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ABSTRACT
Long-term ovariectomized rats received a single injection of 20 μg oestradiol benzoate (OB) which reduced the serum levels of LH for at least 3 days. The inhibitory effects were accompanied by time-dependent alterations of noradrenaline and dopamine turnover rates in the mediobasal hypothalamus (MBH) and the preoptic-anterior hypothalamic brain area (POAH). Oestradiol markedly interfered with the time-dependent variations of noradrenaline and dopamine turnover seen in the MBH of untreated ovariectomized animals during daylight hours. In the POAH the turnover rate of noradrenaline decreased 2 days after priming with OB and then increased in the afternoon of day 3. The increase of noradrenaline turnover in the POAH was accompanied by a low afternoon turnover rate of dopamine in the M BH and by an increased sensitivity of the LH secretory system to progesterone.
Dopamine and noradrenaline turnover involve a time element. While the negative feedback actions of oestradiol do not seem to be associated with changes in dopamine or noradrenaline turnover, the results support the view that the induction of LH afternoon surges depends upon an increase of stimulatory noradrenergic inputs to the POAH and a decrease of inhibitory dopaminergic inputs in the MBH.
J. Endocr. (1985) 106, 303–309
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Single pigeon anterior pituitary glands were incubated with or without a hypothalamus in media containing various drugs. Release of prolactin and growth hormone was quantified by an electrophoretic-densitometric method. The hypothalamus stimulated release of both prolactin and growth hormone from the pituitary gland. Dopamine did not affect hormone release from pituitary glands incubated alone, but inhibited hypothalamus-stimulated release of prolactin and augmented hypothalamus-stimulated release of growth hormone in a dose-related manner. The effects of dopamine were reversed by its antagonist, pimozide. Serotonin stimulated release of prolactin and inhibited release of growth hormone from pituitary–hypothalamus co-incubations, and these effects were blocked by its antagonist, methysergide. Thyrotrophin releasing hormone (TRH) stimulated release of both hormones directly from pituitary glands incubated alone. Dopamine now inhibited TRH-stimulated release of prolactin, without affecting TRH-stimulated release of growth hormone. These results indicate that the neurotransmitters, dopamine and serotonin, affect the in-vitro release of factors from the hypothalamus which control the secretion of prolactin and growth hormone. In addition, dopamine may inhibit release of prolactin directly from the pituitary gland, but only when secretion of prolactin is high initially.
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The inhibitory effects of dopamine and various ergot alkaloids on prolactin secretion were studied using continuously perfused columns of dispersed rat anterior pituitary cells. Bromocriptine (5 nmol/l) and lisuride hydrogen maleate (5 nmol/l) both inhibited prolactin secretion, the effects persisting for more than 3 h after the end of the administration of the drugs. A similar although less long-lasting effect was observed with lergotrile (50 nmol/l) and the new ergoline derivative, pergolide (5 nmol/l). These effects contrasted with the rapid disappearance of the action of dopamine. The potency estimates of the ergots relative to that of dopamine were: lergotrile, 2·3; bromocriptine, 13; lisuride, 15; pergolide, 23.
The dopamine-receptor blocking drugs, metoclopramide and haloperidol, antagonized the prolactin release-inhibiting activity of the compounds; bromocriptine and lisuride showed the highest resistance to this dopaminergic blockade.
The results suggested that the direct effect of the ergot derivatives on dispersed pituitary cells was mediated through dopamine receptors and emphasized the long-lasting action of bromocriptine and lisuride in vitro.
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al. 1981 , Akers 1985 ). Several studies have shown that this PRL pulse is also essential for the initiation of lactation. Treatment at the end of pregnancy with the dopamine agonist bromocriptine (BRO) to suppress the peripartum PRL pulse results
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levels of tyrosine hydroxylase ( Th ), the initial and generally rate-limiting enzyme of CA biosynthesis, in adrenal medulla and the NTS, and dopamine-β-hydroxylase ( Dbh ) mRNA levels in the LC. However, the responses to estrogens are tissue specific
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(Roche) and 1 μl of the following primer pairs: rat or mouse Th , dopamine β-hydroxylase ( Dbh ), AT 1A receptor, AT 2 receptor, or Gapdh (all purchased from Qiagen), and analyzed on an ABI7900HT Real Time PCR instrument (Applied Biosystems). Data
Centre for Paediatrics and Child Health, Department of Paediatric Endocrinology, Department of Endocrinology, Centre for Endocrinology and Diabetes, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, M13 9WL, UK
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Centre for Paediatrics and Child Health, Department of Paediatric Endocrinology, Department of Endocrinology, Centre for Endocrinology and Diabetes, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, M13 9WL, UK
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Centre for Paediatrics and Child Health, Department of Paediatric Endocrinology, Department of Endocrinology, Centre for Endocrinology and Diabetes, Institute of Human Development, Faculty of Medical and Human Sciences, University of Manchester, M13 9WL, UK
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less impressive, and commonly, pituitary radiotherapy and medical therapy were required to control the GH excess. The first medical therapy available for acromegaly was a dopamine agonist. In the 1970s it was discovered that the administration of l
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SUMMARY
Polymorphic cells whose granules give a positive chromaffin reaction have been identified in the liver capsule and gut of the ox, cow and sheep. These cells give a positive argentaffin and Schmorl's reaction in dichromate-fixed material, and fail to couple with alkaline diazonium compounds. These reactions are consistent with the presence of a catechol, and from the work of Bertler, Falck, Hillarp, Rosengren & Torp (1959) it would appear that they contain dopamine.
These chromaffin, dopamine-containing cells are, however, not a special type of cell but are tissue mast cells. Nuclear fast red (Herzberg) is not, as suggested by Falck, Hillarp & Torp (1959a, b), a specific stain for dopamine, but, when prepared with aluminium sulphate, it is specific for sulphated mucopolysaccharides.
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hormones (DAGIN, Ovaprim or LinPe), involves a combination of synthetic, highly potent GnRH agonist with a dopamine antagonist ( Peter et al. 1988 b , Drori et al. 1994 ). However, the use of ground pituitaries is associated with various drawbacks; the
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ABSTRACT
Catecholoestrogens are naturally occurring metabolites of oestrogens which are found in brain tissue and for which a neuroendocrine role has been postulated. However, reports of their effects on prolactin secretion are ambiguous and as yet no defined function has been attributed to them.
The effects of 2-hydroxyoestradiol (2-OHE2) and dopamine on the release of prolactin in vitro by perfused pituitary glands from normal adult female rats at different stages of the oestrous cycle have been investigated. The purity and stability of the 2-OHE2 preparation before and after exposure to pituitary tissue was confirmed by radioenzymatic assay and subsequent thin-layer chromatography. Dopamine (500 nmol/l, 100 nmol/l) was found consistently to suppress release by 60%; this effect was immediate and reversible upon removal of the dopamine. In contrast, the effects of 2-OHE2 (10 nmol/l, 100 nmol/l) were found to vary during the cycle. No effect on prolactin release was evident during either dioestrus or pro-oestrus, but during oestrus a similar, though less potent, suppression of prolactin secretion to that of dopamine was observed (35% suppression compared with controls).
The cyclical variation in the suppressive effect of 2-OHE2 on prolactin secretion in the female rat is compatible with a postulated neuroendocrine role for this catecholoestrogen.
J. Endocr. (1986) 111, 199–204
