Changes in the relationship between cerebrospinal fluid and blood composition produced by ACTH treatment in conscious sheep

It has been proposed that an increase in CSF osmolality could be involved in the genesis of hypertension by activation of central nervous system receptors involved in cardiovascular regulation. ACTH induced hypertension in the sheep is an adrenally dependent model of steroid induced hypertension. This study reports the effect of ACTH administration (20 g/kg/day) for 5 days on the composition of cerebrospinal fluid (CSF) and blood (plasma) in conscious sheep. ACTH increased CSF and plasma osmolality within 24 h associated with parallel increases in both blood and CSF glucose concentrations and plasma and CSF sodium concentration. Plasma potassium fell within 24 h, but CSF potassium did not change over the 5 days of ACTH treatment. Neither calcium nor magnesium changed in either plasma or CSF. CSF phosphate increased and plasma phosphate decreased. CSF and plasma bicarbonate were elevated with ACTH. Plasma chloride decreased after 5 days of ACTH treatment but was not associated with a change in CSF. The relevance of the measured changes in CSF osmolality and composition to the mechanisms involved in the production of ACTH-induced hypertension will be subject of further experimentation.