Dietary supplementation of grape polyphenols to rats ameliorates chronic ethanol-induced changes in hepatic morphology without altering changes in hepatic lipids.

Increase in oxidative stress after chronic ethanol consumption can result in hepatic injury. Because polyphenolic compounds can offer antioxidant protection to the cardiovascular system, this study was designed to investigate whether dietary supplementation of polyphenols from grapes may ameliorate hepatic injury resulting from chronic ethanol consumption. Male Sprague-Dawley rats were administered the following diets for 2 mo: 1) Lieber-DeCarli (L-D) diet with isocaloric amount of maltose instead of ethanol (Basal), 2) the L-D diet with 50g/L ethanol (EtOH); 3) L-D diet with 50 mg/L of grape polyphenols (GP) and 4) ethanol diet with GP (EtOH + GP). Rats given EtOH or EtOH + GP diets had significantly more hepatic triacylglycerols (P < 0.0001) and lipid peroxidation products (P < 0.01) compared with those given the Basal and GP diets. In addition, ethanol ingestion also decreased significantly (P < 0.01) the proportion of 16:0 and increased 18:0 and 18:1 in hepatic phospholipids, suggesting a perturbation of the de novo fatty acid biosynthesis pathways. However, GP supplementation alone and GP added to the ethanol diet did not alter the lipid changes mediated by ethanol except for the levels of 22:6(n-3) which were significantly (P < 0.05) higher in the EtOH + GP group than in the EtOH group. Despite a lack of gross lipid changes, histologic assessment showed significantly (P < 0.05) less hepatic damage in the GP + EtOH group compared with the EtOH group. These results clearly distinguished ethanol-mediated changes in hepatic morphology from the changes in hepatic lipids and further demonstrated the ability of GP to ameliorate hepatic damage resulting from chronic ethanol consumption.

Chronic ethanol treatment reduces the responsiveness of the hypothalamic-pituitary-thyroid axis to central stimulation.

The hypothalamic-pituitary-thyroid (HPT) axis functions abnormally in man and animals chronically exposed to ethanol. The most consistent observation in humans is that the thyrotropin response to thyrotropin-releasing hormone (TRH) is blunted. We have tested the hypothesis that chronic ethanol treatment in rats leads to a diminished responsiveness of the hypothalamus to central stimulation. Animals were maintained on 1 of 3 diets for 4 weeks: (1) laboratory chow and water provided ad libitum (chow-fed), (2) Sustacal chocolate liquid diet with vitamin mixture containing 5% (w/v) ethanol provided ad libitum (ethanol), or (3) Sustacal chocolate liquid diet with vitamin mixture containing sucrose substituted isocalorically (35%) for ethanol and provided in amounts matched to a weight-paired, ethanol-treated animal (pair-fed). At the end of 4 weeks, the animals were evaluated for their response to a single injection of ethanol (3 g/kg, ip) and/or exposure to 5 degrees C. Chronic ethanol treatment produced an increase in TRH mRNA in neurons of the paraventricular nucleus and fully blocked the thyrotropic response to cold exposure. However, chronic ethanol-treated animals did not exhibit altered basal levels of triiodothyronine or thyrotropin, nor did they have an altered response to a single injection of ethanol. These data demonstrate that chronic alcohol exposure alters functioning of the hypothalamic-pituitary-thyroid axis at least in part by affecting TRH neurons of the paraventricular nucleus.

Aberrant hormone balance in fetal autoimmune NZB/W mice following prenatal exposure to testosterone excess or the androgen blocker flutamide.

