Optimal timing of exercise for influencing energy intake in children during school lunch.

INTRODUCTION: Laboratory studies have shown that exercise can reduce energy intake, with a benefit to moderate-to-vigorous physical activity (MVPA) in individuals. The aim of the current study was to identify the impact of MVPA before lunch on ad libitum energy intake in very young children in a natural setting. METHODS: Three conditions were tested on three occasions, each using a counterbalance testing sequence as follows: A) Meal_MVPA: Meal at the beginning of the lunch period followed by a 40-min MVPA (reference condition); B) LPA_meal: 40 min of light intensity exercise session followed by lunch; C) MVPA_meal: MVPA followed by lunch. Children were instructed to eat their ad libitum lunch box (7-9 items) to reach 4/5 on the satiety visual analogue scale. RESULTS: 21 participants [8 boys and 13 girls; 80% normal weight; mean age: 5.6 (standard deviation: 0.5) years] participated in the study. Energy intake was significantly greater in the LPA_Meal condition [509 kcal (95% confidence interval: 448-570)] than in Meal_MVPA [442 kcal (380-504)] (p = 0.011) and MVPA_Meal [432 kcal (371-494)] (p < 0.001) conditions (p < 0.05). The energy from lipids was significantly greater in the LPA_Meal [154 kcal (130-177)] than in Meal_MVPA conditions [120 kcal (97-144)] (p = 0.016). CONCLUSION: The current study may indicate that it is possible for young school children to benefit from anorexigenic exercise in real-life settings. In addition, it was possible to delay mealtime without increasing energy intake when MVPA was provided during the delay period. Finally, the introduction of MVPA prevented an increase in lipid consumption observed for LPA.

Participation of serotonin in the phasic release of LH. I. Evidence from pharmacological experiments.

Subcutaneous implantation of a silastic tubing containing crystalline estradiol in castrated female rats results in a circadian rhythm of LH release. Under such conditions, blockade of serotonin (5-HT) biosynthesis by p-chlorophenylalanine (PCPA) completely inhibits the afternoon elevation of plasma LH. Gonadotropin peaks remain inhibited as long as the concentration of the transmitter is effectively depleted. Intraperitoneal administration or intraventricular infusion of minute doses of the immediate precursor of the amine, 5-hydroxytryptophan (5-HTP), results in the reappearance of the next afternoon rise of plasma gonadotropin, whenever hypothalamic levels of 5-hydroxyindole acetic acid (5-HIAA), the main metabolite of 5-HT, are significantly increased over their value in PGPA-treated animals. The administration of methiothepin, a 5-HT receptor blocker, 9 hours of more prior to the next expected LH rise, similarly inhibits the cycle, whereas a dopamine receptor inhibitor has no effect under the same time conditions. We have concluded that serotoninergic neuron systems can have a positive, permissive effect on the transfer of neural information resulting in phasic gonadotropin release; this action of the amine is different from, but not contradictory to, the known inhibitory effect of 5-HT on the release of LHRH from the median eminence.

Participation of serotonin in the phasic release of luteinizing hormone. II. Effects of lesions of serotonin-containing pathways in the central nervous system.

Circadian LH variations were measured in castrated, estradiol-implanted female rats bearing lesions of the raphe nuclei, in which most serotonin (5-HT) containing ascending projections originate, or mediopontine transections interrupting such projections before they enter the hypothalamus. Previous data indicated that pharmacological blockade of 5-HT biosynthesis abolishes the rhythmic pattern of LH secretion; the present study was intended to check whether surgical depletion of hypothalamic 5-HT had a similar effect and whether such abolition could be correlated with hypothalamic or forebrain endogenous concentrations of the amine and of its metabolite, 5-hydroxyindoleacetic acid (5-HIAA). Maximal inhibition of hypothalamic 5-HT and 5-HIAA concentrations were obtained after complete basal mediopontine transections and after lesions of the medial and the dorsal raphe nuclei; under these conditions, the daily variations in plasma LH were reduced by more than 70%. Smaller lesions, even when they completely destroyed the medial raphe, were much less effective. A good correlation was observed between the amplitude of the LH cycle and the extent of hypothalamic, but not of forebrain, 5-HT and 5-HIAA depletion. However, and in contrast to the results of pharmacological 5-HT inhibition, the cyclic pattern of LH secretion could not be totally abolished by any of these surgical procedures. It is concluded that the dorsal raphe contributes to the regulation of rhythmic LH secretion in castrated female rats bearing estradiol implants by modulating the amplitude of this circadian cycle rather than by generating the rhythmic pattern itself.

