The peptide hormone urotensin II (UII) and its receptor GPR-14 have recently been identified in mammalian species, including man. Subsequent pharmacological studies have described profound cardiovascular effects in non-human primates, suggesting a potential role in related disease states in man. To date, very little is known about the physiology of UII in the rat, the most commonly used species in the study of cardiovascular function. Accordingly, the aims of this study were firstly to develop a specific radioimmunoassay (RIA) to allow the measurement of UII in rat plasma and secondly to determine whether the circulating concentration of UII differs from control values in two models of hypertension, the spontaneously hypertensive rat and the in utero protein restriction model of hypertension.
The rat UII assay was developed from our RIA for flounder UII (Winter et al. 1999). A polyclonal antibody was raised in rabbits against the conserved sequence of the UII peptide (CFWKYC) which is found in all known forms of the hormone. 125I-labelled UII was prepared by the Iodogen method and incubated with antibody and cold rat UII. Antibody bound 125I-labelled UII was separated by addition of bovine λ-globulin and polyethylene glycol, centrifugation and aspiration before counting on a gamma counter.
In utero protein restriction was induced by feeding female Wistar rats a diet containing 9 % protein compared with an isocalorific 18 % protein diet for control animals, from the day of conception until birth and a standard maintenance diet thereafter. This procedure has been shown to increase offspring blood pressure by 20-30 mmHg (Sahajpal & Ashton, 2001). Plasma was collected from anaesthetised control 18 % (n = 5) and hypertensive 9 % (n = 5) rats at 4 weeks of age by decapitation. Plasma was also collected from conscious adult spontaneously hypertensive rats (SHR, n = 13) and control Wistar-Kyoto rats (WKY, n = 9) by decapitation.
The rat UII RIA had a detection limit of 1.6 X 10-15 M with an intra-assay coefficient of variation of 9.2 %. The plasma UII concentration of SHR was significantly higher than that of WKY rats (SHR 20.4 ± 1.9 X 10-12 M vs. WKY 11.8 ± 1.4 X 10-12 M, mean ± S.E.M., P < 0.05, unpaired t test). Similarly, the UII concentration in plasma from hypertensive 9 % protein rats was significantly higher than that from control 18 % rats (9 % 12.7 ± 3.4 X 10-12 M vs. 18 % 2.0 ± 0.6 X 10-12 M, P < 0.05).
Circulating UII concentrations are higher in the SHR and in utero protein restriction models of hypertension by comparison with their normotensive controls. This observation lends support to the suggestion that UII may play a role in cardiovascular disease.
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