Biomedical subjects

J Marcó

Publications and source records attributed to J Marcó.

At least 19 recordsLinked to original sources

PubMed1995

Possible changes in the regulatory mechanisms of pulsatile luteinizing hormone secretion in adult pituitary-grafted female rats.

It is well known that LH is released in an episodic fashion. However, the effects of hyperprolactinemia on luteinizing hormone (LH) pulsatility are not fully understood. The present study was undertaken to describe hyperprolactinemia effects on the regulatory mechanism of LH pulsatility. For this purpose hyperprolactinemia was induced in female rats by the transplantation of two pituitary glands beneath the kidney capsule. Age-matched sham-operated animals were used as controls. We have evaluated the pulsatile pattern of LH in both groups of animals. As expected, pituitary grafting increased mean serum prolactin levels compared with the values found in control animals. Luteinizing hormone-releasing hormone (LHRH) administration did not change serum prolactin levels in control or in pituitary-grafted rats. Thyrotropin-releasing hormone (TRH) administration increased prolactin secretion in both groups. There is an increase in mean values of LH and in the absolute amplitude of LH peaks in pituitary-grafted compared with control rats. No other parameters of LH pulsatility were changed by pituitary grafting. After LHRH administration, LH release was increased and a priming effect after the second administration of LHRH is observed in control rats. In pituitary-grafted animals the responses of LH to LHRH administration was diminished compared with the response observed in control rats. The administration of two pulses of TRH to control rats only decreases the duration of LH pulses. However, in pituitary-grafted animals, TRH administration was followed by a decrease in the mean values of LH and in the absolute amplitude of the LH peaks. Vasoactive intestinal peptide (VIP) administration increased mean values of LH and the absolute and relative amplitudes of LH pulses in sham-operated animals, whereas only the relative amplitude of LH peaks was modified by VIP in pituitary-grafted rats. All these data suggest that hyperprolactinemia induced by pituitary-grafting interfere with the neuromodulator effects on the pulsatile regulatory center of the hypothalamus.

Animals↗

PubMed1994

Acute ethanol administration in diestrus-2 in the rat on pulsatile prolactin and LH release.

Exposure to ethanol is followed by changes in reproductive function in man and animals, characterized by modifications in the secretion patterns of prolactin and luteinizing hormone (LH). As both hormones are secreted in an episodic fashion, the present work was undertaken to study the effects of acute ethanol administration on pulsatile prolactin and LH secretion patterns in adult female rats. Rats were previously cannulated to allow a continuous blood withdrawal to study the pulsatile patterns of prolactin and LH. The mean values of prolactin during the bleeding period and the absolute pulse amplitude of prolactin peaks were significantly increased by acute ethanol administration, whereas a significant decrease of relative pulse amplitude and frequency of this hormone was observed. On the other hand, ethanol administration increased the mean serum LH levels and the absolute and relative amplitudes of LH peaks. Ethanol treatment did not modify either frequency or duration of LH peaks. These data suggest that acute ethanol administration in adult female rats is followed by changes in the pulsatile prolactin and LH secretory patterns, which might be part of the mechanism to explain ethanol effects on the endocrine system.

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PubMed1994

Cyclosporine modifies the pulsatile secretory patterns of prolactin and luteinizing hormone in normal and pituitary-grafted female rats.

This study was designed to examine whether cyclosporine (CyA) acts on the endocrine system by modifying the pulsatile secretion pattern of prolactin and LH. Both pituitary-grafted and sham-operated rats were submitted to a subcutaneous vehicle or CyA (5 mg/kg) treatment daily for 10 days beginning on the day of surgery. Pituitary grafting and/or CyA administration changed the pulsatile pattern of prolactin observed in sham-operated animals. The mean values of serum prolactin were significantly increased by pituitary grafting and the treatment with CyA further increased them. The mean half-life of prolactin was significantly increased in pituitary-grafted rats and was not changed by CyA administration, although it was decreased in sham-operated rats. The frequency of prolactin pulses was significantly decreased in pituitary-grafted as compared to sham-operated controls and was not further modified by CyA administration. However, in sham-operated rats a significant decrease of this parameter was observed. Duration of the prolactin peaks was significantly increased by pituitary grafting, and was not modified by CyA administration in any of the groups studied. The absolute amplitude of the prolactin peaks was significantly increased in pituitary-grafted as compared to sham-operated animals, and the treatment with CyA further increased this parameter in both groups. Mean values of LH were significantly increased in pituitary-grafted as compared to control rats. CyA administration significantly increased LH levels in sham-operated rats and decreased them in pituitary-grafted animals. The mean half-life, the pulse frequency and the duration of LH peaks were not modified by either pituitary grafting or CyA administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Physiological roles of thyrotrophin-releasing hormone and vasoactive intestinal peptide on the pulsatile secretory patterns of prolactin in pituitary-grafted female rats.

