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Biomedical subjects

B Szwarcfarb

Publications and source records attributed to B Szwarcfarb.

At least 37 records · Page 2Linked to original sources
PubMed1991

Hypothalamic luteinizing hormone-releasing hormone content and serum luteinizing hormone levels in male rats during wallerian degeneration of sympathetic nerve terminals after superior cervical ganglionectomy.

The main hypothesis of this study was that sympathetic neurons located at the superior cervical ganglia (SCG) control luteinizing hormone (LH) releasing mechanisms by acting at a hypothalamic site. To test this, medial basal hypothalamus (MBH) luteinizing hormone-releasing hormone (LHRH) content and serum LH levels were measured in male rats subjected to superior cervical ganglionectomy (SCGx) or sham-operation 14 or 38 h earlier, at the time of degeneration of nerve endings post-SCGx. Significantly augmented MBH LHRH levels and decreased circulating LH were found in SCGx rats. In animals subjected to SCGx 14 h earlier and receiving a single injection of the alpha 1-adrenergic blocker prazosin, the beta-adrenergic blocker propranolol or a mixture of both drugs 45 min before sacrifice, only the injection of prazosin prevented the decrease of plasma LH levels. Neither treatment prevented the increase in MBH LHRH content. When prazosin was given every hour starting from the 10th to the 13th h after surgery, it was effective to prevent both the increase of MBH LHRH content and the decrease of serum LH found during sympathetic nerve degeneration. Similar repetitive injections of propranolol resulted in the greatest depression of serum LH, and in the greatest increase of MBH LHRH observed. Serum LH response to LHRH injection was similar in SCGx and sham-operated rats. The data indicate that SCG neurons exert, through inhibitory alpha 1-, and weaker, stimulatory beta-adrenoceptors, a significant influence on LHRH release at a supra-hypophysial site.

Animals↗
PubMed1990

In vivo and in vitro studies on the effect of the serotoninergic system on luteinizing hormone and luteinizing hormone-releasing hormone secretion in prepubertal and peripubertal female rats.

The present investigations were designed to assess the effect of the serotoninergic system on luteinizing hormone (LH) and LH-releasing hormone (LH-RH) secretion in female rats aged 14 and 30 days. The administration of 5-hydroxytryptophan (5-HTP; 75 mg/kg i.p.) increased hypothalamic serotonin (5-HT) concentrations in both age groups, and did not affect hypothalamic norepinephrine (NE) concentrations or release. Serum LH levels were raised by 5-HTP in 14-day-old, but not in 30-day-old rats. Basal and KCl- (28 mM) stimulated LH-RH release by incubated hypothalamic fragments was significantly enhanced when 5-HTP was injected previously to 14-day-old animals. In 30-day-old rats, 5-HTP treatment did not modify basal LH-RH release, and decreased the KCl-stimulated LH-RH output. Similarly, the addition of 5-HT (10(-7) M) to superfused hypothalamic fragments enhanced basal LH-RH release in 14-day-old rats and blocked the increment in LH-RH release evoked by KCl in 30-day-old rats. The present results show that in 14-day-old female rats, the serotoninergic system (activated in vivo by 5-HTP treatment, or in vitro by 5-HT addition) exerts a stimulatory effect on LH-RH, and thus, on LH release. On the contrary, in 30-day-old animals, stimulated LH-RH secretion was inhibited by 5-HT. Apparently, the hypothalamic NE system is not implicated in this response. The participation of this changing effect of 5-HT on LH-RH/LH release at the onset of puberty is postulated.

5-Hydroxytryptophan↗
PubMed1990

Modulatory effect of testosterone on the serotoninergic control of prolactin secretion in prepubertal rats.

