Blindness impairs plasma growth hormone response to L-dopa but not to arginine

Parkinson's disease as a neuroendocrine disorder of circadian function: dopamine-melatonin imbalance and the visual system in the genesis and progression of the degenerative process

For more than 50 years, Parkinson's disease (PD) has been conceptualized as a product of nigro-striatal dopamine (NSD) system degeneration. In spite of a growing body of evidence depicting the mammalian brain as an interrelated complexity of circuitous systems, dopamine (DA) deficiency of the NSD is still regarded as the main problem, with DA replacement being the purpose of therapeutic intervention. For at least 191 years circadian involvement in various aspects of PD, including depression and insomnia, has been recognized as an integral part of the symptom matrix of PD and yet attempts to elucidate the involvement of this system is uncharted territory. The present review attempts a major reorganization of mammalian brain into a coordinated complex involving the NSD and the retinal hypothalamic tract (RHT) as the primary systems involved in the retino-diencephalic/mesencephalic-pineal (RDMP) axis. Secondary systems including the lateral hypothalamus (LH), the area postraema (AP) and the subthalamic nucleus (STN) also form an integral part of this system as they have been shown to be either intimately related to the primary systems of the RDMP axis or have been shown to be significantly involved in the expression and treatment of PD. A large volume of evidence suggests that the RDMP axis is activated during the course of PD and during therapeutic intervention. Four types of neurotoxicity associated with melatonin are identified and the susceptibility of various parts of the RDMP axis to undergo neuropathological change, the tendency for melatonin to induce PD-like behavioural toxicity, and the relationship of this to PD symptomotology are described. This includes adverse effects of melatonin on motor function, hypotension, the adjuvant use of benzodiazepines, depression, insomnia, body weight regulation and various biochemical effects of melatonin administration: all problems currently facing the proposal to introduce melatonin as an adjuvant. It is suggested further that traditional DA replacement may well work by exerting its effect upon the circadian system, rather than simply replacing deficient DA. Activation of the circadian function by antagonizing melatonin with bright light not only has therapeutic value in treating the primary symptoms of PD but it shares a common mechanism with L-dopa in reducing the occurrence of seborrheic dermatitis. Concepts at the centre of understanding pineal function in PD, including pineal calcification, melatonin deficiency, symptomatic versus protective features of melatonin and antioxidative effects, are explained in a counterintuitive context. Intriguing propositions including the role of the retina in the aetiology of PD and that the nigra functions as a retina in this disorder are presented with the intention to provide a new understanding of the underlying compromised function in PD and to provide new treatment strategies. For the first time, abundant evidence is presented describing PD as an endocrine disorder of melatonin hyperplasia. The role of circadian interventive therapies and internal desynchrony in the aetiology and progression of PD provides a new direction for understanding the underlying physiology of a disease which is currently in a state of impasse and provides new hope for those who suffer from its debilitating effects.

Twenty-four hour melatonin pattern in acromegaly: effect of acute octreotide administration

We investigated the melatonin (MT) circadian rhythm before and after somatostatin (octreotide) acute administration in ten subjects (4 M, 6 F. 23-52 yr old) with active acromegaly due to pituitary microadenoma. Blood samples were drawn every 2 hours over a 48-h span; after 24-h basal blood collection, octreotide (Sandostatin, Sandoz) 100 micrograms sc/8 h was administered. As control, 7 healthy adult subjects (3M, 4F; 26-50 yr old) were studied in basal condition over a 24-h span. Plasma MT and GH levels were measured by RIA in each sample, IGF-1 levels were measured by immunoradiometric assay in basal and after octreotide morning samples. The comparisons were made by Mann-U-Withney and Wilcoxon test as appropriate; the existence of a MT circadian rhythm was validated by cosinor analysis; GH and MT values were correlated by Pearson's correlation coefficient. All of 7 control subjects and 2 of 10 acromegalics had significant 24-h MT rhythm. The area under curve (AUC), mesor and amplitude of the MT rhythms in acromegalics were significantly lower than in the controls (p < 0.001, 0.002 and 0.0006, respectively), with an earlier acrophase (median value: 22:14 vs 02:08 h of controls). Basal plasma IGF-1 levels and circadian GH concentrations were significantly increased in acromegalics in comparison with the control group. Octreotide administration significantly reduced GH, restoring a circadian MT rhythm in 5 of 10 acromegalics, with MT mean mesor and AUC not different from controls. Mean amplitude still remained lower than controls (p < 0.0006), with an earlier acrophase (median 00:01 h). No significant correlation was found between individual GH and MT levels. Our data indicate a reduction of MT circadian secretion in acromegaly, due especially to a blunted nocturnal increase with earlier MT peak; moreover, acute octreotide administration increase MT levels without modifying amplitude and phase of night-time secretion significantly. These findings suggest a negative interrelationship between GH and MT secretions or a facilitatory influence of somatostatin on daytime MT release only. This partial recovery of pineal secretion after octreotide in acromegalics could be a clinically significant contribution to improve their quality of life, considering that MT is involved in the regulation of several important functions.

