Short-term mammary blood flow responses to changes in circulating metabolite concentrations

Mammary blood flow (MBF) is locally regulated to match nutrient delivery with demands for milk synthesis. The objective of this experiment was to determine which of the major milk precursors would elicit a MBF response when its concentration was elevated in the arterial supply, and to define the time-course of such a response. Treatments of saline (0.38 g/min), glucose (2.2 g/min), amino acids (complete milk protein profile 2.11 g/min), triacylglycerol (Liposyn(TM) 2.0 & 0.87 g/min), insulin (20 ug/min), or adenosine (3 mg/min), were infused into an external iliac arterial catheter for two periods of 20 minutes. Iliac plasma flow dropped 5, 7, and 25 percent within the first minute of infusion of amino acids, glucose and triglyceride, respectively. Adenosine, a known vasodilator, increased plasma flow by 40% immediately upon infusion, to a maximum of 65%, and quickly returned to baseline values upon cessation of treatment. These results indicate that the mammary gland modifies its blood flow rate within seconds of being exposed to new concentrations of milk precursors and is sensitive to circulating levels of adenosine.