Effect of various hormones on the milk ejection response of tissue isolated from the rat mammary gland

Vasopressin increases milk flow and milk fat concentration in the goat

AIM

The aim of this study was to investigate whether physiological doses of vasopressin affect milk flow and milk composition in goats.

METHODS

Six goats were given vasopressin intravenously at doses of 0.1 ng kg(-1) min(-1) (a low dose, VL), 0.3 ng kg(-1) min(-1) (a medium dose, VM) and 1.0 ng kg(-1) min(-1) (a high dose, VH), oxytocin at 10 ng kg(-1) min(-1) and 0.15 m NaCl during 90 min at random.

RESULTS

Milk flow increased from 1.3 +/- 0.2 to 3.5 +/- 1.0 g min(-1) (VL), from 1.8 +/- 0.4 to 4.3 +/- 0.6 g min(-1) (VM) and from 1.5 +/- 0.2 to 7.9 +/- 0.9 g min(-1) (VH) during the first 30-min infusions (all P < 0.001), respectively, and then declined. The response to oxytocin corresponded to that of VH. Milk fat concentration increased from 2.1 +/- 0.1 to 3.3 +/- 0.4% during VH and from 2.8 +/- 0.6 to 4.1 +/- 0.6% during oxytocin (both P < 0.001), and tended to increase during VM and VL. The mammary blood flow of four goats was studied with ultrasound during VH and oxytocin infusion. Milk flow increased from 1.8 +/- 0.4 to 4.7 +/- 1.0 g min(-1) during VH and from 1.9 +/- 0.3 to 12.4 +/- 2.4 g min(-1) during oxytocin (both P < 0.001). Mammary blood flow decreased from 262 +/- 37 to 53 +/- 7 mL min(-1) (P < 0.001) during VH, but did not change during oxytocin.

CONCLUSION

We conclude that vasopressin increases milk flow and milk fat concentration and suggest that vasopressin, like oxytocin, acts on the myoepithelial cells.

Neurohypophysial-hormone-responsive cell line derived from a dimethylbenzanthracene-induced rat mammary tumour

WRK-1, a cloned cell line derived from a rat mammary tumour, responds to physiological concentrations of vasopressin and pharmacological concentrations of oxytocin with increased incorporation of [14C]acetate into lipids and increased protein accumulation. The presence of pharmacological concentrations of insulin, which itself is active on the WRK-1 cells, further enhances the effects of the neurohypophysial hormones. Unlike the action of vasopressin on other responsive tissues, the stimulation of acetate incorporation by WRK-1 cells is not observed until 24 h after the addition of the hormone. The lipids synthesized in response to the hormones are predominantly polar lipids, rather than the triclyclycerold characteristic of the differentiated mammary gland. [1-Deaminocysteine, 8-D-arginine] vasopressin, a vasopressin analogue that lacks pressor activity, has no effect on WRK-1 cells.

The assay of milk-ejecting activity in the lactating rat

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