Leptin Up-Regulates the Lactogenic Effect of Prolactin in the Bovine Mammary Gland In Vitro

Effect of leptin (L; 0, 1, 10, and 100ng/mL) and prolactin (P; 0 or 1μg/mL) in the presence of insulin (I; 1μg/mL) on albumin synthesis in bovine mammary gland explants. Western blot (WB) analysis of albumin from explants of lactating bovine mammary glands shows that leptin alone increased albumin accumulation in the explants. The greatest accumulation of albumin was observed when prolactin at 1μg/mL and leptin at 100ng/mL were introduced together into the medium. Results are least squares means of the scanning results ± SE (n=3, P<0.01, SEM=0.12). ^A,BBars with different letters differ (P<0.05).

Effect of leptin (0, 10, 50, and 100ng/mL) and prolactin (0, 0.1, and 1μg/mL) on DNA synthesis in bovine mammary gland explants. Cell DNA synthesis was evaluated by [³H]thymidine incorporation. Explants from lactating bovine mammary gland were incubated with leptin, prolactin, or both. Prolactin at 1μg/mL up-regulated DNA synthesis. Leptin at 50ng/mL did not affect DNA synthesis in the explants, but leptin in the presence of prolactin elevated the DNA synthesis in a dose-responsive manner. The greatest rate of DNA synthesis was observed with 1 mg/mL prolactin combined with 100ng/mL leptin. Results are least squares means ± SE (n=3). ^A-DBars with different letters differ (P<0.05).

Effect of leptin (0, 10, and 100ng/mL) and prolactin (0 and 1μg/mL) on apoptosis (caspase-3) in bovine mammary gland explants. Western blot (WB) analysis of caspase-3 protein expression was down-regulated by 60% with addition of 1μg/mL prolactin to a culture containing 100ng/mL leptin in the medium. Results are least squares means of the scanning results ± SE (n=3). ^A,BBars with different letters differ (P<0.05).

Leptin (L; 0 and 100ng/mL) and prolactin (P; 0 and 1μg/mL) regulation of aminopeptidase N/CD13 (APN) expression in bovine mammary gland explants in the presence of insulin (I; 1μg/mL). Western blot (WB) analysis showed that leptin combined with prolactin upregulated the expression of APN by approximately 90%. Results are least squares means of the scanning results ± SE (n=3; P<0.001, SEM = 0.11). ^A,BBars with different letters differ (P<0.05).

Regulation of mammalian target of rapamycin (mTOR) expression in bovine mammary gland explants by leptin (L; 0 and 100ng/mL) and prolactin (P; 0 and 1μg/mL) in the presence of insulin (I; 1μg/mL). Western blot (WB) analysis showed that leptin combined with prolactin upregulated the expression of mTOR by approximately 66%. Results are least squares means of the scanning results ± SE (n=3, P<0.05, SEM=0.12). ^A,BBars with different letters differ (P<0.05).