Milk-ejecting activity induced by prostaglandin F2alpha

Characteristics of the spontaneous milk ejecting activity occurring during human lactation

Continuous recordings of intramammary pressure performed in 158 normal lactating women, and 22 women during spontaneous labor were retrospectively analyzed in order to characterize spontaneous milk ejecting activity (SA). SA appeared as spurts of contraction waves as early as the first post-partum day and throughout the first two months of lactation. The spurts of SA differed from reflex milk ejection evoked by baby's suckling. It showed two different patterns: a) single contraction waves with a rapid rise time, a slow decay time, high amplitude and a short duration; b) multiple contraction waves with a longer rise and decay times, progressively decreasing intensity and a large duration depending on the number of contractions per spurt. The multiple pattern occurred in 34.2% (41/120) of patients at 2.7 +/- 0.1 days of post-partum and increased to 84.3% (59/70) at 34.5 +/- 1.2 days. Accordingly, duration and the area under contraction curves increased throughout lactation. Mammary gland sensitivity to exogenous oxytocin (OT) did not change during the 2 months studies. SA was significantly greater in full nursing mothers than in the partially nursing ones. The existence of a system for milk-ejection different from baby's suckling was further described. A neuroendocrine mechanism and the release of increasing amounts of OT are suggested as important factors in the control of this phenomenon.

Hormonal responses following treatment with different prostaglandin analogues for estrous cycle regulation in cattle

The effect of four different prostaglandin F(2)alpha analogues on secretion of the pituitary hormones prolactin, LH, FSH and oxytocin was evaluated in heifers. In addition, the luteolytic activity was measured by means of progesterone concentrations. For the sake of comparison, the corpus luteum of two heifers was enucleated and the effect on the above hormones determined. There seemed to be no differences among the various analogues concerning their luteolytic action on the corpus luteum. No effect on FSH secretion was observed. Basal concentrations of LH increased about 4 - 5 h after injection of the analogues, concurrently with the decrease of progesterone. Enucleation of the corpus luteum was followed by a similar pattern of hormone secretion. Therefore, the increase in LH concentrations did not appear to be a specific effect of the analogues, but was probably a result of the decrease in progesterone concentration. Within twenty minutes after administration of the analogues a clear increase in plasma prolactin (2-4 h) and oxytocin concentrations (1-2 h) could be demonstrated.

Prostacyclin, thromboxane, and prostaglandin F2 alpha in maternal plasma during breast-feeding

In order to study the role of prostaglandin F2 alpha (PGF2 alpha) prostacyclin (PGI2), and thromboxane A2 in milk ejection, the stable metabolites of these prostanoids, i.e., 13,14-dihydro-15-keto-PGF2 alpha (M-PGF2 alpha), 6-keto-PGF1 alpha, and thromboxane B2, respectively, were measured from serial samples of plasma collected from 11 puerperal women before, during, and after breast-feeding. The plasma M-PGF2 alpha decreased significantly (p less than 0.01) from the level of 253.6 +/- 18.6 pg/ml (mean +/- SE) before suckling to 204.2 +/- 26.1 pg/ml at the end of suckling, but returned to 234.6 +/- 26.1 pg/ml 60 minutes after the end of suckling. The 6-keto-PGF1 alpha concentration also decreased (p less than 0.01) from 246.4 +/- 30.9 to 187.9 +/- 9.9 pg/ml within the first 15 minutes of suckling, whereas the thromboxane B2 levels did not change. Thus, these results suggest that PGF2 alpha and PGI2 are involved with milk ejection and lactation in human beings.

Effect of prostaglandins F2alpha and E2 on milk ejection, blood pressure and blood flow through the mammary artery in the cow

The influence of prostaglandins (PG) F2alpha and E2 on milk ejection, mammary artery blood flow and arterial blood pressure was studied in lactating cows. Injections of both PG in the jugular vein or the carotid artery induced milk ejection after a relatively long latency period. The minimal effective dose amounted to 1 to 5 microng and to 100 to 300 microng for PGF2alpha and PGE2 respectively. In several cases with PGF2alpha and once with PGE2 milk ejection was accompanied with a simultaneous increase in blood flow through the mammary artery whereas arterial blood pressure remained unchanged. Both routes of administration showed the same response. It was suggested that the effect of the PG on the bovine myoepithelium is indirect, possibly secondary to a release of oxytocin from the neurohypophysis.