Vessel reactivity and prejunctional modulatory changes in the portal vein of mature spontaneously hypertensive rats

The prejunctional effects of 2-chloroadenosine on the contractile responses to perivascular nerve stimulation were studied in conjunction with vessel reactivity in portal veins from mature (45-60 weeks) spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) controls. It was found that the contractility of the portal veins to exogenous noradrenaline was enhanced in SHR, while the sensitivity to noradrenaline, as seen from the EC50 values, was not altered. Responses to perivascular nerve stimulation (supramaximal voltage, 0.7 ms pulse duration for 10 s) were also enhanced in spontaneously hypertensive rats compared to WKY controls at all frequencies of stimulation tested (2-64 Hz), although the sensitivity to perivascular nerve stimulation was not changed since a response of 50% of the maximal obtainable was achieved at 8 Hz in both SHR and WKY. However, no evidence for change in the level of prejunctional modulation of nerve stimulation responses or postjunctional modulation of noradrenaline responses by 2-chloroadenosine (0.1-100 microM) was found. In conclusion, in mature SHR, responses to perivascular nerve stimulation and exogenous noradrenaline were found to be enhanced compared to responses in WKY, although there was no difference in the modulatory action of 2-chloroadenosine between SHR and WKY.