Variations of phospholipid methyltransferase(s) activity in the rat pituitary: estrous cycle and sex differences.

We previously demonstrated a specific stimulatory action of estrogens on phosphatidylethanolamine methylation in rat pituitary membranes. To investigate the physiological relevancy of this effect, the activity of methylating enzyme(s) was evaluated during the rat estrous cycle, a period in which both endogenous ovarian steroid levels and the sensitivity of pituitary membrane receptors fluctuate. Anterior pituitary membranes (P2) were prepared from adult female rats at different stages of the estrous cycle and assayed for phospholipid methylation in the presence of S-adenosyl-[methyl-3H]methionine as a donor of 3H-methyl groups. Methylated phospholipids were separated by TLC. Formation of phosphatidyl-mono- and dimethylethanolamine and that of phosphatidylcholine increased significantly in the morning, reaching maximal values on the afternoon of proestrus; they decreased thereafter during estrus, metestrus, and diestrus. Plasma estradiol concentrations increased in late diestrus and then varied similarly with the fluctuations of phospholipid methyltransferase activity throughout the cycle. In parallel, plasma levels of LH and PRL were significantly elevated during the afternoon of proestrus, but remained low throughout the rest of the cycle. Under the same experimental conditions, phospholipid methylation in membranes prepared from mediobasal-hypothalamic structures was not affected. These data demonstrate that under physiological conditions the increased pituitary methyltransferase activity is associated with the progressive increment of plasma estradiol levels occurring shortly before proestrus and precedes the release of LH and PRL. Ovariectomy significantly decreased methyltransferase activity; however, 17 beta-estradiol treatment of ovariectomized rats for 5 days restored the enzyme activity, which was further augmented after progesterone administration. Attempting to investigate variations of pituitary methyltransferase activity in male rats, we demonstrated that the intact males showed weaker activity than that of females; orchidectomy diminished the phospholipid methylation, but adrenalectomy had no effect.

Alpha 1-adrenergic receptor coupling with phospholipase-C is negatively regulated by protein kinase-C in primary cultures of hypothalamic neurons and glial cells.

In the present work we evaluated the interactions of adrenergic receptors with phospholipase-C (PLC) and protein kinase-C (PKC), using an in vitro system of hypothalamic neurons and astroglial cells in primary cultures. The study was performed on immature neurons after 7 days in vitro (7 Div), that is before synaptogenesis, as well as on mature cells (14 Div). Comparisons were made between neurons and glial cells at the corresponding developmental stages. Norepinephrine (NE) increased inositol phosphates (IPs) formation in a dose- and time-dependent manner. The NE effect was mediated by alpha 1-receptor (alpha 1R) and was observed in young cells before synaptogenesis as well as in mature neuronal cultures; its amplitude was enhanced during the latter stage of the neuronal development. The coupling of alpha 1R with PLC was partially sensitive to pertussis toxin treatment and did not implicate the activation of calcium voltage-dependent channels. Activation of PKC by 12-O-Tetradecanoylphorbol 13-acetate (TPA) inhibited in a time-dependent manner the NE-stimulated production of IPs in young and mature hypothalamic neurons; however, in PKC depleted cells NE-induced IPs formation remained unchanged. In hypothalamic astroglial cell cultures the adrenergic stimulus of IPs generation was also mediated by alpha 1R. The effect was observed at both developmental stages, with a greater response in 14 Div cultures, and was insensitive to pertussis toxin treatment. As in neurons, activation of PKC resulted in inhibition of NE-induced IPs formation. These data indicate that functional interrelation between alpha 1R, PLC, and PKC is already present in immature neurons and glial cells and progressively develops in culture.

Dihydropyridine-sensitive calcium channel activity related to prolactin, growth hormone, and luteinizing hormone release from anterior pituitary cells in culture: interactions with somatostatin, dopamine, and estrogens.