F1 hybrid New Zealand Black (NZB) x New Zealand White (NZW) (NZB/W) mice are hormone-sensitive models of the human disease systemic lupus erythematosus. In this study, NZB/W fetuses produced by pregnant NZB mice were compared with F1 C57BL/6 x DBA/2 (C57/DBA2) hybrid fetuses produced by nonautoimmune C57BL/6 females. Dams of both strains were treated with testosterone or the androgen blocker flutamide to alter the hormonal environment in late gestation. Hormonal changes in male fetuses carried by treated dams were of interest because hormonal manipulation using either testosterone or flutamide has been shown to increase longevity in male NZB/W offspring. Testosterone-implanted NZB dams developed the expected elevations in circulating maternal testosterone, whereas C57BL/6 dams treated with either testosterone or flutamide had elevated maternal serum testosterone concentrations. The treatment-induced changes in circulating testosterone in NZB dams and C57BL/6 dams were not reflected in serum from 18-day NZB/W or C57/DBA2 fetuses. Male NZB/W offspring from untreated control NZB dams had unexpectedly high levels of serum estradiol and alpha fetoprotein and relatively low extractable testicular testosterone, compared with nonautoimmune male control fetuses. Maternal testosterone treatments produced a significant decrease in serum estradiol in NZB/W male fetuses, and placental testosterone content was also reduced. Our findings suggest that placental androgen control is regulated differently in the autoimmune NZB-NZB/W vs. the nonautoimmune C57BL/6-C57/DBA2 maternal-placental-fetal unit.

Acute prenatal ethanol exposure and luteinizing hormone-releasing hormone messenger RNA expression in the fetal mouse brain.

Ethanol exposure during critical periods of development results in alterations of central nervous system morphology and function. In this study, the effects of acute ethanol exposure on the number of neurons expressing luteinizing hormone-releasing hormone (LHRH) messenger RNA (mRNA) has been analyzed. Also, the expression of LHRH mRNA in the diagonal band of Broca/preoptic area (DBB/POA) was determined. Pregnant C57BL/6J mice were intubated with two doses of a 25% solution of ethanol or water (2.9 g/kg body weight) 4 hr apart on gestation day 7 (G7), G10, or G11. Animals were killed on G18, and in situ hybridization was utilized to detect neurons expressing LHRH mRNA. The number of neurons expressing LHRH mRNA was determined along their migration route from the rostrum into the forebrain. Ethanol exposure on G7 did not significantly change the number of neurons expressing LHRH mRNA on G18 compared with that in control animals. However, the number of neurons expressing LHRH mRNA in the nasal septum area in animals exposed to ethanol on G10 or G11 was significantly less than the number in control animals (p < 0.05). Prenatal ethanol exposure on any of the aforementioned treatment days did not alter the expression of LHRH mRNA at the level of the DBB/POA on G18 in ethanol-treated animals compared with control animals. Also, neuron-specific enolase mRNA expression at the level of the DBB/POA was not altered by prenatal ethanol exposure. Therefore, ethanol exposure on the aforementioned treatment days did not differentially affect LHRH mRNA expression compared with neuron-specific enolase mRNA expression at the level of the DBB/POA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute ethanol administration and cold exposure on the hypothalamic-pituitary-thyroid axis.

A single dose of ethanol increases cellular levels of the mRNA encoding thyrotropin-releasing hormone (TRH) in neurons of the paraventricular nucleus (PVN), but blocks the cold-induced increase in the levels of this mRNA. Because the thyrotropic response to cold is dependent upon TRH secretion, we hypothesized that ethanol uncouples the stimulus-induced regulation of TRH secretion from the stimulus-induced regulation of TRH expression. We employed two complementary strategies to test this hypothesis. The first was to determine whether ethanol alters pituitary sensitivity to TRH. Animals given a single intraperitoneal injection of ethanol (3 g/kg) that produced a blood alcohol concentration of nearly 300 mg/100 mL exhibited the same increase in circulating levels of TSH following an intravenous infusion of TRH. Thus, ethanol does not appear to alter pituitary sensitivity to TRH. Second, we tested whether ethanol blocks the cold induction of c-fos expression in TRH neurons of the PVN. Both cold exposure and ethanol induced the expression of c-fos in the PVN and in TRH neurons; the effects of cold and ethanol on c-fos expression were additive. Thus, ethanol clearly does not block the cold activation of TRH neurons.

