Prolactin administration during the luteal and follicular phase of the oestrous cycle of gilts

Clustering of multi-tissue transcriptomes in gilts with normal cyclicity or delayed puberty reveals genes related to pubertal development†

In gilts, puberty is marked by standing estrus in the presence of a boar. Delayed puberty (DP; failure to display pubertal estrus) is a major reason for gilt removal. To investigate the physiological determinants underlying DP in gilts, transcriptomic data from tissues relevant to estrus and puberty, such as mediobasal hypothalamus, anterior pituitary gland, ovarian cortex, olfactory bulb, amygdala, and hippocampus, were obtained from age-matched DP (n = 8) and cyclic control gilts at follicular phase (n = 8) and luteal phase (n = 8) of the estrous cycle. A gene expression module analysis via three-way gene × individual × tissue clustering using tensor decomposition identified pituitary and ovary gene modules contributing to regulation of pubertal development. Analysis of gene expression in the hypothalamic-pituitary-ovary axis identified reduced expression of hypothalamic genes critical for stimulating gonadotropin secretion (KISS1 and TAC3) and reduced expression of LHB in the anterior pituitary of DP gilts compared with their cyclic counterparts. Consequently, luteinizing hormone-induced genes in the ovary important for folliculogenesis (OXTR, RUNX2, and PTX3) were less expressed in DP gilts. Other intrafollicular genes (AHR, PTGS2, PTGFR, and IGFBP7) and genes in the steroidogenesis pathways (STAR and CYP11A1) necessary to complete the ovulatory cascade were also less expressed in DP gilts. This is the first clustering of multi-tissue expression data from DP and cyclic gilts to identify genes differentially expressed in gilts of similar ages but at different levels of sexual development. A critical lack of gonadotropin support and reduced ovarian responsiveness underlie DP in gilts.

The involvement of prolactin in the regulation of adrenal cortex function in pigs

We investigated the in vivo and in vitro effect of prolactin (PRL) on porcine adrenal cortex function. The in vivo study was performed on 10 multiparous sows. Blood was sampled every 4 h beginning on the 17th day of the estrous cycle and continuing for 6 subsequent days. Plasma was stored at -20 degrees C until steroid hormones analysis was completed. PRL or saline were administered iv for 48 h in 2 h intervals. Injections of PRL began 4-20 h after the preovulatory LH surge. At the end of the sampling period sows were slaughtered and adrenals were immediately dissected. Adrenals were frozen at -70 degrees C for determination of adrenal cortex steroid hormones content. At the end of PRL treatment period mean plasma level of cortisol in control sows was significantly lower than that of PRL-treated sows. Moreover, the area under the mean plasma cortisol concentration curve was significantly higher in PRL-treated sows in comparison to controls. The mean cortisol adrenal content was significantly higher in adrenal cortex of PRL-treated sows than that of controls. PRL did not affect adrenal cortex concentration of androstenedione (A(4)), testosterone (T), dehydroepiandrosterone (DHEA) and estradiol (E(2)). Dehydroepiandrosterone sulfate (DHEAS) was not found in porcine adrenal cortex. In the in vitro experiment adrenal glands were removed immediately after slaughter of 6 crossbred gilts. Dispersed adrenocortical cells were incubated for 8 h with or without porcine PRL. Prolactin stimulated cortisol secretion in a dose-dependent manner. These results suggest that PRL is one of the key factors involved in the regulation of adrenal cortex function in pigs.

Prolactin and insulin levels in lactating sows in relation to nursing frequency

It has been established that sows up- or down-regulate their milk production as the frequency of nursings is changed. The amount of udder massage by piglets might also influence milk production. To investigate whether these effects are associated with changes in prolactin or insulin levels, we enforced five sows each to nurse either every 35 min (MIN35) or every 70 min (MIN70) over a 26- to 28-hr period. Milk production was measured during the first 24 hr of this period. During the last three to four nursings, blood was collected every 5 min. Plasma prolactin levels increased after milk ejection (P < 0.05), whereas insulin levels increased only briefly in MIN70 sows. Sows nursing every 35 min had lower basal (P < 0.001) and maximal (P < 0.05) concentrations of insulin than MIN70 sows. There were no differences between the two groups in prolactin levels. Nursings with a postejection udder massage longer than 90 s tended to induce a higher increase in prolactin (P < 0.1) than nursings with a shorter massage. When the effects of imposed nursing frequency were removed, there was an across-sows positive residual correlation between average prolactin levels (P < 0.05) and the duration of post-ejection udder massage during the preceding 24 hr. We conclude that when milk production of a sow is changed by altering the nursing frequency within natural limits, the necessary alteration in catabolic state of energy metabolism may be associated with altered insulin levels. The duration of udder massage in a single nursing might have only a slight immediate impact on prolactin levels, but may influence prolactin levels more substantially if increased for a period of 24 hr.