night in growth hormone-insufficient children

OBJECTIVE The aim of the study was to investigate whether pyridostigmine, a cholinesterase inhibitor which is thought to act at the hypothalamus to inhibit somatostatin secretion, would augment spontaneous or GHRH-stimulated serum GH levels in patients with GH-insufficiency. DESIGN Oral pyridostigmine 60 mg or placebo was administered at the start of a 9-h subcutaneous infusion of either GHRH (1-29)NH2 10 micrograms/kg/h or saline control. Studies were performed during the daytime (0900-1800 h) in five patients, and the night-time (2100-0600 h) in a further five. PATIENTS Ten short, pre-pubertal children (aged 6-11 years; eight boys) with growth hormone insufficiency were studied. MEASURES Blood for serum GH was sampled every 20 min, and analysed using the PULSAR program. RESULTS The subcutaneous infusion of GHRH 10 micrograms/kg/h increased mean serum GH levels (+/- SEM): by day 17.7(+/- 6.8) vs placebo 2.2(+/- 0.4) mU/l (P less than 0.01), and by night 26.9(+/- 3.3) vs 5.5(+/- 1.3) mU/l (P less than 0.05). There was a significant rise in mean 'baseline' GH concentration: by day 5.5(+/- 1.7) vs 1.0(+/- 0.0) mU/l (P less than 0.05); and night 8.2(+/- 2.7) vs 1.3(+/- 0.3) mU/l (P less than 0.05). Pyridostigmine failed to produce a significant overall increase in either spontaneous or GHRH-stimulated GH secretion by day or night, although there was a significant rise in mean GH levels during the 3 h following pyridostigmine administration in the morning: 4.4(+/- 1.1) vs 2.4(+/- 0.5) mU/l (P less than 0.001). GHRH or pyridostigmine given singly or in combination had no significant effect on the number of pulses. Side-effects attributable to pyridostigmine occurred in seven children. CONCLUSIONS Pyridostigmine, either on its own or as an adjuvant therapy in combination with GHRH, acts for only a brief time and does not offer any potential benefit in the management of children with short stature.

The effect of ketoconazole and transdermal estradiol on serum sex steroid hormones levels

In this randomized, open-label trial, 24 subjects were studied. There were 12 subjects with essential hypertension and 12 normotensive controls who received, after an initial control period, 48 h of treatment with a transdermal estradiol patch or ketoconazole tablets every 8 h for six doses, or in combination. LHRH (100 micrograms) and ACTH (250 micrograms) were given at 48 h of each treatment. Each treatment was one week apart. In both normotensive and hypertensive men ketoconazole reduced adrenal and gonadal androgens, raised 11-deoxycortisol and 17 alpha-hydroxyprogesterone levels; blunted the rise of cortisol to ACTH and had no effect on the response of LH to LHRH. Transdermal estradiol raised serum estradiol levels, blunted the time to peak plasma concentration of LH to LHRH and produced a normal response to ACTH. Although baseline level of total and free testosterone and DHEA-S were lower in hypertensive men, the response of the pituitary (LH) to LHRH and adrenal axis with ACTH were similar in both normotensive and hypertensive men. Blood pressure was unaffected by any of the treatment interventions in either normotensive or hypertensive men. Although ketoconazole or transdermal estradiol reduce androgens, there was no evidence that this reduction in androgens was involved with the short term regulation of blood pressure in hypertensive men.

Aspects of growth hormone control in diabetes

Growth Hormone (GH) has been implicated in the development of retinal new vessels that characterise diabetic proliferative retinopathy. Formerly, pituitary ablation was successful in causing such new vessels to regress but this approach has been largely superseded by panretinal photocoagulation. A clearer understanding of the GH abnormalities in diabetes might not only shed light on the process of retinal new vessel formation but could also provide a means for pharmacological suppression of GH in those patients not fully responding to laser photocoagulation. In this review, GH control in diabetes is considered with particular reference to studies in patients with diabetic retinopathy.

Growth hormone response to desmethylimipramine in depressed and suicidal adolescents

Desipramine 75 mg i.m. was given in the morning to 20 adolescents with major depressive disorder and 23 normal controls. Depressed adolescents secreted significantly less growth hormone (GH) over the next 2 h than did normal adolescents, although a substantial proportion of the differences were accounted for by the depressed adolescents who had a specific suicidal plan or attempt during the episode. Severity of depression or the presence of other depressive symptoms did not predict GH secretion within the depressed group. Age, sex and maturational factors in the control of GH are discussed. It is concluded that these differences in GH secretion probably reflect differences in CNS beta-adrenergic and/or serotonergic function. Suicidality and depression may have different psychobiological correlates in adolescents.

GH feedback occurs through modulation of hypothalamic somatostatin under cholinergic control: studies with pyridostigmine and GHRH

We have studied the effect of increased cholinergic tone on the GH response to growth hormone-releasing hormone (GHRH) and on GH feedback, using pyridostigmine, an acetylcholinesterase inhibitor. In six healthy male adult volunteers 120 mg oral pyridostigmine increased basal GH secretion compared to placebo and augmented the GH response to 100 micrograms i.v. GHRH (1-29) NH2; the effect was more than the additive effect of pyridostigmine and GHRH when each was given alone. Pretreatment with 2 IU methionyl-hGH given i.v. abolished the serum GH response to GHRH given 3 h later, demonstrating a negative feedback loop of GH on the response to GHRH; this inhibited response to GHRH was restored in subjects given pyridostigmine as well as methionyl-hGH. The data demonstrate that enhanced cholinergic tone releases GH, augments the serum GH response to GHRH and unblocks the negative feedback effect of methionyl-hGH pretreatment on the GH response to GHRH. These results suggest that GH negative feedback effects on its own secretion occur predominantly through increased hypothalamic somatostatin secretion; this somatostatin secretion is under inhibitory cholinergic control.

Growth hormone and prolactin secretion after growth hormone-releasing hormone administration, in anorexia nervosa patients, normal controls and tamoxifen-pretreated volunteers

Anorexia nervosa is associated with several abnormalities in GH secretion elicited by different stimuli. To investigate the precise mechanism of this alteration, GHRH was administered to 14 women: a group of eight anorexia nervosa patients in the acute phase of their illness and a control group of six age-matched volunteers. As patients with anorexia nervosa have chronic low oestrogen values, the volunteer women of the control group underwent a second GHRH test after pretreatment with the oestrogen receptor blocker tamoxifen. GHRH 1-29 (1 microgram/kg i.v.) induced a GH peak (mean +/- SEM) of 28.2 +/- 5.1 ng/ml (GH ng/ml x 2 = mU/l) at 30 min in the anorectic patients. This value was no different from the GHRH-stimulated GH peak in the control women (28.1 +/- 10.0 ng/ml). Tamoxifen pretreated women had a GH peak after GHRH of 35.6 +/- 9.7 ng/ml, not significant versus control test. Compared with the control group, oestrogen levels were significantly lower in anorectic patients and higher in tamoxifen-treated women. GHRH administration induced a small PRL peak at 15 min that was similar in the three groups tested. After this 15 min peak, PRL in both anorexic and tamoxifen-treated women returned toward basal values steadily. However, in untreated control women a second PRL peak was evident at 60 min. In conclusion, GHRH-induced GH secretion in anorexia nervosa patients was similar to that in control subjects and in controls under oestrogen receptor blockade.