Fluid balance and arterial blood pressure during intracarotid infusions of atrial natriuretic peptide (ANP) in water-deprived goats

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Abstract
The aim of this study was to investigate if atrial natriuretic peptide (ANP) plays a role in the control of water balance in goats and whether ANP affects the increase in mean arterial blood pressure (MAP) which accompanies drinking in water-deprived animals. Bilateral intracarotid infusions werc made in female adult goats deprived of water for 48 h. ANP (1.5 μg min-1, n = 5, or 4.75 μg min-1, n = 5) was infused for 40 min. In control experiments isotonic saline (n= 7) was infused. The goats got access to water 35 min after the start of the infusions. During saline infusions they drank 2.9 ± 0.4 litres, during the low dose of ANP 1.9 ± 0.6 litres (ns. vs saline), and during the high dose of ANP 0.6 ± 0.2 litres (P < 0.01 vs saline). Plasma vasopressin conccntration did not change during saline infusions until after drinking, when it decreased. The vasopressin concentration increased in one goat after infusion of the low dose of ANP and in two goats after the high dose of ANP. The low dose of ANP caused no change in hlAP in four goats, but MAP dropped in the one in which vasopressin concentration increased. MAP fell in all goats infused with the high dose (P < 0.01), with the largest changes occurring in animals showing increased vasopressin concentration. Dhdring the act of drinking a temporary increase of MAP wahd observed when saline or the low dose of ANP was infused, hut this response was attenuated during infusions of the high dose. Plasma adrenaline concentration did nut change during the infusions until the animals drank, when it tended to increase. In connection with drinking, plasma noradrenaline concentration increased during both doses of ANP, hut not during saline. Mean plasma protein concentration increased by 16.5% and 12.5% during low and high doses of ANP respectively. The renal Na excretion increased by about three times during the low dose of ANP, and by about 10 times during the high dose of ANP. The K excretion increased for both doses of ANP. In conclusion, our results indicate that pharmacological doses of ANP are needed to attenuate water intake in dehydrated goats and that even such high doses do not decrease the plasma vasopressin Concentration. Instead, no change or a large increase in the vasopressin concentration was observed, the latter probably secondary to a fall in MAP. We have confirmed in goats that drinking in water-deprived animals is accompanied by a transient increase in MAP, and hake shown that this increase is diminished when infusions of ANP cause reduced water consumption.,