Much is known about the fact that thyrotrophin-releasing hormone (TRH) and vasoactive intestinal peptide (VIP) stimulate prolactin secretion but areas of uncertainty remain. This work was undertaken to describe the effects of TRH and VIP on the pulsatile secretion pattern of prolactin, in adult sham-operated and pituitary-grafted hyperprolactinaemic female rats. Two pulses of TRH (1 microgram/rat) or one pulse of VIP (20 micrograms/rat) were given 60 or 120 min after the period of blood sampling. Pituitary grafting increased the mean values of prolactin, absolute amplitude and duration of the peaks and decreased their frequency, compared with control animals. In sham-operated rats, TRH elevated prolactin levels by increasing the absolute and relative amplitudes and duration of the pulses, along with a decrease in their frequency. No priming effects of TRH were observed in this study. Hyperprolactinaemia blunted TRH effects on the pulsatile secretion pattern of prolactin. In sham-operated rats, VIP administration increased the absolute and relative amplitudes of the prolactin peaks. None of the other parameters studied were changed. In pituitary-grafted animals, VIP administration increased the absolute and relative amplitudes of the prolactin peaks but to a lesser extent compared with controls. These data suggest that TRH and VIP affect prolactin pulsatility differentially. The effects of TRH and VIP were blunted to some extent by exposure to previously elevated circulating prolactin levels.

Animals↗

PubMed1994

Ovariectomy at different stages of the estrous cycle modifies the pulsatile secretory pattern of prolactin in rat.

The role of estrogens in the synchronization of pulsatile prolactin secretion throughout the estrous cycle in the adult female rat is studied. Mean values of prolactin, in sham-operated animals increased from diestrus-2 to proestrus and then decreased to the values found at diestrus-1. Ovariectomy did not modify the pattern which follows mean serum levels of the hormone throughout the estrous cycle; although increased values of prolactin were found at both proestrus and estrus, when compared to control animals. No changes in mean values of the hormone were observed at any other phase of the estrous cycle. The number of peaks was fairly constant in sham-operated rats in any phase of the estrous cycle, but a decrease in its number, after ovariectomy, was observed at proestrus and estrus. The absolute amplitude of the peaks increased numerically but not statistically significant from diestrus-2 to proestrus, then decreasing to diestrus-1 in control animals whereas an increase in the absolute amplitude of the prolactin peaks was detected in proestrus and estrous after ovariectomy. The duration of the prolactin peaks was not changed either by the phase of the estrous cycle or by ovariectomy. The relative amplitude of the prolactin peaks was only changed in rats ovariectomized at diestrus-1, as compared to sham-operated animals. All these data indicated that changes in estrogen/secretion by ovariectomy throughout the estrous cycle of the rat induced a differential effect on the pulsatile pattern of prolactin, being more marked in proestrus and estrus, associated with the highest circulating estrogen levels.

Animals↗

PubMed1993

Pulsatile prolactin secretory patterns throughout the oestrous cycle in the rat.

Prolactin secretion throughout the oestrous cycle in the rat remains at a low level and fairly constant, with the exception of the surge at pro-oestrus. The present study was designed to characterize possible changes in pulsatile patterns of prolactin during the oestrous cycle of the adult female rat. Mean values of prolactin increased from dioestrus-2 to pro-oestrus and then decreased to the values found at dioestrus-1. The number of peaks remained fairly constant in any phase of the oestrous cycle. The absolute amplitude of the peaks increased numerically but was not statistically significant from dioestrus-2 to pro-oestrus then decreasing until dioestrus-1. No changes in the relative amplitude or duration of the peaks throughout the oestrous cycle were detected. The results indicated that there is a similar pulsatile pattern of prolactin at any stage of the oestrous cycle, when samples were obtained during the morning.

