Characterization of the isolated rat mesenteric vascular-intestinal loop preparation.

The isolated mesenteric vascular-intestinal loop preparation has been shown to be an important model of resistance vessel hemodynamics reflective of both physiological and pathological conditions. The present experiments were performed to characterize the isolated rat mesenteric vascular-intestinal loop preparations. The mesenteric vasculature with intestine was perfused with modified Krebs-Ringer bicarbonate solution at a constant flow of 5 mL/min. To examine spontaneous norepinephrine overflow, the perfusate and superfusate were collected for 4-min periods from 36 to 60 min after the start of the perfusion. The norepinephrine overflow from the mesenteric vasculature was also determined in response to field stimulation (FS). Basal spontaneous endogenous norepinephrine overflow was relatively constant. The spontaneous norepinephrine overflow was increased by guanethidine (10(-5) M) but was not influenced by tetrodotoxin (3 x 10(-7) M), cocaine (10(-6) M), or prazosin (10(-6) M) treatment. Field stimulation (4-12 Hz) caused frequency-dependent pressor responses and increases in norepinephrine overflow. When norepinephrine overflow was expressed as amount/stimulus (picogram/stimulus), it was frequency independent. The pressor responses to FS were abolished by guanethidine (10(-5) M), tetrodotoxin (3 x 10(-7) M), and prazosin (3 x 10(-8) M). Prazosin at 10(-6) M significantly augmented the FS-induced endogenous norepinephrine overflow. Thus, these results indicate that the isolated rat mesenteric vascular-intestinal loop preparation is an excellent model for demonstrating resistance changes in isolated vascular beds while simultaneously measuring endogenous catecholamine overflow.