Abstract
1. Dose-response effects of arginine vasopressin on renal haemodynamics were studied in conscious and in pentobarbitone-anaesthetized rats infused with 77 mM-NaCl at 5.2 and 2.6 ml h-1 respectively. 2. Vasopressin at 0.8 pmol h-1 (100 g body weight)-1 did not have a significant effect on arterial blood pressure in conscious or anaesthetized rats. Increasing the dose to 2.5 pmol h-1 (100 g body weight)-1 induced a pressor effect in conscious rats but not in anaesthetized rats. A pressor response was observed in the latter at a dose of 10 pmol h-1 (100 g body weight)-1. 3. Pressor doses of vasopressin of 100 pmol h-1 (100 g body weight)-1 and less did not significantly alter the clearance of p-aminohippurate (PAH) in either conscious or anaesthetized rats. A dose of 1000 pmol h-1 (100 g body weight)-1 significantly decreased PAH clearance in both conscious and anaesthetized animals. 4. Inulin clearance was unchanged by non-pressor doses of vasopressin in both conscious and anaesthetized rats. Moderately pressor doses decreased inulin clearance in conscious animals only. The highest dose administered (1000 pmol h-1 (100 g body weight)-1) decreased inulin clearance in both conscious and anaesthetized rats. 5. Pressor doses of vasopressin had a biphasic effect on the filtration fraction in conscious rats. The filtration fraction decreased with doses of vasopressin at the lower end of the pressor range but increased with the highest dose of 1000 pmol h-1 (100 g body weight)-1. In contrast the filtration fraction did not change significantly with moderate pressor doses in anaesthetized rats but was increased by doses of 100 and 1000 pmol h-1 (100 g body weight)-1. 6. It is concluded that pressor doses of vasopressin lower than 100 pmol h-1 (100 g body weight)-1 do not decrease renal plasma flow rate in conscious or pentobarbitone-anaesthetized rats. The results suggest that the inconsistent effects of vasopressin on renal blood flow reported in the literature are due, at least in part, to the wide range of doses used.