CONTINUOUS MEASUREMENT OF VASCULAR-RESPONSES IN CONSECUTIVE SECTIONS OF CAT SKELETAL-MUSCLE VASCULATURE INCLUDING CHANGES IN PERMEABILITY TO ALBUMIN - EFFECTS OF HISTAMINE-LIKE AGONISTS

The method described allows continuous simultaneous monitoring of blood flow, tissue volume, and protein content in a highly controlled peripheral vascular bed, which makes the method suitable for studying the direct effects of inflammatory mediators on blood vessels. Edema formation resulting from increased hydrostatic pressure only and edema formation resulting from both increased hydrostatic pressure and increased vascular permeability to protein can be distinguished. The two mechanisms are clearly demonstrated using the selective histamine receptor agonists dimaprit and 2-(2-aminoethyl)pyridine. Interaction with histamine H2-receptors induces vasodilatation and edema formation without any increase in vascular permeability, whereas interaction with histamine H1-receptors induces vasodilatation and edema formation associated with increased vascular permeability to proteins. The results also indicate the need for care in designing experiments for studying drug effects on vascular permeability because prior administration of a drug, even though the dose is too low to increase vascular permeability itself, may inhibit increases in vascular permeability in response to subsequent larger doses. © 1978.