Changes of melanin-concentrating hormone related to LHRH release in the median eminence of rats.

The present research was carried out to study the distribution of melanin-concentrating hormone (MCH) fibers in the median eminence of rats and to evaluate if changes in the MCH content of the median eminence could be related to the release of LHRH. Immunocytochemical studies in the median eminence of males and estrous females showed the presence of MCH fibers, mainly in its internal layer. Diestrous and proestrous animals displayed MCH immunoreactivity in both the internal and external layers of the median eminence.

Melanin-concentrating hormone stimulates the release of luteinizing hormone-releasing hormone and gonadotropins in the female rat acting at both median eminence and pituitary levels.

The purpose of this study was to investigate whether melanin-concentrating hormone (MCH) acts directly on the median eminence and on the anterior pituitary of female rats regulating LHRH and gonadotropin release. In addition, immunohistochemistry was used to examine the density and distribution of MCH-immunoreactive fibers in the median eminence of proestrous rats. MCH-immunoreactive fibers were found in both the internal and external layers of the median eminence and in close association with hypophysial portal vessels.

Suckling-induced serum prolactin levels are modified by interference with milk ejection in lactating rats.

The aim of this study was to determine whether suckling-induced prolactin (PRL) levels were modified when milk ejection was impaired. Milk ejection impairment was achieved in two experimental models: a) depriving the dam of sleep during suckling and b) increasing the nonsuckling intervals in lactating dams. Sleep deprivation blocked milk ejection and enhanced suckling-induced PRL levels in dams that had been previously separated from their pups.

Involvement of Catecholestrogens in the release of pituitary hormones.

Catecholestrogens (CE), natural metabolic products of 17ß-estradiol and estrone, were assayed in anterior and posterior pituitary lobes and in the median eminence of the rat. The highest CE values were found in the median eminence and the lowest in the anterior pituitary. The CE concentrations in pars nervosa and pars intermedia of the posterior pituitary were quite similar.

Release of prolactin and growth-hormone by pituitary grafts. Role of the neurointermediate lobe.

The release of prolactin (PRL) and growth hormone (GH) of pituitary grafts and in situ glands was investigated using perifusion techniques. Whole pituitary or anterior lobe grafts were used. The grafts or the in situ glands were incubated alone in a chamber.

Gamma-aminobutyric acid in the genital tract of the rat during the oestrous cycle.

The highest values of gamma-aminobutyric acid (GABA) in the genital tract of the rat at different stages of the oestrous cycle were found in the oviduct (3.5-7 micrograms/mg protein) and the lowest in the ovary (50-100 ng/mg protein). The values for uterus and vagina ranged between 80 and 150 ng/mg protein.

Dopamine enters lactotrophs and reaches their secretory granules.

The presence of dopamine in the lactotroph cell, as well as in isolated prolactin secretory granules, was demonstrated by means of an histochemical reaction for electron microscopy. Biochemical assays further confirmed the presence of dopamine in the secretory granules. Autoradiographic preparations examined by light microscopy showed dopamine internalization in dispersed anterior pituitary cells.

An uneven distribution of choline acetyltransferase activity in the pituiatry neurointermediate lobe of the rat.

The neurointermediate lobe of the pituitary gland of male rats was assayed for choline acetyltransferase (CAT) activity. Precise microsample punches were obtained from neurohypophysial tissue, pure pars intermedia tissue and from the junction area between them. The level of CAT activity (pmol/h per microgram protein) in the neurohypophysis, pars intermedia and junction area were 0.