Responses to systemic angiotensin II in lactating and non-lactating goats

This study aimed at investigating whether lactation affects the dipsogenic, hypertensive and volumetric effects of angiotensin II (Ang II) in a low-yielding goat adapted to arid conditions. Six black Moroccan goats were given intravenous infusions of Ang II at 8 ng kg-1 min-1 for 90 min during lactation and a non-lactation period. To further test the dipsogenic response, 5 of them were given Ang II at the consecutively increasing doses 10, 20, 50 and 100 ng kg-1 min-1 (10 min at each dose). The body weight was 32 +/- 1 kg in both periods and the daily milk production was 22 +/- 2 ml kg-1. No drinking was observed during infusions of Ang II in any of the goats. The rise of the mean arterial pressure to Ang II was attenuated in lactating animals and this was not steroid-dependent since the plasma progesterone level was low (< 0.2 nmol 1(-1)). Total plasma protein concentration decreased during Ang II infusions, and the ratio albumin/total proteins was unchanged, indicating that haemodilution had occurred. It is concluded that Ang II does not elicit drinking in the arid adapted Moroccan goats and we suggest that these goats have an elevated thirst threshold. However, haemodilution and an attenuated blood pressure response to Ang II occur in the lactating Moroccan goat, as has previously been observed in high-yielding Swedish domestic goats.