Steven M. Yellon

Daily Melatonin Administration to Middle-Aged Male Rats Suppresses Body Weight, Intraabdominal Adiposity, and Plasma Leptin and Insulin Independent of Food Intake and Total Body Fat

Pineal melatonin secretion declines with aging, whereas visceral fat, plasma insulin, and plasma leptin tend to increase. We have previously demonstrated that daily melatonin administration at middle age suppressed male rat intraabdominal visceral fat, plasma leptin, and plasma insulin to youthful levels; the current study was designed to begin investigating mechanisms that mediate these responses. Melatonin (0.4 microg/ml) or vehicle was administered in the drinking water of 10-month-old male Sprague Dawley rats (18/treatment) for 12 weeks. Half (9/treatment) were then killed, and the other half were submitted to cross-over treatment for an additional 12 weeks. Twelve weeks of melatonin treatment decreased (P<0.05) body weight (BW; by 7% relative to controls), relative intraabdominal adiposity (by 16%), plasma leptin (by 33%), and plasma insulin (by 25%) while increasing (P<0.05) locomotor activity (by 19%), core body temperature (by 0.5 C), and morning plasma corticosterone (by 154%), restoring each of these parameters toward more youthful levels. Food intake and total body fat were not changed by melatonin treatment. Melatonin-treated rats that were then crossed over to control treatment for a further 12 weeks gained BW, whereas control rats that were crossed to melatonin treatment lost BW, but food intake did not change in either group. Feed efficiency (grams of BW change per g cumulative food intake), a measure of metabolic function, was negative in melatonin-treated rats and positive in control rats before cross-over (P<0.001); this relationship was reversed after cross-over (P<0.001). Thus, melatonin treatment in middle age decreased BW, intraabdominal adiposity, plasma insulin, and plasma leptin, without altering food intake or total adiposity. These results suggest that the decrease in endogenous melatonin with aging may alter metabolism and physical activity, resulting in increased BW, visceral adiposity, and associated detrimental metabolic consequences.

DAILY MELATONIN ADMINISTRATION AT MIDDLE AGE SUPPRESSES MALE RAT VISCERAL FAT, PLASMA LEPTIN, AND PLASMA INSULIN TO YOUTHFUL LEVELS

Human and rat pineal melatonin secretion decline with aging, wheras visceral fat and plasma insulin levels increase. Melatonin modulates fat metabolism in some mammalian species, so these aging-associated melatonin, fat and insulin changes could be functionally related. Accordingly, we investigated the effects of daily melatonin supplemntation to male Sprague Dawley rats, starting at middle age (10 months) and continuing into old age (22 months). Melatonin was added to the drinking water (92%) of which was consumed at night) at a dose (4μ g/ml) previously reported to attenuate the aging-associated decrease in survival rate in male rats, as well as a 10-fold lower doase. The higher dosage produced nocturnal plasma melatonin levels in middle-aged rats which were 15-fold higher than in young (4 months) rats; nocturnal plasma melatonin levels in middle-aged rats receiving the lower dosage were not significantly different from young or middle-aged controls. Relative (% of body wt) retroperitoneal and epididyma...

Short day lengths augment stress-induced leukocyte trafficking and stress-induced enhancement of skin immune function

Environmental conditions influence the onset and severity of infection and disease. Stressful conditions during winter may weaken immune function and further compromise survival by means of hypothermia, starvation, or shock. To test the hypothesis that animals may use photoperiod to anticipate the onset of seasonal stressors and adjust immune function, we evaluated glucocorticoids and the distribution of blood leukocytes in Siberian hamsters (Phodopus sungorus) exposed to long day lengths (i.e., summer) or short day (SD) lengths (i.e., winter) at baseline and during acute stress. We also investigated the influence of photoperiod and acute stress on a delayed-type hypersensitivity response in the skin. SDs increased glucocorticoid concentrations and the absolute number of circulating blood leukocytes, lymphocytes, T cells, and natural killer cells at baseline in hamsters. During stressful challenges, it appears beneficial for immune cells to exit the blood and move to primary immune defense areas such as the skin, in preparation for potential injury or infection. Acute (2 h) restraint stress induced trafficking of lymphocytes and monocytes out of the blood. This trafficking occurred more rapidly in SDs compared to long days. Baseline delayed-type hypersensitivity responses were enhanced during SDs; this effect was augmented by acute stress and likely reflected more rapid redistribution of leukocytes out of the blood and into the skin. These results suggest that photoperiod may provide a useful cue by which stressors in the environment may be anticipated to adjust the repertoire of available immune cells and increase survival likelihood.

