Investigation of the mechanism of action of growth hormone in stimulating lactation in the rat

Abstract

The role of GH was examined using an antiserum to rat GH (anti-rGH). When administered to lactating rats on day 2 of lactation it was without effect, whereas bromocriptine markedly suppressed milk production, with no additional effect of combined treatment. On day 6 of lactation, treatment with anti-rGH was also without effect, whilst bromocriptine again suppressed milk production. Combined treatment, however, suppressed milk synthesis completely, suggesting that GH was capable of maintaining about 50% of normal milk yield in the absence of prolactin at day 6 of lactation. By day 14 of lactation, anti-rGH treatment alone was capable of decreasing milk yield by about 20%, and again milk secretion only stopped completely when GH and prolactin were suppressed. These data suggest that the role of GH in supporting lactation increases as lactation progresses. The effects of GH in stimulating growth and in increasing milk yield in ruminants have been proposed to be mediated via insulin-like growth factor-I (IGF-I). In rats treated with anti-rGH, both IGF-I and IGF-II were decreased in serum. The concentration of the major IGF-binding protein (IGFBP-3) was not, however, affected by inhibition of GH or prolactin individually, but was decreased in animals treated with bromocriptine and anti-rGH. In animals given both bromocriptine and anti-rGH, concurrent treatment with recombinant bovine GH maintained milk yield at 50% of control values and normalized serum IGF-I, IGF-II and IGFBP-3 concentrations. By contrast, concurrent treatment with IGF-I or IGF-II, despite normalizing their respective concentrations in serum, failed to affect milk yield.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of maternal lactation performance during prolonged lactation in the mouse by mouse GH and long-R3-IGF-I is linked to changes in mammary signaling and gene expression

“…The results are also consistent with the reported ability of IGF-I to improve nitrogen retention in female rats (Tomas et al 1993). Along with the effects on body composition, however, the fact that milk production was increased in three independent mouse studies suggests that IGF-I, like GH, may be more effective at stimulating milk production in mice than in rats (Flint et al 1992, Su & Cheng 2004, Hadsell et al 2005). …”

Lactogenic Activity of Rats Stimulated by <em>Gunnera Perpensa</em> L. (Gunneraceae) from South Africa

“…However, growth hormone (GH) is needed to support milk production when prolactin is reduced (Flint et al 1992). In this study, the levels of GH and prolactin did not significantly change in the presence of the plant's extracts.…”

Intestinal effects of milkborne growth factors in neonates of agricultural importance.

“…If goats are milked at frequent intervals, the galactopoietic response to IGF-I is abolished (Prosser and Davis, 1992), whereas the response to bST is not (Davis et al, 1991). Finally, neither IGF-I nor IGF-II was able to reinstate lactation in rats treated with anti-somatotropin antibodies (Flint et al, 1992(Flint et al, , 1994.…”