THE EFFECTS OF RADIATION ON THE CONTRACTILE ACTIVITY OF GUINEA PIG MESENTERIC LYMPHATICS

Abstract

In order to assess the effects of irradiationon lymphatic function, the contractionfrequency and maximum and minimumdiameters of guinea pig mesenteric collectinglymphatic vessels were measured in vivo 4 hoursafter 1000 rads of abdominal irradiation. Themean contraction frequency for lymphaticsfrom irradiated guinea pigs (7.6±0. 7) wassignificantly higher than for normals (nonirradiated)(4.7 ±O. 7) during an initial controlobservation period, but there was no differencein maximum or minimum diameter between thetwo groups during this period. Topical applicationof 1O-4M noradrenaline (NA) significantlyincreased contraction frequency in both groups;lymph vessel diameter significantly decreasedafter NA in irradiated, but not in normal guineapigs. Intravenous infusion of calcium dobesilate(200 mg/kg) caused a significant increase in thecontraction frequency of lymphatic vessels inboth normal (to 9.4± 1.5) and irradiated (to9.B±1.2) animals, but diameter was notsignificantly altered. Thus, lymphatic vesselsfrom irradiated guinea pigs were still responsiveto exogenous stimuli 4 hours post-irradiationand were initially pumping more actively thanthose from normal guinea pigs, presumably inresponse to radiation-induced edema. They alsoexhibited a supersensitivity to the vasoconstrictiveeffects of NA, perhaps due to analteration of the pacemaker or smooth musclecells by irradiation.