Maureen E. Troiani

Bio: Maureen E. Troiani is an academic researcher from University of Texas Health Science Center at San Antonio. The author has contributed to research in topics: Melatonin & Pineal gland. The author has an hindex of 13, co-authored 19 publications receiving 363 citations.

Norepinephrine or isoproterenol stimulation of pineal N-acetyltransferase activity and melatonin content in the Syrian hamster is restricted to the second half of the daily dark phase

Abstract: Seven experiments were performed to investigate the sensitivity of the hamster pineal gland to exogenously administered norepinephrine (NE). In these studies NE (1 mg/kg) administration was preceded (

Swimming depresses nighttime melatonin content without changing N-acetyltransferase activity in the rat pineal gland

Abstract: Recently, it was shown that a 1.5-ml subcutaneous saline injection depressed N-acetyltransferase (NAT) activity and melatonin content in the rat pineal gland at night. The present studies were undertaken to determine if another perturbation, swimming, could duplicate this response. Rats swam at 23.10 h (lights out at 20.00 h) for 10 min and were killed 15 and 30 min after the unset of swimming. Pineal NAT activity was found to be unaffected while melatonin content was depressed dramatically. Hydroxyindole-O-methyltransferase (HIOMT) activity as well as the content of serotonin (5HT), 5-hydroxytryptophan (5HTP) and 5-hydroxyindoleacetic acid (5HIAA) were not changed by this treatment. In a second study, pineal melatonin again was depressed without a concomitant drop in NAT activity. Mean serum melatonin at 15 min after onset of swimming was increased although the rise was not statistically significant. In the final study, it was found that NAT activity was slightly increased in intact rats and unchanged in adrenalectomized rats at 7 min after swimming onset. At 15 min both intact and adrenalectomized animals had NAT activity values similar to those of controls. Pineal melatonin content in intact and adrenalectomized rats plummeted to 50% of control values at 7 min and fell further to 25% at 15 min. While the rate of melatonin synthesis was not directly measured, lack of change in the activities of the enzymes involved in melatonin synthesis and the contents of two melatonin precursors suggests that swimming depresses pineal melatonin content by enhancing melatonin efflux from the gland.

Neither the pituitary gland nor the sympathetic nervous system is responsible for eliciting the large drop in elevated rat pineal melatonin levels due to swimming.

Abstract: Since the pineal gland is an end organ of the sympathetic nervous system, stress might increase the synthesis of its hormone, melatonin The stress of a 10 min swim, which elicits a marked rise in circulating catecholamines, causes a dramatic depression of high pineal melatonin levels at night within 15 min after swimming onset N-acetyltransferase (NAT) activity is unaffected by the treatment at 15 or 30 min after swimming onset Within 90 min after initiation of a 15 min swim, high nighttime pineal melatonin levels are restored while NAT values remain elevated The swimming-induced reduction in high pineal melatonin levels is not influenced by either hypophysectomy, superior cervical ganglionectomy, prazosin (α1-adrenergic receptor blocker) pretreatment, yohimbine (α2-adrenergic receptor blocker) pretreatment, or reserpine (amine depletor) pretreatment These results indicate that neither hormones secreted from the pituitary gland nor catecholamines secreted from the sympathetic nerves are involved in eliciting the dramatic reduction in elevated pineal melatonin levels in the rat

Adrenalectomy prevents changes in rat pineal melatonin content and N-acetyltransferase activity induced by acute insulin stress.

Abstract: The activity of N-acetyltransferase (NAT) and the content of melatonin (MEL) in the rat pineal have been shown to be sensitive to several types of stressors This study was designed to assess the role of the adrenals in mediating the effect of one such stressor, insulin-induced hypoglycemia, on pineal synthetic activity Intact and bilaterally adrenalectomized (ADX) adult male rats were kept under light:dark cycles of 14:10 (lights on 0600 h) and injected intraperitoneally with 10 IU insulin at 1300 h, and groups (n = 8) were killed 2, 3, or 4 h postinjection Plasma catecholamines were assayed by means of high performance liquid chromatography and radioimmunoassay was used to assess pineal NAT activity and MEL content All injected groups were rendered hypoglycemic by insulin administration Compared to uninjected controls, plasma epinephrine in hypoglycemic intact rats rose after 2 h, whereas epinephrine did not change in hypoglycemic ADX animals The increase in epinephrine in intact animals was correlated with a rise in NAT activity at 2 h Moreover, pineal MEL content at 2, 3, and 4 h was significantly greater than control values In contrast, no changes in pineal biosynthetic function were found in ADX rats This differential response by intact and ADX rats suggests that an adrenal product (possibly epinephrine) is responsible for mediating the stimulatory effects of acute insulin-induced hypoglycemic stress on the rat pineal

The Pharmacological Basis of Therapeutics

Abstract: The Pharmacological Basis of Therapeutics A Textbook of Pharmacology, Toxicology and Therapeutics for Physicians and Medical Students. By Prof. Louis Goodman and Prof. Alfred Gilman. Pp. xiii + 1383. (New York: The Macmillan Company, 1941.) 50s. net.

