THE PHYSICOCHEMISTRY OF [H- ROLES OF PCO2, STRONG IONS, AND THEIR HORMONAL REGULATORS(] AND RESPIRATORY CONTROL )

I describe how the dietary intake of strong ions potentially affects t he regulation of ventilation and the Pco(2) of body fluids in two ways . First, changing the dietary intake of NaCl can alter the concentrati on difference between strong cations and strong anions (the [SID] of S tewart) of body fluids. Experimental observations indicate that the [S ID] in brain fluids or cerebrospinal fluid ([SID](CSF)) could be the s timulus to central chemoreceptors. [SID](CSF) consistently predicts ve ntilatory regulation of Pco(2), whereas [H+](CSF) does not. Pco(2) act s as a stimulus to ventilation independently of [SID](CSF) and possibl y at higher as well as lower centers of the nervous system. I relate t he concept of [SID] regulation of arterial Pco(2) to the alphastat hyp othesis of protein function, respiratory control, and [H+] homeostasis . Second, altering the dietary intake of NaCl changes the levels of ho rmones involved in salt and water balance. Angiotensin II acts central ly to stimulate ventilation. Evidence for the roles of both the renal and brain renin-angiotensin systems in respiratory control, and the mo dulation of respiratory control by vasopressin are reviewed. These pep tide systems probably act via circumventricular organs of the brain to affect respiratory control and (or) by changing strong ion concentrat ions in brain fluids. Questions to be resolved on the role of [SID](CS F) and hormones in respiratory adaptations, and experiments required t o improve our understanding of the control of ventilation, are address ed in the concluding comments.