Impact of arginine supplementation on serum prolactin and mRNA abundance of amino acid transporter genes in mammary tissue of lactating sows

l-Arginine supplementation for pregnant and lactating sows may improve the performance of piglets: A systematic review

The objective was to conduct a systematic review to clarify the effects of l-arginine supplementation in pregnant and lactating sows on plasma hormone levels, milk production and composition, the body condition of sows and piglet performance. In April 2023, an online search and a systematic search were performed in the following databases: Embase, Scopus, SciELO, Web of Science, PubMed and Science Direct. The combinations of keywords used were sow and arginine and lactation; sow and arginine and lactating; sow and arginine and gestation; sow and arginine and gestating; sow and arginine and pregnancy; sow and arginine and reproduction; piglet and arginine; and sow and arginine and mammary gland. In total, 21 scientific articles with original data were selected according to preestablished criteria. Among the 21 articles, seven (33%) reported measurements of some plasma hormones, and among these, six reported an increase in the levels of at least one hormone, namely, estradiol, insulin-like growth factor 1 (IGF-1), insulin, follicle stimulating hormone, growth hormone or prolactin, with l-arginine supplementation. The parameters of milk were evaluated in 11 studies (52%), one reported an increase in protein content, and one reported an increase in IGF-1 content in milk with supplementation of this amino acid. Of the 14 studies that evaluated the performance parameters of piglets, only four reported improvements in some parameters of piglets from sows that received supplementation. Dietary supplementation of arginine for sows in the final third of gestation and/or lactation may alter the plasma levels of some hormones, which may reflect in greater development of the mammary gland tissue and, consequently, promote benefits on the performance of piglets. However, more studies are needed to evaluate the real impact of this amino acid supplementation on the physiology of the sows, in general, and the performance of suckling piglets.

Interactions of amino acids and hormones regulate the balance between growth and milk protein synthesis in lactating rats fed diets differing in protein content

Insulin-like growth factor-I (IGF-I), growth hormone (GH), and prolactin (PRL) play important roles in milk protein synthesis, and their plasma concentrations were reported to be affected by dietary protein intake. To investigate the relationship between circulating amino acid (AA) and concentrations of these hormones, 18 Wistar rats aged 14 wk were assigned to a low (LP; 9% protein), standard (SP; 21% protein), or high-protein (HP; 35% protein) diet from parturition through day 15 of lactation. Plasma, liver, pituitary gland, skeletal muscle, and mammary gland samples were collected at the end of treatment. Circulating and hepatic IGF-I concentrations increased linearly with elevated dietary protein concentrations (P < 0.0001). Rats receiving the HP diet had higher circulating GH (P < 0.01) and pituitary PRL concentrations (P < 0.0001) but lower pituitary GH concentration (P < 0.0001) relative to those in rats receiving the LP and SP diets. Pearson correlation test performed on composed data across treatments showed that several circulating AAs were correlated with circulating and tissue concentrations of IGF-I, GH, and PRL. Multiple linear regression analyses identified Leu, Gln, Ala, Gly, and Arg as the main AAs associated with hormone responses (R2 = 0.37 ~ 0.80; P < 0.05). Rats fed the LP and HP diets had greater Igf1 and Ghr gene expression in skeletal muscle than those fed the SP diets (P < 0.01). However, LP treatment decreased Prlr mRNA abundance in mammary glands as compared with the SP and HP treatments (P < 0.05). The HP diets increased AA transporter expression (P < 0.01) but decreased mammalian target of rapamycin (P < 0.05) and 70 kDa ribosomal protein S6 kinase 1 (P < 0.01) phosphorylation in mammary glands as compared with the LP and SP diets. The results of the present study suggested that several circulating AAs mediated the effects of dietary protein supply on concentrations of IGF-I, GH, and PRL, which in turn altered the metabolism status in peripheral tissues including the lactating mammary glands.