Hyperprolactinemia using domperidone in prepubertal gilts: Effects on hormonal status, mammary development and mammary and pituitary gene expression

Regulatory roles of dopamine D2 receptor in milk protein production and apoptosis in mammary epithelial cells

Dopamine D2 receptors (D2Rs) play crucial roles in regulating diverse physiological functions of the central nervous system and peripheral organs. D2Rs are also expressed in mammary glands. However, which cell types express D2Rs and whether they are involved in milk production remains unclear. The present findings revealed that D2Rs are expressed in the apical regions of the lateral membranes of mammary epithelial cells (MECs) in lactating mice. We also investigated the effects of the D2R agonist bromocriptine and/or antagonist domperidone on intracellular cAMP levels, milk protein production, and apoptosis in a lactation culture model of MECs that produce major milk components like lactating MECs in vivo. We found that bromocriptine decreased intracellular cAMP levels, whereas domperidone dose-dependently neutralized this effect. Bromocriptine also inhibited casein and lactoferrin production and suppressed activities of STAT5 and glucocorticoid receptors (GRs). Domperidone neutralized the inhibition of casein production as well as STAT5 and GR inactivation induced by bromocriptine. Furthermore, D2R activation by bromocriptine induced apoptosis and inactivated ERK, a signaling molecule responsible for promoting cell proliferation and survival. Domperidone attenuated ERK inactivation and apoptosis induced by bromocriptine. These findings suggest that D2Rs play regulatory roles in milk protein production and apoptosis in MECs.

Oral administration of domperidone in the first or third week of lactation: effects on prolactin concentrations and mammary gene expression in sows and piglet growth

The scope of the present study is endocrine and metabolic control of sow lactation. This project aimed to determine the impact of increasing prolactin concentrations via oral administration of the dopamine receptor antagonist domperidone in the first or third week of lactation in sows. Effects on sow hormonal and metabolic status, lactational performance, and gene expression in mammary epithelial cells were determined. Primiparous sows were divided in 3 treatments: 1) 10 mL of vehicle (table syrup) per os twice daily during the first and third weeks of lactation (Control, CTL, n = 23), 2) 0.5 mg/kg of domperidone per os twice daily during the first week of lactation (LACT1, n = 23), or 3) 0.5 mg/kg of domperidone given per os twice daily during the third week of lactation (LACT3, n = 22). Treated sows also received 10 mL of the vehicle twice daily during the other treatment period. Litter size was standardized to 12 ± 1 and piglets were weighed at birth, 24 h, and on d 8, 15, 22 (weaning), 35, and 56. Sow feed intake was recorded daily. Representative milk samples were obtained on d 7 and 21 of lactation for compositional analyses, and milk fat globules were used to measure mRNA abundances of various genes. Jugular blood samples were obtained from sows on d 1, 7, 14, and 21 of lactation to measure concentrations of prolactin, IGF-1, insulin, urea, and FFA. Concentrations of prolactin were increased (P < 0.01) at the end of the 7-d treatment period with domperidone, whether imposed in the first (LACT1) or third (LACT 3) week of lactation. No other blood variables were affected by treatments and neither was milk composition (P > 0.10). Sow BW, backfat thickness, or feed intake were not altered by treatments (P > 0.10), but piglet BW tended to be greater in litters from LACT3 compared with CTL sows on d 22 and 35 (P ≤ 0.10). Gene expression of EGF in milk fat globules tended to be (LACT1, P < 0.10) or was increased (LACT3, P < 0.05) after treatment, and the effect in LACT1 sows was maintained until d 21 of lactation. The mRNA abundance of SPP1 was increased (P < 0.05) in LACT1 vs CTL sows on d 7, and that of 3 major milk proteins tended to be (CSN1S2 and WAP, P < 0.10) or was greater (LALBA, P < 0.05) in LACT3 vs CTL sows on d 21 of lactation. Oral administration of domperidone during the first or third week of lactation increased prolactin concentrations and altered mRNA abundances of selected genes in milk fat globules. Yet, only the LACT 3 treatment positively affected piglet performance.

Dietary supplementation with lysine (protein) stimulates mammary development in late pregnant gilts

