Changes in renal haemodynamis and electrolyte excretion after intraventricular infusion of carbachol in conscious sheep.

Infusion of carbachol at 10 nmol x min-1 for 30 min into one lateral cerebral ventricle of conscious sheep caused long-lasting increases in arterial blood pressure, heart rate and haematocrit. The increase in haematocrit resulted from release of red blood cells from the spleen. The systemic cardiovascular changes were accompanied by increased glomerular filtration rate (G.F.R.), renal plasma flow (R.P.F) and renal blood flow (R.B.F) which did not return to pre-carbachol levels within 180 min post-carbachol. Intracerebroventricular (ICV) infusion of carbachol increased the rates of sodium excretion and clearance, potassium excretion and clearance, osmolal clearance and solute-free water reabsorption and increased the concentration of vasopressin in arterial plasma. The increase in sodium excretion rate was caused by increased sodium filtration associated with a fall in the proportion of filtered sodium being reabsorbed. The increase in potassium excretion rate resulted mainly from increased potassium secretion possibly stimulated by increased distal sodium delivery and by increased vasopressin levels. The observed effects of ICV carbachol infusion resembled those previously reported for ICV infision of hyperosmotic sodium solutions.