Prenatal ethanol exposure: changes in regional brain catecholamine content following stress.

Previous studies have shown that fetal ethanol exposure (FEE) may have long-term effects on the function of catecholaminergic neurons in different regions of the CNS. The present study is the first to examine the effects of FEE on regional brain catecholamine responses following acute stress (a single 60-min restraint stress), repeated stress (single periods of restraint stress on 1, 5, or 10 consecutive days), and recovery from stress (recovery for up to 60 min in the home cage following a single 60-min period of restraint stress). Both male and female offspring from FEE, pair-fed (PF), and ad libitum-fed control (C) groups were tested in adulthood to determine catecholamine content in the cortex, hypothalamus, and hippocampus. A single period of restraint reduced cortical norepinephrine (NE) content in FEE and PF animals compared with that in the cortex of C animals, and reduced hypothalamic NE content in FEE female offspring below that found in animals in all other groups. In contrast, hippocampal NE content was higher in FEE than in C animals following a single period of restraint; PF animals had intermediate levels of hippocampal NE and did not differ significantly from either FEE or C animals. Following repeated periods of restraint, cortical NE content was lower in FEE than in C animals; PF animals once again had intermediate levels of NE. Importantly, basal (nonstressed) NE content did not differ among groups in any brain area examined. In addition, several significant changes in regional brain catecholaminergic responses to acute stress were observed in animals across all treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol blocks the cold-induced increase in thyrotropin-releasing hormone mRNA in paraventricular nuclei but not the cold-induced increase in thyrotropin.

The effects of a single intraperitoneal injection of ethanol (3 g/kg b.wt.) on the hypothalamic-pituitary-thyroid system was explored as a possible explanation of the hypothermic effect of ethanol. Serum thyroid hormones were significantly reduced by ethanol injection, but ethanol did not affect the cold-induced increase in serum thyroid hormones or thyroid-stimulating hormone (TSH). Since cold-exposure stimulates serum levels of TSH and thyroid hormones by stimulating thyroid-releasing hormone (TRH) release from neurons of the PVN, these findings demonstrate that ethanol did not block pituitary response to TRH or thyroid response to TSH. Paradoxically, ethanol increased cellular levels of TRH mRNA in the paraventricular nucleus (PVN), and blocked the cold-induced increase in TRH mRNA, suggesting that ethanol uncouples the regulation of TRH gene expression from the regulation of TRH release specifically in neurons of the PVN. Measurements of the effects of ethanol on TRH mRNA in thalamus, and beta-actin, vasopressin, somatostatin and corticotropin-releasing hormone (CRH) mRNAs in the PVN in addition to TRH mRNA revealed very specific effects of ethanol on the TRH neuronal system.

Effects of in utero ethanol exposure on the development of LHRH neurons in the mouse.

Prenatal ethanol exposure has been shown to result in craniofacial malformations as well as alterations of central nervous system morphology and function. Previous studies have demonstrated that acute ethanol exposure on gestational day 7 in the developing C57BL/6J mouse resulted in craniofacial abnormalities similar to that of children with fetal alcohol syndrome. We investigated the effect of ethanol on the migration and number of immunoreactive LHRH (irLHRH) neurons in this strain of mouse. Pregnant mice were intubated with 2 doses of a 25% solution of ethanol 4 h apart on gestational day 7 (G7). Control animals were intubated with water. Animals were sacrificed on G14 or G18 and immunocytochemistry was used to identify irLHRH neurons that were visualized by light microscopy. Fetal ethanol administration did not substantially affect the migration of the LHRH neurons from the medial nasal placode into the forebrain on G14 or G18. The total number of irLHRH neurons was not significantly different on G14 in ethanol-exposed animals as compared to the number in control animals. However, the total number of irLHRH neurons on G18 was significantly less (P less than 0.03) in 4 neuroanatomical regions in fetal ethanol-exposed mice compared to those in control mice; the nasal septum, the traverse area superior to the cribriform plate and ventromedial to the olfactory bulbs, the arch area which included the olfactory tubercle, medial septal nuclei and anterior hypothalamus in G18 fetuses, and preoptic area of the brain. Coronal investigation of the number of irLHRH neurons on G18 indicates that the loss of irLHRH neurons occurred predominantly in the medial region of the rostrum and brain.

