THE ANTIDIURETIC ACTION OF MORPHINE: ITS SITE AND MODE OF ACTION IN THE HYPOTHALAMUS OF THE DOG

¹ Physiology Department, Edinburgh

1. Observations made on dogs show that morphine sulphate administered during the course of a water diuresis is antidiuretic, whether it is given intravenously (0·08 mg./ kg.) to the unanæsthetized animal, or injected into the supraoptic nuclei (4-32 ug.) under chloralose ancesthesia.

2. After section of the supraoptic tracts the injection of morphine sulphate intravenously into the unanæsthetized dog does not cause antidiuresis.

3. The release of adrenaline from the suprarenal medulla is not a factor in the antidiuretic action of morphine.

4. In unanæsthetized dogs into whose supraoptic nuclei DFP has previously been injected, the intravenous administration of morphine sulphate consistently causes an inhibition of the rate of urine flow.

5. Acute tolerance of the antidiuretic response to morphine is not seen on giving two or three small doses in the course of a few hours.

6. Consideration of the results leads to the conclusion that morphine induces antidiuresis by a direct effect on the supraoptic cells, causing the release of the antidiuretic hormone of the posterior lobe of the pituitary. This effect of morphine is unrelated to cholinesterase.