Acute 60 Hz magnetic field exposure effects on the melatonin rhythm in the pineal gland and circulation of the adult Djungarian hamster

Yellon SM. Acute 60Hz magnetic field exposure effects on the nucleation rhythm in the pineal gland and circulation of the adult Djungarian hamster. J. Pineal Res. 1994; 16: 136–144.

Influence of photoperiod on immune cell functions in the male Siberian hamster

The present study tested the hypothesis that immune cell function is influenced by ambient photoperiod. The male Siberian hamster served as the experimental model because day length regulates a variety of seasonal adaptations in physiology. Adult hamsters were in long days (16 h of light daily), which sustains gonadal function, or transferred to short days (8 h) for >4 wk to induce testes regression. Blood was drawn from the ocular sinus or splenocytes obtained to assess basal indexes of immune cell function. In hamsters in short days, natural killer cell cytolytic capacity, as well as spontaneous blastogenesis in both whole blood and isolated lymphocytes, were enhanced compared with that in hamsters in long days. By contrast, phagocytosis and oxidative burst activity by both granulocytes and monocytes were suppressed in hamsters by exposure to short days versus long days. Selective changes in immune cell function coincided with short-day-induced gonadal atrophy. These findings raise the hypothesis that photoperiod regulation of physiological adaptations, including distinct immune cell functions, may help individuals anticipate seasonal challenges posed by opportunistic diseases or climate to facilitate survival.

The Role of Leukocyte Traffic and Activation in Parturition

Objective: This review focuses on the contribution of immune cell trafficking and activities during the initial phase of activation in the process of parturition. Although uterine contractile activity has been the predominant focus for the mechanism that initiates labor, significant cellular and biochemical chanes cause remodeling of the cervix well before term. A convergence of evidence suggests that inflammatory processes that involve prostaglandins, nitric oxide, cytokines, as well as systemic and paracrine endocrine mediators may enhance uterine contractility, promote ripening of the cervx, and thus constitute an integrative hypothesis for the initiation of labor. Methods: Techniques to study the uterus and cervix of pregnant and virgin C3H/HeN mice included light and fluorescence microscopy. Tissues were processed by histochemistry and immunofluorescence. Analytic approaches to enumerae macrophages and assess activation included quantitative stereologic morphometry and laser scanning cytometry. Results: The transition between relative quiescene of the uterus and enhanced contractility involed migration of macrophages from the uterine endometrium and activation of macrophages in the cervix. Before birth, macrophages migrae into the cervix and are activated in the myometrium. Conclusion: Immune cell trafficking and activation are part of the initial mechanism that promotes ripening of the cervix, enhances uterine contractility, and initiates parturition. Markers for the conclusion of pregnancy may have diagnostic or therapeutic value to assess the normal progress of labor or identify women at risk of preterm labor.

Aging-dependent changes in the effect of daily melatonin supplementation on rat metabolic and behavioral responses

Pineal melatonin secretion has been reported to commonly decrease with aging, whereas intra‐abdominal adiposity, plasma insulin and plasma leptin levels tend to increase. We recently demonstrated that daily melatonin administration starting at middle age suppressed male rat intra‐abdominal fat, plasma leptin and plasma insulin to youthful levels, suggesting that aging‐related changes in pineal melatonin secretion and in energy regulation may be functionally related. Accordingly, we have now investigated the effects of daily melatonin treatment on energy regulation in young versus middle‐aged male Sprague–Dawley rats. Addition of melatonin to the drinking water (0.2 μg/mL) produced nocturnal and diurnal plasma melatonin concentrations in middle‐aged rats (12 months) equivalent to those of young adult (5 months) rats. Administration of this melatonin dosage every day for 10 wk starting at 10 months of age suppressed (P<0.01) relative intra‐abdominal fat, non‐fasted plasma insulin and plasma leptin by 27, 39, and 51%, respectively (vs. vehicle‐treated controls). In contrast, administration of melatonin for 10 wk starting at 3 months of age did not significantly alter (P>0.10) any of these parameters. The melatonin administration stimulated (102%, P<0.001) behavioral responsiveness of the middle‐aged rats in a test of response to novelty, restoring youthful levels, but did not significantly alter behavioral responsiveness of the young rats. These results suggest that suppression of intra‐abdominal adiposity and plasma leptin and insulin levels and stimulation of behavioral responsiveness in response to daily exogenous melatonin begins at middle age, coincident with and likely dependent upon the aging‐associated decline in endogenous pineal melatonin secretion. These results further suggest that appropriate melatonin supplementation may potentially provide therapy or prophylaxis not only for the insulin resistance, increased intra‐abdominal fat and resulting pathologies that occur with aging, but also for some aging‐associated behavioral changes.