The administration of 5-hydroxytryptophan (5-HTP) induced a prolactin release in male and female prepubertal rats at 20 days of age. This response was significantly higher in male than in female rats. Neonatal androgenization of the females significantly increased the release of prolactin induced by 5-HTP treatment compared to the values observed in males; thus, the neonatal exposure to androgens seems to be responsible for the sexual differences in the prolactin response to 5-HTP. In a second series of experiments the effect of this serotoninergic precursor on prolactin release in prepubertal (16, 26, and 30 days of age), peripubertal (45-day-old) and adult male rats was studied. Castration significantly decreased the prolactin release response to 5-HTP in prepubertal rats. The administration of testosterone to castrated rats markedly increased the prolactin release response to 5-HTP. Neither castration nor testosterone administration modified the prolactin response to 5-HTP in peripubertal and adult rats. These results appear to indicate that testosterone modulates the serotoninergic control of prolactin secretion during the prepubertal stage. The control of prolactin levels could be one of the mechanisms by which testosterone participates in the sexual maturation.

5-Hydroxytryptophan↗
PubMed1990

Sexual maturation modifies the catecholaminergic control of gonadotrophin secretion and the effect of ovarian hormones on hypothalamic neurotransmitters in female rats.

alpha-Methyl-p-tyrosine (alpha-MT), a competitive inhibitor of tyrosine hydroxylase, was used to block the synthesis of hypothalamic catecholamines in immature female rats of 14, 16 and 30 days of age and in castrated adults. The administration of alpha-MT (300 mg/kg body weight, free base) induced a significant decay in the hypothalamic content of norepinephrine (NE) and dopamine (DA) within the first 120 min. A second dose (150 mg/kg body weight), given 2 h after the first injection, did not further modify the low catecholamine levels observed 120 min after the first alpha-MT administration. The administration of 300 mg/kg body weight of alpha-MT induced a significant increase in LH concentrations in rats aged 14 and 16 days. On the contrary, after an alpha-MT injection, a significant LH decrease was observed in 30-day-old and in adult castrated rats. alpha-MT also increased FSH levels in prepubertal rats of 16 days of age, but no change occurred in 30-day-old and in adult rats. The administration of estrogen-progesterone (EP) to prepubertal rats of 16 days of age induced a significant decrease in serum LH levels as well as in the serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA) concentrations in the anterior-preoptic hypothalamic area (AH-POA), but not in the medial basal hypothalamus. No modifications in the catecholamine content of these hypothalamic areas were observed in this age group after EP administration. On the contrary, in 30-day-old rats, EP induced a significant LH release as well as an increase in AH-POA concentrations of 5-HT, 5-HIAA and catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1989

Effects of H1 and H2 histamine receptor antagonists on positive feed-back effect of estrogen on LH in prepubertal female rats.

The aim of the present study was to determine whether histaminergic central mechanisms which exert a well known effect on gonadotrophin secretion are involved in the development of the positive feed-back effect of estrogen-progesterone (E-P) on LH secretion that normally occurs in female rats about 20-22 days old. The administration of histamine H2 (cimetidine and ranitidine) or H1 (diphenhydramine) receptor blocking agents did not modify the onset of the LH release response to E-P. Nevertheless cimetidine, ranitidine and diphenhydramine potentiated the LH release induced by ovarian steroids at 23 days of age. These results appear to indicate that histaminergic pathways are involved in the magnitude of the LH response to E-P in prepubertal female rats rather than in the maturation of this mechanism.

Animals↗
PubMed1989

Effect of serotoninergic system on FSH secretion in male and female rats: evidence for stimulatory and inhibitory actions.