The goal of this project was to determine if standardized ileal digestible (SID) lysine provided at 40% above estimated requirements, with the concomitant increase in protein intake, from days 90 to 110 of gestation would stimulate mammary development in gilts. From day 90 of gestation, Yorkshire × Landrace gilts were fed 2.65 kg of either a conventional diet (CTL, control, n = 19) providing 18.6 g/d of SID Lys or a diet providing 26.0 g/d of SID Lys via additional soybean meal (HILYS, n = 19). Both diets were isoenergetic. Jugular blood samples obtained on days 90 and 110 of gestation were used to measure concentrations of insulin-like growth factor-1 (IGF-1), metabolites, and amino acids (AA). Gilts were necropsied on day 110 ± 1 of gestation to obtain mammary glands for compositional analyses, immunohistochemistry, and analysis of mRNA abundance for AA transporters and markers of cell proliferation and differentiation. The HILYS gilts gained more body weight (P < 0.01) during the experimental period compared with CTL gilts, and had greater fetal weights (1.29 vs. 1.21 ± 0.03 kg, P < 0.05). There was no difference in circulating IGF-1, glucose, or albumin (P > 0.10) between HILYS and CTL gilts on day 110 of gestation, whereas concentrations of urea and free fatty acids were greater (P < 0.01), and those of Trp and Ala were lower (P < 0.05), in HILYS than CTL gilts. The provision of lysine at 40% above estimated requirements increased total mammary parenchymal mass by 44%, as well as total parenchymal fat, protein, DNA, and RNA (P < 0.01). The mRNA abundance of ACACA was greater (P < 0.05) in HILYS than CTL gilts, while only the AA transporter SLC6A14 tended (P < 0.10) to be greater. Results demonstrate that providing dietary Lys above current National Research Council recommendations in late gestation increases mammary development in gilts. Results also indicate that Lys may have been limiting for protein retention. These data suggest that the use of a two-phase feeding strategy during gestation, whereby dietary Lys is increased from day 90, could benefit potential sow milk yield in the subsequent lactation.

Prolactin and the swine mammary gland

Prolactin is a hormone that is most important for mammary development in swine. It is also essential for both the onset and the maintenance of lactation. In early studies, exogenous recombinant porcine prolactin was used to detect its biological effects on mammary tissue. In these studies, a stimulatory role of prolactin for mammary development of prepubertal gilts was demonstrated. However, when injected throughout lactation, prolactin did not increase sow milk yield likely because mammary receptors were saturated. The secretion of prolactin is largely under negative regulation via dopamine. Inhibition studies using the dopamine agonist bromocriptine showed that prolactin is required in the last third of gestation to sustain mammary development in gilts. When creating a hyperprolactinemic state during that same period, with the dopamine antagonist domperidone, differentiation of mammary epithelial cells was stimulated and milk yield in the subsequent lactation was increased. Domperidone given throughout lactation also led to greater milk yield. A study using domperidone in prepubertal gilts, however, did not reproduce the stimulatory effect of exogenous prolactin on mammary development and demonstrated that timing of the prolactin increase in relation to age of the animals is most important to elicit a response on mammary tissue. Attempts were made to use feed ingredients such as the plant extract from milk thistle, sylimarin, to stimulate prolactin secretion in sows. However, even though prolactin concentrations were increased, this augmentation was not important enough to have an impact on mammary development in late gestation or to increase milk yield. The current knowledge that hyperprolactinemia has beneficial effects for mammary development at various physiological stages and can enhance milk yield in swine leads to new avenues in elaborating strategies that could be used at the farm level to improve sow lactation performance.

Providing domperidone throughout lactation enhances sow lactation performance

The goal of this project was to determine the effects of domperidone given throughout lactation on hormonal and metabolic status, lactational performance, and gene expression in mammary epithelial cells of sows. Second parity sows were divided in two treatment groups: 1) daily intramuscular injections with canola oil (Control, CTL, n = 24), or 2) daily intramuscular injections with 0.5 mg/kg body weight (BW) of domperidone (DOMP, n = 23). Injections were given at 08h05 starting the day after farrowing until weaning. Over the first 4 d of treatment, DOMP sows also received 0.5 mg/kg BW of domperidone per os twice daily, whereas CTL sows were fed the vehicle. Litter size was standardized to 11 ± 1 within 24 h of birth and piglets were weighed at birth, 24 h postpartum, and on days 7, 22 (weaning on day 23), 35, and 56. Sow feed intake was recorded daily. Representative milk samples were obtained aseptically on day 21 of lactation from 15 sows per treatment for compositional analyses and milk fat globules were used to measure mRNA abundances of various genes. Jugular blood samples were obtained from all sows on days 2, 8, 16, and 23 of lactation to measure concentrations of prolactin, insulin-like growth factor-1 (IGF-1), leptin, adiponectin, insulin, glucose, urea, and free fatty acids (FFA). Concentrations of prolactin (P < 0.001) and FFA (P < 0.01) were increased in DOMP compared with CTL sows, whereas concentrations of insulin were decreased (P < 0.05). Urea concentrations were increased by treatment (P < 0.05) on days 16 and 23 of lactation, and those of IGF-1 were increased (P < 0.01) on day 16. Piglets from DOMP sows were heavier than those from CTL sows on day 22 (P < 0.01). Milk composition was unaffected by treatment. The mRNA abundance in milk fat globules for casein beta and whey acidic protein were lower (P ≤ 0.05) in DOMP than CTL sows. The long form of the prolactin receptor and the signal transducer and activator of transcription 5A mRNA abundances tended to be lower (P < 0.10) in DOMP than CTL sows. In conclusion, hyperprolactinemia induced by domperidone during lactation affected the endocrine and metabolite status of sows and stimulated growth of their suckling piglets.