The in situ blood perfused rat mesentery; a model for assessing modulation of adrenergic neurotransmission.

The present study describes a method for the in situ blood perfusion of the rat mesentery and compares this method with the in vitro method of McGregor. The in situ method gives stable baseline perfusion pressures for over 2 h and consistent vasoconstrictor responses to both periarterial nerve stimulation (NS) and exogenous norepinephrine (NE). The responses to NS are blocked by phentolamine and reserpine whereas the responses to NE are blocked by phentolamine but potentiated by reserpine. The threshold responses to NS and NE were 3 Hz and 100 ng, respectively, in the in situ preparation and 11 Hz and 200 ng, respectively, in the in vitro preparation. When the effects of prostaglandin E2 (PGE2) were examined in indomethacin-treated mesenteries, PGE2 decreased the responses to both NS and NE in the in situ preparation, but in the in vitro preparation, PGE2 enhanced the response to NS and NE. Thus, the in situ blood perfused rat mesentery is a stable and reproducible model for examining the effects of drugs and hormones on adrenergic neurotransmission and responses to exogenous norepinephrine.