Dopaminergic mediation of beta-endorphin-induced prolactin secretion

Intracisternal administration of synthetic human beta-endorphin increases plasma praolactin concentration, and this effect is blocked by naloxone. Drugs which stimulate dopamine receptors (apomorphine or bromocriptine) or increase availability of dopamine (pargyline) inhibited the effect of beta-endorphin on plasma prolactin. Drugs which antagonize dopamine receptors (haloperidol) or decrease availability of dopamine (alpha-methyltyrosine) potentiated the effect of beta-endorphin on plasma prolactin. Some of these drugs act only in neurons and not in anterior pituitary, supporting a brain site of action for these drug interactions with beta-endorphin which altered prolactin secretion. These pharmacological studies provide support for a concept of dopaminergic mediation of beta-endorphin-induced prolactin secretion.     

The molecular regulation of Chinook salmon gonadotropin beta-subunit gene transcription

Expression of the gonadotropin beta-subunit genes is tightly regulated both cell-specifically and by the regulatory hormones to achieve the appropriate gonadotropic hormone levels required for reproductive development and function. Although the cDNA sequences of these genes are highly conserved across species, their promoter sequences are not and few functional studies have been carried out to understand the molecular mechanisms through which their expression is regulated. We and others have carried out several studies on the LHbeta gene promoter of Chinook salmon (Oncorhynchus tschawytscha), and also isolated the FSHbeta gene from the same species. We present here a review of these studies and also novel data pertaining to both genes, in an attempt to collate the current understanding of the molecular regulation of the gonadotropin beta-subunit genes in these fish.     

Purification and properties of an avian prolactin.

Prolactin was isolated from chicken adenohypophyses by extraction of the frozen glands with alkaline ethanol and chromatography on Sephadex G100 and DEAE-cellulose. The resulting preparation was homogeneous in disc electrophoresis on polyacrylamide gel and had strong pigeon crop sac stimulating activity. The chicken prolactin had significant mammotrophic activity in pseudopregnant rabbits. Furthermore, a radioactively labeled preparation showed binding to mammary tissue in vivo. The amino acid composition of the purified avian prolactin closely resembles that of mammalian prolactin preparations and the isoelectric point is also similar in both cases.     

Aldolase C/zebrin gene regulation by prolactin during pregnancy and lactation

Prolactin (PRL) is necessary for the genesis of mammary alveolar buds and for lactation. A cDNA library enriched for PRL-dependent genes was made by suppression subtractive hybridization. Aldolase C/zebrin (AldC/zebrin), a “brain-specific” aldolase, was found to be PRL-dependent in the mouse mammary glands. AldC/zebrin was preferentially expressed in the alveolar buds. Expression of the gene in the ovary was also evident. During pregnancy, mammary AldC/zebrin mRNA levels were elevated beginning at midpregnancy (d 10 of pregnancy) in accordance with the genesis of the lobuloalveolar system, and the expression level was gradually increased through the end of pregnancy. Lactating mammary gland contained a very high level of AldC/zebrin mRNA, and the gene expression decreased during involution. By contrast, levels of aldolase A and B mRNA expression in the mammary glands were less affected by pregnancy and lactation. The selective regulation of AldC/zebrin may contribute to a shift in nutrient metabolism during pregnancy and lactation to facilitate epithelial growth and biosynthesis of milk constituents.