“…This could be expected from the observation of a decreased mast cell count in the myocardium of 24-month rats7, since mast cells are said to be the main source of endogenous hepa rin10. Our studies with enzyme inhibitors and heparin31 reveal the tissue enzymatic system to be closely related to the "clearing factor" or lipoprotein lipase (12,16,17,19,23 ancj many others). Therefore, if heparin is the physiological activator of "clearing factor" and of lipolysis within the tissues as well, a fall in lipolytic activity, parallel with the decrease in the number of mast cells, may be expected.…”