Mechanism of suppression of cardiac L-type Ca(2+) currents by the phospholipase A(2) inhibitor mepacrine.

Phospholipase A(2) plays a crucial role in the release of arachidonic acid (AA) from membrane phospholipids and in myocardial injury during ischemia and reperfusion. Mepacrine, a phospholipase A(2) inhibitor, has been shown to protect the heart from ischemic injury. In order to examine the mechanism of this protection, we investigated the effects of mepacrine on the L-type Ca(2+) current (I(Ca,L)) in rat single ventricular myocytes. Extracellular application of mepacrine significantly inhibited I(Ca,L) in a tonic- and use-dependent manner. The inhibition was also concentration-dependent with an IC(50) of 5.2 microM. Neither the activation nor the steady-state inactivation of I(Ca,L) was altered by mepacrine. The mepacrine-induced inhibition of I(Ca,L) was reversible after washout of the inhibitor. Addition of 1 microM AA partially reversed the mepacrine-induced inhibition of I(Ca,L). Intracellular dialysis, with 2 mM cAMP, significantly increased I(Ca, L), but did not prevent the mepacrine-induced inhibition of I(Ca,L). In addition, extracellular application of isoproterenol or membrane permeable db-cAMP did not reverse the mepacrine-induced inhibition of I(Ca,L). Biochemical measurement revealed that incubation of ventricular myocytes with mepacrine significantly reduced intracellular cAMP levels. The mepacrine-induced reduction of cAMP production was abolished by addition of AA. Our results demonstrate that mepacrine strongly inhibits cardiac I(Ca,L). While mepacrine is a phospholipase A(2) inhibitor and reduces cAMP production, its inhibitory effect on I(Ca,L) mainly results from a direct block of the channel. Therefore, we speculate that the protective effect of mepacrine during myocardial ischemia and reperfusion mostly relates to its blockade of Ca(2+) channels.

Finasteride therapy does not alter bone turnover in men with benign prostatic hyperplasia--a Clinical Research Center study.

Benign prostatic hyperplasia is often treated with finasteride, which inhibits the conversion of testosterone to dihydrotestosterone (DHT). Aside from the prostate, other androgen-dependent tissues seem to be unaffected by selective DHT deficiency, but the effect on bone density in humans has not yet been defined. To study this question, we compared indices of bone turnover and bone mineral density in 35 men treated with finasteride with controls. Bone resorption was assessed by measuring urinary excretion of N-telopeptide cross-links of type I collagen and hydroxyproline, and bone formation was assessed by measuring serum osteoncalcin and bone-specific alkaline phosphatase. Bone density of the spine and hip were assessed by dual energy x-ray absorptiometry. We found that finasteride-treated patients had mean DHT levels 81% lower than controls (P < 0.0001). There were no significant differences between the two groups in any of the markers of bone turnover or measures of bone density. These results suggest that testosterone can maintain bone density in men even in the absence of DHT. Although long term studies are needed, our results suggest that men who take finasteride are not at increased risk for bone loss.

Adenosine triphosphate-sensitive K+ channels mediate postcardioplegia coronary hyperemia.

The purpose of the present study was to examine the role of adenosine triphosphate-sensitive potassium channels in mediating the coronary hyperemic response after crystalloid cardioplegia. Thirteen pigs were placed on normothermic cardiopulmonary bypass support. Hearts were arrested with cold (4 degrees C) crystalloid ([K+] 25 mmol/L) cardioplegic solution for 60 minutes. In seven of these pigs, hearts were then reperfused for 60 minutes with warm blood, and the animal was separated from cardiopulmonary bypass. The in vivo responses to the intracoronary administration of the K+ adenosine triphosphate channel blocker glibenclamide (50 gm/kg per minute) or the K+ adenosine triphosphate channel opener pinacidil (2 gm/kg per minute) were evaluated before cardiopulmonary bypass (baseline) and after 2 minutes and 60 minutes of reperfusion in the cardioplegia-reperfusion group. Under baseline conditions, glibenclamide and pinacidil induced a respective decrease and increase in coronary blood flow and an increase and a decrease in coronary vascular resistance. Coronary responses to glibenclamide and pinacidil were markedly enhanced after 2 minutes or 60 minutes of postcardioplegia reperfusion. In vitro responses of coronary arterioles (90 to 180 microns) were examined in a pressurized, no-flow state with video microscopy. The contractile response of coronary arterioles to glibenclamide and the relaxation response to pinacidil were significantly enhanced 2 minutes or 60 minutes after reperfusion (all p < 0.05 versus control). The response to pinacidil was markedly inhibited by glibenclamide, which confirms these antagonistic effects on K+ adenosine triphosphate channels. Decreased tissue concentrations of adenosine triphosphate in the coronary arterial smooth muscle and myocardium were observed after cardioplegia and persisted for up to 60 minutes of reperfusion (both p < 0.05 versus control). These results suggest that coronary hyperemia associated with postischemic cardioplegia is mediated in part by activation of K+ adenosine triphosphate channels in the coronary microcirculation.

