Impact of gestational and lactational phthalate exposure on hypothalamic content of amino acid neurotransmitters and FSH secretion in peripubertal male rats.

This study investigated the effect of the pre- and perinatal exposure to di-(2-ethylhexyl) phthalate (DEHP) on the neuroendocrine parameters that regulate reproduction in peripubertal male rats. DEHP at dose of 3 and 30mg/kg bw/day was administered orally to female rat since pregnancy onset until weaning. The male litters were sacrificed at 30 days of age to determine gonadotropin serum level and the hypothalamic contents of the amino acids aspartate and gamma-aminobutyric acid. No changes in gonadotropin, aspartate and gamma-aminobutyric acid levels were detected at the low dose. DEHP 30mg/kg bw/day reduced testis weight and serum FSH, in correlation with a significant increase in the inhibitory GABAergic tone and a reduction in the stimulatory effect of aspartate on gonadotropin level. This study provides unknown data regarding changes in the hypothalamic contents of the amino acid neurotransmitters, which are involved in the neuroendocrine regulation of reproductive axis, in peripubertal male rat offspring from dams exposed to DEHP during gestational and lactational periods. This could be related with the gonadotropin modifications also here described.

Low dose 4-MBC effect on neuroendocrine regulation of reproductive axis in adult male rats.

4-Methylbenzylidene camphor (4-MBC) is an ultraviolet absorbent. The objective of this paper was to evaluate the effect of 4-MBC low-dose exposure on the neuroendocrine reproductive regulation in male rats. Wistar male adult rats were injected sc. with 4-MBC during 5 days with a dose of 2 and 10mg/kg or during 2 days with a dose of 2 and 20mg/kg. In all rats serum prolactin, LH and FSH concentration were assayed. The hypothalamus of rats injected during 2 days were also dissected to study GnRH release. Rats that received 2 and 10mg/kg of 4-MBC during 5 days showed a decrease in the LH and FSH serum concentration. In rats injected during 2 days, serum LH decreased with 2 and 20mg/kg and FSH decreased with 2mg/kg of 4-MBC. In vitro hypothalamic GnRH release also decreased in these animals. These results show that low doses of 4-MBC inhibit the reproductive axis in adult male rats.

Effect of leptin on LH levels and hypothalamic release of GnRH. Its relationship with the hypothalamic neurotransmitter amino acids system in adult male rats.

The objective of the present paper was to determine the effect of leptin on the reproductive axis in adult male rats, as well as the hypothalamic mechanisms involved in this effect. For this purpose, we studied the in vivo effect of leptin in adult male rats on serum LH levels, and the in vitro effect on hypothalamic GnRH and amino acid neurotrasmitter release. For in vivo experiments, animals were injected i.p. with leptin at a dose of 30, 100 and 300 microg/kg. In the in vitro experiments, hypothalamic samples were incubated for 60 min in Earle's medium with leptin: 10(-9), 10(-10) and 10(-12) M for GnRH determination, and 10(-10) M for amino acids evaluation. Finally, we studied the effect of the lowest effective leptin dose on plasma LH levels in peripubertal male rats to compare the effect between this group and adults. Leptin induces significant decreases of serum LH levels with the different studied doses (p < 0.01 vs. control) in adult male rats, while in peripubertal male rats, it induced a significant (p < 0.01 vs. control) increment in serum LH levels. On the other hand, in vitro leptin in adult male rats, significantly decreases GnRH release as well as the hypothalamic release of glutamate (GLU). In contrast, leptin increased the GABA release by this hypothalamus in these animals. These results indicate that leptin has an inhibitory effect on the GnRH-LH axis in adult male rats and this effect appears to be connected with an inhibition of hypothalamic release of GLU (the excitatory amino acid) and a stimulatory effect on GABA release (the inhibitory amino acid). On the other hand, in peripubertal male rats, leptin showed a stimulatory effect.

Hypothalamic nitric oxide synthase activity during sexual maturation in female rats. Effects of estrogens.

OBJECTIVES: To determine the hypothalamic activity of nitric oxide synthase (NOS, the enzyme involved in the synthesis of nitric oxide NO) during sexual maturation in prepubertal (15 days old) and peripubertal female rats (30 days old) as well as the effect of estradiol administration on this neurotransmitter system. METHODS: Hypothalamic samples containing the anterior preoptic and medial basal areas (APOA-MBH) were homogenized with HEPES 20 mM, pH = 7.4 and NOS activity was determined in APO-MBH after 10 minutes of incubation by the conversion of 14C arginine to 14C citrulline. RESULTS: The hypothalamic concentration of NOS is significantly higher in peripubertal than in prepubertal rats. Treatment with EB increased significantly the activity of the enzyme in both groups compared with control and the increases was similar at both ages. CONCLUSIONS: These results clearly demonstrated that the hypothalamic NOS activity increases in peripubertal rats as compared with prepubertal animals. Estradiol has a similar stimulatory effect on hypothalamic NOS activity at both ages of sexual maturation, indicating that the increase in NOS during sexual maturation is connected with the peripubertal increase of estradiol rather than an increase in the sensitivity of the enzyme to the ovarian hormone.

