I just came across this article called, "High Blood Pressure Climbs in Winter." It is based on research done in France with the elderly. One of the things mention was that they noticed an increase in a type of hormone called catecholamines. I think this article will help us understand why the cold also triggers other responses in our bodies.
Catecholamines are hormones that are released by the adrenal glands in situations of stress such as psychological stress or low blood sugar levels. If this doesn't sound familair, then read on. Catecholamines cause general physiological changes that prepare the body for physical activity (fight-or-flight response). Some typical effects are increases in heart rate, blood pressure, blood glucose levels, and a general reaction of the sympathetic nervous system. Some drugs, like tolcapone (a central COMT-inhibitor), raise the levels of all the catecholamines. (from Wikapedia)
http://www.webmd.com/hypertension-high-blood-pressure/news/20090112/high-blood-pressure-climbs-in-winter?ecd=wnl_wmh_011909http://en.wikipedia.org/wiki/CatecholamineReta
