Endocrine Abstracts

The abundance of class 1 cytokine receptors for hepatic growth hormone (GH) and long form of prolactin (PRL) receptor peak near to term coincident with the rise in fetal plasma PRL. The extent to which maintenance of high plasma PRL may alter mRNA abundance for the GH or PRL receptors is not known. The present study aimed to determine whether chronic administration of PRL alters the hepatic GH and/or prolactin (PRL) receptor mRNA abundance in livers of 1-week-old lambs.

Six pairs of weight matched, day old triplet lambs were entered into the study and randomly assigned to ovine PRL (2mg/daily) or vehicle treatment. Jugular vein catheters were inserted into each lamb to allow daily treatment for six days. On day seven tissue samples were taken from all lambs following euthanasia. Total hepatic RNA was extracted and abundance of GH and long form of PRL receptors were determined using RT-PCR. Results are given as means and SEM in arbitrary units (a.u.) as a ratio of 18S rRNA and expressed as a percentage of a reference sample present on all gels.

Chronic administration of PRL at a dose of 2mg/ml/day and sufficient to raise plasma PRL from 47.6 plus/minus 0.6 to 240.5 plus/minus 3.5 ng ml^-1 had no effect upon lamb body or liver weight at 7 days of age. Hepatic GH receptor mRNA abundance was significantly down regulated in PRL-treated lambs when compared to vehicle treated lambs (vehicle 130.2 plus/minus 23.4; prolactin 55.4 plus/minus 13.3 a.u., p <0.05). However, PRL treatment had no affect on the abundance of mRNA for the long form of PRL receptor.

In conclusion, chronic PRL administration during postnatal life down regulates hepatic GH receptor transcript levels but not long form of PRL receptor.