Animals↗

PubMed1993

In vitro effect of ethanol on LH and FSH secretion by pituitary glands of female rats.

The effect of ethanol (EtOH) on LH and FSH release in vitro has been studied in order to determine whether the effect of alcohol observed in vivo could be mediated by a direct action at the level of the anterior pituitary. Pituitary glands were incubated for 4 hours in TC-199 medium with or with 100 mM ethanol. Basal gonadotrophin release was examined as well as secretion stimulated by luteinizing hormone releasing hormone (LHRH) in the presence or absence of cycloheximide. The total amount of LH and FSH released during the incubation period was calculated. Ethanol did not significantly alter basal gonadotrophin release or LHRH-stimulated FSH release. However, LH secretion induced by LHRH was decreased by EtOH when compared to the LHRH-stimulated group. Cycloheximide decreased the LHRH-stimulated release of LH and FSH but this effect was not altered by EtOH. The results show that EtOH alters the release but not the synthesis of gonadotrophins by a direct effect on the anterior pituitary gland.

Animals↗

PubMed1993

Ethanol-induced alterations in gonadotrophins secretion during the estrous cycle of rats.

The effects of ethanol administration during a preovulatory period on both serum and pituitary gonadotrophin concentrations were studied in female rats. The animals were injected with 2 g/kg of ethanol (30% v/v, in saline solution) at 18:00 hr of diestrous 2. Hormonal levels were measured by RIA at different times during the estrous cycle, especially during the proestrus day. The preovulatory LH surge was inhibited using ethanol. Serum LH levels decreased between 16.00 and 20.00 hr of proestrus (P < 0.01). The levels of FSH in serum were slightly depressed by ethanol between 12.00 and 17.00 hr of proestrus (P < 0.05 with respect to the control set), but the values during the proestrus surge (18.00-20.00 hr) were unaffected. Ethanol augmented pituitary hormonal content during the periods in which serum hormonal levels decreased (P < 0.05 with respect to the control set) but it did not affect gonadotrophins synthesis. The increase in pituitary gonadotrophin concentrations induced by ethanol during the proestrus day is due to the accumulation of the hormone which was not released before. The preovulatory LH surge was re-established in the next cycle (5th day after treatment). These effects of ethanol on gonadotrophin levels could explain the previously observed anovulatory effects induced by ethanol administration in diestrous.

Animals↗

PubMed1992

Effects of hyperprolactinemia on prolactin and LH pulsatile pattern in female rats.

Prolactin (PRL) and luteinizing hormone (LH) secretions are very closely-related. To further understand these mechanisms, the pulsatile secretion pattern of both hormones in experimentally-induced hyperprolactinemia has been studied in adult female rats. Hyperprolactinemia was induced by the transplanting of two pituitary glands. Nine days after the transplant operation, rats were bled (75 or 100 microliters/7 min for 3 h). Serum samples were analyzed for prolactin and LH values by RIA. Hyperprolactinemia modifies pulsatile PRL secretion by increasing the absolute amplitude and duration of the peaks together with a decrease in their frequency. Also, the mean values of the hormone during the whole studied period were increased. Hyperprolactinemia was followed by an increase in the mean values of LH and in the absolute amplitude of the peaks. All these results suggest that hyperprolactinemia induced by pituitary grafting in adult female rats, is followed by a significant change in prolactin and LH pulsatility, which may explain, to some extent, the effects of hyperprolactinemia on reproduction.

Animals↗

PubMed1991

Two-parameter mobile phase optimization for the simultaneous high-performance liquid chromatographic determination of dopamine, serotonin and related compounds in microdissected rat brain nuclei.

A new high-pressure liquid chromatography method with electrochemical detection is described that allows the simultaneous determination of dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylacetic acid, 5-hydroxytryptophan and 5-hydroxyindoleacetic acid in microdissected nuclei from individual rat brains. No sample pre-treatment steps are required. Resolution and analysis time were optimized by a simple limited optimization procedure, involving two-parameter factorial design.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1991

Direct action of ethanol on pituitary prolactin secretion in vitro.

