1. ACTH administration (20 μg day−1 kg−1) to sheep produces hypertension associated with a raised cardiac output and hypokalaemia.

2. The aim of the present experiments was to detail the haemodynamic changes associated with restoration of the extracellular potassium concentration in sheep with ACTH-induced hypertension.

3. After 7 days of ACTH treatment potassium chloride (10 mmol/h) was infused for 3 days to restore plasma [K+] to the pre-ACTH value.

4. ACTH reduced plasma [K+] from 4.4 ± 0.1 to 3.2 ± 0.2 mmol/l but 3 days of potassium chloride infusion returned plasma [K+] to 4.3 ± 0.2 mmol/l.

5. ACTH increased mean arterial pressure from 67 ± 2 to 88 ± 1 mmHg in the first 7 days and it remained elevated during potassium chloride infusion (91 ± 5 mmHg on day 10).

6. Cardiac output rose with 7 days ACTH treatment from 4.9 ± 0.2 to 6.0 ± 0.6 l/min but fell progressively with potassium chloride infusion to 4.9 ± 0.3 l/min on day 10.

7. These studies suggest that potassium status or extracellular [K+] may play a role in determining the haemodynamic profile associated with steroid-induced hypertension.

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