Role of Catecholamines in Stimulating the Release of Pituitary Ovulating Hormone(s) in Rats

This study tests the hypothesis that changes in the dynamics of depletion of hypothalamic catecholamines (CA) may affect the stimulation of ovulation. Partial as well as total depletions of CA were attempted by appropriately timed injections of reserpine and inhibitors of monoamine-oxidase. Treatment with reserpine in the morning of proestrus inhibited spontaneous ovulation and elevated the electrical threshold of the medial preoptic area but did not alter the threshold for inducing ovulation by stimulating the median eminencearcuate nucleus region. At high levels of current both areas responded similarly with stimulation of ovulation. Complete blockade of the electrically stimulated release of ovulating hormone was obtained 18–20 hr after treatment with reserpine. However, even after this prolonged reserpine action inhibitors of monoamine-oxidase restored enough CA to support electrically stimulated but not spontaneous ovulation. Infusions into the third ventricle indicated that CA act as neural triggers in the mechanism of ovulation. Epinephrine was the most effective CA in triggering ovulation in proestrous pentobarbitalblocked rats. (Endocrinology86: 988, 1970)