1. The sensitivity of mesenteric resistance arterioles to [arginine]vasopressin (AVP) was investigated in spontaneously hypertensive rats (SHR) and control Wistar–Kyoto rats (WKY). No difference in pAVP (–log dose of AVP producing 50% of the maximum response) was observed [SHR 0.21 ±0.03 m-units/ml (n = 10) vs WKY 0.15 ±0.06 m-units/ml (n = 9)], although SHR vessels exhibited greater absolute tension development.

2. Both strains of rat displayed tachyphylaxis to repeated stimulation with AVP, and oscillatory tension changes were observed in all vessels from SHR and rarely in WKY vessels at activating concentrations of AVP.

3. AVP did not elicit a contractile response after noradrenaline-induced calcium depletion.

4. After vessels were depleted of calcium by using a combination of calcium-free media and noradrenaline stimulation, restoration of calcium in the presence of AVP elicited a greater contractile response in SHR vessels.

5. The results therefore provide evidence for an increased calcium response to AVP in SHR resistance vessels, although this was only demonstrable by calcium recovery experiments.

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