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

Objectives of this experiment were to determine if the domperidone protocol previously used for gestating gilts can also lead to hyperprolactinemia in growing gilts, and to assess the effects of such a protocol on hormonal status, mammary development and gene expression in mammary and pituitary tissue of gilts at puberty. The impact on future lactation performance was also determined. At 75 ± 3 kg body weight (BW), gilts were divided between: 1) controls (CTL), receiving daily intramuscular (IM) injections of canola oil (1.1 mL) for 29 d (n = 41), and 2) treated (DOMP), receiving daily IM injections with 0.5 mg/kg BW of the dopamine receptor antagonist domperidone for 29 d (n = 40). In addition to that daily injection, treated gilts also received twice daily IM injections with 0.5 mg/kg BW of domperidone over the first 3 d of treatment. Fifteen gilts per treatment were sacrificed at 210 ± 5 d of age to collect mammary glands (for compositional analysis and gene expression) and the anterior pituitary (for gene expression). Remaining gilts were bred and allowed to farrow. Blood was sampled at the onset of treatment and on days 14 and 30. Gilts that farrowed were also blood sampled on days 3 and 20 of lactation. Blood was assayed for prolactin (PRL), leptin, insulin-like growth factor 1 (IGF-1), urea, free fatty acids and glucose. Concentrations of PRL increased after 14 d and 30 d of treatment (P < 0.01) and were lesser on day 3 of lactation in DOMP than CTL gilts (P < 0.01). At puberty, there were tendencies (P < 0.10) for total parenchymal protein and DNA to be greater in DOMP than CTL gilts. Treatment did not affect mRNA abundance of PRL or the long form of the PRL receptor genes in the pituitary gland at puberty but expression level of the dopamine receptor D2 and PRL genes was much lower in pubertal than late-pregnant gilts (P < 0.001). Furthermore, many genes related with PRL had a much greater expression level in late pregnancy than at puberty. On day 20 of lactation, CTL sows had greater concentrations of urea than DOMP sows (P < 0.01). The growth rate of litters was not affected by treatment nor was milk composition (P > 0.10). Even though PRL concentrations were increased with treatment, the absence of effect on mammary development was either due to timing relative to developmental stage, whereby treatment was initiated when gilts were too young, or was because all PRL receptors may have been saturated thereby preventing biological action of additional PRL.