Renal functional effects of endothelins: dependency on cytochrome P450-derived arachidonate metabolites.

The renal tubular and hemodynamic effects of endothelin-1 (ET-1) were studied in the rat in terms of the participation of cytochrome P450 monooxygenases (CYP450)-derived arachidonic acid (AA) metabolites. The availability of specific mechanism-based inhibitors of CYP450-dependent AA metabolism has greatly facilitated studies designed to link AA metabolites generated by CYP450 to renal function. Eicosanoid products synthesized by cyclooxygenase (COX) and CYP450 can account for the renal functional effects of ET-1. Inhibition of COX decreased glomerular filtration rate (GFR) and potentiated the depression of GFR elicited by ET-1. In contrast, inhibition of CY-P450-dependent AA metabolism enhanced GFR and blunted ET-1 induced increase in renal vascular resistance, yet reduced the diuretic response to ET-1. Thus, CYP450-dependent AA products depress GFR and renal blood flow, while promoting sodium excretion. The effects of ET-1 on renal function correspond to those of 20-HETE, the predominant renal CYP450-derived AA metabolite.

Cryptolepine-induced vasodilation in the isolated perfused kidney of the rat: role of G-proteins, K+ and Ca2+ channels.

The isolated perfused kidney of the rat was used to examine the contribution by guanosine triphosphate (GTP)-binding (G-) proteins, K+ and Ca2+ channels to the vasodilator actions of cryptolepine (5-methylquindoline). In normal Krebs-Henseleit buffer (4.7 mM KCl), cryptolepine elicited dose-dependent reductions in perfusion pressure of phenylephrine-preconstricted kidneys. The reductions in perfusion pressure by cryptolepine at bolus doses of 2.5, 5, and 10 micrograms were -18.0 +/- 3.4, -30.6 +/- 5.3, and -38.3 +/- 6.8 mm Hg, respectively (n = 19). In K(+)-free (0 mM KCl) Krebs-Henseleit solution, the vasodilator response to cryptolepine was reduced by 44.7 +/- 5.7% (n = 5; P < 0.01). The addition of ouabain (10(-4) M) further reduced cryptolepine-induced vasodilation to 63.0 +/- 7.2% (n = 11: P < 0.01) of the control. A combination of both conditions did not abolish the vasodilator responses to cryptolepine, suggesting the involvement of additional mechanisms. In 80, as opposed to 20 mM KCl, the reductions in perfusion pressure by cryptolepine, 2.5, 5, and 10 micrograms were markedly reduced to -0.8 +/- 0.8, -2.3 +/- 1.4, and -4.0 +/- 2.1 mm Hg, respectively (P < 0.01; n = 6). Responses to acetylcholine and diazoxide, an adenosine triphosphate (ATP)-dependent K+ channel activator, were also markedly reduced, suggesting the involvement of K+ channels for these agents. Furthermore, tetraethylammonium (5 and 10 mM), a non-specific K+ channel blocker, inhibited the vasodilator responses to cryptolepine (n = 5; P < 0.01) and to diazoxide and acetylcholine in a dose-related manner. However, glibenclamide (5 and 10 microM), an ATP-sensitive K+ channel blocker, inhibited the vasodilator responses to diazoxide and acetylcholine but was without effect on cryptolepine-induced vasodilation. This suggests that cryptolepine activates K+ channels which are tetraethyl ammonium- but not glibenclamide-sensitive. In pertussis toxin-treated rats, the vasodilator response to cryptolepine was not affected while that to acetylcholine and especially diazoxide was markedly inhibited. This suggests that, unlike diazoxide and acetylcholine, the K+ channels activated by cryptolepine are not coupled to pertussis toxin-sensitive G-proteins. In the presence of verapamil (5 microM) and cobalt chloride (1 mM), Ca2+ channel blockers, the vasodilator response to cryptolepine was inhibited (n = 5; P < 0.01), suggesting that Ca2+ flux across membranes is also involved in cryptolepine-induced vasodilation in the rat kidney.

