Pituitary 5-hydroxytryptamine nerves--a possible link with pituitary hormone secretion

Area of Science:

• Neuroendocrinology
• Physiology

Background:

• The pituitary gland's innervation by 5-hydroxytryptamine (5-HT) nerves is not fully understood.
• Investigating the roles of 5-HT and dopamine (DA) in pituitary hormone secretion is crucial.

Purpose of the Study:

• To examine the concentrations of 5-HT and DA in different pituitary lobes under conditions of altered hormone secretion.
• To compare the responses of 5-HT and DA systems in various pituitary lobes.

Main Methods:

• Measurement of 5-HT and DA concentrations in rat pituitary lobes (anterior, neural, intermediate) under different physiological conditions.
• Experimental conditions included dehydration, increased salt intake, acute exsanguination, and ether anesthesia.
• Long-term (2-year) monitoring of 5-HT and DA levels in normal male and female rats.

Main Results:

• Prolonged increased hormone secretion (dehydration/salt intake) decreased 5-HT in the anterior lobe (AL) but increased DA in the neural lobe (NL) and intermediate lobe (IL).
• Acute stimulation (exsanguination/ether) decreased AL 5-HT while increasing NL and IL 5-HT, indicating differential responses.
• 5-HT concentrations were lowest in the AL compared to other regions, with DA levels varying significantly across lobes.

Conclusions:

• The 5-HT system in the anterior pituitary lobe responds differently to physiological stimuli compared to the neural and intermediate lobes.
• Pituitary 5-HT and DA neuronal systems are activated independently, suggesting distinct regulatory roles in endocrine states.
• These findings highlight the complex neurochemical regulation of the pituitary gland.