Activation of Cl secretion during chemical hypoxia by endogenous release of adenosine in intestinal epithelial monolayers.

Intestinal ischemia is characterized by rapid early inhibition of absorptive function and the appearance of net secretion, although why active secretion persists in the setting of a mucosal energy deficit is unknown. The cryptlike epithelial line T84, a well-characterized model of intestinal Cl- secretion, develops a prominent increase in short-circuit current (Isc, indicative of active Cl- transport) in response to "hypoxia" induced by metabolic inhibitors. The increased Isc is associated with the initial decrease in monolayer ATP content. The Isc is transient and disappears with progressive energy depletion, although graded degrees of ATP depletion induce a more sustained Isc response. Chromatographic analysis and secretory bioassays show that the Isc response to metabolic inhibitors is related to the endogenous release of adenosine into the extracellular space in quantities sufficient to interact locally with stimulatory adenosine receptors. Unlike its classical role as a metabolic feedback inhibitor, adenosine appears to function as an autocrine "feed-forward" activator of active intestinal Cl- secretion. These studies suggest a novel role for adenosine in the conversion of the gut from an absorptive to a secretory organ during ischemic stress, thus contributing to the initial diarrheal manifestation of intestinal ischemia.

Bone density is normal in male rats treated with finasteride.

Bone is an androgen-dependent tissue. It is not known whether normal bony growth and mineralization in males is dependent on testosterone alone, or whether its metabolite, dihydrotestosterone (DHT), also is required. To answer this question, we examined the effect of finasteride, an inhibitor of DHT synthesis, on bone in rats. Three-month-old male rats were treated with placebo, finasteride, or orchidectomy. The bone mineral densities (BMD) of the spine and whole body were measured in vivo by dual x-ray absorptiometry at weeks 0 and 11, and the BMD of the femur and tibia were measured ex vivo at week 11. Histomorphometric analysis was performed on the proximal tibia at week 11. The increase in spine and whole body BMD in finasteride-treated rats did not differ from that in controls, whereas these values were significantly lower in orchidectomized rats. Similarly, the BMD of the femur and tibia and the cancellous bone volume of the proximal tibia in finasteride-treated rats did not differ from those in controls, whereas these values were significantly lower in orchidectomized rats. In summary, bone development and density were normal in rats treated with finasteride. We conclude that selective DHT deficiency is not deleterious to the male rat skeleton.

Chicken soup revisited: calcium content of soup increases with duration of cooking.

Because low dietary calcium intake may accelerate bone loss, patients often are advised to increase their dietary intake of calcium. However, some patients may be unable to tolerate good calcium sources such as dairy products. We postulated that the calcium content of soups and stews could be increased by prolonged cooking with a beef bone. Three experiments were done to prove this theory: (1) a bone soup made with a beef bone and distilled water, cooked for 24 hours; (2) a bone-vegetable soup cooked the same way; and (3) a vegetable soup made the same way but without the bone. It was concluded that prolonged cooking of a bone in soup increases the calcium content of the soup when cooked at an acidic, but not at a neutral pH.

Specificity of urinary excretion of cross-linked N-telopeptides of type I collagen as a marker of bone turnover.

Urinary excretion of cross-linked N-telopeptide of type I collagen (NTX) has been reported to be a specific indicator of bone resorption. We studied the utility of a new immunoassay for NTX as an indicator of changes in bone resorption caused by treatment with pamidronate (APD) followed by T3. Twenty-two male subjects received either placebo (Group 1) or APD on study days 1-2 (Group 2). One week later all subjects received T3 100 micrograms/day (days 8-15). Urinary NTX, pyridinoline (PYD), hydroxyproline (HYP), and creatinine (cr) were measured on 2-hour fasting urine samples at baseline (day 1), after APD/placebo (day 8), after T3 (day 16), and at days 30 and 58. NTX/cr excretion fell 85% after treatment with APD (P < 0.001 versus baseline), but not after placebo. The fall in mean urinary NTX after receiving APD was greater than the fall in PYD (25%) or HYP (31%) (P < 0.001 NTX versus PYD and HYP). After treatment with APD, NTX excretion remained suppressed below baseline until day 58, whereas PYD and HYP excretion returned to baseline by study day 16. Persistence of APD's effect on bone until day 58 was suggested by the fact that serum calcium and parathyroid hormone levels had not returned to baseline by day 58. On day 16, after all subjects were treated with T3, urinary NTX/cr rose significantly (P < 0.01) in Group 1 (-bisphosphonate) but not in Group 2 (+bisphosphonate).(ABSTRACT TRUNCATED AT 250 WORDS)

Parenteral pamidronate prevents thyroid hormone-induced bone loss in rats.

