Dose-response of arginine-vasopressin (AVP) on blood pressure (MAP), renal macro and micro cortical and medullary flowsin anesthetized rabbits

AVP is a vasopressor used in various clinical vasoplegic situations. Little is known about AVP effect on intact animal for MAP and renal circulation. Anesthetized (pentobarbital) ventilated New Zealand rabbits (2.5–3.3 kg) were studied.

Measured parameters

MAP, systolic (SVRen) and diastolic (DVRen) renal blood flow velocities (20 MHz pulsed Doppler); laser Doppler cortical Fl_cort and medullary Fl _med flows.

Baseline values

Table 1

Incremental boluses of AVP (1, 2.5, 5, 10, 25, 50, 100, 250, 500 and 1000 ng, 1 ng = 0.4 mU) were i.v. injected. Recording maximal effect, data were expressed in absolute difference from baseline (Δ related to AVP dose).

Dataprocessing

Best statistical curve fit (Fig. 1).

Figure

Results

Two linear curves for MAP, SVRen variations were observed (Fig. 1) with two different slopes (slope1 [doses from 1 to 25 ng AVP] = 0.17 & –0.12 and slope 2 [doses from 50 to 1000 ng AVP] = 0.01 & –0.02 respectively). EC50 (AVP dose inducing half of the response) was calculated from both curves: EC1_MAP = 9 ng; EC2_MAP = 662 ng; EC1_SVRen. = 13 ng; EC2_SVRen = 349 ng. The shift from curve 1 to curve 2 occurred at 40 ng for MAP and 68 ng for SVRen of AVP. For DVRen, Fl_cort, Fl_med no linear relation was observed at low AVP doses. For higher AVP doses, similar negative slopes have been calculated: DVRen –0.01; Fl_cort –0.01; Fl_med –0.003.

Conclusion

MAP and SVRen react strongly to low AVP doses whereas DVRen Fl_cort Fl_med did not. At higher dose, Fl_med is better preserved than DVRen and Fl_cor.