Polyamine transport and metabolism in mouse mammary gland. General properties and hormonal regulation

Mouse mammary gland has been shown to possess a transport system for spermidine, spermine, and putrescine. The uptake system for sperimidine, as studied in detail on mammary explants in culture is a time-dependent, energy-requiring process which can be stimulated by insulin and prolactin. The stimulatory effect of insulin involves both enhancement of Vmax for spermidine influx and prevention of efflux of the polyamine, whereas prolactin, in the presence of insulin, elicits a greater increase in Vmax for spermidine. Studies are also reported on the effects of temperature, concentration, and various inhibitors on this system. The accumulated spermidine exists virtually in an unchanged form with little metabolic conversion to either spermine or putrescine or to its conjugated form. In contrast, spermine and putrescine, both of which are also taken up by mammary explants, undergo metabolic conversion to spermidine.