Neurosecretion in the Hypothalamus and Posterior Pituitary after Irradiation and Injection of Chemical Radioprotectors in the Rat

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Abstract
Acute whole-body exposure to 800 to 200 R of 200-kV X-rays induces instant activation of the neurosecretory processes in the hypothalamus and posterior hypophysis in rats, as observed by histochemical techniques. The same neurosecretory response is observed after exposures to 700 or 400 R or X-rays delivered at an exposure rate of 10 R/min. as well as after exposures to 1000 or 800 R of 137cs gamma-rays at the rate of 1 R/min. Partial irradiation of the head alone or irradiation of the animal''s body, with the head shielded, induces the same neurosecretory response. The neurosecretory response to lethal or sublethal doses constitutes an important and necessary link in the stress reaction of mammals to ionizing radiation. Cysteamine (150 mg/kg of body weight in intraperitoneal injection) and cystamine (same radioprotective dose) stimulate the neuro-secretion of normal nonirradiated rats. Subsequent exposure to X-rays (700 R or 400 R) further intensifies this process.