SUMMARY Recent data from our laboratory suggest that sex steroids promote contractile function in cardiac muscle of rainbow trout (Oncorhynchus mykiss Walbaum), and there are sex differences in hormone signaling and cardiac function. The current study investigated whether steroid-induced inotropism in electrically paced (0.5 Hz, 14°C) ventricle strips at 90%Lmax (1) has a metabolic requirement for exogenous glucose and (2) is associated with enhanced intracellular Ca2+ storage and release from the sarcoplasmic reticulum (SR). We also explored whether sex differences exist in extracellular Ca2+(Ca2+o) or cardiac sensitivity to Ca2+o. In the absence or at low concentrations (1 or 2 mmol l-1) of exogenous glucose, resting tension and relaxation time were increased selectively in cardiac tissue from females. Increasing glucose promoted twitch force in a bell-shaped manner, with 5 mmol l-1representing the optimal concentration for both sexes. The positive inotropic effects of physiological concentrations of testosterone (T) and 17β-estradiol (E2) in male and female trout ventricle strips,respectively, developed slowly (10-45 min) and were not apparent in glucose-free medium, in medium containing iodoacetate (IAA), an inhibitor of glycolysis, or medium containing 5 mmol l-1 lactate or pyruvate. Male ventricle strips had increased inotropic responses to glucose and T compared with female strips exposed to glucose and E2. Furthermore, sexually maturing males showed a greater inotropic response than immature males or females. Pretreatment with ryanodine (a specific blocker of SR Ca2+release) also eliminated the inotropic effects of sex steroids and exogenous glucose and reduced the post-rest potentiation of contractile force (a marker of SR Ca2+ storage). By contrast, the inotropic effects of epinephrine (Epi) or elevated Ca2+o were faster(developing within 1-3 min) and were not diminished by the presence or absence of glucose or by pretreatment with IAA or ryanodine. Sex differences were also found in responsiveness to caffeine (males > females) and the relationship between Ca2+ concentration and force development above baseline. The Ca2+50 was lower in female cardiac tissue than males, suggesting greater Ca2+ sensitivity, and although plasma albumin was higher in females, total and ionized plasma Ca2+ did not differ between the sexes. For the first time, our study highlights the importance of extracellular glucose, glycolytic activity and SR Ca2+ storage and release for sex steroid-induced inotropism in the trout ventricle. Conversely, the inotropes Epi and elevated[Ca2+o] do not require the presence or metabolism of exogenous glucose or the SR for signaling their positive effects on contractility. These results also demonstrate novel sex-related differences in cardiac reliance on exogenous glucose, Ca2+ sensitivity and SR function and thus should be considered in future studies.
BACKGROUND AND PURPOSE: Patient preparation for myelography and postprocedural monitoring varies widely between practices, despite published guidelines. Our aim was to examine the current practice variations in discontinuing reportedly seizure thresholdlowering medications before myelography and to assess the reported incidence of postmyelographic seizures. MATERIALS AND METHODS: An e-mail survey was sent to American Society of Neuroradiology members concerning the number of postmyelographic seizures experienced in the past 5 years, the presence of an institutional policy for discontinuing seizure threshold-lowering medications, and the type of myelographic contrast used. We compared the postmyelographic seizure frequency in the responses. RESULTS: Of 700 survey responses, 57% reported that they do not discontinue seizure threshold-lowering medications before myelography. Most (97%) indicated never having a patient experience a seizure following myelography. The number of postmyelographic seizures between those who discontinue seizure threshold-lowering medications and those who do not was not statistically significant (OR ϭ 2.13; 95% CI, 0.91-4.98; P ϭ .08). Most (95%) reported using nonionic hypo-osmolar agents. CONCLUSIONS: Survey results revealed widely variable practices for patient myelography preparation and postprocedural monitoring. We found no difference in reported seizures between those who discontinued seizure threshold-lowering medications and those who did not. In light of our findings, we propose that discontinuing reportedly seizure threshold-lowering medications is not warranted with the current nonionic water-soluble contrast agents and may be potentially harmful in some instances. This work supports revision of existing recommendations to withhold such medications before myelography.
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