Blood pressure response to angiotensin II in pregnant and lactating goats maintained on high or low sodium intake

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Abstract
Goats were kept on either high (274 mmol day-1) or low (68 mmol day-1) sodium intake during pregnancy, lactation, and anoestrus. High salt (HS) animals had about three times greater renal Na excretion than low salt (LS) animals, but the differences in plasma volume, protein concentration, and haematocrit were generally not significant. Angiotensin II (AII) was infused intravenously for 28-min periods in doses of 0.30, 0.75, or 1.00 nmol min-1. The increase in mean arterial blood pressure (MAP) during AII infusions was greater in HS than in LS goats, but became attenuated in all animals during the course of the pregnancy. In LS goats the MAP rise was smaller in late pregnancy than during lactation and anoestrus. In HS goats the rise in MAP was exaggerated in early pregnancy and was similar to lactation and anoestrus values in late pregnancy. During lactation and anoestrus the goats showed similar MAP increase in response to AII infusions. The pulse pressure was greater during AII infusions performed in early pregnancy, lactation and anoestrus than in late pregnancy. Cardiac arrhythmias were noted during AII infusions, most frequently during lactation and in HS goats in early pregnancy. The results show that a moderately elevated sodium intake causes a significantly higher MAP increase in response to AII infusions during pregnancy. This abolishes the reduction of the MAP increase to AII infusions during late pregnancy as compared to anoestrus; a phenomenon which is observed in goats on a low sodium intake.