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. In the first series of in vitro experiments, median eminences and anterior pituitaries were incubated in Krebs-Ringer bicarbonate buffer containing two MCH concentrations (10(-10) and 10(-8) M). The lowest MCH concentration (10(-10) M) increased (P < 0.01) LHRH release only from proestrous median eminences. Anterior pituitaries incubated with both MCH concentrations also showed that 10(-10) M MCH increased gonadotropin release only from proestrous pituitaries. In the second series of experiments, median eminences and pituitaries from proestrous rats were incubated with graded concentrations of MCH. MCH (10(-10) and 10(-9) M) increased (P < 0.01) LHRH release from the median eminence, and only 10(-10) M MCH increased (P < 0.01) LH and FSH release from the anterior pituitary. The effect of MCH on the stimulation of both gonadotropins from proestrous pituitaries was similar to the effect produced by LHRH. Simultaneous incubation of pituitaries with MCH and LHRH did not modify LH but increased the FSH release induced by LHRH. The present results suggest that MCH could be involved in the regulation of preovulatory gonadotropin secretion.

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. When milk ejection is blocked in litter-deprived dams, mammary glands are not evacuated and they remain engorged. Suckling stimuli were not the cause of the difference in suckling-induced serum PRL levels in control and sleep-deprived dams. The engorgement of the mammary glands may play a role, as a maximum suckling-induced PRL increase was not observed in nonseparated SD dams with nonengorged mammary glands. Moreover, suckling-induced PRL levels were decreased when engorged mammary glands of SD dams were evacuated through an oxytocin injection. A parallel increase between suckling-induced PRL levels and mammary gland weight was observed in the experiments in which milk ejection was impaired through an increase in the intervals of nonsuckling, providing additional support for a relationship between mammary gland engorgement and the regulation of suckling-induced PRL levels.

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. The hypophysis of dioestrous-1 glands were used as controls. Both types of grafts released PRL an GH to the medium, being the PRL release of the anterior lobe graft higher than that of the whole pituitary graft. The in situ pituitary glands of grafted animals released less PRL than the control dioestrous glands. Also, the in situ glands of whole pituitary grafted animals released less PRL than the hypophysis of animals which bore grafts of only the anterior lobe. No difference in GH secretion, either by the graft or by the in situ gland was observed when whole pituitary or anterior grafts were used. These results provide a further support to the hypothesis that a pituitary graft under the kidney capsule exerts profound modifications in the function of the in situ hypophysis. The presence of the neurointermediate lobe (NIL) in the graft is modulatory to the release of PRL.

Release of prolactin and growth-hormone by pituitary grafts role of the neurointermidiate lobe

Usando técnicas de perfurasión, se estudió la liberación de PRL y de GH de los transplantes hipofisarios y de las correspondientes hipófisis in situ. Se utilizaron transplantes de hipófisis total o de lóbulo anterior hipofisario solamente. Las hipófisis de hembras en el estadio Diestro-1 del ciclo estral se utilizaron como controles. Tanto los transplantes como las hipófisis in situ se incubaron solas en una cámara de perfusión. Ambos tipos de transplante liberaron PRL y GH al medio, siendo la liberación de PRL del transplante de lóbulo anteior mayor que la liberación por el transplante de hipófisis total. Las glándulas in situ de los animales transplantados liberaron menos PRL que las glándulas animales con transplante de hipófisis total menor que la de las hipófisis de animales con transplante de lóbulo anterior solamente. No se encontraron diferencias en la liberación de GH entre los dos tipos de transplante ni entre los dos tipos de hipófisis in situ. Estos resultados sugieren que la presencia de un transplante hipofisario bajo la cápsula renal produce profundas modificaciones en la función de las hipófisis in situ. :a presencia del lóbulo neurointermedio en el transplante modula la liberación de PRL (AU)

Release of prolactin and growth-hormone by pituitary grafts role of the neurointermidiate lobe

Usando técnicas de perfurasión, se estudió la liberación de PRL y de GH de los transplantes hipofisarios y de las correspondientes hipófisis in situ. Se utilizaron transplantes de hipófisis total o de lóbulo anterior hipofisario solamente. Las hipófisis de hembras en el estadio Diestro-1 del ciclo estral se utilizaron como controles. Tanto los transplantes como las hipófisis in situ se incubaron solas en una cámara de perfusión. Ambos tipos de transplante liberaron PRL y GH al medio, siendo la liberación de PRL del transplante de lóbulo anteior mayor que la liberación por el transplante de hipófisis total. Las glándulas in situ de los animales transplantados liberaron menos PRL que las glándulas animales con transplante de hipófisis total menor que la de las hipófisis de animales con transplante de lóbulo anterior solamente. No se encontraron diferencias en la liberación de GH entre los dos tipos de transplante ni entre los dos tipos de hipófisis in situ. Estos resultados sugieren que la presencia de un transplante hipofisario bajo la cápsula renal produce profundas modificaciones en la función de las hipófisis in situ. :a presencia del lóbulo neurointermedio en el transplante modula la liberación de PRL

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. The hypophysis of dioestrous-1 glands were used as controls. Both types of grafts released PRL an GH to the medium, being the PRL release of the anterior lobe graft higher than that of the whole pituitary graft. The in situ pituitary glands of grafted animals released less PRL than the control dioestrous glands. Also, the in situ glands of whole pituitary grafted animals released less PRL than the hypophysis of animals which bore grafts of only the anterior lobe. No difference in GH secretion, either by the graft or by the in situ gland was observed when whole pituitary or anterior grafts were used. These results provide a further support to the hypothesis that a pituitary graft under the kidney capsule exerts profound modifications in the function of the in situ hypophysis. The presence of the neurointermediate lobe (NIL) in the graft is modulatory to the release of PRL.

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. The hypophysis of dioestrous-1 glands were used as controls. Both types of grafts released PRL an GH to the medium, being the PRL release of the anterior lobe graft higher than that of the whole pituitary graft. The in situ pituitary glands of grafted animals released less PRL than the control dioestrous glands. Also, the in situ glands of whole pituitary grafted animals released less PRL than the hypophysis of animals which bore grafts of only the anterior lobe. No difference in GH secretion, either by the graft or by the in situ gland was observed when whole pituitary or anterior grafts were used. These results provide a further support to the hypothesis that a pituitary graft under the kidney capsule exerts profound modifications in the function of the in situ hypophysis. The presence of the neurointermediate lobe (NIL) in the graft is modulatory to the release of PRL.

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. GABA (10-30 ng/microliter) was also found in fluid in the ovarian bursa. At 11:00 h, on the day of oestrus, GABA content increased in the ovaries but values in the oviducts were maximal at 11:00 h on the day of pro-oestrus. Variations in GABA content of the vagina were also found. Uterine cervix or uterine horn showed no changes during the oestrous cycle. The GABA content was not uniform throughout the oviduct: the highest values were found in the portion next to the ovary. At 10 days after removal of the right oviduct, GABA values in the ovary and ovarian bursa fluid decreased on the operated side. At 1 month after surgery, the values in ovary were normal but the values in ovarian bursa fluid were still low, suggesting that the source of ovarian GABA was not the oviduct. The variations observed in the present paper suggest an involvement of GABA in reproductive physiology.

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. Isolated anterior pituitary lactotroph cells incorporated more [3H]dopamine than a fraction containing other 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 0.390 +/- 0.038 (S.E.M.), 0.228 +/- 0.042 and 1.824 +/- 0.268 respectively. These values show an uneven distribution of CAT in the neurointermediate lobe. The hypothesis of a cholinergic system located in the junction area has been advanced.