Effects of gabaergic and serotoninergic systems on hypothalamic content of catecholamines during sexual development in female rats.

OBJECTIVES: The aim of the present investigation was to determine whether the catecholaminergic system is involved in gabaergic and serotoninergic effects on gonadotrophin secretion during sexual development. To this end, we studied the effect of GABAergic and serotoninergic systems on hypothalamic catecholamine content at different stages of sexual development. METHODS: The effect of GABA A and GABA B agonists and 5-hydroxy-L-tryptophan on hypothalamic noradrenaline and dopamine content were determined in prepubertal (16 days old) and peripubertal (30 days old) rats. RESULTS: At 16 days of age GABA agonists did not modify hypothalamic noradrenaline content, whereas a significant decrease in catecholamine concentration was observed in peripubertal rats at 30 days of age. Similar changes were observed with GABA agonists administration on dopamine hypothalamic levels, i.e no effects at 15 days of age and a significant decrease at 30 days. The administration of 5-hydroxy-l-tryptophan (5-HTP) induced a decrease of hypothalamic concentration of noradrenaline and dopamine at both ages. CONCLUSION: Results indicate that the GABAergic system modifies the hypothalamic catecholamine content in peripubertal but not in prepubertal rats while serotonin has an inhibitory effect at both stages of sexual maturation. Even though both systems induce similar ontogenic modifications on the gonadotrophin axis (stimulatory effect in prepubertal and inhibitory action in peripubertal and adult rats) the present results appear to indicate that GABAergic and serotoninergic systems regulate gonadotrophin secretion by different hypothalamic mechanisms.

Changes in the effect of testosterone on hypothalamic nitric oxide synthetase during sexual maturation. Its relationship with GnRH release.

OBJECTIVES: To determine the effect of testosterone administration to prepubertal (15 days old) and peripubertal rats (30 days old) on hypothalamic nitric oxide synthetase (NOS), and GnRH release. METHODS: Hypothalamic samples containing the anterior preoptic and medial basal areas (APO-MBH) were incubated for 30 minutes in 500 l of Earle's medium with glucose (1 mg/ml) and bacitracin (20 mM). GnRH was determined by RIA in the medium and NOS activity was determined in APO-MBH after 10 min of incubation by the conversion of (14) C arginine to (14) C citrulline. RESULTS: Treatment with testosterone propionate, significantly decreased NOS hypothalamic activity in prepubertal male rats. ( CONTROL: 58.41 +/- 0.85; Testosterone: 25.61 +/- 1.40, p<0.001) and had no effect in peripubertal male rats (CONTROL 49.28 +/- 1.50; Testosterone 51.48 +/- 5.2 pmoles NO/10 min/hypothalamus). On the other hand, in prepubertal rats the treatment decreased Gn-RH release ( CONTROL: 3.62 +/- 0.23; Testosterone: 1.38 +/- 0.11 (pg/ml medium, p<0.001) and had no effect on Gn-RH release in 30 days old rats ( CONTROL: 3.65 +/- 0.33;Testosterone: 4.15 +/- 0.36 pg/ ml, medium). CONCLUSION: These results clearly demonstrated that testosterone has an inhibitory effect on hypothalamic NOS activity in prepubertal rats while it did not affect the concentration of this neurotransmitter system in peripubertal rats. This pattern is similar to that observed with GnRH hypothalamic release since testosterone has an inhibitory effect in prepubertal rats and did not modify the GnRH release in peripubertal rats. Taking into account the well known stimulatory effect of NO on GnRH and the decrease in the sensitivity of GnRH-gonadotrophin axis to the inhibitory feedback effect of testosterone during sexual maturation and the onset of puberty, it is proposed that the changes here described are connected with maturational modifications in the sexual hormones on-GnRH axis connected with the onset of puberty.

Efecto de la activacion gabaergica sobre la maduracion sexual en ratas hembras peripuberales / Effect prologed gabaergic activation on the pubertal development of female rats

Evaluamos 1) efecto del tratamiento prolongado (días 23-29 postnatales) con ácido aminooxiacético (AAOA) sobre el desarrollo puberal en ratas hembra; este tratamiento aumentó el contenido de GABA (p< 0.002), disminuyendo el de GnRH y glutamato (p < 0.05 y < 0.02) en hipotálamo. La LH (p < 0.05) y el estradiol (p < 0.005) séricos cayeron. La apertura vaginal fue a los 30.8 + 0.6 días en los controles, y a los 36.7 + 0.98 días en las tratadas (p < 0.0001). 2) A los 30 días, el tratamiento agudo con AAOA redujo la liberación ex vivo de GnRH y de glutamato la de taurina. Este efecto fue similar al observado agregando al medio agonistas GABA-A y B. Conclusiones: la activación peripuberal del sistema GABAérgico frena el eje reprodutor, produciendo un retraso en el desarrollo. Esto podría atribuirse a la existencia, en esta etapa, de interrelaciones fisiológicas entre los aminoácidos que regulan la secreción de GnRH (GABA, glutamato, taurina).