In the present work, we determined the activity of voltage-dependent dihydropyridine (DHP)-sensitive Ca2+ channels related to PRL, GH, and LH secretion in primary cultures of pituitary cells from male or female rats. We investigated their modulation by 17 beta-estradiol (E2) and their involvement in dopamine (DA) and somatostatin (SRIF) inhibition of PRL and GH release. BAY-K-8644 (BAYK), a DHP agonist which increases the opening time of already activated channels, stimulated PRL and GH secretion in a dose-dependent manner. The effect was more pronounced on PRL than on GH release. BAYK-evoked hormone secretion was further amplified by simultaneous application of K+ (30 or 56 mM) to the cell cultures; in parallel, BAYK-induced 45Ca uptake by the cells was potentiated in the presence of depolarizing stimuli. In contrast, BAYK was unable to stimulate LH secretion from male pituitary cells, but it potentiated LHRH- as well as K+-induced LH release; it had only a weak effect on LH secretion from female cell cultures. Basal and BAYK-induced pituitary hormone release were blocked by the Ca2+ channel antagonist nitrendipine. Under no condition did BAYK affect the hydrolysis of phosphoinositides or cAMP formation. Pretreatment of female pituitary cell cultures with E2 (10(-9) M) for 72 h enhanced LH and PRL responses to BAYK, but was ineffective on GH secretion. DA (10(-7) M) inhibited basal and BAYK-induced PRL release from male or female pituitary cells treated or not treated with E2 (10(-9) M). SRIF (10(-9) and 10(-8) M) reversed BAYK-evoked GH release to the same extent in cell cultures derived from male or female animals. It was ineffective on BAYK-induced PRL secretion in the absence of E2, but antagonized it after E2 pretreatment. The effect was dependent upon the time of steroid treatment and was specific, since 17 alpha-estradiol was inactive. In addition, DA and SRIF decreased the 45Ca uptake induced by the calcium agonist. These data demonstrate that DHP-sensitive voltage-dependent calcium channels of the L type present on different pituitary cells are not equally susceptible to BAYK activation under steady state basal conditions, indicating that their spontaneous activity and/or distribution vary according to the cell type; their activity is modulated by sex steroids. In addition, these data suggest that Ca2+ channels represent a possible site of DA and SRIF inhibition of PRL and GH release, respectively, by gating calcium entry into the corresponding cells.

Estradiol modulates protein kinase C activity in the rat pituitary in vivo and in vitro.

17 beta-Estradiol (E2) alters different functions of pituitary cells, including cell sensitivity to several neurohormones such as LHRH, TRH, somatostatin, or dopamine, presumably by affecting receptor coupling mechanisms. Attempting to pinpoint the membrane processes underlying this modulation, we studied the effect of E2 on pituitary kinase-C (PKC) activity, a major signal transduction enzyme. The distribution of calcium- and phospholipid-dependent partially purified PKC (chromatography on DEAE-52 cellulose columns) was evaluated in membrane and cytosol fractions from anterior pituitaries of ovariectomized (OVX) or OVX plus E2-treated rats. E2 administration by implants to OVX animals increased significantly both soluble and particulate enzyme activity. The effect increased progressively from 24 h to 5 days after E2 treatment. Administration of 17 alpha-estradiol, an inactive stereoisomer of E2, was ineffective, pointing to stereospecific interaction. Total destruction of neural connections to the pituitary (complete hypothalamic lesions) did not modify the enzyme response to E2 administration, indicating a direct effect of the steroid on pituitary PKC activity. A direct E2 (10(-9) M) effect was confirmed in primary mixed cultures of pituitary cells; it was time dependent (15-96 h) and specific, and reflects a genomic E2 action. E2 treatment for shorter times had no effect on the enzyme levels or the membrane redistribution of PKC activity. In contrast, under the same experimental conditions phorbol esters (12-O-tertadecanoyl-phorbol-13-acetate (TPA] induced a rapid and sustained translocation of the enzyme. PKC activity was found in all pituitary cell types, with maximal activity in fractions of gonadotropes and thyrotropes, as evaluated in cultures enriched in certain types of pituitary cells separated by means of unit gravity gradient sedimentation. E2 treatment (10(-9) M; 72 h) significantly increased both soluble and particulate enzyme levels in all cell types. In addition, administration of E2 (10(-9) M; 72 h) to cell cultures strongly increased the TPA-evoked LH and PRL release. These results indicate that E2-induced changes in pituitary function include selective effects of the steroid on PKC activity involved at different levels in the coupling mechanisms.

Estradiol activates methylating enzyme(s) involved in the conversion of phosphatidylethanolamine to phosphatidylcholine in rat pituitary membranes.