The suppression by lipopolysaccharide of cytochrome P450-dependent renal vasodilation in the rat is mediated by nitric oxide.

The isolated perfused kidney of the rat was used to examine the hypothesis that lipopolysaccharide-induced nitric oxide (NO) production inhibits cytochrome P450-dependent vasodilation. The vasodilator responses to arachidonic acid and bradykinin were examined as the response to arachidonic acid is wholly dependent, and that to bradykinin partly dependent on cytochrome P450 metabolism. In endotoxin-treated rats, the vasodilator response to arachidonic acid was inhibited, and those to bradykinin and acetylcholine were enhanced. Following treatment with phenobarbitone, the inducer of certain isoforms of cytochrome P450 enzymes, the vasodilator effects of all three agonists, especially that of arachidonic acid, were amplified. Lipopolysaccharide inhibited the effect of phenobarbitone on the vasodilator effect of arachidonic acid and bradykinin but enhanced that of acetylcholine. The effect of lipopolysaccharide was antagonized by haemoglobin, a NO antagonist, and N omega-nitro-L-arginine, an inhibitor of NO synthase, suggesting that the inhibitory effect of lipopolysaccharide on arachidonic acid- and bradykinin-induced vasodilation was mediated by NO/NO synthase. N omega-Nitro-L-arginine enhanced vasodilation induced by arachidonic acid while that induced by bradykinin or acetylcholine was reduced, implying that endogenous NO inhibits vasodilator cytochrome P450 metabolites in the rat kidney. Pretreatment with dexamethasone, an inhibitor of inducible NO synthase, resulted in inhibition of the lipopolysaccharide modulation of arachidonic acid-induced vasodilation, suggesting that the inducible NO synthase is the target of the inhibitory effect of lipopolysaccharide. The inhibitory effect of lipopolysaccharide was mimicked by nitroprusside, the L-arginine-independent NO donor, and by L-arginine, the biosynthetic precursor of NO. The effect of L-arginine, but not of nitroprusside, was antagonized by N omega-nitro-L-arginine, suggesting a specific role for NO synthase in the inhibitory effect of lipopolysaccharide in the inhibition of cytochrome P450-dependent vasodilation in the rat kidney.

Study of efficacy of Lamstreptocide A & B on cases of dermatophilosis within the Caribbean.

The efficacy of Lamstreptocide A & B was studied on 9 natural cases of bovine and caprine dermatophilosis in 8 different farms in St. Kitts, employing standard histopathologic and bacteriological methods. The lesions of 5 of the treated cases were dried-up, and there was marked peeling-off of scabs of a severely affected case exposing erythematous underlying tissue, at 3 weeks post-application of the product. Apart from 3 mild cases which were not available for follow-up studies and which were reported to have recovered, there was no outright recovery of the 5 animals after treatment at 3 weeks, and even after a second application of the product. An in vitro sensitivity test of the product revealed a slowing down of growth of Dermatophilus congolensis at concentrations in excess of 1% by agar-streak method. However, there was no inhibition of growth of the bacterium by an agar-impregnated sensitivity method.

Study of efficacy of lamstreptocide a & b on cases of dermatophilosis within the Caribbean

The efficacy of Lamstreptocide A & B was studied on 9 natural cases of bovine and caprine dermatophilosis in 8 different farms in St. Kitts, employing standard histopathologic and bacteriological methods. The lesions of 5 of the treated cases were dried-up and there was marked peeling-off of scabs of a severely affected case exposing erythematous underlying tissue, at 3 weeks post-application of the product. Apart from 3 mild cases which were not available for follow-up studies and which were reported to have recovered, there was no outright recovery of the 5 animals after treatment at 3 weeks, and even after a second application of the product. An in vitro sensitivity test of the product revealed a slowing down of growth of Dermatophilus congolensis at concentrations in excess of 1 percent by agarstreak method. However, there was no inhibition of growth of the bacterium by an agar-impregnated sensitivity method (AU)