Lactation affects pressor, volumetric and natriuretic responses to angiotensin II in goats

Demands on cardiovascular function and fluid turnover increase during lactation and pregnancy in the goat, but the hormonal status is different. This study is aimed at investigating the effects of hypertensive angiotensin II (ANGII) in lactating goats. The results were compared with those of pregnancy and control conditions. ANGII (0.5 microgram min-1) was infused intravenously for 60 min (n = 6). The rise in blood pressure in response to ANGII was attenuated during lactation as in pregnancy (P < 0.001 vs control period). ANGII caused reflex bradycardia. Plasma protein concentration decreased by 7.5% during infusions in lactating goats (pregnancy: 9%; control period: 4.5%). Renal Na excretion increased by 260% (lactation), by 400% (pregnancy; n.s. vs. lactation), and by 800% (control period; P < 0.01 vs. lactation). The glomerular filtration rate was unchanged during ANGII infusions in lactating animals, but increased in the other periods. Effective renal plasma flow decreased. ANGII raised aldosterone from < 34.5 pmol l-1 to 539 +/- 80 pmol l-1 (lactation) and to 428 +/- 41 pmol l-1 (control; P < 0.05 vs. lactation), and from 72 +/- 9 to 651 +/- 103 pmol l-1 (pregnancy; P < 0.01 vs. lactation). Plasma progesterone was undetectable during lactation, but varied from 0 to 17 nmol l-1 during control conditions and was 16 +/- 1 nmol l-1 during pregnancy. Oestradiol 17 beta was 181 +/- 22 pmol l-1 in pregnant goats, and undetectable in lactating animals. In conclusion, lactation affects ANGII-induced changes in cardiovascular and fluid regulation, but in this period the effects were not related to progesterone or oestradiol 17 beta.