Author(s): Zaporozhan VN, Dolomatov SI
Purpose of this work was to study renal function in white rats following a single dose of exogenous tiroxin (T4) on a background of non-selective NO-synthase blocker or inhibition of angiotensin-1 converting enzyme. The experiment was performed with males of outbred white rats (body mass = 140-180 g). Three days prior to T4 injection, the animals drank water solution of captopril (20 mg/l) or were injected intra-gastrically with water solution of non-selective NO-synthase blocker N(omega)-NLA (1 mg/100 g of body mass) over 3 days preceding T4 injection. A single dose of sodium chloride T4 on 1% starch gel (50 microg/100 g of body mass) was injected intragastrically; 5% water loading was given one hour later. Urine and plasma samples were analyzed for osmolality; creatinine, nitrites, nitrates and proteins were measured in urine samples. Tirozine was found to moderately decrease creatinine clearance and increase excretion of proteins, osmotically active substances (OAS), nitrites and nitrates with urine, and raise concentrations of stable nitrogen oxides, primarily nitrates in blood plasma. Pre-block of ACE by captopril intensified diuresis and inhibited renal excretion of OAS, nitrites and nitrates in response to T4 injection. However, captopril failed to prevent the decrease in creatinine clearance and the level of proteinuria. Pre-block of NO synthesis resulted in marked decreases in creatinine clearance, excretion of OAS and nitrites, and moderation of diuresis comparing with intact rats and rats treated with T4 only.