Contractile properties of lymphatics from the human lower leg

Lower leg lymphatics, taken from seven volunteers, were investigated in vitro. Isometric contractions were induced by noradrenaline, 5-hydroxytryptamine (5-HT), prostaglandin F2 alpha (PGF2 alpha), and the thromboxane A2 (TXA2)-mimetic U-44069. Noradrenaline induced phasic contractions in 6 of 7 segments. The amplitude of the contractions were up to 100% of a previous K+ (124mM)-induced contraction and the frequency at 10(-6)M of noradrenaline was 5-13 min-1. These contractions were unaffected by propranolol (10(-6)M), but they were abolished by phentolamine (10(-6)M). Noradrenaline had an Emax (tonic contraction) of 7% of the K+ (124mM) contraction (n = 7) and the pEC50-value was 6.9 (n = 3). The corresponding values for 5-HT were 21% (n = 5) and 6.4 (n = 3). PGF2 alpha elicited contractions in all segments investigated (Emax = 87%, pEC50 = 5.8, n = 5). U-44069 had high contractile capacity and potency in all investigated segments (Emax = 137%, pEC50 = 8.9, n = 7). Phasic contractions were elicited also by 5-HT, PGF2 alpha and U-44069. Compared to earlier studies of human peripheral lymphatics, these results show that there are regional differences in susceptibility to these vasoactive agents.