Histamine release by sugar polymers in the rat

Different responses of rodent mast cells to lysophosphatidylserine

The lysophosphatidylserine-induced activation of mast cells has been studied in preparations obtained from different rodents. In mouse and gerbil peritoneal mast cells lysophosphatidylserine behaves as an agonist, inducing noncytotoxic histamine release at 0.2-8 microM. In rat peritoneal and pleural mast cells lysophosphatidylserine is ineffective, but the histamine-releasing activity becomes manifest upon the addition of suboptimal concentrations of other mast cell activators. The common structure-activity relationship shows the link between these effects of lysophosphatidylserine but the calcium requirement indicates differences in the mechanism of action. Histamine release in mouse mast cells is independent of external calcium. Thus, lysophosphatidylserine induces mobilization of endogenous calcium stores in these cells. By contrast, histamine release in gerbil and rat mast cells is dependent on the addition of external calcium indicating that the phospholipid promotes calcium influx. While in gerbil mast cells calcium influx is promoted by lysophosphatidylserine alone, in rat it requires the combined action of the phospholipid and other mast cell agonists. Differently from lysophosphatidylserine, compound 48/80 elicits histamine release in rat and gerbil mast cells. Mouse mast cells are unaffected. Thus, gerbil mast cells are the only preparation in which the action of these two agonists can be observed simultaneously.

Neurotensin-induced increase in intestinal blood flow in the anesthetized rat

Cardiac output (CO) and blood flow to major organs were investigated in pentobarbital-anesthetized rats using 85Sr and 141Ce labelled microspheres (MS) of 15 microns diameter injected into the left ventricle. Changes in organ blood flow and CO were measured after intraventricular dextran (3.4 mumol/kg/min) and intravenous neurotensin (NT) at two different rates, 2.5 nmol/kg/min and 0.125 nmol/kg/min. Dextran, known to give anaphylactoid response in rats, reduced the mean arterial pressure (MAP) from 118 +/- 17 to 55 +/- 8 mmHg (p less than 0.001) concomitant with a 56% decline in CO and significant decreases in blood flow to most organs. At 2.5 nmol/kg/min, NT caused a pattern of changes in MAP, CO and organ blood flow similar to that obtained with dextran, and thus consistent with an indirect response via mast cell stimulation. NT injected at 0.125 nmol/kg/min resulted in a significant increase (30%) in blood flow to the small intestine (p less than 0.01) without changes in MAP or CO. Vascular resistance decreased by 30% in the small intestine (p less than 0.01) and by 20% in the large intestine (p less than 0.05). The results show that circulating NT, at concentrations below those eliciting hypotension, enhances intestinal blood flow without significant changes in other organs.