Possible role of dopamine and noradrenaline in the regulation of prolactin secretion from an ectopic anterior pituitary gland in female rats

Abstract

It was recently reported that anterior pituitary tissue transplanted to an ectopic site contains measurable amounts of dopamine and noradrenaline. To examine the possibility of local catecholaminergic control of prolactin secretion from ectopic pituitaries, pituitary grafted and sham-operated female rats were submitted to several pharmacological treatments modifying catecholamine synthesis. Administration of a single dose of alpha-methyl-p-tyrosine (alpha-MPT) significantly reduced dopamine content in the graft, while noradrenaline content was not modified. Similar changes in the contents of dopamine and noradrenaline after alpha-MPT administration were observed in the hypothalamus and in the in-situ pituitary in both grafted and sham-operated rats. Plasma concentrations of prolactin were increased in both grafted and sham-operated rats after administration of alpha-MPT. A single injection of L-3,4-dihydroxyphenylalanine (L-DOPA) increased dopamine content in the ectopic pituitary gland without altering the noradrenaline content, and produced similar effects in the hypothalamus and in-situ pituitary of grafted and control rats. Plasma prolactin concentrations were decreased by L-DOPA in both pituitary grafted and control rats. Administration of DL-treo-dihydroxyphenylserine (DOPS) increased noradrenaline content in the ectopic pituitary and reduced plasma prolactin concentrations in pituitary grafted rats. In contrast, injection of DOPS to control rats increased both hypothalamic noradrenaline content and plasma prolactin concentrations. These results suggest that dopamine and noradrenaline present in the ectopic pituitary tissue have a role in mediating prolactin release from pituitary transplants.

Effects of cyclosporine at the hypothalamic-pituitary axis in pituitary-grafted young female rats

“…As expected, pituitary grafting increased hypothalamic DA turnover, as measured by the DOPAC/DA index, confirming previous studies (Cramer et al 1979, Gudelsky & Porter 1979, Esquifino et al 1987a). There was also a decrease in hypothalamic NE and serotonin contents, the latter only at 8 days (King et al 1985).…”

“…Differential PRL regu¬ latory mechanisms operating on the ectopie tissue have also been observed (Fernández-Ruiz et al 1987a, Agrasal et al 1988, 1989, and confirmed by finding high levels of DA and its biosynthetic enzyme, tyrosine hydroxylase, in the ectopie gland (Iturriza et al 1983. Furthermore the ectopie pituitary gland can release hormones other than PRL (Esquifino et al 1987a). …”

“…The ectopie circulating PRL is associated with an increase in DA turnover at the hypothalamo-pituitary axis (Fernández-Ruiz et al 1987a) which is also found in hypophysectomized rats bearing ectopie pituitaries (Fernández-Ruiz et al 1987fc). Differential PRL regu¬ latory mechanisms operating on the ectopie tissue have also been observed (Fernández-Ruiz et al 1987a, Agrasal et al 1988, 1989, and confirmed by finding high levels of DA and its biosynthetic enzyme, tyrosine hydroxylase, in the ectopie gland (Iturriza et al 1983. Furthermore the ectopie pituitary gland can release hormones other than PRL (Esquifino et al 1987a).…”

“…Other central neurotransmitters, such as nor¬ epinephrine (NE) and serotonin, are also involved in the regulation of PRL release (Andersson et al 1981, Voogt & Carr 1981, Day et al 1982. The presence of an ectopie pituitary leads to an increase in plasma PRL levels mainly from the ectopie gland (Esquifino et al 1987a(Esquifino et al , 1990. The ectopie circulating PRL is associated with an increase in DA turnover at the hypothalamo-pituitary axis (Fernández-Ruiz et al 1987a) which is also found in hypophysectomized rats bearing ectopie pituitaries (Fernández-Ruiz et al 1987fc).…”

“…The presence of an ectopie pituitary leads to an increase in plasma PRL levels mainly from the ectopie gland (Esquifino et al 1987a(Esquifino et al , 1990. The ectopie circulating PRL is associated with an increase in DA turnover at the hypothalamo-pituitary axis (Fernández-Ruiz et al 1987a) which is also found in hypophysectomized rats bearing ectopie pituitaries (Fernández-Ruiz et al 1987fc). Differential PRL regu¬ latory mechanisms operating on the ectopie tissue have also been observed (Fernández-Ruiz et al 1987a, Agrasal et al 1988, 1989, and confirmed by finding high levels of DA and its biosynthetic enzyme, tyrosine hydroxylase, in the ectopie gland (Iturriza et al 1983.…”