Hypothalamic control of plasma renin activity.

The participation of the hypothalamus in the regulation of plasma renin activity (PRA) in rats was studied by applying electric stimulation to the supramammilar region (50 Hz, 1 ms, 150 muA), general hypoxia (90% N2 + 10% O2), and hypovolemia (peritoneal dialysis with 5.5% glucose) as stimuli of renin secretion. These techniques were combined with bilateral renal denervation and electrocoagulation in the supramammilar nuclei. PRA was determined by means of RIA (Radioimmunoassay) for AI with 2-h incubation. Our investigations showed that: 1. Electric stimulation, hypoxia and hypovolemia cause an increase of PRA against the controls by 127%, 465% and 197%, respectively. 2. After electrocoagulation the hypoxic stimulus remains ineffective, whereas hypovolemia is manifested. 3. Electric stimulation in rats with denervated kidneys produces no effect. These results suggested that: a) Diminution of the extracellular volume, without hypoxia, is in itself a powerful stimulus of renin secretion. b) The posterior hypothalamus is closely connected with the regulation of PRA as an obligatory unlocking link of the reaction by the organism to general hypoxic stimuli. The control function of the hypothalamus is realized in this case by means of the sympathetic part of the vegetative nervous system.