In vitro pituitary prolactin, growth hormone and follicle stimulating hormone secretion during sexual maturation of female rats primed with melatonin.

The influence of in vivo melatonin administration on in vitro pituitary follicle stimulating hormone (FSH), growth hormone (GH) and prolactin secretion, as well as the possible influence of dopamine (DA) were evaluated in prepubertal (31-day-old), pubertal (33-day-old) and adult female rats at diestrus phase of the sexual cycle. The in vitro pituitary hormone secretions were evaluated at basal rate for the first hour of incubation only, in Krebs Ringer phosphate (KRP) (I1) and after a second hour of incubation with KRP (I2) or with KRP+DA (I2 plus DA). I1PRL secretion was significantly higher in 33-day-old control and melatonin treated (MEL) rats as compared to I2 periods. However, in 31-day-old rats I1 secretion was higher than in the I2 or I2+DA periods, in MEL rats. In vitro GH secretion was significantly higher at I1 than during I2 periods in the control 31- and 33-day-old groups, but not in MEL rats. The only significant effect of DA was the elevation of GH in prepubertal MEL rats. In vitro FSH release was increased by melatonin in 31- and 33-day-old female rats. No differences in PRL, GH and FSH secretion were found in adult rats. In conclusion, the results show that melatonin effects upon in vitro pituitary gland activity are reproductive-stage-dependent modifying the secretory capacity of the lactotrop, gonadotrop and somatotrop during prepubertal and pubertal ages but not in adult rats studied at a quiescent phase of the sexual cycle.

Ageing and melatonin influence on in vitro gonadotropins and prolactin secretion from pituitary and median eminence.

The effect of ageing and/or melatonin (MEL) on in vitro gonadotropins, luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) release and tissue content from pituitary and median eminence (ME) were investigated. Gonadotropins and PRL basal release (I-1) from hemipituitaries of young cyclic-rats was decreased by MEL to levels shown in old acyclic rats. Pituitary tissue content of LH and PRL were not affected by ageing or MEL treatment. However, pituitary FSH tissue content was decreased by ageing and MEL, suggesting a different regulatory mechanism. MEL inhibitory influence on pituitary hormones is mainly exerted on the secretory process. This effect is only exerted in young rats. ME LH and PRL release and content were significantly lower than in pituitary. However, FSH release and content in ME showed values similar to those found in the pituitary. This study confirms that the functional capacities of pituitary gland and ME are maintained during reproductive senescence.

Developmental changes of hypothalamic, pituitary and striatal tachykinins in response to testosterone: influence of prenatal melatonin.

Substance P (SP) and neurokinin A (NKA), members of the family of mammalian tachykinins, are involved in the regulation of many physiological functions and are widely distributed in mammalian tissues. In this report, the effects of prenatal melatonin on the postnatal developmental pattern of NKA, and SP, and on testosterone secretion were investigated. Also, tachykinin response to the administration of testosterone propionate (TP) was studied. The brain areas studied were medio-basal-hypothalamus, pituitary gland and striatum. Male rat offspring of control or melatonin treated mother rats were studied at different ages of the sexual development: infantile, juvenile or prepubertal periods, and pubertal period. Both groups received exogenous TP (control-offspring+TP and MEL-offspring+TP), or the vehicle (control-offspring+placebo and MEL-offspring+placebo). Hypothalamic concentrations of all peptides studied in control-offspring+placebo remained at low levels until the juvenile period, days 30-31 of age. After this age, increasing concentrations of these peptides were found, with peak values at puberty, 40-41 days of age, then declining until adulthood. In the MEL-offspring+placebo a different pattern of development was observed; hypothalamic concentrations of NKA and SP from the infantile period until the end of juvenile period were significantly higher than in control-offspring+placebo. TP administration exerted a more marked influence on MEL-offspring than on control-offspring and prevented the elevation in tachykinin concentrations associated with prenatal melatonin treatment. TP administration to control-offspring resulted in significantly reduced (P < 0.05) tachykinin concentration only at 40-41 days of age, and increased (P < 0.01) during infantile period as compared to control-offspring+placebo. Pituitary NKA concentrations were lower than in the hypothalamus. In control-offspring+placebo pituitary NKA levels did not show significant changes throughout sexual development. A different developmental pattern was observed in MEL-offspring+placebo, with significantly increased (P < 0.05) pituitary NKA concentrations at 35-36 days of age than in control-offspring+placebo. TP administration to control-offspring influenced pituitary NKA levels at the end of the infantile and pubertal periods, showing at both stages significantly higher (P < 0.05) NKA levels as compared to control-offspring+placebo. NKA levels in MEL-offspring+TP were only affected at 21-22 days of age, showing significantly increased (P < 0.01) values as compared to MEL-offspring+placebo. Striatal tachykinin concentrations in control-offspring did not undergo important modifications throughout sexual development, but during the prepubertal period they started to increase. Maternal melatonin and TP injections produced short-lived alterations during the infantile period. The results showed that prenatal melatonin delayed the postnatal testosterone secretion pattern until the end of the pubertal period and postnatal peptide secretion in brain structures. Consequently, all functions depending of the affected areas will in turn, be affected.