Pineal Melatonin: Cell Biology of Its Synthesis and of Its Physiological Interactions*

Abstract: I Introduction UNTIL 35 yr ago, most scientists did not take research on the pineal gland seriously The decade beginning in 1956, however, provided several discoveries that laid the foundation for what has become a very active area of investigation These important early observations included the findings that, 1), the physiological activity of the pineal is influenced by the photoperiodic environment (1–5); 2), the gland contains a substance, N-acetyl-5-methoxytryptamine or melatonin, which has obvious endocrine capabilities (6, 7); 3), the function of the reproductive system in photoperiodically dependent rodents is inextricably linked to the physiology of the pineal gland (5, 8, 9); 4), the sympathetic innervation to the pineal is required for the gland to maintain its biosynthetic and endocrine activities (10, 11); and 5), the pineal gland can be rapidly removed from rodents with minimal damage to adjacent neural structures using a specially designed trephine (12) Since the mid 1960s, research on t

One molecule, many derivatives: a never-ending interaction of melatonin with reactive oxygen and nitrogen species?

Abstract: Melatonin is a highly conserved molecule. Its presence can be traced back to ancient photosynthetic prokaryotes. A primitive and primary function of melatonin is that it acts as a receptor-independent free radical scavenger and a broad-spectrum antioxidant. The receptor-dependent functions of melatonin were subsequently acquired during evolution. In the current review, we focus on melatonin metabolism which includes the synthetic rate-limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites. Recent evidence indicates that the original melatonin metabolite may be N 1 -acetyl-N 2 -formyl-5-methoxykynuramine (AFMK) rather than its commonly measured urinary excretory product 6-hydroxymelatonin sulfate. Numerous pathways for AFMK formation have been identified both in vitro and in vivo. These include enzymatic and pseudo-enzymatic pathways, interactions with reactive oxygen species (ROS)/reactive nitrogen species (RNS) and with ultraviolet irradiation. AFMK is present in mammals including humans, and is the only detectable melatonin metabolite in unicellular organisms and metazoans. 6-Hydroxymelatonin sulfate has not been observed in these low evolutionary-ranked organisms. This implies that AFMK evolved earlier in evolution than 6-hydroxymelatonin sulfate as a melatonin metabolite. Via the AFMK pathway, a single melatonin molecule is reported to scavenge up to 10 ROS/RNS. That the free radical scavenging capacity of melatonin extends to its secondary, tertiary and quaternary metabolites is now documented. It appears that melatonin's interaction with ROS/RNS is a prolonged process that involves many of its derivatives. The process by which melatonin and its metabolites successively scavenge ROS/RNS is referred as the free radical scavenging cascade. This cascade reaction is a novel property of melatonin and explains how it differs from other conventional antioxidants. This cascade reaction makes melatonin highly effective, even at low concentrations, in protecting organisms from oxidative stress. In accordance with its protective function, substantial amounts of melatonin are found in tissues and organs which are frequently exposed to the hostile environmental insults such as the gut and skin or organs which have high oxygen consumption such as the brain. In addition, melatonin production may be upregulated by low intensity stressors such as dietary restriction in rats and exercise in humans. Intensive oxidative stress results in a rapid drop of circulating melatonin levels. This melatonin decline is not related to its reduced synthesis but to its rapid consumption, i.e. circulating melatonin is rapidly metabolized by interaction with ROS/RNS induced by stress. Rapid melatonin consumption during elevated stress may serve as a protective mechanism of organisms in which melatonin is used as a first-line defensive molecule against oxidative damage. The oxidative status of organisms modifies melatonin metabolism. It has been reported that the higher the oxidative state, the more AFMK is produced. The ratio of AFMK and another melatonin metabolite, cyclic 3-hydroxymelatonin, may serve as an indicator of the level of oxidative stress in organisms.

The melatonin rhythm: both a clock and a calendar.

Abstract: The paper briefly reviews the data which shows that the circadian production and secretion of melatonin by the pineal gland can impart both daily, i.e., clock, and seasonal, i.e., calendar, information to the organism. The paper summarizes the 3 patterns of nocturnal melatonin production that have been described. Clearly, regardless of the pattern of nocturnal melatonin production a particular species normally displays, the duration of nightime elevated melatonin is proportional to the duration of the night length. Since daylength under natural conditions changes daily the melatonin rhythm, which adjusts to the photoperiod sends time of year information to the organism. The melatonin receptors which subserve the clock message sent by the pineal gland in the form of a melatonin cycle may reside in the biological clock itself, namely, the suprachiasmatic nuclei (SCN). The melatonin receptors that mediate seasonal changes in reproductive physiology are presumably those that are located on the pars tuberalis cells of the anterior pituitary gland. Besides these receptors which likely mediate clock and calendar information, melatonin receptors have been described in other organs. Interestingly, the distribution of melatonin receptors is highly species-specific. Whereas the clock and calendar information that the melatonin cycle imparts to the organism relies on cell membrane receptors, a fact that is of some interest considering the high lipophilicity of melatonin, recent studies indicate that other functions of melatonin may require no receptor whatsoever.