Pamidronate (APD) is a bisphosphonate that prevents bone loss from a variety of causes. We studied the role of APD in preventing thyroid hormone-induced bone loss. A total of 32 rats were assigned to one of four treatment groups: (1) -APD/triiodothyronine (-T3), (2) -APD/+T3, (3) +APD/-T3, or (4) +APD/+T3. In the first of two studies, the rats received APD for the first week and T3 for the second week, and then their blood was analyzed for alkaline phosphatase and osteocalcin. Alkaline phosphatase and osteocalcin were significantly higher (p < 0.05) in hyperthyroid rats (-APD/+T3, 3.9 +/- 0.25 mukat/liter and 23 +/- 1.6 nM, respectively) than in control animals (2.53 +/- 0.28 mukat/liter and 18.3 +/- 1.4 nM, respectively). Hyperthyroid rats pretreated with APD (+APD/+T3) had levels of alkaline phosphatase and osteocalcin no different from controls. In a second study, rats were divided into the same four groups, except they received APD/placebo and T3/placebo concomitantly for 3 weeks. At the end of the study, bone mineral density (BMD) of the femur, spine, and whole body was measured by dual-energy x-ray absorptiometry, and the calcium content of the femora was measured directly. In hyperthyroid rats (-APD/+T3) BMD was significantly lower than in controls in the spine (0.201 +/- 0.004 versus 0.214 +/- 0.002 g/cm2, p < 0.05) and femur (0.204 +/- 0.003 versus 0.218 +/- 0.002, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Further study and characterization of the yellow pigments in follicular fluid that are related to oocyte quality.

OBJECTIVE: To characterize the 455-nm (yellow) absorbing pigments in human follicular fluid (FF). DESIGN: Serum and FF samples obtained from patients undergoing in vitro fertilization were analyzed for carotenoids, bilirubin, and beta-glucuronidase concentrations. Spectrophotometric analysis in the visible spectrum was performed on FF samples, and the delta OD455 absorbance was calculated. RESULTS: Thin-layer chromatography confirmed the presence of beta-carotene and bilirubin in FF. The mean (+/- SD) contribution of bilirubin and carotenoids to the FF delta OD455 absorbance was 64% +/- 9.6% and 22.7% +/- 12.1%, respectively. Bilirubin fractions in serum and FF samples were then compared. The median unconjugated bilirubin concentration in FF was lower than that in the serum (0.130 versus 0.288 mg/dL; P < 0.0001). The median conjugated bilirubin concentration was higher in the FF when compared with the serum (0.129 versus 0.101 mg/dL; P = 0.0018). beta-Glucuronidase levels in the FF were significantly lower when compared with serum concentrations. CONCLUSIONS: Bilirubin is the major contributor to the FF 455-nm spectrophotometric peak. The higher levels of conjugated bilirubin noted in the FF could in part be explained by the lower levels of beta-glucuronidase.

Intracellular calcium and ventricular function. Effects of nisoldipine on global ischemia in the isovolumic, coronary-perfused heart.

Ischemia-induced ventricular dysfunction has been shown to be associated with increased diastolic and systolic intracellular concentrations of free, ionized calcium ([Ca2+]i). The present study was designed to determine the effects of the Ca2+ antagonist nisoldipine on the relationship between [Ca2+]i and left ventricular contraction and relaxation during ischemia and reperfusion on a beat-to-beat basis. Nine isovolumic coronary-perfused ferret hearts were made globally ischemic for 3 min and reperfused for 10 min. Ischemia and reperfusion were repeated during perfusion with a buffer containing 10(-8) M nisoldipine. From left ventricular developed pressure, time to peak pressure and time to 50% pressure decline were obtained. [Ca2+]i was determined with the bioluminescent protein aequorin. Global ischemia caused a rapid decline in contractile function and a significant increase in diastolic [Ca2+]i, from 0.35 to 0.81 microM, and in systolic [Ca2+]i, from 0.61 to 0.96 microM. During reperfusion, [Ca2+]i returned to baseline while ventricular function was still impaired. Relaxation was more affected than systolic contractile function. Nisoldipine significantly reduced the ischemia-induced rise in diastolic [Ca2+]i to 0.62 microM, and in systolic [Ca2+]i to 0.77 microM, and lessened the decrease in contractile function. Nisoldipine significantly accelerated the decline in [Ca2+]i during reperfusion and improved recovery of contractility and relaxation. These effects were associated with a significant diminution in ischemic lactate production. Taken together, our results provide direct quantitative evidence on a beat-to-beat basis that the calcium antagonist nisoldipine can ameliorate ischemia-induced abnormalities in [Ca2+]i handling, an effect that was associated with improved myocardial function during early reperfusion.