Prenatal melatonin influences developmental changes of tachykinins in response to estradiol benzoate

What do we really know about the safety and efficacy of melatonin for sleep disorders?

Melatonin is a hormonal product of the pineal gland, a fact that is often forgotten. Instead it is promoted as a dietary supplement that will overcome insomnia, as an antioxidant and as a prescription only drug in most countries outside the United States of America and Canada. The aim of this review is to step back and highlight what we know about melatonin following its discovery 60 years ago. What is the role of endogenous melatonin; what does melatonin do to sleep, body temperature, circadian rhythms, the cardiovascular system, reproductive system, endocrine system and metabolism when administered to healthy subjects? When used as a drug/dietary supplement, what safety studies have been conducted? Can we really say melatonin is safe when it has not been systematically studied and many studies show interactions with a wide range of physiological processes? Finally the results of studies investigating the efficacy of melatonin as a drug to alleviate insomnia are critically evaluated. In summary, melatonin is an endogenous pineal gland hormone with specific physiological functions in animals and humans, with its primary role in humans to maintain synchrony of sleep with the day/night cycle. When administered as a drug it affects a wide range of physiological systems and has clinically important drug interactions. With respect to efficacy for treating sleep disorders, melatonin can advance the time of sleep onset but the effect is modest and variable. In children with neurodevelopmental disabilities melatonin appears to have the greatest impact on sleep onset but little effect on sleep efficiency.

15 years on the Editorial Board of PEPTIDES

In this article, part of an issue of PEPTIDES celebrating the many years of dedication of Dr. A.J. Kastin as Editor-in-Chief of the journal, I describe how I first met him and how our friendship and collaboration developed. In 1970 I joined Dr. A.V. Schally's team at the Endocrine and Polypeptide Laboratories of Tulane University and the V.A. Hospital and it was at that time that I met Dr. Kastin for the first time. In 1984 I joined Dr. Schally's team for the second time and I began publishing part of my research findings in PEPTIDES. Afterward many more results from the research work were also published in PEPTIDES. I became a member of the Editorial Board of the same journal in 1999. It was going to be a very interesting experience. Some of my observations as a reviewer for PEPTIDES are described in the present article. Finally, I expressed my warmest congratulations to Dr. A.J. Kastin for the outstanding job that he carried out as Editor-in-Chief of PEPTIDES.

Tachykinin family genes and their receptors are differentially expressed in the hypothyroid ovary and pituitary

Plasma tachykinin levels are known to be altered with sexual acyclicity and loss of reproductive function. Ovulatory dysfunction, as seen in postmenopausal women, is also often encountered in hypothyroid patients. To know the involvement of different tachykinin genes in hypothyroidism-associated reproductive disorders, we performed DD-PCR with the pituitary RNA of control and hypothyroid rats to see the differentially expressed gene profile. Subsequently, we selected a few clones, tachykinin being one of them. Since its expression was up regulated in hypothyroidism as it does in the sexually acyclic females, we wanted to correlate these two phenomena with hypothyroidism associated reproductive disorders. We observed differential expression of tac2 along with other tk genes and their receptors in rat pituitary and ovary, which suggests that hypothyroidism affects the expression of these genes in these tissues. The experiments were repeated in ovarian tissue obtained at surgery from hypothyroid human patients, which showed similar expression pattern of TAC3 (equivalent to rat tac2) and their receptors as in rat ovary. Significant reduction of tac2 expression in reproductively less active rat ovary suggests the association of tac2 with reproductive senescence. Our results suggest that decline in reproductive function in hypothyroidism is associated with altered expression level of tac2 and its receptors. Further investigation in this area could elucidate the possible mechanism of tachykinins' involvement in loss of sexual cyclicity and other reproductive disorders associated with hypothyroidism.

Age differences in neurokinin A and substance P from the hypothalamus, pituitary, pineal gland, and striatum of the rat. Effect of exogenous melatonin

Previous data showed that aging of the central nervous system (CNS) is associated with widespread changes in tachykinin gene expression. However, there are no data about the possible role of exogenous melatonin in modulating the tachykinergic system during aging. The aim of this work was to analyze the age-dependent changes on neurokinin A (NKA) and substance P (SP) levels in hypothalamus, pituitary, pineal gland and striatum and the role of exogenous melatonin on these changes. We studied female rats at three different ages: 5-month-old (cyclic), 15-month-old (preacyclic) and 25-month-old (acyclic). Hypothalamic tachykinin levels increase when female rats reached acyclicity, this increase was blunted in acyclic-melatonin-treated rats. However, melatonin treatment in young cyclic rats resulted in significantly increased values as compared to controls. Pituitary NKA concentrations did no show age-dependent changes in control rats, however, in both, preacyclic and acyclic-melatonin-treated rats significantly increased values of pituitary NKA were found compared to controls. In the pineal gland, a marked decrease of NKA levels was observed in acyclic-control rats. Melatonin treatment did not alter this decrease. In the striatum, NKA and SP concentrations were significantly reduced in preacyclic- and acyclic-control rats compared to young cyclic rats, melatonin had no effect on striatal tachykinins. Our results indicate that melatonin may regulate tachykinin stores during aging mainly on structures of the neuroendocrine-reproductive axis.

Prenatal melatonin exposure affects luteinizing hormone and hypothalamic and striatal neuropeptide Y in the male rat offspring

The present study examines the influence of prenatal melatonin on the hypothalamic and striatal neuropeptide Y (NPY) concentrations as well as on luteinizing hormone (LH) levels. Male rat offspring of control and melatonin treated mother rats were studied at different ages of the sexual development: infantile, prepubertal, pubertal and adult ages. Hypothalamic NPY levels were much higher during the juvenile than throughout the infantile period. After prenatal melatonin treatment significantly higher values since day 15 up to 35, also at 60 days of age were found, as compared with controls. Striatal NPY levels were lower than in hypothalamus. Again, NPY in the striatum from offspring of melatonin treated mother rats showed significantly higher values than the respective controls at most of the ages studied. However, prenatal melatonin exerted an inhibitory influence upon LH secretion pattern, since decreased concentrations up to 25 days of age and delayed peak values at pubertal age were observed. The present study also suggest that the effect of NPY upon LH secretion is related to sexual development, since NPY exerted opposite effect in infantile than in pubertal period and melatonin administration during intrauterine life prevented this effect.