Vasopressin in brain of spontaneously hypertensive rats

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Abstract
In stroke-prone spontaneously hypertensive rats (SHRSP) and in normotensive Wistar-Kyoto rats (WKY), arginine vasopressin (AVP) was measured by means of a radioimmunoassay in the plasma, the pituitary gland, the hypothalamus, and the brain stem. In 6-and 14-wk-old SHRSP, the plasma concentration of AVP was lower than in age-matched WKY (P < 0.01), whereas it was elevated at 28 wk of age (P < 0.01). In the pituitary of 6-wk-old SHRSP, AVP was higher than in WKY (P < 0.05), but no such difference was found in older rats. In the hypothalamus and the brain stem, AVP content was reduced in all age groups of SHRSP. Plasma osmolality was diminished in 28-wk-old SHRSP only (P < 0.01), whereas hematocrit in all age groups was higher in SHRSP than in WKY. Evidently the secretion of AVP and possibly its synthesis in the hypothalamus are reduced in SHRSP. Whether the reduced AVP content in the brain stem is related to the sustained elevation of blood pressure has to be studied further.