The present experiments were designed to assess the effect of the serotoninergic system on FSH secretion in prepubertal (16-, 18-, 20-, 26- and 30-day-old) and adult (60-day-old) male and female rats. The intraperitoneal administration of 5-hydroxytryptophan (5-HTP), a serotonin (5-HT) precursor, induced a significant increase of FSH levels in male rats at 16, 26, 30 and 60 days of age (p less than 0.01) but not at 18 and 20 days. In the females, no modifications in FSH concentrations in prepubertal and adult rats were observed after 5-HTP injection. These results indicate that there are sexual differences in the effect of the serotoninergic system on FSH secretion. Orchidectomy performed in prepubertal (30-day-old) and adult rats (60 days) besides increasing FSH levels, reversed the response of this hormone to 5-HTP administration, since in castrated rats the 5-HT precursor induced a significant decrease in serum FSH concentrations. The administration of 5-HTP to 30 day-old castrated rats treated with testosterone induced FSH release as it did in control animals of this age. In the adult castrated rats the administration of testosterone abolished the inhibitory effect of 5-HTP observed in castrated rats but did not invoke the stimulatory action of 5-HTP observed in the controls. This difference between prepubertal and adult rats appears to be related to a decrease in the sensitivity to testosterone of the central mechanism which controls FSH secretion. These results indicate that 5-HTP stimulates FSH release in normal rats and inhibits FSH release in castrated rats, testosterone concentration being a relevant factor in determining the 'type' of effect produced. The hypothalamic concentrations of 5-HT and 5-hydroxy-indoleacetic acid (5-HIAA) are significantly higher at the ages at which 5-HTP induces FSH release than at other ages suggesting that hypothalamic turnover of these substances is related is related to the releasing effect of 5-HTP on FSH.

5-Hydroxytryptophan↗
PubMed1987

Role of sexual differentiation of the hypothalamus in the differential effect of the serotoninergic system on LH in prepubertal male and female rats.

5-hydroxytryptophan (5-HTP), a serotonin precursor, has been shown to induce LH release in female but not in male rats at 16, 18 and 20 days of age. The purpose of this study was to investigate the role of neonatal gonadal hormones on 5-HTP-induced LH release in male and female rats of 16 and 20 days of age. The following groups of rats were studied control females, androgenized females, control males, and castrated males. Androgenization and castration were performed within 48 h of birth. 5-HTP administration increased LH concentration in normal females and castrated males at 16 and 20 days of age. The LH release response to 5-HTP was significantly lower at 20 than at 16 days of age in both groups. Neonatal androgenization abolished the LH release response in prepubertal female rats. These results indicate that neonatal exposure to androgen is responsible for the sex difference in the LH response to 5-HTP, which may be associated with a regulatory action of serotonin on the cyclic hypothalamic control of gonadotrophin secretion.

5-Hydroxytryptophan↗
PubMed1987

Effect of naloxone on the development of the positive feed-back action of oestrogen-progesterone on LH secretion in rats.

The purpose of this study was to examine the role of opiate peptides in the development of the positive feedback effect of ovarian hormones (Oe-P) on the LH secretion that matures in female rats at about the age of 20-22 days. Oe-P administration at the age of 14 days induced a significant decrease of LH levels. A single injection of naloxone (5 mg/kg) induced a significant release of LH. This release was completely blocked by Oe-P administration. At the age of 20 days, Oe-P did not induce any significant change of LH levels, whereas naloxone increased the serum LH concentration. On the other hand, injection of Oe-P into naloxone-treated rats induced a significant rise in LH that was significantly higher than that observed with naloxone alone (P less than 0.025). Oe-P administration induced a positive feedback effect on LH at the age of 25 days. At this age, naloxone also increased LH levels and a significant potentiation of the LH release in response to Oe-P was observed in a group treated with naloxone. These results indicate that naloxone advances the development of the positive feedback mechanism of ovarian hormones on LH secretion and potentiates this mechanism after its maturation. On this basis it is proposed that the probable inhibitory effect of opiates on the onset of the positive feedback mechanism is related to the well-known participation of the opiate system in the onset of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Effect of the serotoninergic system on luteinizing hormone secretion in prepubertal female rats.

