Enhancement of renal but not haemodynamic effects of atrial natriuretic peptide (1-28) in sheep treated with ACTH

The effect of hypovolemia on the renal and cardiovascular responses to atrial natriuretic factor (ANF) infusion

The renal and cardiovascular effects of ANF infusion have been examined in separate series of experiments; in conscious instrumented sheep following either hemorrhage (10 mL/kg body weight) or removal of 500 mL of plasma by ultrafiltration. Renal arterial infusion of hANF (99-126) at 50 micrograms/h increased sodium excretion from 99 +/- 30 to 334 +/- 102 (p less than 0.05) in normal animals, and from 77 +/- 31 to 354 +/- 118 mumol/min in hemorrhaged animals. Similarly in sheep following ultrafiltration, cardiac output and stroke volume were reduced by intravenous infusion of ANF (100 micrograms/h), although these effects were less marked than those observed in normal animals. The rapid modulation of natriuretic responses to ANF observed in volume expanded animals is not seen in this model of acute volume depletion suggesting that the mechanism through which the renal response to ANF is modulated in low sodium or volume states is not simply the reverse of that which produces rapid enhancement of response following blood volume expansion.

Hemodynamic interactions of atrial natriuretic factor with the sympathetic nervous system in sheep

The hemodynamic effects of short-term infusion of atrial natriuretic factor (ANF) were observed in sheep with combined alpha/beta adrenoceptor pharmacological blockade. The effect of ANF on the sympathetically-mediated baroreflex system was observed in conscious sheep in which aortic and vena caval balloon occluders had been surgically implanted. ANF infused at 100 micrograms/h for 60 min produced similar effects on blood pressure, cardiac output and stroke volume during alpha/beta-adrenoceptor blockade, compared to the responses seen in normal sheep, however the increases in heart rate and total peripheral resistance were reduced. ANF markedly enhanced the gain of the baroreceptor-heart rate reflex in the sheep. This effect may mediate the large increase in heart rate which is associated with a small fall in blood pressure during short-term infusion of ANF. In conclusion, the sympathetic nervous system plays an important role in regulating the reflex cardiovascular responses to short-term infusion of ANF in sheep. The large species variation in the hemodynamic responses to ANF may be related to differing degrees of stimulation or inhibition of the baroreceptor system to affect heart rate and/or peripheral resistance.

Renal effects of atrial natriuretic factor (99-126) in potassium loaded sheep

1. The renal response to renal arterial infusion of synthetic atrial natriuretic factor (ANF 99-126) was examined in conscious sheep following dietary K loading, and compared with the response in normal sheep. 2. Renal arterial infusion of ANF in K loaded sheep increased the excretion of Na and Ca, but did not affect the excretion of K. 3. The natriuretic effect of ANF was attenuated in K loaded animals, possibly as a consequence of the reduction in Na status which is associated with K loading.