Renal responses to angiotensin II in conscious dogs: effects of aspirin and indomethacin

Acute intrarenal infusion of ANG II does not stimulate immediate early gene expression in the kidney

ANG II is capable of stimulating expression of immediate early genes such as egr-1 and c-fos in a variety of cultured cells, including cells of renal origin. To investigate whether ANG II can stimulate early growth response gene expression in vivo, we studied the effects of acute renal artery infusion of low-dose ANG II (2.5 ng small middle dot kg(-1) small middle dot min(-1)) or vehicle on the renal expression of c-fos and egr-1 genes in rats. ANG II infusion for 30 or 240 min decreased renal vascular conductance by approximately 13 and 8%, respectively, compared with the vehicle group. Expression of the early growth response genes c-fos and egr-1 was analyzed using Northern blot hybridization. No significant upregulation of c-fos or egr-1 mRNA levels was detected in rats that received ANG II for either 30 or 240 min, compared with the vehicle groups. We conclude that ANG II, at doses that cause significant physiological effects, does not increase the renal expression of c-fos or egr-1 genes over periods of up to 4 h in vivo.

Thromboxane mediates renal hemodynamic response to infused angiotensin II

Since we had found that angiotensin II (Ang II), but not phenylephrine (PE), increased the excretion of thromboxane (Tx) and raised mean arterial pressure (MAP) by a Tx-dependent mechanism, we tested the role of TxA2 in mediating Ang II-induced changes in renal hemodynamics. For series 1, groups of anesthetized rats received an i.v. infusion of Ang II (50 ng.kg-1.min-1). When infused with a vehicle, Ang II increased MAP, renal vascular resistance (RVR) and the excretion of TxB2 factored by GFR. A PGH2-TxA2 receptor antagonist, SQ-29,548, or three days of pretreatment with a TxA2 synthase inhibitor UK-38,485, which reduced excretion of TxB2 by 80%, blunted the rise in MAP and RVR induced by Ang II. In contrast, three days of pretreatment with indomethacin did not alter the renal vascular response to Ang II. For series 2, groups of rats received Ang II at a higher rate (500 ng.kg-1.min-1) while the RPP was stabilized at +11 to +15 mm Hg with a suprarenal aortic clamp. SQ-29,548 and UK-38,485 both prevented Ang II-induced reductions in GFR and blocked 80% of the increase in RVR. For series 3, infusions of phenylephrine at an equipressor dose to series 2 of 30 micrograms.kg-1.min-1 with control of RPP at +14 mm Hg also increased RVR but this was not blunted by SQ-29,548.

IN CONCLUSION

1.) infusion of Ang II increases excretion of filtered TxB2, causes dose-dependent increases in RVR and, at high doses, reduces GFR.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal handling and effects of salicylic acid in the isolated perfused rat kidney

The renal handling of salicylic acid (SA) and its effects on renal function were studied in the isolated perfused rat kidney (IPK). The renal handling of SA is dominated by reabsorption and only a small fraction of the filtered SA is excreted into the urine. Reabsorption is a passive process and is dependent on urinary pH. Because of the extensive reabsorption, no decrease in perfusate concentration can be observed in the course of the IPK experiment. SA accumulated slightly in the IPK and this accumulation is concentration dependent. Small amounts of SA were converted to salicyluric acid (SU), the glycine conjugate of SA. SA concentrations higher than 100 micrograms/ml caused an immediate increase in urinary flow and in fractional excretion of sodium, potassium, chloride and calcium. Fractional excretion of glucose increased gradually. Glomerular filtration rate, renal perfusion flow, renal pressure and fractional excretion of magnesium were not affected by SA. The effects were dependent on the SA concentration. Although SA is a classical non-steroidal antiinflammatory drug (NSAID), its influence on renal function appears to be different from other NSAIDs which are usually associated with a reduction in urinary flow and salt excretion.