Received October 22, 2003
Revised January 13, 2004
Accepted after revision February 18, 2004
Neuroendocrinology/endocrinology
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The effect of changes in arterial pCO2 on neuroendocrine
function in man
Richard M Leach 1
Mary L Forsling 2*
1 St Thomas' Hospital
2 GKT School of Medicine
* To whom correspondence should be addressed. E-mail: mary.forsling{at}kcl.ac.uk.
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Abstract |
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There is evidence that changes in aterial PCO2 (PaCO2), as well as PO2, influence neuroendocrine function. The hypontraemia and fluid retention (cor pumonale) seen in chronic obstructive airways disease (COPD) and type II respiratory failure is associated with increased vasopressin release. This study examines the specific effects of altered PaCO2 on hormone release from the posterior and anterior pituitary. The study was performed in 20 ventilated ICU patients in the late recovery phase of their illness. None had primary respiratory disease. Control blood samples were taken and the alveolar ventilation was then adjusted to allow the PaCO2 increase or decrease for a period of 3h during which time further blood samples were taken for the determination, by radioimmmunoassy of vasopressin, oxytocin, growth hormone and cortisol. Urine output and electrolyte concentrations were also measured. Circulating concentrations of growth hormone and oxytocin increased with increasing PaCO2. Vasopressin release showed a similar pattern up to a PaCO2 of approximately 6.0 kPa, above which vasopressin concentrations were inversely related to PaCO2. There was no significant effect on cortisol concentrations. No significant effects were established in urinary parameters during the short period of this study. Thus an increase in CO2 is associated with stimulated pituitary hormone release. The effect on the neurohypophysial hormones may account for the fluid retention and hyponatreamia seen in COPD and hence provide a rationale for treatment.
Key Words:
Carbon dioxide, Pituitary, Vasopressin