Fetal alcohol exposure and effects of LHRH and PMA on LH beta-mRNA expression in the female rat.

Fetal alcohol exposure (FAE) is associated with a variety of physiological and behavioral dysfunctions. Effects of FAE on reproduction have been described that include delayed puberty, altered gonadotrophin secretion and steroidogenesis, and altered sexual behavior. Earlier work suggested that pituitary function was compromised in adult fetal alcohol-exposed female rats. This study examined the effects of LHRH and PMA in vitro on LH beta-mRNA expression in pituitary fragments from FAE animals; a separate experiment examined the effects of estradiol-17 beta on LH beta-mRNA under similar conditions. The results indicate that the pituitary glands of FAE females have a reduced ability to respond to these three stimuli. The reason for this reduced responsiveness to LHRH, PMA, and estradiol-17 beta is not clear, but the alterations suggest that LH synthesis is impeded following fetal ethanol exposure.

Effect of testosterone replacement on the alteration of steroid metabolism in the hypothalamic-preoptic area of male hamsters treated with melatonin.

Adult male hamsters were maintained under 14 hours of light per day and randomly assigned to groups that received daily afternoon melatonin (25 micrograms) or vehicle injections. Animals from both groups were killed following 4, 8, and 12 weeks of treatment. By 12 weeks, the melatonin-treated hamsters had significant reductions in the weights of the testes and seminal vesicles, serum testosterone levels, and activities did not differ between groups. In a second experiment, hamsters were hypothalamic-preoptic area (HPOA) aromatase activities. Hypothalamic-preoptic area 5 alpha-reductase activities did not differ between groups. In a second experiment, hamsters were again treated with melatonin or vehicle for 12 weeks prior to being killed. After 10 weeks of treatment, groups of melatonin-treated animals received subcutaneous silastic capsules (5, 10, or 20 mm) filled with testosterone. Animals in two other groups were given blank implants or no implants at all. Two weeks later, at autopsy, reproductive organ weights, serum testosterone levels, and HPOA aromatase activities were significantly suppressed by melatonin administration. 5 alpha-Reductase activity in the HPOA was not affected. Hamsters that had been given the 10- and 20-mm testosterone implants exhibited normal seminal vesicle weights and HPOA aromatase activities. These results suggest that melatonin-induced reduction of HPOA aromatase activity is mediated by decreased circulating levels of testosterone.

Prenatal ethanol exposure and opiatergic influence on puberty in the female rat.

Fetal alcohol exposure (FAE) is associated with a variety of physiological and behavioral dysfunctions, including deficits to reproductive function. FAE has also been shown to increase brain beta-endorphin levels. This study sought to determine whether the common delay of the onset of puberty in fetal alcohol-exposed animals could be due to increased opiate inhibition of LH release. Prepubertal female rats were injected with an opiate antagonist, naltrexone, over days 26-29. This naltrexone treatment led to an acceleration of vaginal opening and first estrus in FAE animals; had no effect on chow-fed or pair-fed controls. The vaginal opening and first estrus advancement in FAE animals occurred at a lower body weight indicating independence from growth-promoting effects of the drug treatment. It is concluded that delays in puberty in FAE animals are not directly due to pituitary pathology, but are related, at least in part, to increased inhibition of the LHRH neuron and functional impairment of gonadotrophin secretion.

Reduced sensitivity of hypothalamic-preoptic area norepinephrine and dopamine to testosterone feedback in adult fetal ethanol-exposed male rats.

