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Stimulation of prolactin cell differentiation in vitro by a milk-borne peptide
1Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston 29425.
Insights
Maternal milk contains factors that stimulate prolactin (PRL) cell development in neonatal rats. Early lactation milk is more effective than late lactation milk in promoting PRL cell differentiation, indicating a milk-borne peptide signal.
Area of Science:
- Endocrinology
- Developmental Biology
- Cell Biology
Background:
- Normal expression of prolactin (PRL)-secreting cells in neonatal rats depends on maternal signals during early lactation.
- Previous findings suggested a potential milk-borne factor influencing the development of PRL cells.
- The specific role of milk composition in inducing PRL cell differentiation remained to be elucidated.
Purpose of the Study:
- To investigate if milk from early lactation directly stimulates the differentiation of PRL-secreting cells in vitro.
- To compare the effects of early and late lactation milk extracts on pituitary cell differentiation.
Main Methods:
- Anterior pituitary cells from 1-day-old rats were cultured for 6 days with aqueous milk extracts.
- Milk extracts were sourced from early (days 2-4) and late (days 15-16) lactation periods.
- Reverse hemolytic plaque assays were used to quantify PRL and growth hormone (GH) secreting cells.
Main Results:
- Both early and late lactation milk extracts significantly stimulated PRL cell differentiation compared to controls.
- Early lactation milk was over twice as effective as late lactation milk in promoting PRL cell differentiation (P < 0.05).
- Late lactation milk enhanced GH secretion capacity more than early lactation milk, suggesting differential bioactivity.
Conclusions:
- A milk-borne peptide(s) between 2000-6000 daltons specifically stimulates PRL-secreting cell differentiation in vitro.
- This PRL differentiation-inducing bioactivity is significantly more abundant in milk from early lactation.
- These findings highlight the crucial role of early maternal milk composition in neonatal endocrine development.
Abstract:
We have previously reported that the normal expression of PRL-secreting cells in neonatal rats requires a maternal signal specific to the first few days of lactation. These results raised the possibility that a milk-borne factor(s) ingested by the neonate and absorbed into the circulation might induce the ontogenic appearance of PRL cells. The purpose of the present study was to determine whether milk from this period could directly stimulate the differentiation of PRL secretors in culture. Monodispersed anterior pituitary cells from 1-day-old pups were cultured for 6 days with aqueous extracts of milk from early (days 2, 3, and 4) and late (days 15 and 16) lactation and then subjected to reverse hemolytic plaque assays for PRL and GH release. We found that the addition of milk extracts (10 mg/ml) from either early or late lactation stimulated the differentiation of PRL secretors (to 6.1 +/- 1.0% and 2.4 +/- 0.7% of all pituitary cells, respectively; mean +/- SE; n = 3) above that in control cultures without milk (0.2 +/- 0.2%). Thus, early milk was more than twice as effective as late milk in this regard (P less than 0.05). This effect appeared to be specific to PRL cell differentiation, since the relative abundance of GH secretors was not different between cells treated with either early or late milk (29.3 +/- 4.8% and 33.7 +/- 3.9%, respectively). On the other hand, late milk was more than twice as effective as early milk at increasing the capacity of GH secretors to release hormone (P less than 0.05). Preliminary characterization by gel filtration chromatography and proteolytic hydrolysis indicates that the bioactivity that differentiates PRL secretors is a small peptide(s) of 2000-6000 daltons. Taken together, our results demonstrate that a milk-borne peptide(s) is capable of specifically stimulating the differentiation of PRL-secreting cells in vitro, and that this bioactivity is more prevalent in milk from early lactation.