17 beta-Estradiol (E2) affects the sensitivity of pituitary cells to several neurohormones as LHRH, TRH, or dopamine, presumably by modulating receptor coupling mechanisms. We attempted to pinpoint the membrane processes underlying this modulation and studied the effect of E2 on pituitary membrane phospholipid methylation. Anterior pituitary membranes prepared from ovariectomized (ovx) or ovx plus E2-treated rats were assayed for phospholipid methylation. Methylated phospholipids were separated by TLC. Incorporation of [3H]methyl groups into phospholipids increased with membrane concentration and incubation time with S-adenosyl-L-methyl [3H]methionine; it was not Mg2+ dependent and was inhibited in a dose-dependent manner by S-adenosyl-L-homocysteine, methyltransferase inhibitor. pH was found to be critical. Formation of phosphatidyl-monoethanolamine, phosphatidyl-dimethylethanolamine, and phosphatidylcholine was markedly stimulated by treatment with E2. The effect increased progressively when animals were killed 15 h to 5 days after E2 implantation. The response involved a shift in the maximum velocity (Vmax) although there was no change in the available substrate for the methylating enzyme. This change in Vmax probably reflects changes in the amount of the methylating enzyme itself. Administration of 17 alpha-estradiol, an inactive stereoisomer of E2 was ineffective, pointing to a stereospecific interaction. After differential centrifugation of pituitary membranes, the highest specific methyltransferase activity was found in light mitochondrial (L) and microsomal (P) fractions and the lowest in nuclei (N) and the heavy mitochondrial (M) fractions. After sucrose density gradient centrifugation, methylated phospholipids were preferentially recovered from fractions corresponding to the endoplasmic reticulum and/or secretory granules. E2 treatment for 5 days did not modify the subcellular distribution of methyltransferase activity but stimulated it in all fractions; in contrast, it did not modify the activity of the other enzymes measured as fraction markers. Under the same experimental conditions, phospholipid methylation in membranes prepared from cortex, and anterior and mediobasal hypothalamic structures was not affected by the steroid, with the exception of a slight increment of [3H]methyl incorporation into mediobasal hypothalamic membrane phospholipids after 5 days of E2 treatment. These results indicate that E2-induced changes in pituitary responsiveness might be concomitant with selective effects of the steroid on specific membrane enzymatic activities involved in coupling mechanisms.

Effect of neonatal administration of steroids or gonadectomy upon oestradiol-induced luteinizing hormone release in rats of both sexes.

Implantation of oestradiol into adult rats of both sexes induced different patterns of LH secretion depending on the time at which gonadectomy or testosterone injection were performed. Castration 2 h after birth allowed an LH peak to occur daily at 18.00 h, but its amplitude was lower than that of adult gonadectomized female rats treated with oestradiol. Castration 24 h after birth elicited two kinds of response; a circadian discharge of LH lower than that of male rats gonadectomized 2 h after birth or a steady low level of LH. The LH rhythmicity induced by implantation of oestradiol was not seen after castration at 8 weeks of age. Neonatal administration of testosterone to female rats prevented the LH peak induced by oestradiol that was seen in adult ovariectomized rats. Neonatal or adult ovariectomy did not interfere with the rhythmical response of LH after implantation of oestradiol. Thus, it is concluded that sexual differentiation of the hypothalamus is primarily of masculine origin.

Circadian rhythm of luteinizing hormone secretion in the ovariectomized rat implanted with oestradiol.

Implantation of a solid source of oestradiol into ovariectomized rats produced constant plasma concentrations of the hormone over a long period of time. Under these conditions, LH is released in a circadian pattern with a very marked peak in the afternoon. This circadian rhythm is synchronized to the light--darkness cycle, since it follows exactly a shift in the nycthemeral cycle. The first peak appeared on day 3 after placement of the oestrogen implant; its amplitude was constant from days 3 to 9 after implantation, and decreased gradually during prolonged implantation. The afternoon peak was not correlated with changes in the pituitary sensitivity to exogenous LH releasing hormone (LH-RH), since the LH response to increasing doses of the peptide could be superimposed in the morning and in the afternoon. However, the decreased amplitude of the rhythm observed after more than 9 days of implantation seemed to depend upon a progressive desensitization of the pituitary gland to LH-RH. Pituitary LH content also decreased as a function of implantation time. It is concluded that, under conditions of constant plasma oestradiol concentrations and of constant pituitary sensitivity to LH-RH, a daily activation of the neural trigger releasing pituitary gonadotrophins occurs.

alpha 1-adrenergic receptor involvement in the LH surge in ovariectomized estrogen-primed rats.

