beta-Endorphin and met-enkephalins: their distribution, modulation by estrogens and haloperidol, and role in...

A single dose of 0.5 micrograms beta-endorphin injected intraventricularly in unanesthetized male rats bearing chronic intraventricular and intrajugular cannulas led to a sevenfold stimulation of plasma prolactin (PRL) levels 10 to 20 min after injection of the peptide, while a dose of 2 micrograms of beta-endorphin led to a comparable stimulation of plasma growth hormone (GH) concentration. Met-Enkephalin was much less potent than beta-endorphin in stimulating PRL and GH release. Naloxone, a specific opiate antagonist, completely blocked the stimulation of GH and PRL release at the doses of 0.5 and 12.5 mg/kg, respectively. beta-Endorphin and Met-enkephalin from 41 discrete brain nuclei were measured by radioimmunoassay (RIA). beta-Endorphin was found in the hypothalamus medial preoptic nucleus, nucleus interstitialis striae terminalis (NIST), nucleus medialis thalami, and periaqueductal gray. Met-Enkephalin was found predominantly in the globus pallidus, NIST, medial preoptic nucleus, nucleus amygdaloideus centralis, and nucleus lateralis hypothalami. Treatment with both estrogens and haloperidol led to differential effects on Met-enkephalin content in various brain nuclei. Estrogen treatment increased Met-enkephalin levels in globus pallidus, NIST, medial and lateral preoptic nuclei, and periaqueductal gray, while a decrease of the Met-enkephalin content in the nucleus amygdaloideus centralis was found. Haloperidol treatment led to a stimulatory effect in striatum, medial and lateral preoptic nuclei, and interpeduncular nucleus.