Central Actions of Adenosine on Pituitary Secretion of Prolactin, Luteinizing Hormone and Thyrotropin

Pituitary hormones were measured in plasma in unanesthetized male and female rats prepared with venous and ventricular cannulae following ventricular infusions of adenosine and two adenosine receptor agonists. Adenosine (10, 100, and 200 nmol) injected intraventricularly caused dose-related rises in plasma prolactin (PRL) in males; in females, only the 100- and 200-nmol doses increased PRL. Similar doses of adenosine had little effect on plasma levels of luteinizing hormone (LH) and thyrotropin (TSH) in the same animals. The adenosine receptor agonists L-N6-phenylisopropyladenosine (L-PIA) and 5'-N-ethyl-carboxamideadenosine (NECA) potently stimulated prolactin secretion at doses of 10 and 50 nmol when administered into the lateral ventricle, and at a dose of 2.5 nmol when administered into the third ventricle. The secretion of PRL was antagonized by the adenosine receptor antagonist theophylline (25 nmol), when theophylline was coadministered with NECA and L-PIA. TSH levels were reduced slightly but significantly following the 10- and 50-nmol infusions of L-PIA into the lateral ventricle. The less potent D-isomer of PIA (D-PIA) did not significantly stimulate PRL release. Coupled with studies indicating the presence of adenosine in the basal hypothalamus, our observations indicate a potential neuroendocrine role for this purine in prolactin secretion.