The circadian pattern of LH release observed in ovariectomized estrogen-implanted rats was inhibited by blockade of alpha-adrenergic receptors by phenoxybenzamine; in contrast, blockade of beta-receptors by propranolol was ineffective. Prasozin, an alpha 1-antagonist, was as effective as phenoxybenzamine, whereas yohimbine, an alpha 2-antagonist, was effective only at high doses. Neither phenoxybenzamine nor prazosin were able to modify the LHRH-induced release of LH from superfused pituitaries. These results suggest an involvement of hypothalamic alpha 1-receptors in the control of circadian LH release.

Influence of shock-induced fighting and social factors on pituitary-adrenal activity, prolactin and catecholamine synthesizing enzymes in rats.

The present experiment investigated changes in pituitary-adrenal activity, prolactin and catecholamine synthesizing enzymes in rats exposed to electric shocks in pairs or individually, in comparison to animals receiving no shock and tested in pairs or alone. Pairs of rats repeatedly exposed to electric shocks displayed a lower activation of the pituitary-adrenal system but a stronger activation of the sympathetic-adrenal medullary system than rats shocked individually. There was no differential release of prolactin according to the social setting in which shock occurred. Social factors by themselves influenced plasma corticosterone levels but not plasma levels of ACTH and prolactin nor catecholamine synthesis. The results are discussed in relation to the postulated beneficial effects of fighting on physiological activation produced by electric shock.

[Ether and penthrane on LH and prolactin (author's transl)]. / Ether et penthrane sur la sécrétion de LH et prolactine chez la ratte ovariectomisée prétraitée par l'oestradiol et la progestérone

The effects of long-term anesthesia with methoxyflurane on plasma LH and prolactin concentrations were compared to those induced by exposure to ether. Methoxyflurane significantly decreased prolactin levels and had a slight effect of LH, whereas ether produced an important release of prolactin without affecting LH.

[Effect of cerebral serotonin on cyclic LH release in rats]. / Interaction de la sérotonine cérébrale avec la libération cyclique de LH chez la ratte

An experimental increase in serotonin (5-HT) induced shortly before the "critical period" of ovulation control blocks the release of LH. Administration of a synthesis inhibitor of the amine p-chlorophenylalanine, (pCP) is ineffective when given during the critical period. However, pCP given in the evening of dioestrus II (18 to 24 hours before the "critical period") blocks ovulation. That 5-HT is specifically involved in this delayed effect of the drug is shown by the ability of increasing doses of 5-hydroxytryptophane (5-HTP) to induce with pCP a graded restoration of LH release when given together. This result, obtained in immature rats, has been confirmed in cyclic ones. A positive, permissive effect of 5-HT containing neurons on neural processes leading to LH release and ovulation is thus postulated. This action affects early stages of the LH release regulating mechanisms, in contrast to the classically described inhibiting effect of the amine, which blocks the actual release of LH-RH at the median eminence level during the critical period.

[In vitro study of the interaction between neuromediators and neuropeptides involved in hypothalamic neurosecretion control (author's transl)]. / Interactions entre neuromédiateurs et neuropeptides impliqués dans le contrôle de la neurosécrétion hypothalamique in vitro.

Luteinizing hormone-releasing hormone (LHRH) and somatostatin (SRIF) release was assessed in superfused slices of mediobasal hypothalamus. Release of both neurohormones by depolarizing agents (K+, 56mM ; veratridine, 50 muM) was shown to be Ca2+-dependent, according with the stimulus-secretion coupling hypothesis. Opiates (beta endorphin, 10(-7)M and D-ALA2-Met-enkephalinamide 10(-7)M) did not alter the spontaneous release of LHRH and SRIF, but inhibited significantly the K+-induced neuropeptide release. The effect was reversed by the opiate antagonist naloxone (10(-7)M), while naloxone was ineffective by itself. Vasoactive intestinal peptide (VIP 10(-9)M) significantly inhibited K+ evoked release of SRIF ; LHRH release was unaffected. The effect of VIP on SRIF release was dose-dependent ; secretin, a partial VIP agonist, was also active at higher doses. The data suggest that : 1) opiates, acting through specific opiate receptors located on LHRH and SRIF neurons, modulate the release of the neurohormones ; 2) the inhibitory effect of opiates could be due to an inhibition of calcium influx through voltage-dependent calcium channels ; 3) this interaction may account for the stimulation of growth hormone and the inhibition of luteinizing hormone observed after systemic administration of opiates ; 4) VIP inhibits SRIF release, by acting on VIP receptors present on MBH SRIF terminals ; the effect is consistent with the stimulation of GH reported after in vivo administration of the peptide.