A melanocyte-stimulating hormone-releasing factor in hypothalamic extracts

¹ Instituto de Investigación Médica Mercedes y Martín Ferreyra, Córdoba, Argentina

Intravenous injection of rat stalk median eminence (SME) extracts to rats produced a decrease in the pituitary melanocyte-stimulating hormone (MSH) activity. This effect was not obtained with injection of cerebral cortex extract, nor with histamine, norepinephrine, vasopressin, or oxytocin. A slight decrease occurred with epinephrine. The response to 2, 1, 1/2, 1/4, and 1/8 of SME was linearly related to the logarithm of the doses. It is inferred that hypothalamic extracts evoked a decrease in MSH pituitary content, since doses of 1/4 SME, which lowered the pituitary MSH activity more than 50%, did not modify the concentration in ACTH. No changes in MSH pituitary activity were obtained in animals submitted to stress. It is concluded that SME extracts contain a MSH-releasing factor which acts directly on the hypophysis and not through the nervous system, since it is effective in rats with hypothalamic lesions in the median eminence area.

Key Words: hypophysis intermediate lobe

Submitted on May 1, 1964

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