[Effect of microionophoretic administration of met-enkephalin into various brain structures on secretion of...

The influence of local microiontophoretic met-enkephalin injections upon luteinizing and thyrotropic hormone (LH and TTH) secretion and spontaneous electric neuron activity was studied. It was shown that opioid injection into the hypothalamic arcuate nucleus (HAN) decreases 3-fold the blood LH concentration and its injection into the hypothalamic paraventricular nucleus (HPN) inhibits similarly the TTH secretion. Both effects are completely blocked by nalorphin--a concurrent opiate antagonist. Nalorphin alone has no pronounced endocrine effect. Met-enkephalin exerts a dose-dependent neurotropic action. Nalorphin blocks mainly the pentapeptide inhibiting effects. A direct correlation between endocrine and neurotropic opioid action was not observed. It appears to be due to polyfunctions of the structures studied and to a wide spectrum of met-enkephalin biological activity.