Blood oxygen partial pressure affects plasma prolactin concentration in humans

Area of Science:

• Physiology
• Endocrinology
• Neuroscience

Background:

• Plasma prolactin (PRL) regulation is complex and influenced by various physiological factors.
• Oxygen partial pressure (PO2a) is a critical physiological parameter that can affect hormonal responses.
• The role of serotonin (5-HT) in mediating PRL responses to altered oxygen levels requires investigation.

Purpose of the Study:

• To investigate the acute and chronic effects of altered blood oxygen partial pressure on plasma prolactin concentrations.
• To explore potential mediation of these responses via central serotonergic pathways.

Main Methods:

• Two studies (A and B) involving male subjects inhaling different oxygen-nitrogen gas mixtures.
• Study A: Acute exposure (105 min/day for 6 days) to varying oxygen fractions (14%-100%).
• Study B: Chronic exposure (30 min/day for 14 days) to 14% or 100% oxygen, with neuroendocrine testing of serotonergic function using buspirone.

Main Results:

• Acute inhalation of higher oxygen fractions (≥60% O2) increased plasma PRL concentration, with higher PO2a inducing greater secretion.
• Increased PO2a also led to an earlier decline in plasma PRL despite continued oxygen inhalation.
• Chronic exposure to decreased oxygen (14% O2) increased basal PRL, while increased oxygen (100% O2) decreased it; however, PRL response to buspirone was unaffected.

Conclusions:

• Acute hyperoxia stimulates plasma prolactin secretion, but this response is transient.
• Chronic adaptation of basal plasma PRL levels to altered oxygenation occurs independently of central serotonergic receptor function.
• These findings suggest distinct mechanisms for acute PRL regulation by oxygen and long-term adaptation.