SUMMARY1. The release of antidiuretic hormone (ADH) has been studied in the chloralose anaesthetized cat after microinjection of various agents directly into the brain, in particular the supraoptic nucleus of the hypothalamus (SON). The concentration of ADH in jugular venous blood was determined using the waterloaded, alcohol anaesthetized rat assay. The position of the microinjection cannula was located post mortem in stained brain sections.2. Nicotine, noradrenaline (NA) and hypertonic saline caused release of ADH, whereas microinjections of isotonic saline did not affect the blood level of the hormone.3. Nicotine administered to other sites in the central nervous system (c.N.s.) could also cause ADH release. Hypertonic saline proved to be an ineffective stimulus at all the tested sites outside the supraoptic region. 4. The ganglion-blocking agents hexamethonium and pempidine inhibited the releasing action of nicotine at the SON in most of the experiments. These blocking drugs had no effect on osmotic release. When administered alone, both hexamethonium and pempidine had variable, but analogous effects on the hormone output.5. The a-adrenoreceptor blocking drug, phentolamine, stimulated ADH release, but the fl-receptor blocking drug, propranolol, had no such effect.Both drugs appeared to have inhibitory action on noradrenergic release of AIDH, but neither had a consistent effect on the osmotic release of the hormone.

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