Efecto de la activacion gabaergica sobre la maduracion sexual en ratas hembras peripuberales / Effect prologed gabaergic activation on the pubertal development of female rats

Evaluamos 1) efecto del tratamiento prolongado (días 23-29 postnatales) con ácido aminooxiacético (AAOA) sobre el desarrollo puberal en ratas hembra; este tratamiento aumentó el contenido de GABA (p< 0.002), disminuyendo el de GnRH y glutamato (p < 0.05 y < 0.02) en hipotálamo. La LH (p < 0.05) y el estradiol (p < 0.005) séricos cayeron. La apertura vaginal fue a los 30.8 + 0.6 días en los controles, y a los 36.7 + 0.98 días en las tratadas (p < 0.0001). 2) A los 30 días, el tratamiento agudo con AAOA redujo la liberación ex vivo de GnRH y de glutamato la de taurina. Este efecto fue similar al observado agregando al medio agonistas GABA-A y B. Conclusiones: la activación peripuberal del sistema GABAérgico frena el eje reprodutor, produciendo un retraso en el desarrollo. Esto podría atribuirse a la existencia, en esta etapa, de interrelaciones fisiológicas entre los aminoácidos que regulan la secreción de GnRH (GABA, glutamato, taurina). (AU)

Control nervioso de la ovulación: mecanismo íntimo de acción del citrato de clomifeno / Nervous control of the ovulation: intimate mechanism of action of the clomiphen citrate

Las distintas series de experimentos que constituyen el presente trabajo han tenido por finalidad estudiar los complejos mecanismos que participan en el control nervioso de la secreción de gonadotrofinas de la anterohipófisis, como así también determinar los factores nerviosos implicados en el diferente ritmo sexual de secreción de gonadotrofinas. En estos estudios han sido utilizados parámetros que permiten valorar directamente cambios en la actividad neuronal, como son el metabolismo oxidativo (consumo de oxígeno, producción de ácido láctico, actividad de enzimas del ciclo de Krebs, producción de C1402 a partir de glucosa-U-C14) y el metabolismo protéico (incorporación de fenilalanina-H3 en proteínas). Estos parámetros fueron determinados, mediante el uso de microtécnicas en áreas hipotalámicas y corteza cerebral. Teniendo en cuenta que el control nervioso de la secreción gonadotrófica de la hipófisis se realiza mediante la formación en el hipotálamo de sustancias de origen protéico, denominadas "factores liberadores", hemos considerado que los cambios en el metabolismo hipotalámico están relacionados, con variaciones en la síntesis nerviosa de estos factores. En la primer serie de experimentos se ha estudidado el efecto de la castración y de las hormonas sexuales "in vivo" e "in vitro" sobre el metabolismo oxidativo y protéico de diversas áreas hipotalámicas, como así también de la corteza cerebral e hipófisis...(TRUNCADO)(AU)

Control nervioso de la ovulación: mecanismo íntimo de acción del citrato de clomifeno / Nervous control of the ovulation: intimate mechanism of action of the clomiphen citrate

Las distintas series de experimentos que constituyen el presente trabajo han tenido por finalidad estudiar los complejos mecanismos que participan en el control nervioso de la secreción de gonadotrofinas de la anterohipófisis, como así también determinar los factores nerviosos implicados en el diferente ritmo sexual de secreción de gonadotrofinas. En estos estudios han sido utilizados parámetros que permiten valorar directamente cambios en la actividad neuronal, como son el metabolismo oxidativo (consumo de oxígeno, producción de ácido láctico, actividad de enzimas del ciclo de Krebs, producción de C1402 a partir de glucosa-U-C14) y el metabolismo protéico (incorporación de fenilalanina-H3 en proteínas). Estos parámetros fueron determinados, mediante el uso de microtécnicas en áreas hipotalámicas y corteza cerebral. Teniendo en cuenta que el control nervioso de la secreción gonadotrófica de la hipófisis se realiza mediante la formación en el hipotálamo de sustancias de origen protéico, denominadas "factores liberadores", hemos considerado que los cambios en el metabolismo hipotalámico están relacionados, con variaciones en la síntesis nerviosa de estos factores. En la primer serie de experimentos se ha estudidado el efecto de la castración y de las hormonas sexuales "in vivo" e "in vitro" sobre el metabolismo oxidativo y protéico de diversas áreas hipotalámicas, como así también de la corteza cerebral e hipófisis...(TRUNCADO)