Effects of captopril on arterial blood pressure,plasma renin activity and vasopressin concentration in sodium-repleted and sodium-deficient goats: A serial study during pregnancy,lactation and anestrus

The effects of captopril (intravenous loading dose of 20 mg, 1 h later followed by 10 mg infused during the next h) on arterial blood pressure and plasma renin activity were followed in 4 goats during the last months of pregnancy, during lactation and during anestrus. Experiments were made both when the animals were sodium-repleted and sodium-deficient. Furosemide and dietary restriction were used to deprive the animals of sodium. In sodium-replete animals, captopril caused a more pronounced fall in mean arterial blood pressure and a larger increase in plasma renin activity (PRA) when the animals were pregnant than when they were lactating or in anestrus. During sodiumdeficient conditions the response was similar as during sodium repletion in pregnant goats. In anestral goats, PRA rose in response to captopril, but the blood pressure fall was similar as when the goats were sodium-replete. In lactating sodium-deficient goats, captopril caused a marked fall in mean arterial blood pressure concomitant with a 2–3 times higher rise in PRA than during corresponding sodium-repletion experiments. The respiratory rate was elevated in pregnant animals and increased further during captopril. The plasma vasopressin concentration did not change during captopril-induced hypotension. If the blood pressure fell ≥10 mmHg the animals became very quiet and occasionally they fell asleep. All goats delivered healthy kids. The fact that the blood pressure fall was marked and consistent in all animals during pregnancy, but less and more variable during anestrus indicates that the activity of the renin-angiotensin system is of greater importance for blood pressure maintenance during pregnancy than during anestrus. The exaggerated effects in lactating sodium-deficient animals were probably due to a more efficient salt depletion, these animals losing extra salt via the milk.