The adrenergic system and the cardiovascular effects of platelet activating factor (1-0-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine) in SHR and WKY rats

Renal vascular and sympathetic nerve responses to hypotension induced by platelet-activating factor in anesthetized dogs

This experiment was designed to determine renal sympathetic and renal vascular responses to platelet-activating factor (PAF)-induced hypotension in anesthetized dogs with and without systemic baroreceptor denervation. The left kidney was perfused at a constant flow, and renal perfusion pressure and efferent left renal sympathetic nerve activity were measured simultaneously. Intrarenal injection of PAF (1.25-5.0 x 10(-2) micrograms/kg, n = 6) produced a dose-dependent increase in renal perfusion pressure without any change in systemic blood pressure. An intravenous injection of PAF (10 micrograms/kg) to intact animals (n = 7) caused an initial increase in renal nerve activity (157 +/- 14%) followed by a gradual reduction below baseline (72 +/- 7%) with concomitant systemic hypotension (from 116 +/- 7 to 46 +/- 6 mmHg). Renal perfusion pressure increased significantly from 84 +/- 2 to 161 +/- 33 mmHg concomitant with an increase in renal nerve activity at 1 min and was maintained at this elevated level throughout the experiment. Similar responses of renal nerve activity and renal perfusion pressure were found in animals with complete systemic baroreceptor denervation (n = 7). These results suggest that renal vascular response during PAF-induced hypotension may presumably be mediated by a direct vasoconstrictor effect of PAF on the renal vasculature and that baroreceptor reflex is not involved in either renal sympathetic or renal vascular changes.

Platelet activating factor and systemic anaphylaxis in Nippostrongylus brasiliensis-sensitized rats: differential effects of PAF antagonists

1. The effects of two platelet-activating factor (PAF) antagonists, WEB 2086 and BN 52021, in reducing the changes in extravasation (Evans blue technique) and blood flow (radiolabelled microsphere method) to various organs and tissues following anaphylactic shock in the Nippostrongylus brasiliensis-sensitized rat were investigated. 2. Both antagonists attenuated anaphylaxis-induced increases in plasma protein leak in the trachea, stomach and small intestine, although they did not block extravasation in the colon and kidneys. 3. Anaphylaxis-induced decreases in blood flow to the adrenals were effectively antagonized by WEB 2086, although this antagonist did not reverse blood flow decreases to any other tissues. BN 52021, on the other hand, did not alter anaphylaxis-induced decreases in blood flow to the adrenals, but effectively prevented dramatic decreases in blood flow to the large and small bowel and spleen. 4. Anaphylactic shock produced marked reduction in blood pressure that was partly reversed by WEB 2086, whereas BN 52021 effectively blocked the decreases in cardiac output. 5. Thus, PAF is responsible for some of the haemodynamic and extravasation of protein changes associated with systemic anaphylaxis in the rat, although the differential inhibition observed with the two antagonists suggests that PAF alters vascular responsiveness through different mechanisms in selected tissues.

Plasma levels of atrial natriuretic peptides in conscious adult spontaneously hypertensive rats

The effects of acute volume expansion and acute salt loading on the plasma levels of immunoreactive atrial natriuretic peptides (ir-ANP's) were investigated in conscious adult (16 weeks) Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Basal plasma concentrations of ir-ANP's were similar (108 +/- 9 pg/ml and 105 +/- 8 pg/ml, respectively) in hypertensive and normotensive rats. In both strains mean arterial pressure, heart rate and plasma catecholamines were unaltered by acute volume expansion but significantly elevated by acute salt loading. However, both acute volume expansion and acute salt loading increased plasma concentrations of ir-ANP's similarily in SHR and WKY rats, independent of blood pressure or plasma catecholamine levels. Our findings show that chronic hypertension in SHR does not result in changes in basal or VOL- and SAL-stimulated levels of circulating ir-ANP's.