title: Normal mammary gland growth and lactation capacity in pregnant relaxin-deficient mice.
abstract: Pups born to mice with a targeted deletion of relaxin or its receptor (Rxfp1) die within 24 h postpartum. This has been attributed, in part, to abnormal mammary gland development in relaxin-mutant mice (Rln-/-). However, mammary development is normal in relaxin receptor-mutant (Rxfp1-/-) mice. The present study aimed to verify the mammary phenotypes in late pregnant and early lactating Rln-/- mice and to test the hypothesis that relaxin is involved in milk protein synthesis. Comparisons between late pregnant and early lactating wildtype (Rln+/+) and Rln-/- mice showed no differences in lobuloalveolar structure or ductal branching in the mammary gland. Mammary explants from Rln-/- mice also expressed beta-casein and alpha-lactalbumin in response to lactogenic hormones at a similar level to Rln+/+ mice, implying normal milk protein synthesis. Pregnant Rln-/- mice infused with relaxin for 6 days gave birth to live pups without difficulty, and 96% of pups survived beyond 7 days. This is in contrast with the 100% pup mortality in saline-treated Rln-/- mice or 3-day relaxin-treated Rln-/- mice. Pups born to relaxin-treated Rln-/- dams weighed significantly less than Rln+/+ pups but had similar growth rates as their wildtype counterparts. In summary, relaxin is not critical for mammary gland development or beta-casein and alpha-lactalbumin expression in late pregnant mice. In addition, Rln-/- dams did not need to be treated with relaxin postpartum for the pups to survive, suggesting that relaxin has no role in the maintenance of lactation in mice.
authors.affiliation: Department of Zoology, The University of Melbourne, Parkville, Vic. 3010, Australia. ljparry@unimelb.edu.au
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Parry
authors.forename: Lenka A
authors.initials: LA
authors.lastname: Vodstrcil
authors.forename: Anna
authors.initials: A
authors.lastname: Madden
authors.forename: Stephanie H
authors.initials: SH
authors.lastname: Amir
authors.forename: Katrina
authors.initials: K
authors.lastname: Baldwin
authors.forename: Mary E
authors.initials: ME
authors.lastname: Wlodek
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Nicholas
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001724:Birth Weight; D002364:Caseins / Q000378:metabolism; D005260:Female; D005838:Genotype; D005865:Gestational Age; D015918:Infusion Pumps, Implantable; D055104:Infusions, Subcutaneous; D007768:Lactalbumin / Q000378:metabolism; D007774:Lactation / Q000235:genetics / Q000378:metabolism*; D008098:Litter Size; D008321:Mammary Glands, Animal / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009924:Organ Culture Techniques; D010641:Phenotype; D011247:Pregnancy; D012333:RNA, Messenger / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D012065:Relaxin / Q000008:administration & dosage / Q000172:deficiency* / Q000235:genetics; D013997:Time Factors
chemical_list: D002364:Caseins; D012333:RNA, Messenger; C478103:RXFP1 protein, mouse; D043562:Receptors, G-Protein-Coupled; D012065:Relaxin; D007768:Lactalbumin