Experimental studies on cardiovascular disorders and cellular Ca handling in shell-less chick embryos.

1. Chick embryos rendered Ca deficient by long-term culture outside the eggshell develop hypertension/tachycardia. 2. In this study, the hypertension of the shell-less (SL) chick embryo has been characterized by comparing their cardiovascular response to adrenergic drugs and cellular Ca handling function with normal (NL) embryos. 3. Before and after the administration of noradrenaline (NA), phentolamine (PA), isoproterenol (IP), and propranolol (PP), blood pressure and pulse rate were measured. 4. Baseline blood pressure was consistently higher in SL embryos. In both embryos, blood pressure was elevated by NA and PP, but lowered by IP and PA. Pharmacological sensitivity to NA and PA was higher in SL embryos. Serum Ca was lower in SL embryos, while myocardial calcium content was not different. At the cellular level, Ca handling was studied using red blood cells (RBC) from SL and NL embryos under varying osmotic and ionic conditions by analysing 45Ca uptake and cell volume regulation. 5. Two features of RBC Ca uptake were apparent: (i) Na-Ca exchange was functional since Ca uptake was dependent on external Na; (ii) Ca uptake was dependent on total ionic electrochemical gradient. The SL RBC had greater ion permeability, more active Na-Ca exchange function and higher Ca pumping out capacity. 6. These systemic and cellular properties of the SL embryo indicate that it is a novel and useful experimental system to study the relationship between Ca homeostasis and the development of hypertension.