Endocrine feedback of testosterone (T) in regulation of the hypothalamus is via the effects of T on the noradrenergic system. The current experiment was performed to determine the effects of fetal ethanol exposure (FEE) on the norepinephrine (NE) and dopamine (DA) content in the hypothalamic-preoptic area (HPOA) of adult male rats, and the response of NE and DA to T administration. Pregnant rats were exposed to diets containing either a liquid diet containing ethanol, a liquid diet containing sucrose isocalorically substituted for ethanol, or a chow and water diet. Male offspring were castrated or sham-operated at 45 days of age. The animals received either testosterone propionate (TP) or an oil vehicle. HPOA was collected at 55 days of age from each animal and NE and DA content was measured by HPLC-EC. There was no significant alteration of NE or DA content in the HPOA in FEE animals compared to catecholamine levels in animals derived from dams on the control diets. Castration had no significant effect on NE and DA content in the chow-fed or pair-fed animals. TP administration significantly reduced NE content only in the chow- and pair-fed animals but not in the FEE animals. DA content in the HPOA was not affected by castration, but TP administration also resulted in significantly reducing DA content in chow- and pair-fed castrate male rats but not in FEE castrate male rats. The results indicate that FEE alters the response of the noradrenergic and dopaminergic neurons in the HPOA to T administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroanatomic and neurochemical abnormalities in nonhuman primate infants exposed to weekly doses of ethanol during gestation.

Ethanol was orally administered once per week to 54 gravid pigtailed macaques (Macaca nemestrina) in doses of 0.0, 0.3, 0.6, 1.2, 1.8, 2.5 or 4.1 gm/kg from the 1st week in gestation or in doses of 2.5, 3.3 or 4.1 gm/kg from the 5th week. Mean maternal peak plasma ethanol concentrations (MPPEC's) ranged from 24 +/- 6 mg/dl at the 0.3 g/kg dose to 549 +/- 71 mg/dl at the 4.1 g/kg dose. Thirty-three live born infants were assessed for abnormalities of physical and behavioral development. Ocular pathology, neuropathologic and neurochemical assessements were done on 31 animals at 6 months postnatal age. Microphthalmia was noted in three of the 26 animals exposed to ethanol. Retinal ganglion cell loss was significantly associated with intra-uterine ethanol exposure. Microphthalmia and retinal ganglion cell loss was observed in both the delayed and full-gestational exposed animals. No structural anomalies were found in the brains via gross inspection or light microscopy. Chemical abnormalities in the striatal nuclei were identified. Striatal dopamine concentrations increased with increasing MPPEC exposure (0-249 mg/dl) among animals exposed weekly to ethanol throughout gestation. Striatal dopamine concentrations decreased with increasing MPPEC exposure (260-540 mg/dl) among animals whose weekly exposure to ethanol was delayed until the 5th week of gestation. The same pattern of association was also noted between MPPEC and ultrastructural alterations in the caudate nucleus. The extent of ultrastructural alterations increased with increasing MPPEC among the full-gestational exposed animals and decreased with increasing MPPEC among the delayed-dose animals.

Inhibition of testicular steroidogenesis in the neonatal rat following acute ethanol exposure.

