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Previous noninvasive studies of the mean heart rate of embryonic birds have prompted an investigation into the instantaneous heart rate (IHR), which may be informative in developmental studies of cardiac rhythm. Using the acoustocardiogram (ACG), a noninvasive, long-term measuring system for embryonic IHR is developed, and the IHR in chickens during the last half of embryonic development is determined. The system, which uses a micro-computer, samples the ACG at a frequency of 50 Hz, restores the ACG wave by sinc function and calculates the IHR with an error in accuracy of less than 1 beat min-1. It was found that characteristic, transient bradycardia begins to appear late in the second week of incubation, and, with the additional development of transient tachycardia, the embryonic cardiac rhythm becomes more arrhythmic towards hatching. Simultaneous measurements of IHR with somatic movements showed no relationship between arrhythmia and embryonic activities. This system is useful, providing new evidence on long-term IHR developmental patterns.

Background: Anterior chamber miotic solutions are widely used during anterior chamber surgery. We examined the effects of solutions containing miotic agents such as carbachol and/or acetylcholine on corneal endothelial pumping activity., Methods: We monitored, in vitro, the transendothelial electrical potential difference of isolated rabbit corneal endothelial preparations. As controls, we used solutions without miotics., Results: We found that a solution containing 55 mM acetylcholine and minimal amounts of salts (Miochol E) maintains transendothelial electrical potential difference some 30% above control levels for up to 4 h. Two other solutions, one including balanced salts and 0.55 mM carbachol (Miostat), the other a mixture of 0.19 mM carbachol and 55 mM acetylcholine plus minimal salts, are adequate to maintain the potential difference at control levels. Lastly, a solution with acetylcholine but without any salts (Miochol) greatly decreases the potential difference, to 30% of the control level, in 100 min., Conclusion: Our results indicate that: (1) 55 mM (1%) acetylcholine stimulates the endothelial electrical potential difference; (2) addition of 0.19 mM (0.003%) carbachol negates the stimulatory effect of acetylcholine; and (3) absence of electrolytes severely depresses the endothelial electrical activity.

Background: Anterior chamber miotic solutions are widely used in ophthalmic surgery to induce pupillary contraction. We investigated whether the acetylcholine, carbachol, or mannitol present in perfusing solutions can affect corneal endothelial function., Methods: Freshly dissected deepithelized rabbit corneas were mounted in a Dikstein-Maurice chamber at 36 degrees C. The endothelial sides were perfused with six solutions: (A) 55 mM (1%) acetylcholine Cl plus modified balanced salts; (B) control for A, with acetylcholine Cl replaced by sucrose; (C) 0.55 mM (0.01%) carbachol Cl plus balanced salts; (D) balanced salts solution (BS; control for C); (E) 3% mannitol plus modified balanced salts; and (F) modified balanced salts (control for E, with mannitol replaced by sucrose). Corneal thickness was followed for 3 h in each experiment. The effect of solution E did not differ from that of solution F., Results: The carbachol-containing solution produced a small increase in corneal thickness compared to the control solution, while the acetylcholine-containing solution resulted in corneal thickness lower than that in control preparations., Conclusion: From these data, acetylcholine is harmless to the endothelium, and may actually stimulate its fluid pump mechanism. Carbachol, on the other hand, appears to have a detrimental effect.

Measurements of electrical potential difference across isolated rabbit corneal endothelium (transendothelial electrical potential difference, TEPD) were used to evaluate the effect of two commonly used commercially prepared intraocular irrigation balanced salt solutions, BSS and BSS+, together with our own standard bicarbonate-containing control solution (BS). The highest and most durable TEPD values were obtained by using BSS+; TEPD began at 550 microV, peaked at 600 microV 1 h later, and then decreased slowly down to some 300 microV after about 8 h. Gassing BSS+ with an air/5% CO2 mixture was optimal; gassing it with air reduced the TEPD values slightly, by about 10%. On the other hand, perfusion with BSS gassed with air had a rapid and marked adverse effect; the TEPD, which began at some 500 microV, fell down precipitously to about 50 microV after 1 hour. In contrast, perfusion with BSS on the endothelial side with the addition of BS to the stromal side, both sides being gassed with an air/5% CO2 mixture, maintained the TEPD at levels near those obtained with BSS+. We attribute the adverse effect by BSS to the absence of bicarbonate in it. From these and past results, we conclude that BSS cannot be recommended for intraocular use as a properly balanced saline solution.

The authors investigated whether fluorescein sodium affects the in vitro endothelial function of rabbit corneas. As an index of this function, the transendothelial electrical potential difference (TEPD) was used. The TEPD in a balanced salts and glucose (BSG) control solution increased for the first 30 min and then decayed slowly, reaching about 60% of its original value after 5 hr. When a BSG solution containing 5 micrograms/ml of fluorescein sodium was used, the TEPD time course was similar to the control solution. Since this fluorescein sodium concentration is about sevenfold higher than that seen in the anterior chamber of ocular patients, these results reassure users that no toxic effect of fluorescein is discernible at concentrations relevant to ophthalmic practice. With a fluorescein sodium concentration of 500 micrograms/ml, the TEPD decreased below control values after 4 hr of exposure, but such a concentration is approximately 5000-fold higher than that seen in the anterior chamber of patients. The adverse effect of fluorescein on TEPD is probably irrelevant for standard systemic clinical use.