Medroxyprogesterone Acetate Modulates Remodeling, Immune Cell Census, and Nerve Fibers in the Cervix of a Mouse Model for Inflammation-induced Preterm Birth

To determine whether a progestational agent can modify inflammation-induced preterm cervical ripening, mice on day 15 of gestation were given an intrauterine injection of (1) saline, (2) lipopolysaccharide, (3) an intramuscular injection of medroxyprogesterone acetate alone prior to lipopolysaccharide, or (4) medroxyprogesterone acetate alone. Cervices were obtained 6 hours later, then fixed, sectioned, and processed to stain collagen structure or to identify immune cells or nerve fibers. Cervical remodeling was induced by lipopolysaccharide treatment compared with that in saline controls, an effect blocked by medroxyprogesterone acetate pretreatment. Moreover, lipopolysaccharide reduced macrophages and enhanced neutrophils in the cervix, effects also forestalled by medroxyprogesterone acetate pretreatment. Although the density of nerve fibers was not altered by lipopolysaccharide, medroxyprogesterone acetate reduced innervation in the cervix. Thus, progestational treatment forestalls the inflammation-induced reduction in collagen structure and immune cell traffic through a mechanism that is independent of nerve fiber density. These findings raise the possibility that progestational treatment may regulate ripening of the cervix early in the process leading to preterm birth.

DELAYED PUBERTY IN THE MALE DJUNGARIAN HAMSTER : EFFECT OF SHORT PHOTOPERIOD OR MELATONIN TREATMENT ON THE GNRH NEURONAL SYSTEM

The effect of short days or timed melatonin treatments on the number and neuroanatomical location of gonadotropin-releasing hormone (GnRH) neurons was studied in the brain of the pubertal male Djungarian hamster. At the beginning of the rapid phase of testicular growth and onset of peak gonadotropin secretion (15 days of age), males were treated for 10 days with either short days (10 L:14 D; n = 6), or remained in long days (16 L:8 D; n = 5) and injected each afternoon with melatonin. These treatments arrested testicular growth compared to the gonadal development that occurred in long-day controls (n = 9). Every brain section (60 microns) from the olfactory bulb to the anterior hypothalamus was processed for GnRH immunocytochemistry and viewed under brightfield light microscopy. GnRH cell bodies had smooth contours and were morphologically bipolar or unipolar. The number of bipolar neurons was similar regardless of treatment (about 170/brain). However, fewer unipolar GnRH cell bodies (p less than 0.05) were found in males in short days (73 +/- 11) or in males administered melatonin (72 +/- 14) compared to the unipolar number in hamsters in long days (132 +/- 14). With respect to neuroanatomical distribution, significantly fewer unipolar GnRH neurons were found in the medial preoptic area of males treated with short days or melatonin (55-70% decrease) compared to cell numbers in long-day controls. The melatonin-treated hamsters also had reduced numbers of unipolar GnRH neurons in the diagonal band of Broca relative to the number of unipolar neurons in long-day controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian myometrial and endocrine rhythms in the pregnant rhesus macaque: Effects of constant light and timed melatonin infusion

Six chronically catheterized rhesus macaques maintained on a 12-hour-light/dark cycle (lights on from 7 AM to 7 PM) showed a nocturnal uterine activity rhythm with peak contractile events between 9 and 11 PM (p less than 0.05). In blood samples collected at 3-hour intervals over a 24-hour period, we determined that plasma melatonin and progesterone concentrations were elevated at night whereas estradiol, estrone, and cortisol reached peak concentrations in the early morning (p less than 0.05). Lights were then left on for the remainder of the study. After 12 days in constant light, daily rhythms in uterine activity and plasma steroid levels were relatively unchanged, whereas melatonin concentrations were suppressed. Animals then received a timed infusion of melatonin (0.2 mg/kg/hr each day from 7 PM to 6 AM daily until delivery). The nocturnal uterine activity rhythm and the rhythms in plasma steroid concentrations were maintained. We conclude that the 24-hour patterns in maternal uterine activity and plasma steroid hormone levels are circadian rhythms generated by an endogenous biologic clock and do not appear to be driven by the pattern of melatonin in circulation.