We have previously reported detrimental effects of in utero ethanol exposure on testicular steroidogenic enzyme activity in newborn rats. It is now reported that in utero ethanol exposure during Day 12 of gestation through birth has no apparent morphological effect on the testes of Day 1 neonatal rats. It appears that the detrimental effects of ethanol on testicular steroidogenesis can be manifested at the biochemical level in the absence of morphological effects. However, it remained unknown as to whether acute exposure to ethanol would elicit similar biochemical effects as chronic ethanol exposure on testicular steroidogenesis. To test this possibility ethanol was injected at 0, 1, or 2 g/kg intraperitoneally (IP) into rats of various postnatal ages. Plasma ethanol and testosterone levels as well as testicular 17 alpha-hydroxylase and C17,20-lyase activities were measured. The results indicate that acute exposure to ethanol significantly (p less than 0.05) inhibits the catalytic activity of testicular 17 alpha-hydroxylase in the newborn rat testis. This inhibition was specific since the activity of testicular C17,20-lyase was not affected. In conjunction with the reduction in testicular enzyme activity, plasma testosterone levels were reduced to 30% of the control levels in newborn animals receiving ethanol. In older animals, i.e., postnatal Day 20 and 40 rats, plasma testosterone levels were reduced, but not significantly, following ethanol treatment. Furthermore, testicular enzyme activity was not significantly reduced following ethanol treatment in these same older animals. These results suggest that the newborn rat testis is especially sensitive to the effects of ethanol.

Ontogeny of light-induced decrease of N-acetyltransferase activity in explanted chick pineal glands.

The ontogeny of chick pineal serotonin N-acetyltransferase (NAT) activity was investigated in explanted chick pineal glands at 4, 10 and 21 d of age. Nocturnal levels of the enzyme and the response of the enzyme to light exposure were determined in pineal glands maintained in short-term culture at each age. The results indicate that nocturnal NAT activity was increased in the glands from older birds. Nocturnal levels of NAT activity at the time of the initiation of the experiment were threefold greater in glands from 21-d-old birds as compared to that in glands from 4-day-old chicks. The response to light was similar in all three ages examined; light induced a significant decrease in NAT activity within 60 min in explanted glands from 4-d-old chicks and within 180 min in the glands from the 10- and 21-d-old chicks. A paradoxical transient increase in enzyme activity occurred immediately (within 5 min) following light exposure which was significant in the glands from the youngest chicks, and present, but more variable, in the older chicks. These data indicate that the nocturnal enzyme activity is greater in glands from older birds, but that light exposure of explanted glands initiates a transient rise followed by a decrease in NAT activity at all three ages.

Effects of fetal alcohol exposure on brain 5 alpha-reductase/aromatase activity.

The local formation of the testosterone metabolites 5 alpha-dihydrotestosterone and 17 beta-estradiol within the hypothalamic-preoptic area (HPOA) is essential for the normal sexual differentiation of the male central nervous system (CNS) during a perinatal critical period in the rat. Testosterone, the substrate for these reactions, is derived primarily from synthesis within the fetal testis. Fetal alcohol exposure (FAE) during this critical period profoundly affects fetal testicular steroidogenesis as well as the sexual differentiation of the CNS. The present study was conducted to determine whether FAE directly affects the local metabolism of androgens within the developing CNS or whether reduced androgen substrate, via a testicular lesion, is a more likely explanation for the known effects of FAE on the CNS. The enzymatic activities of 5 alpha-reductase and aromatase were simultaneously quantitated in the newborn rat HPOA following FAE. Neither the enzymatic activity of 5 alpha-reductase, aromatase nor their ratio were significantly influenced (P greater than 0.05) by FAE with respect to controls. FAE apparently does not alter the disposition of the androgens within the newborn rat HPOA. These results support the hypothesis that FAE alters the sexual differentiation of the CNS through inhibition of androgen biosynthesis at the level of the perinatal rat testis.

Effects of light and an alpha-2-adrenergic agonist on serotonin N-acetyltransferase activity in chick pineal gland.

Pineal serotonin N-acetyltransferase (NAT) is the enzyme that catalyzes the production of N-acetylserotonin from serotonin and is the rate limiting step in the biosynthesis of melatonin in the chick pineal gland. Chick pineal NAT activity is decreased by light and by noradrenergic agents that act at the alpha-2-adrenergic receptor. Light-induced inhibition of nocturnal NAT activity can be demonstrated by exposing 4-day-old chicks to light, or by exposing pineal gland explants cultured in vitro either to light or to UK 14,304 (an alpha-2-adrenergic agonist). The inhibition by either light or UK 14,304 is preceded by a transient, but consistent rise in NAT activity. The paradoxical, transient light-induced rise in enzyme activity is mimicked by UK 14,304 which suggests a similarity in mechanisms of light and adrenergic signal transduction associated with the regulation of NAT activity.