The effect of ethanol on prolactin release in vitro has been studied in order to investigate the direct action of ethanol on pituitary gland of the female rats. Animals were sacrificed in diestrus 2 and pituitary glands were incubated in TC-199 medium containing dopamine, noradrenaline, serotonin, TRH or cycloheximide with or without ethanol. The total amount of prolactin after the incubation period was calculated. Alcohol significantly increased the prolactin release in all groups. Cycloheximide and dopamine decreased the prolactin synthesis, but ethanol reduced the effect of dopamine. It is concluded that part of ethanol-induced hyperprolactinaemia, is due to a direct action of the alcohol on pituitary, affecting release and/or synthesis of prolactin.

Animals↗

PubMed1989

[Effect of progesterone and estradiol on the regulation of pulsatile secretion of LH in the various phases of the estrous cycle of rats].

The normal changes on LH pulse amplitude and frequency throughout the estrous cycle and the specific role of Progesterone (P) and Estradiol (E) on pulsatile LH release have been determined in rats at the different stages of the estrous cycle. The effects on pulsatile LH release 24 h after ovariectomy (OVX), have been studied, as well as the way the normal values of the pulsatile release was re-established, when the physiological levels of P and/or E were restored by implantation of either P, E, or both Silastic capsules in OVX rats 24 h early. Our data during the rat estrous cycle, have confirmed that the lowest pulsatile LH release was on estrus, and the largest LH pulses were obtained on diestrus day 1, when the plasmatic levels of both P and E were lowest. Moreover, a variable ovarian steroid effect has been found at the different stages of the cycle. In estrus and diestrus day 2, both steroids were necessary to restore the normal values of the pulsatile LH release in OVX rats 24 h before, while in proestrus, the main steroid was Estradiol, although a non steroidal ovarian factor was also necessary to restore the normal pulse amplitude. Finally, in diestrus day 1 there was an absence of an ovarian steroid negative feedback on pulsatile LH release, because the levels of both steroids were too low in this stage, to exert a regulatory role on pulsatile LH release.

Animals↗

PubMed1989

[Changes in the prolactin levels after administration of ethanol in diestrus 2].

The effect of ethanol administered at 18.00 h. of diestrus 2 on prolactin secretion has been studied in rats. Serum levels and pituitary content of prolactin were measured at 30, 60, 90 and 120 min. after administration of different doses of ethanol (0.5, 2 and 4 g/kg). Moreover, the variation of the prolactin release was determined at different hours of the rat estrous cycle, after administration of a single dose of ethanol (2 g/kg) at 18.00 h of diestrus. 2. Serum prolactin levels were significantly elevated after the preovulatory administration of ethanol with all the doses tested. The hyperprolactinemia appeared 60 min after ethanol treatment and the high prolactin levels were maintained during all the estrous cycles, especially in the proestrus day. The normal levels were re-established the 5th day after treatment. The ethanol produced a byphasic effect on pituitary prolactin content. During the first post-treatment hours, the pituitary prolactin concentration decreased with respect to the control group, but 24 hours after treatment, these values were increased and the normal concentration was restored 36 hours after treatment.

Animals↗

PubMed1985

Further evidence for effects of ethanol on gonadotrophins and prolactin secretion in female rats.

The effect of different doses of ethanol (0.5, 1.0, 2.0 and 4.0 g/kg) on LH, FSH and prolactin levels has been studied in female rats. Ethanol was administered in preovulatory periods (18 hr of diestrous or 9 hr of proestrous) and hormonal levels were measured at the 18 hr of proestrous. Ethanol administered at the 18 hr of diestrous produces a biphasic effect on serum LH levels. High doses of alcohol significantly decreased LH levels, whereas low doses (0.5 g/kg) increased the hormonal levels. When ethanol-treatment was at the 9 hr of proestrous, it only decreased LH levels with the dose of 4.0 g/kg. Serum FSH levels were unaffected by the preovulatory administration of ethanol. Serum prolactin concentrations were significantly elevated after i.p. administration of ethanol at the 18 hr of diestrous and the 9 hr of proestrous. The hyperprolactinemia is more pronounced in the rats treated at the 9 hr of proestrous. The results of these studies suggest that the ability of ethanol to modify LH and prolactin levels is due to a central depression caused for alcohol. These effects of ethanol could be mediated by the hypothalamic releasing factors and/or could be due to a direct action on the pituitary function. The sum of these effects produces important failures of the reproductive function in the female rat.

