Demonstration of in vivo mammogenic and lactogenic effects of recombinant ovine placental lactogen and mammogenic effect of recombinant ovine GH in ewes during artificial induction of lactation

The present study demonstrates that ovine placental lactogen (oPL) (ovine c horionic somatotrophin) may have an important role in die mammogenesis and/ or lactogenesis of the ewe. Its effects were compared with that already des cribed for ovine growth hormone (oGH). In the first experiment, 40 nulliparous ewes were induced to lactate by mea ns of a 7 day (days 1-7) oestro-progestative treatment (E-2+P-4). The ewes from Group 1 (n=12) received no further treatment, while those of the other groups received either recombinant oGH (roGH, 28 mu g/kg, i.m., twice dail y, Group 2, n=12) or recombinant oPL (roPL, 79 mu g/kg, i.m., twice daily, Group 3, n=12) from day 11 to 20. All ewes received 25 mg hydrocortisone ac etate (HC) twice daily on days 18-20. Control Group 00 (n=2) received no st eroid treatment at all, and the control Group 0 (n=2) received only the E-2 +P-4 treatment. Thirteen ewes (three front each experimental group and the two of each control group) were slaughtered at the end of hormone treatment s (day 21) before any milking stimulus. The 27 remaining ewes from Groups 1 -3 were machine-milked and milk yields recorded daily from day 21 to 76. Th e E-2+P-4 treatment enhanced the plasma levels of oPRL, oGH and IGF-I betwe en days 1 and 7 by 1.5, 2.3 and 2.6 times respectively (P=0.002); roGH trea tment induced a highly significant enhancement of IGF-I plasma levels from day 11 to 20, whereas a similar effect appeared for roPL-treated ewes only from day 17 to 20 (P<0.01). Eight weeks after the last exogenous hormone in jections, milk yields of both roGH and roPL-treated groups progressively ro se to twice that of unsupplemented groups (P<0.001). The mammary DNA conten t on day 21 was higher for animals which received either oGH or oPL but, du e to individual variations in so few samples (n=3), this difference was not significant. No beta-casein was measured in mammary tissue from control ew es, whereas steroid-treated ewes (E-2+P-4+HC) had higher casein concentrati ons regardless of subsequent hormonal treatment on days 11-20 (P<0.001). be ta-casein concentrations in mammary parenchyma of roGH-treated ewes did not differ from that of ewes which received only E-2+P-4+HC; roPL supplementat ion clearly enhanced expression of beta-casein (P<0.001), IGF-I stimulation by either roGH or roPL was more precisely examined during a second experiment, in which two twice-daily i.m. doses (58 or 116 mu g/k g) of either roGH or roPL were administered to four groups of six ewes that were E-2+P-4 treated as those of Experiment 1. A control group (n=6) recei ved no exogenous hormone from day 11 to 13. On day 13, hourly blood samples were taken from all ewes over 11 h. Both doses of roGH significantly stimu lated IGF-I in a dose-dependent manner. The 58 mu g/kg dose of roPL did not significantly stimulate IGF-I, but although being somewhat less efficient than the 58 mu g/kg dose of roGH, the 116 mu g/kg dose of roPL significantl y stimulated IGF-I secretion (P<0.001). These results suggest that mammogenesis and/or lactogenesis in the ewe is i n part controlled by somatotrophic hormones such as oGH and oPL and that IG F-I could be one of the mediators of these hormones.