Plasma Prolactin Concentration Increases after Hypercapnia Acidosis

Abstract

Responses of plasma prolactin (PRL) concentration to alterations in carbon dioxide pressure (pCO₂) induced by 4 min of rebreathing out of a bag with 6 l gas initially containing a concentration of 93 % O₂ and 7 % CO₂ (hypercapnia hyperoxia; HH) and 4 min of voluntary hyperventilation (VH) at a respiratory rate of 28 - 32 per minute were investigated in ten males. During rebreathing in HH, an augmentation of pCO₂ from 40.2 ± 2.1 to 63.7 ± 5.4 mmHg and a decrease of pH from 7.4 ± 0.02 to 7.32 ± 0.04 were found in capillary blood (p < 0.01). Neither breathing frequency (BF) nor plasma PRL changed during this period. After two minutes of post-rebreathing, pCO₂ and pH returned to basal values. BF increased from 2 min of rebreathing (12.4 ± 1.9 breath/min) until 11 min of recovery period (18.1 ± 4.9 breath/min) (p < 0.01), while plasma PRL increased from end of rebreathing (11.59 ± 1.49 ng/dl) to 11 min of recovery period (13.63 ± 1.97 ng/dl) (p < 0.01). In VH, hyperventilation decreased pCO₂ from 39.91 ± 2.62 to 21.73 ± 2.59 mmHg (p < 0.01) and increased pH from 7.39 ± 0.04 to 7.58 ± 0.04 (p < 0.01) in capillary blood. After four minutes of recovery from hyperventilation, pH and pCO₂ were back to their basal values. No changes in plasma PRL were found throughout VH. This present pilot study’s new finding is that plasma PRL increases after hypercapnia acidosis. This indicates that acidosis-induced central chemoreflex function increases phrenic nerve activity based on serotonergic modulation, leading to an augmentation of BF. As serotonin is also the main PRL-releasing factor, this might have had the collateral effect of causing PRL release and delayed appearance in the peripheral circulation.

Key words

Prolactin · Acidosis · Hyperventilation · Serotonin · Chemosensitivity

References

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