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The changes found in the neurosecretory axons of the neural lobe of the hypophysis were studied in rats treated with furosemide for three days: over the whole period of treatment, the animals, according to each group, were deprived or not of water. In the animals with free access to water the axons contained neurosecretory granules with scarce content and low electron density; only some of them had vacuoles and autophagic bodies. In the animals deprived of water axon morphology was variable and axons showing vacuoles and autophagic bodies were abundant, as well as those presenting lamellar and dense bodies and also those in which filaments prevailed. The most outstanding modifications in this last group of animals were related to the dehydration and were not found in those animals which were given access to water again and which were in consequence rehydrated.

The supraoptic nucleus of male and female rats treated with met-enkephalin or naloxone and met-enkephalin was examined with light microscopical immunocytochemistry for Arginine-vasopressin. Both genders exhibited the same distribution of immunostained magnocellular neurons. Met-enkephalin treatment caused an increase in number of immunostained vasopressin neurons. This effect was more pronounced in females than in males. Naloxone treatment diminished immunoreactive cytoplasmic vasopressin in males more effectively than in females. In enkephalin-treated animals numerous vasopressin immunoreactive varicosities appeared within the supraoptic nucleus, but were mostly absent in naloxone-treated animals and in controls. Our results indicate that met-enkephalin treatment either stimulates vasopressin synthesis or inhibits secretion. It is likely that steroid hormones mediate the action of enkephalin on vasopressin secretion in a specific manner.