Effects of various ambient temperatures and of heating and cooling the hypothalamus and cervical spinal cord on antidiuretic hormone secretion and urinary osmolality in XXXX .

@entity1707 @entity6085
1. Plasma @entity6085 concentration, urinary and plasma osmolality and haematocrit were measured in young @entity1707 placed in cold, thermoneutral, warm and hot ambient temperatures. In some experiments a thermode placed in the hypothalamus or over the cervical spinal cord was heated or cooled at various ambient temperatures. 2. Plasma @entity6085 concentration remained at a low level (0-5--5 muu. ml.-1) over 2 hr or 3 hr periods when the @entity1707 were in cold, thermoneutral or warm ambient temperatures. A hot environment, which caused a marked rise in the @entity1707 ' rectal temperature, was associated with a large rise in plasma @entity6085 level. 3. The rise in plasma @entity6085 level which occurred during an increase in body temperature was consistently and completely suppressed by simultaneous cooling of the thermode in the pre-optic region to 5 to 10 degrees C. When the thermode was in the region of the supraoptic nucleus the rise in @entity6085 was only partly suppressed, and when it was over the cervical cord it was only sometimes suppressed. 4. Cooling the thermodes in any position at a cold or thermoneutral ambient temperature, or heating them at a thermoneutral or warm ambient temperature, caused no consistent change in @entity6085 . 5. A diuresis, with a urinary flow-rate of at most 1 ml. min-1 and minimal urinary osmolality of 53 m-osmole kg-1, was observed on only three occasions, twice during cooling of a thermode in the hypothalamus and once after the end of a period when the thermode was heated. In each case, the plasma @entity6085 was less than 2 muu. ml.-1. 6. A slight rise of haematocrit in cold ambient conditions and a slight fall in the warm were observed. Otherwise changes in haematocrit were trivial, and a shift of water between vascular system and interstitium could not be invoked to account for changes in @entity6085 levels. Observed variation of plasma osmolality was also slight.
