Rate-sensitive contractile responses of lymphatic vessels to circumferential stretch.

Phasic contractile activity in rat portal vein is more sensitive to the rate of change in length than to absolute length and this response is widely assumed to be a general characteristic of myogenic behaviour for vascular smooth muscle. Previously, we found that rat lymphatic vessels exhibit phasic contractile behaviour similar to that of portal vein. In the present study, we hypothesized that lymphatic muscle would exhibit rate-sensitive contractile responses to stretch.

Modulation of lymphatic muscle contractility by the neuropeptide substance P.

Substance P (SP) is a neuropeptide associated with sensory innervation of lymphoid tissue and a suspected modulator of lymphatic function in inflammation. Only a few studies have examined the effects of SP on lymphatic contraction, and it is not clear to what extent SP acts directly on the lymphatic muscle and/or endothelium or indirectly through changes in intraluminal filling pressure secondary to increases in capillary permeability/filtration. We tested the effects of SP on the spontaneous contractions of rat isolated mesenteric lymphatic vessels under isometric and isobaric conditions, hypothesizing that low concentrations would stimulate lymphatic pumping by enhancing lymphatic muscle contraction in a manner complementary to the effect of increased preload.

Length-dependence of lymphatic phasic contractile activity under isometric and isobaric conditions.

Objective: Experiments were designed to determine if the effect of preload on the spontaneous contractile activity of rat mesenteric lymphatics would be different under isometric and isobaric conditions.

Methods: Isobaric protocols on cannulated, pressurized rat mesenteric lymphatics ( approximately 120 microm, ID) measured the effects of lumenal pressure on contraction amplitude, frequency, and rate of diameter change (dD/dt). Analogous protocols were conducted using a wire myograph to determine the effects of passive force (preload) on the characteristics of spontaneous, isometric force transients.

An automated method to control preload by compensation for stress relaxation in spontaneously contracting, isometric rat mesenteric lymphatics.

Objective: Our objective was to devise a system to automatically correct for stress relaxation of isometric rat mesenteric lymphatics (90-120 microm, ID). Stress relaxation is a particular problem in isometric studies of highly distensible vessels and is evident as a time-dependent, secondary decline in force after an abrupt length increase. Because the phasic contraction pattern of lymphatics is exquisitely sensitive to changes in preload, stress relaxation makes stable contraction patterns difficult to achieve and analyze.