Prenatal ethanol exposure alters steroidogenic enzyme activity in newborn rat testes.

We have examined the in utero effects of ethanol exposure on testicular steroidogenesis in newborn male pups. Pregnant Sprague-Dawley rats were fed a liquid ethanol diet (35% ethanol-derived calories), a pair-fed isocaloric liquid diet, or a standard laboratory rat chow and water diet beginning on Day 12 of gestation and continuing through parturition. Although there were no significant differences in the enzymatic activity of 5-ene-3 beta-hydroxysteroid dehydrogenase/isomerase or C17,20-lyase, the enzymatic activity of 17 alpha-hydroxylase was significantly (p less than 0.01) reduced (i.e., approximately 36%) in the ethanol-exposed pups compared to those from the pair-fed and chow treatment groups. This lesion in testicular steroidogenic enzyme activity in newborn male pups exposed to alcohol in utero was transient as 17 alpha-hydroxylase activity from the ethanol-exposed animals returned to control levels by postnatal Day 20 and remained at control levels through adulthood (postnatal Day 60). These data suggest that the suppression of the perinatal testosterone surge in male rats exposed to alcohol in utero and the associated long term demasculinizing effects of prenatal ethanol exposure might be the result of reduced testicular steroidogenic enzyme activity in the perinatal animal.

Effects of melatonin and thyroxine treatment on reproductive organs and thyroid hormone levels in male hamsters.

The effects of exogenous thyroid hormone administration on melatonin-induced gonadal atrophy were studied in young adult male hamsters. Animals were given daily afternoon injections of 25 micrograms melatonin and/or thrice-weekly injections of 7 micrograms thyroxine. A control group received injections of saline vehicle only. No significant effect of either treatment was seen on body weight. Melatonin-treated animals had significantly reduced testicular and seminal vesicle weights, compared with vehicle-treated control animals: serum T4 levels and the FT4I were reduced by melatonin treatment, but serum T3 and the FT3I were increased. No effect of melatonin was seen on in vitro T3 uptake. Thyroxine treatment alone, while leading to elevated serum T4 levels and FT4I, had no effect on T3, the FT3I, or T3 uptake. Thyroxine treatment normalized circulating T4 levels and the FT4I in melatonin-treated animals, without preventing the melatonin-induced testicular regression. The results are taken as evidence that the inhibitory effects of melatonin on gonadal and thyroid function are independently mediated.

Effects of daily afternoon melatonin administration on body weight and thyroid hormones in female hamsters.

Female hamsters were treated each afternoon for 8 weeks with subcutaneous injections of 25 micrograms of either melatonin or vehicle solution. Animals were sacrificed in either the morning or afternoon of diestrus and proestrus, along with their respective melatonin-induced acyclic pairs. Melatonin-treated hamsters had significantly greater mean body weights than did the vehicle-treated hamsters (P less than 0.05). Terminal mean serum T4 levels and free thyroxine index (FT41) were significantly reduced (P less than 0.05) in melatonin-treated hamsters compared with values obtained from animals subjected to the vehicle alone. In addition, T4 levels, FT41, T3 levels, and FT31 were significantly influenced by day and time of sacrifice independently of the melatonin treatment. T3 uptake was significantly lower on the morning of proestrus in melatonin-treated animals. These results demonstrate that chronic afternoon melatonin administration in female hamsters results in the loss of estrous cyclicity, a significant gain in body weight, and the reduction of T4 levels and T3 uptake. Changes in serum T3 levels are a function of the time of sample collection and are not influenced by melatonin treatment. In addition, these data indicate that thyroid function in general changes during the estrous cycle in these animals.