Animals↗

PubMed1984

Changes in serum LH and FSH following preovulatory administration of ethanol in rats.

The effect of different single doses of ethanol (1.0, 2.0 and 4.0 g/kg) on serum LH and FSH has been studied in rats treated during preovulatory periods (18th h of diestrous). High doses of ethanol (2.0 and 4.0 g/kg) decreased serum LH levels at the 18th h of proestrous, 24 h after ethanol administration, inhibiting the preovulatory LH surge. No changes were observed in FSH levels. These effects could be mediated through the inhibition of the hypothalamic releasing factors.

Animals↗

PubMed1984

[Effect of ethanol in the pre-ovulatory period on the ovarian cycle, progesterone and estradiol in the rat].

The effect of high doses of ethanol (2 and 4 g/kg) administered to rats in pre-ovulatory periods (18th hour of diestrus) was studied. Plasma levels of estradiol and progesterone were measured at 10 hours of oestrus and changes in the ovarian cycle and the number of mature follicles were recorded. Compared with the control group, the receptive phase of estrus of the treated animals was longer lasting over 2 to 3 days. There was also an increase in the number of mature follicles as well as an increase in the plasma level of estradiol on the morning of estrus. Progesterone values showed no significant variations. Ethanol administered at the 18th hour of diestrus inhibits ovulation but not follicle development and allows the maintenance of high levels of estrogens on the morning of estrus. As a result the keratinization of the vaginal epithelium and the estrus phase are prolonged by 2 or 3 days.

Animals↗

PubMed1983

[Effect of ethanol in preovulatory periods on LH, FSH, prolactin and ovulation in rats].

The effect of ethanol (4 g/kg) as well as the role of serotoninergic neurons on the rate of ovulation and plasma LH, FSH and prolactin secretion have been studied in rats at preovulatory periods (18th hour of diestrus). It has been found that administration of ethanol in preovulatory periods decreased the number of ovules per rat (p less than 0.001), the number of ovulating rats and LH levels (p less than 0.001). These effects were accompanied by an increase in prolactin concentration (0.05 greater than p greater than 0.02), which was followed by a diffuse luteinization in the ovarian tissue. These results showed that ethanol had an effect of central depression in preovulatory periods. These effects could be mediated through the hypothalamic releasing factors. Under previous serotonin depletion with p-chlorophenylalanine (PCPA: 300 mg/kg), ethanol caused similar effects on LH and FSH levels as compared with the control group with PCPA. However, prolactin concentration was not increased. These results showed that serotoninergic neurons could be mediated in changes caused by ethanol on prolactin secretion, but do not affect directly in changes caused on LH and FSH secretion.

Animals↗

PubMed1982

[Effect of p-chlorophenylalanine on LH, FSH, prolactin and ovulation in the rat].

The effect of p-chlorophenylalanine (PCPA: 300 mg/kg) on the rate of ovulation and plasma LH, FSH and prolactin secretion has been studied in rats at preovulatory periods (18th hour of diestrus) and post-ovulatory periods (9th hour of metaestrus). In both experimental groups, results showed that administration of PCPA caused an increase in both prolactin concentration and number of mature ovarian follicles (p less than 0.001). No changes were observed in FSH levels. LH concentration, however, decreased (p less than 0.001) and ovulation became totally inhibited. Rats treated at the 9th hour of metaestrus exhibited a marked luteinization as well as an increased number of corpus luteum in the ovaric tissue (p less than 0.001), whereas those treated at the 18th hour of diestrus underwent no luteinization and merely showed a greater number of mature ovarian follicles (p less than 0.001). PCPA, therefore, seems not to have a double effect on ovulation, LH, FSH, and prolactin secretion regardless of the pre or post-ovulatory periods. Changes observed in the ovaric tissue might be due to an increase in plasma prolactin concentration which appears earlier in the preovulatory than in the post-ovulatory treated animals. This difference may explain the double effect that has been attributed to the ovaric cycle and reproductive behavior.

Animals↗