Endocrine disorders in septo-optic dysplasia (De Morsier syndrome)--evaluation and follow up of 18 patients

Septo-optic dysplasia (SOD) is characterized by hypoplasia of the optic nerve, various types of forebrain defects and hormonal deficiencies. We have studied the clinical and endocrinological characteristics of 18 such patients retrospectively to: (1) better define the endocrine abnormalities in children with SOD; and (2) to find approaches for the interdisciplinary long-term care of children with SOD. The children were seen at the Children's Hospital of the University of Munich from 1976 to 1992 (8 boys, 10 girls; age at initial presentation: 1 day-13 years of age, mean 1.9 years). Unilateral hypoplasia of the optic nerve was found in 7 cases, bilateral hypoplasia in 11. Sonographic, CCT or MRI yielded the following results: 4 of the patients had a cavum septum pellucidum, 3 patients had hypoplasia of the cerebellum, 1 aplasia of the corpus callosum and 1 aplasia of the fornix. An empty sella with or without an ectopic pituitary was seen in 4 cases. Height standard deviation score (SDS) at time of diagnosis was -4.0 to +0.4, mean -2.92. Endocrine deficiencies were present in all 11 patients who had undergone endocrinological investigations. Seven patients suffered from isolated growth hormone (GH) deficiency or multiple hypopituitarism. One had diabetes insipidus centralis, 2 had hypogonadotropic hypogonadism, 1 had hypothyroidism and 2 adrenal insufficiency. Hypothalamic testing was performed only in a subset of patients: in 5 of 11 children tested a thyrotropin releasing hormone (TRH test), in two out of nine a gonadotropin releasing hormone (GnRH) test, and in three out of six GH releasing hormone (GHRH) test yielded abnormal results. High prolactin levels were measured in two out of five patients.

CONCLUSION

SOD is characterized by optic nerve hypoplasia and a variety of endocrine deficiencies. In addition, forebrain malformations are present in most SOD patients. Hormonal disorders are present in some SOD patients which may be of hypothalamic origin and need to be investigated systematically.

Melatonin and the pituitary-thyroid axis status in blind adults: a possible resetting after puberty

OBJECTIVE

Increased levels of free thyroid hormones have been previously described in prepubertal blind subjects and have been thought to be a consequence of a partial target organ refractoriness due to the early and prolonged lack of light perception. The aim of this study was to clarify whether this abnormality is permanent or transient and the interrelationships between melatonin and thyroid hormone secretion.

MEASUREMENTS

Total and free thyroid hormones, TSH, thyroxine-binding globulin (TBG), reverse triiodothyronine (rT3) and melatonin were measured in plasma samples obtained at 0800 h (two hours after lights-on) in a group of 11 totally (group 1) and 16 partially (group 2) blind adult patients and in 10 age-matched healthy subjects.

RESULTS

Both totally and partially blind patients showed melatonin levels higher than in controls (330 +/- 106 pmol/l, group 1 and 361 +/- 159 pmol/l, group 2, respectively; controls: 53 +/- 12 pmol/l, P < 0.001 vs both groups), but fT4, fT3, T4, T3 TSH, rT3 and TBG concentrations showed no significant differences from controls.

CONCLUSIONS

A possible resetting of pituitary-thyroid axis regulation can occur in blindness after puberty; variations of melatonin secretion could play a role in this. The inhibitory effect of melatonin on thyroid gland function found in animals does not seem to occur in humans. Elevated melatonin levels, both in patients with total blindness and in those with light perception only, suggest that more complex mechanisms other than light signalling are involved in the changes of melatonin secretion in blindness.

Normal plasma insulin-like growth factor I levels and impaired final stature in adult blind subjects

The aim of this study was to determine if changes in IGF-1 levels and in final stature occur in blind adult subjects. Eighteen subjects (4 females and 14 males) with total blindness (Group 1) and 26 subjects (5 females and 21 males) with only light perception (Group 2), living at an Institute for blind adult subjects in Naples, Italy, were studied. Their height and weight were compared to British standards. Plasma morning IGF-1 levels, measured by IRMA method were compared to those of 18 normal controls (6 females and 12 males) matched for age and weight. A high prevalence of short stature was demonstrated especially in Group 1 (p = 0.00005 by chi-square for trend test) but was also present in Group 2 (p = 0.02). No alterations in weight distribution were observed in both groups. Basal IGF-I levels in both Group 1 and Group 2 were similar to those of controls: IGF-1 (M +/- SE), 30.9 +/- 2.9 nmol/L and 37.9 +/- 2.7 nmol/L, respectively, vs 33.3 +/- 2.9 nmol/L, NS. High prevalence of final short stature in both groups confirms a negative influence of total or partial blindness on growth. These complex mechanisms appear to involve more than alterations in GH and IGF-I secretion.