Modulation of the cyclic AMP content of rat renal inner medulla by oxygen: possible role of local prostaglandins.

Abstract

A B S T R A C T The lower 02 tension and more active anerobic metabolism that pertain in the inner medulla (IM) of kidney relative to cortex (C) are well recognized, but there is no evidence that 02 availability constitutes a limitinig or regulatory factor in IM metabolism or function. In the present in vitro study, we examined the effects of 02 on adenosine 3',5'-monophosphate (cAMP) imietabolism in slices of rat renal C and IM. After a 20-min incubation of slices in Krebs Ringer bicarbonate buffer with 95% 02 + 5% C02 serving as the gas phase, the cAMP content of IM wZas 6-10-fold higher than that of C in either the presence or absence of 2 mM 1-methvl-3-isobutylxanthine in the incubation media. In slices of IM incubated for 20 min with 1-methyl-3-isobutvlxanthine, cAMP was 22.5±+SE 2.48 pmol/mg wet weight at 95% 02 and 4.37 without 02. Oxygenation of 02-deprived IM increased cAMP twtofold in 2 min, an effect fully expressed in 5 min (fivefold increase 17 August 1976. which had been incubated at 95% 02. In slices of IM previously exposed to indomethacin or meclofenamate at 95% 02, a maximally effective concentration of exogenous prostaglandin E, restored cAMP and adenylate cyclase activitv to levels which approximated those observed at 95% 02 in the absence of an inhibitor of prostaglandin synthesis. These results suggest that 02 enhancement of cAMP content in IM may be mediated at least in part by local prostaglandinis.

Calcium-dependent action of osmolality on adenosine 3',5'-monophosphate accumulation in rat renal inner medulla: evidence for a relationship to calcium-responsive arachidonate release and prostaglandin synthesis.

“…), kidneys were excised and chilled immediately in 0.85% NaCl at 0-4°C. The renal capsules were removed and slices of inner medulla prepared with a Stadie-Riggs microtome as previously described in detail (4).…”

“…Routinely, a total of 40-50 mg of inner medulla was present per flask in incubations conducted in the absence of IBMX, whereas 10-15 mg of tissue was used in incubations containing the phosphodiesterase inhibitor. cAMP content of tissue slices was extracted with 50 mM sodium acetate pH 4.0 at 95°C and assayed by the protein binding method (4,12,13). Authenticity of the determinations was verified as previously described (4,12).…”

“…cAMP content of tissue slices was extracted with 50 mM sodium acetate pH 4.0 at 95°C and assayed by the protein binding method (4,12,13). Authenticity of the determinations was verified as previously described (4,12).…”

“…Osmotic effects on tissue cAMP levels were not accounted for by fluctuations in tissue wet weight, ATP content, or an altered partitioning of cAMP between tissue and media as a function of media tonicity (1,2). Earlier observations have indicated that the high cAMP levels encountered in rat inner medullary slices incubated in standard Krebs buffer (305 mosM) and at the high gasphase 02 content routinely employed in such in vitro studies is related to an accelerated rate of formation of prostaglandin (PG)E2, a well-recognized agonist of cAMP in renal medulla (4,5). Exposure of inner medullca to a high 02 tension has been shown to enhance PGE2 synthesis, and thereby tissue cAMP accumulation (4)(5)(6).…”

“…Earlier observations have indicated that the high cAMP levels encountered in rat inner medullary slices incubated in standard Krebs buffer (305 mosM) and at the high gasphase 02 content routinely employed in such in vitro studies is related to an accelerated rate of formation of prostaglandin (PG)E2, a well-recognized agonist of cAMP in renal medulla (4,5). Exposure of inner medullca to a high 02 tension has been shown to enhance PGE2 synthesis, and thereby tissue cAMP accumulation (4)(5)(6). The effects of osmolality on inner medullary prostaglandin synthesis have also been studied previously (6)(7)(8)(9).…”