The effect of 5-hydroxytryptophan (5-HTP), a serotonin precursor, and p-chloroamphetamine (PCA), a serotonin neurotoxin, selective for serotoninergic neurons, that depletes serotonin (5-HT) levels in brain, on the luteinizing hormone (LH) release response to estrogen-progesterone (E-P) was studied in prepubertal female rats of different ages. E-P decreased LH levels on days 16, 18 and 20, increasing the levels of the pituitary hormone at day 26 of age. Destruction of the serotoninergic system advanced the onset of the positive feed-back mechanism, since the rats pretreated with PCA showed at day 20 an LH release by E-P administration while in the controls of the same age the ovarian hormones decreased the LH concentration. On the other hand, PCA potentiated the positive feed-back mechanism of E-P on LH in 26-day-old rats, while at this age the LH release response to E-P was significantly reduced by the administration of 5-HTP. These results suggest that the serotoninergic system has an inhibitory effect on the development of the positive feed-back of ovarian steroids on LH secretion, that could be representative of a regulatory participation of serotonin in the onset of puberty. 5-HTP stimulated LH release on days 16, 18 and 20, but did not modify the LH concentration of day 26. Since between 20 and 26 days of age the positive feed-back mechanism matures, the possibility arise that the modification in the effect of serotonin on LH release on day 26 is connected with the physiological changes in the gonadotropin control that occur after day 20 in the female rat.

5-Hydroxytryptophan↗
PubMed1985

Sexual differences in the effect of serotonin on LH secretion in rats.

The effect of 5-hydroxytryptophan (5-HTP), a serotonin (5-HT) precursor, on luteinizing hormone (LH) secretion was studied in prepubertal male and female rats of different ages. In females 5-HTP stimulated LH release on days 16, 18 and 20 but not in older rats (26, 30, 35 days of age). No effects of 5-HTP on LH levels were observed in males. The positive feed-back mechanism of oestrogen-progesterone (E-P), that normally matures in the female between 20 and 26 days, was inhibited by 5-HTP in all the ages studied during prepuberty (26, 30 and 35 days old). On the other hand, in adult ovariectomized rats, 5-HTP administration not only decreased the high LH levels induced by ovariectomy, but the LH release response to E-P as well. These results indicate that there are sexual differences in the effect of 5-HT on LH in prepubertal rats younger than 26 days old. Administration of p-chloroamphetamine (PCA) a serotonin neurotoxin selective for serotoninergic neurons that depletes 5-HT levels in the brain, induced a significant increase in the LH release response to LRH in females, but had no effect in males. These results, besides suggesting a probable pituitary participation in the 5-HT action on LH secretion in the female, appear to indicate the existence of sexual differences in the effect of 5-HT in adult rats.

5-Hydroxytryptophan↗
PubMed1975

Effects of castration, and testosterone in vitro, on the hypothalamic synthesis of different peptide fractions.

The incorporation of [3H]tyrosine ([3H]tyr) into different hypothalamic peptide fractions isolated from normal and castrated rats on a Sephadex G-25 column has been studied in vitro. Luteinizing hormone releasing factor (LH-RF) activity was determined in the different fractions by measuring their ability to elicit release of radioimmunoassayable luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in ovariectomized rats treated with oestrogen and progesterone. For a further purification, the fraction with LH-RF activity was applied to a CM-Sephadex G-25 column eluted with a gradient of ammonium acetate. The large radioactive peptides emerged from the Sephadex G-25 column in fraction S-1, while the small peptides with LH-RF activity were eluted in fraction S-2. Gonadectomy significantly increased the incorporation of [3H]tyr into the peptides of fractions S-2. Only in the purified fraction with LH-RF activity was the radioactivity incorporated higher in gonadectomized than in normal rats. The enhanced incorporation in fraction CM-3 observed after castration implies an increase in the hypothalamic synthesis of peptides with LH-RF activity. The addition of testosterone (2 mug/ml) to the incubation medium of hypothalamus from gonadectomized rats, corrected these modifications. Gonadectomy decreased the incorporation of tyrosine into the large peptides, and incubation with testosterone corrected this change. The modifications in the incorporation of [3H]tyr into the large and small peptides produced by castration appear to indicate that gonadectomy, as well as stimulating the production of LH-RF, enhances the synthesis of other hypothalamic peptides while inhibiting the synthesis of proteins. On the other hand an increase in the breakdown of large peptides into small peptides cannot be excluded.

Animals↗